{ "source_file": "Gr8_B_learner_eng.txt", "title": "Grade 8 B", "table_of_contents": [ { "section_id": "1", "title": "Energy and Change" }, { "section_id": "2", "title": "Static electricity" }, { "section_id": "1.1", "title": "Friction and static electricity" }, { "section_id": "4", "title": "Energy transfer in electrical systems" }, { "section_id": "2.1", "title": "Circuits and current electricity" }, { "section_id": "2.2", "title": "Components of a circuit" }, { "section_id": "2.3", "title": "Effects of an electric current" }, { "section_id": "8", "title": "Series and parallel circuits" }, { "section_id": "3.1", "title": "Series circuits" }, { "section_id": "3.2", "title": "Parallel circuits" }, { "section_id": "3.3", "title": "Other output devices" }, { "section_id": "12", "title": "Visible light" }, { "section_id": "4.1", "title": "Radiation of light" }, { "section_id": "4.2", "title": "Spectrum of visible light" }, { "section_id": "4.3", "title": "Opaque and transparent substances" }, { "section_id": "4.4", "title": "Absorption of light" }, { "section_id": "4.5", "title": "Reflection of light" }, { "section_id": "4.6", "title": "How do we see light?" }, { "section_id": "4.7", "title": "Refraction of light" }, { "section_id": "20", "title": "Planet Earth and Beyond" }, { "section_id": "21", "title": "The solar system" }, { "section_id": "1.1", "title": "The Sun" }, { "section_id": "1.2", "title": "Objects around the Sun" }, { "section_id": "1.3", "title": "Earth's position in the solar system" }, { "section_id": "25", "title": "Beyond the solar system" }, { "section_id": "2.1", "title": "The Milky Way Galaxy" }, { "section_id": "2.2", "title": "Our nearest star" }, { "section_id": "2.3", "title": "Light years, light hours and light minutes" }, { "section_id": "2.4", "title": "What is beyond the Milky Way Galaxy?" }, { "section_id": "30", "title": "Looking into space" }, { "section_id": "3.1", "title": "Early viewing of space" }, { "section_id": "3.2", "title": "Telescopes" } ], "front_matter": "Natural Sciences\nGrade 8-B (CAPS)\nEXPLORE\nA World Without Boundaries\nEXPLORE\nA World Without Boundaries\n\n\n.\n1\nH\n.\n3\nLi\n.\n11\nNa\n.\n19\nK\n.\n37\nRb\n.\n55\nCs\n.\n87\nFr\n.\n4\nBe\n.\n12\nMg\n.\n20\nCa\n.\n38\nSr\n.\n56\nBa\n.\n88\nRa\n.\n21\nSc\n.\n39\nY\n.\n57-71\nLa-Lu\n.\n89-103\nAc-Lr\n.\n22\nTi\n.\n40\nZr\n.\n72\nHf\n.\n104\nRf\n.\n23\nV\n.\n41\nNb\n.\n73\nTa\n.\n105\nDb\n.\n24\nCr\n.\n42\nMo\n.\n74\nW\n.\n106\nSg\n.\n25\nMn\n.\n43\nTc\n.\n75\nRe\n.\n107\nBh\n.\n26\nFe\n.\n44\nRu\n.\n76\nOs\n.\n108\nHs\n.\n27\nCo\n.\n45\nRh\n.\n77\nIr\n.\n109\nMt\n.\n28\nNi\n.\n46\nPd\n.\n78\nPt\n.\n110\nDs\n.\n29\nCu\n.\n47\nAg\n.\n79\nAu\n.\n111\nRg\n.\n30\nZn\n.\n48\nCd\n.\n80\nHg\n.\n112\nCn\n.\n31\nGa\n.\n13\nAl\n.\n5\nB\n.\n49\nIn\n.\n81\nTl\n.\n113\nUut\n.\n6\nC\n.\n14\nSi\n.\n32\nGe\n.\n50\nSn\n.\n82\nPb\n.\n114\nUuq\n.\n7\nN\n.\n15\nP\n.\n33\nAs\n.\n51\nSb\n.\n83\nBi\n.\n115\nUup\n.\n8\nO\n.\n16\nS\n.\n34\nSe\n.\n52\nTe\n.\n84\nPo\n.\n116\nUuh\n.\n9\nF\n.\n17\nCl\n.\n35\nBr\n.\n53\nI\n.\n85\nAt\n.\n117\nUus\n.\n10\nNe\n.\n2\nHe\n.\n18\nAr\n.\n36\nKr\n.\n54\nXe\n.\n86\nRn\n.\n118\nUuo\n.\n1\n.\n2\n.\n3\n.\n4\n.\n5\n.\n6\n.\n7\n.\n8\n.\n9\n.\n10\n.\n11\n.\n12\n.\n13\n.\n14\n.\n15\n.\n16\n.\n17\n.\n18\n.\n57\nLa\n.\n58\nCe\n.\n59\nPr\n.\n60\nNd\n.\n61\nPm\n.\n62\nSm\n.\n63\nEu\n.\n64\nGd\n.\n65\nTb\n.\n66\nDy\n.\n67\nHo\n.\n68\nEr\n.\n69\nTm\n.\n70\nYb\n.\n71\nLu\n.\n89\nAc\n.\n90\nTh\n.\n91\nPa\n.\n92\nU\n.\n93\nNp\n.\n94\nPu\n.\n95\nAm\n.\n96\nCm\n.\n97\nBk\n.\n98\nCf\n.\n99\nEs\n.\n100\nFm\n.\n101\nMd\n.\n102\nNo\n.\n103\nLr\n.\nTransition Metal\n.\nMetal\n.\nMetalloid\n.\nNon-metal\n.\nNoble Gas\n.\nLanthanide\n.\nActinide\n.\nPeriodic Table of the Elements\n.\nNo\nElement\n\n.\nNatural Sciences\nGrade 8-B\nCAPS\ndeveloped by\nfunded by\nDeveloped and funded as an ongoing project by the Sasol Inzalo\nFoundation in partnership with Siyavula and volunteers.\nDistributed by the Department of Basic Education\n\n.\nCOPYRIGHT NOTICE\nYour freedom to legally copy this book\nYou are allowed and encouraged to freely copy this book. You can photocopy,\nprint and distribute it as often as you like. You can download it onto your\nmobile phone, iPad, PC or flashdrive. You can burn it to CD, email it around or\nupload it to your website.\nThe only restriction is that you cannot change this version of this book, its cover\nor content in any way.\nFor\nmore\ninformation\nabout\nthe\nCreative\nCommons\nAttribution-NoDerivs 3.0 Unported (CC-BY-ND 3.0) license, visit:\nhttp://creativecommons.org/licenses/by-nd/3.0/\nThis book is an open educational resource and you are encouraged to take full\nadvantage of this.\nTherefore, if you would like a version of this book that you can reuse, revise,\nremix and redistribute, under the Creative Commons Attribution 3.0 Unported\n(CC-BY) license, visit our website, www.curious.org.za\n\n.\nAUTHORS' LIST\nThis book was written by Siyavula with the help, insight and collaboration of volunteer\neducators, academics, students and a diverse group of contributors. Siyavula believes\nin the power of community and collaboration by working with volunteers and\nnetworking across the country, enabled through our use of technology and online tools.\nThe vision is to create and use open educational resources to transform the way we\nteach and learn, especially in South Africa.\nSiyavula Coordinator and Editor\nMegan Beckett\nSiyavula Team\nEwald Zietsman, Bridget Nash, Melanie Hay, Delita Otto, Marthélize Tredoux, Luke\nKannemeyer, Dr Mark Horner, Neels van der Westhuizen\nContributors\nDr Karen Wallace, Dr Nicola Loaring, Isabel Tarling, Sarah Niss, René Toerien, Rose\nThomas, Novosti Buta, Dr Bernard Heyns, Dr Colleen Henning, Dr Sarah Blyth, Dr\nThalassa Matthews, Brandt Botes, Daniël du Plessis, Johann Myburgh, Brice Reignier,\nMarvin Reimer, Corene Myburgh, Dr Maritha le Roux, Dr Francois Toerien, Martli\nGreyvenstein, Elsabe Kruger, Elizabeth Barnard, Irma van der Vyver, Nonna Weideman,\nAnnatjie Linnenkamp, Hendrine Krieg, Liz Smit, Evelyn Visage, Laetitia Bedeker, Wetsie\nVisser, Rhoda van Schalkwyk, Suzanne Grové, Peter Moodie, Dr Sahal Yacoob, Siyalo\nQanya, Sam Faso, Miriam Makhene, Kabelo Maletsoa, Lesego Matshane, Nokuthula\nMpanza, Brenda Samuel, MTV Selogiloe, Boitumelo Sihlangu, Mbuzeli Tyawana, Dr Sello\nRapule, Andrea Motto, Dr Rufus Wesi\nVolunteers\nIesrafeel Abbas, Shireen Amien, Bianca Amos Brown, Dr Eric Banda, Dr Christopher\nBarnett, Prof Ilsa Basson, Mariaan Bester, Jennifer de Beyer, Mark Carolissen, Tarisai\nChanetsa, Ashley Chetty, Lizzy Chivaka, Mari Clark, Dr Marna S Costanzo, Dr Andrew\nCraig, Dawn Crawford, Rosemary Dally, Ann Donald, Dr Philip Fourie, Shamin Garib,\nSanette Gildenhuys, Natelie Gower-Winter, Isabel Grinwis, Kirsten Hay, Pierre van\nHeerden, Dr Fritha Hennessy, Dr Colleen Henning, Grant Hillebrand, Beryl Hook,\nCameron Hutchison, Mike Kendrick, Paul Kennedy, Dr Setshaba David Khanye, Melissa\nKistner, James Klatzow, Andrea Koch, Grove Koch, Paul van Koersveld, Dr Kevin\nLobb, Dr Erica Makings, Adriana Marais, Dowelani Mashuvhamele, Modisaemang Molusi,\nGlen Morris, Talitha Mostert, Christopher Muller, Norman Muvoti, Vernusha Naidoo,\nDr Hlumani Ndlovu, Godwell Nhema, Edison Nyamayaro, Nkululeko Nyangiwe, Tony\nNzundu, Alison Page, Firoza Patel, Koebraa Peters, Seth Phatoli, Swasthi Pillay, Siyalo\nQanya, Tshimangadzo Rakhuhu, Bharati Ratanjee, Robert Reddick, Adam Reynolds,\nMatthew Ridgway, William Robinson, Dr Marian Ross, Lelani Roux, Nicola Scriven, Dr\nRyman Shoko, Natalie Smith, Antonette Tonkie, Alida Venter, Christie Viljoen, Daan\nVisage, Evelyn Visage, Dr Sahal Yacoob\nA special thanks goes to St John's College in Johannesburg for hosting the first planning\nworkshop for these workbooks and to Pinelands High School in Cape Town for the use\nof their school grounds for photography.\nTo learn more about the project and the Sasol Inzalo Foundation, visit the website at:\nwww.sasolinzalofoundation.org.za\n\n.\n\n.\nTable of Contents\nEnergy and Change\n2\n1\nStatic electricity\n4\n1.1\nFriction and static electricity\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n4\n2\nEnergy transfer in electrical systems\n20\n2.1\nCircuits and current electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20\n2.2\nComponents of a circuit\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22\n2.3\nEffects of an electric current\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30\n3\nSeries and parallel circuits\n52\n3.1\nSeries circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52\n3.2\nParallel circuits\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63\n3.3\nOther output devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74\n4\nVisible light\n84\n4.1\nRadiation of light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84\n4.2 Spectrum of visible light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89\n4.3 Opaque and transparent substances . . . . . . . . . . . . . . . . . . . . . . . . . 94\n4.4 Absorption of light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98\n4.5 Reflection of light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101\n4.6 How do we see light? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107\n4.7 Refraction of light\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .\n111\nPlanet Earth and Beyond\n142\n1\nThe solar system\n144\n1.1\nThe Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144\n1.2\nObjects around the Sun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153\n1.3\nEarth's position in the solar system . . . . . . . . . . . . . . . . . . . . . . . . . . 178\n2\nBeyond the solar system\n188\n2.1\nThe Milky Way Galaxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188\n2.2\nOur nearest star . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193\n2.3\nLight years, light hours and light minutes . . . . . . . . . . . . . . . . . . . . . . 194\n2.4 What is beyond the Milky Way Galaxy?\n. . . . . . . . . . . . . . . . . . . . . . . 201\n3\nLooking into space\n212\n3.1\nEarly viewing of space\n. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212\n3.2\nTelescopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218", "chapters": [ { "title": "Energy and Change", "content": "Energy and Change\n\nWhich object gave up some of its electrons in the diagram?\nDoes this object now have more positive or more negative charges?\nWhich object gained electrons in the diagram?\nDoes this object now have more positive or more negative charges?\n• When an object has more electrons than protons overall, then we say that\nthe object is negatively charged.\n• When an object has fewer electrons than protons overall, then we say that\nthe object is positively charged.\nHave a look at the following diagram which illustrates this.\nSo, we now understand the transfer of electrons that takes place as a result of\n.\n.\n7\n.", "chapter_id": "1" }, { "title": "Static electricity", "content": "Chapter 1.\nStatic electricity\n\nfriction between objects. But, how did that result in your hair rising when you\nbrought the charged balloon close to your hair in the last activity? Let's look at\nwhat happens when oppositely charged objects are brought together.\n.\nACTIVITY: Turning the wheel\n.\nMATERIALS:\n• 2 curved watch glasses\n• 2 perspex rods\n• cloth: wool or nylon\n• plastic rod\n• small pieces of torn paper\nINSTRUCTIONS:\n1. Place a watch glass upside down on the table.\n2. Balance the second watch glass upright on the first watch glass.\n3. Rub one of the perspex rods vigorously with the cloth.\n4. Balance the perspex rod across the top of the watch glass.\n5. Rub the second perspex rod vigorously with the same cloth.\n6. Bring the second perspex rod close to the first perspex rod. What do you\nsee happening?\n7. Repeat the activity but instead of the second perspex rod, use the plastic\nrod. What do you see happening?\n8. Next, bring a rod that you have rubbed close to small pieces of torn paper\nlying on the table. What do you observe?\nQUESTIONS:\n1. What happened when you brought the second perspex rod close to the\nfirst perspex rod?\n..\n8\n.\nEnergy and Change\n\n.\n2. What happened when you brought the plastic rod close to the first\nperspex rod?\n3. What happened when you brought the plastic rod close to the pieces of\npaper?\n.\nWhen we rubbed the perspex rods with the cloth, electrons were transferred\nfrom the perspex to the cloth. What charge do the perspex rods now have?\nBoth the perspex rods now have the same charge. Did you notice that objects\nwith the same charge tend to push each other away? We say that they are\nrepelling each other.\nWhen we rubbed the plastic rod with the cloth, electrons were transferred from\nthe cloth to the plastic rod. What charge does the plastic rod now have?\nThe perspex rod and the plastic rod now have opposite charges. Did you notice\nthat objects with different charge tend to pull each other together? We say that\nthey are attracting each other.\n.\nVISIT\nDiscover more with a\nsimulation on rubbing\nballoons and a jersey.\nbit.ly/GzwlIt\nIn the example of the pieces of paper being attracted to the ruler, the paper\nstarts off neutral. However, as the negatively charged plastic rod is brought\ncloser, the electrons in the paper that are nearest to the rod will begin to move\naway, leaving behind a positive charge on the surfaces of the paper that are\nnearest to the rod. The paper is therefore attracted to the rod because opposite\ncharges attract. Another example is dust that is attracted to newly polished\nglasses.\nWe have now observed the fundamental behaviour of charges.\nIn summary, we can say:\n• If two negatively charged objects are brought close together, then they\nwill repel each other.\n• If two positively charged objects are brought close together, then they will\nrepel each other.\n• If a positively charged object is brought near to a negatively charged\nobject, they will attract each other.\n.\nVISIT\nOpposites attract and like\nrepel (video)\nbit.ly/16ThzBL\n.\n.\n9\n.\nChapter 1.\nStatic electricity\n\nDo you now understand why your hair rises and is attracted to the balloon after\nyou rub the balloon on your hair? Write a short description to explain what is\nhappening using the words: electrons, transfer, negative charge, positive\ncharge, opposite, attract, repel.\nSparks, shocks and earthing\n.\nNEW WORDS\n• flammable\n• ignite\nA large build-up of charge on an object can be dangerous. When electrons\ntransfer from a charged object to a neutral object we say that the charged\nobject has discharged.\nDischarging can take place when the objects touch each other. But the\nelectrons can also transfer from one object to another when they are brought\nclose, but not touching. When electrons move across an air gap they can heat\nthe air enough to make it glow. The glow is called a spark.\n.\nVISIT\nA video showing the\ndangers of sparks of static\nelectricity at a petrol\nstation.\nbit.ly/17mYLiC\nAn electrostatic spark between two objects.\nSparks can be harmless, but they can also be very dangerous. Sparks can cause\nflammable materials to ignite. You will probably have noticed that you may not\nsmoke cigarettes or have open flames near petrol tanks at petrol stations. This\nis because petrol fumes are very explosive and only need a small amount of\nheat to start them burning. A small electrostatic spark is enough to ignite\nflammable petrol fumes.\nElectrostatic discharge can also cause electric shocks. Have you ever been\nshocked by a shopping trolley while you are pushing it around a shop? Or have\nyou walked across a carpeted room and then shocked yourself when you touch\nthe door handle to leave the room? You have experienced an electric discharge.\nElectrons move from the door handle onto your skin and the movement of the\nelectrons causes a small electric shock. Small electric shocks can be\nuncomfortable but mostly harmless. Large electric shocks are extremely\ndangerous and can cause injury and death.\nDo you know where else we can see sparks due to static electricity? Look at the\nphoto for a clue!\n..\n10\n.\nEnergy and Change\n\nLightning is a huge electrostatic discharge.\nDuring a thunderstorm, there is friction in the atmosphere between the particles\nthat make up clouds, causing the build-up of regions of charge. Once the\ndifference in charge between two regions becomes great enough, electrostatic\ndischarge becomes possible. A lightning flash is a massive discharge between\ncharged regions within clouds, or between clouds and the Earth.\n.\nDID YOU KNOW?\nLightning bolts can\ntravel at about 210 000\nkm/h and get as hot as\n30 000 °C.\n.\nVISIT\nHow to survive a lightning\nstrike.\nbit.ly/18nTOps\nIn order to discharge extra electrons safely from an object we must earth it.\nEarthing means that we connect the charged object to the ground (the Earth)\nwith an electrical conductor. The extra electrons travel along the conductor and\nenter the ground without causing any harm. The Earth is so large that the extra\ncharge does not have any overall effect.\nFor example, think of the metal trolleys in shopping centres. Have you ever\nnoticed that they normally have a metal chain hanging at the bottom which\ndrags along the floor? This is to earth the trolley if it gets a charge so that\ncharge cannot build up on the trolley. This protects the person pushing the\ntrolley from getting a shock.\n.\nACTIVITY: Research the practical applications of\nstatic electricity\n.\nINSTRUCTIONS:\n1. Use the internet or your school or community library to find information\nabout the practical applications of static electricity.\n2. Research one useful effect of static electricity and one problem caused by\nstatic electricity.\n3. Write a short paragraph explaining your research.\n.\n.\n11\n.\nChapter 1.\nStatic electricity\n\n.\n.\nWe are now going to look at two instruments which demonstrate static\nelectricity.\nVan de Graaff generator\nThe Van de Graaff generator is a machine which uses friction to generate a large\nbuild-up of electric charge on a metal dome.\n.\nVISIT\nShould a person touch 20\n000 Volts? Visit this link\nto find out!\nbit.ly/19mUtun\n.\nDID YOU KNOW?\nThe fundamental idea\nof using friction in a\nmachine to generate a\ncharge dates back to\nthe 17th century, but the\ngenerator was only\ninvented by Robert Van\nde Graaffin 1929 at\nPrinceton University.\nThe Van de Graaff generator can be used to demonstrate the effects of an\nelectrostatic charge. The big metal dome at the top becomes positively\ncharged when the generator is turned on. When the dome is charged it can be\ndischarged by bringing another insulated metal sphere close to the dome. The\nelectrons will jump to the dome from the metal sphere and cause a spark.\n.\nVISIT\nWatch this video so see\nhow a Van de Graaff\ngenerator works\nbit.ly/1a5YNKE\nThese girls are touching the large dome of a Van de Graaff generator.\nYou can also touch the dome and your hair will rise. Why do you think this\nhappens?\nElectroscope\nAn electroscope is an early scientific instrument used to identify the presence of\na charged object or it can be used to identify the type of charge on a charged\nobject.\n..\n12\n.\nEnergy and Change\n\nAn electroscope used in a laboratory.\nThe following images show some drawings of different types of electroscopes.\nAn early example of an electroscope with\none gold strip at the bottom and a ball at\nthe top.\nAnother example of an electroscope with a\ndisc at the top and two gold foil strips at\nthe bottom.\nThe electroscope is made up of an earthed metal box with glass windows.\nThere is a metal rod hanging down and at the end are two strips of thin gold foil\nattached to it. A disc or ball is attached to the top of the metal rod, as seen in\nthe illustrations above. When the metal ball or disc at the top is touched with a\ncharged object, or a charged object is brought near to it, the gold foil strips\nspread apart, indicating that the object has a charge.\nLook at the next illustration which shows how this works.\n.\n.\n13\n.\nChapter 1.\nStatic electricity\n\nThe positively charged rod attracts electrons to the disc from the gold foil strips.\nThe disc at the top becomes negatively charged and the gold foil strips at the\nbottom become positively charged. Why do the gold foil strips move apart?\nYou can make a simple electroscope with everyday items. Let's try.\n.\nACTIVITY: Making a simple electroscope\n.\nMATERIALS:\n• glass jar, with lid\n• 14 gauge copper wire, about 12 cm in length\n• plastic straw or plastic tubing\n• 2 small pieces of aluminium foil\n• piece of wool cloth\n• plastic ruler\n• glass rod\nINSTRUCTIONS:\n.\nVISIT\nMake your own\nelectroscope (video)\nbit.ly/18JyxWc\n1. Twist one end of the copper wire into a spiral shape. This will increase its\nsurface area.\n2. Make a hole in the jar lid and push a small piece of the plastic tubing\nthrough the hole.\n3. Put the other end of the copper wire through the straw so that the spiral\nend is on the outside of the lid.\n4. Make a hook out of the pointed end of the copper wire.\n5. Cut two rectangular strips of aluminium foil.\n6. Put each piece of aluminium foil onto the hook. Make a small hole in the\naluminium foil to allow it to hang from the hook.\n7. Carefully put the hook end of the copper wire into the glass jar and close\nthe jar.\n8. Rub the ruler with the wool cloth for a minute.\n9. Bring the ruler close to the spiral end of the copper wire.\nQUESTIONS:\n1. What did you observe when you brought the ruler close to the copper\nwire?\n2. What happens if you move the ruler away from the copper wire?\nWhy do the pieces of aluminium foil move apart? When you rubbed the plastic\nruler with the wool cloth, the ruler became negatively charged. When the\nnegatively charged ruler is brought close to the copper wire, the electrons on\n..\n14\n.\nEnergy and Change\n\n.\nthe wire are repelled downwards towards the aluminium foil. The pieces of\naluminium foil then have extra electrons on them and they both become\nnegatively charged. Two objects which are negatively charged will repel each\nother and so the pieces of aluminium foil move away from each other.\n3. Write a short paragraph to explain what would happen if you brought a\npositively charged object close to your electroscope.\n.\n. .\nSUMMARY:\n.\nKey Concepts\n• Objects are usually neutral because they have the same number of\npositive and negative charges.\n• Objects can become negatively or positively charged when friction\n(rubbing) results in the transfer of electrons between objects.\n• Protons and neutrons cannot be transferred, only electrons can be\ntransferred by friction.\n• If an object has more electrons than protons, then it is negatively\ncharged.\n• If an object has fewer electrons than protons, then it is positively\ncharged.\n• Like charges repel each other, i.e. negative repels negative; positive\nrepels positive.\n• Opposite charges attract each other, i.e. negative attracts positive;\npositive attracts negative.\n• A discharge of the electrons from a charged object can cause sparks\nor shocks of static electricity, especially when the air is dry.\n.\nConcept Map\nComplete the following concept map to summarise what you have learnt in\nthis chapter about charge and static electricity.\n.\n.\n15\n.\nChapter 1.\nStatic electricity\n\n.\n\n.\n.\nREVISION:\n.\n1. Complete the following sentences. Just write the missing word on the line\nbelow.\na) An object which has a negative charge is said to have\nelectrons than protons. [1 mark]\n2. An object which has a positive charge is said to have\nelectrons than protons. [1 mark]\n3. Sarah uses a plastic comb to comb her hair. The comb becomes negatively\ncharged. The comb is negatively charged because the comb has: [1 mark]\na) gained electrons\nb) gained protons\nc) lost electrons\nd) lost protons\n4. A perspex strip was rubbed with a cloth and became positively charged.\nThe correct explanation for why the perspex rod becomes positively\ncharged is that: [1 mark]\na) the perspex rod got extra protons from the cloth.\nb) the perspex rod got extra protons due to friction.\nc) protons were created as the result of friction.\nd) the perspex rod lost electrons to the cloth due to friction.\n5. Look at the following images in the table. Redraw the images in the second\ncolumn to show how the spheres will move because of the nature of the\ncharges. Write an explanation in the last column. [6 marks]\nCharged spheres\nDraw how they will\nmove\nExplanation\n.\n.\n17\n.\nChapter 1.\nStatic electricity\n\n.\n6. Complete the table by working out the overall charge on each object.\nShow your calculations. State whether the object is positively charged,\nnegatively charged or neutral and why. [9 marks]\nObject\nOverall charge\nWhy is it positive,\nnegative or neutral?\n7. The ruler in this photo has been rubbed with a cloth. Describe what is\nhappening in this photo and why. [4 marks]\nWhat is happening?\n..\n18\n.\nEnergy and Change\n\n.\n8. Sometimes, when you are pushing a trolley, you can get a small shock.\nExplain why this would happen. [2 mark]\n9. Why does your jersey make a crackling sound when you pull it over your\nhead? [2 mark]\n10. Why do trucks transporting petrol drag a short length of metal chain on\nthe road as they drive? [2 mark]\n11. What do you think these two girls are touching on the left of the photo?\nExplain your answer and what is happening to them. [3 marks]\nWhat is happening in this photo?\nTotal [32 marks]\n.\n.\n.\n19\n.\nChapter 1.\nStatic electricity\n\n. .\n2\n.\nEnergy transfer in electrical systems\n..\n20\n..\nKEY QUESTIONS:\n• What is an electric current?\n• What is an electric circuit?\n• Where does the energy come from in a circuit?\n• What are components?\n• How do we draw electric circuits?\n• What effects can an electric current produce?\n• Why does the element in a light bulb glow and the element in a kettle\nbecome hot?\n• What is an electromagnet and are they useful to us?\n• How do you plate metal rings and earrings in gold to produce jewellery?\nIn the last chapter we looked at static electricity. We are now going to focus on\ncurrent electricity. You will already be familiar with some of the concepts and\nterminology about electricity from previous grades. This year we are going to\nrevise some of these concepts and also extend our knowledge about electricity.\n.\n2.1 Circuits and current electricity\nWhat is an electric current?\nAn electric current is the movement of charge in a closed, conducting circuit.\nAs we know from Chapter 1, and also from Matter and Materials, the electrons in\nan atom are arranged in the outer space around the central nucleus. We saw in\nthe last chapter how electrons can be transferred between objects resulting in a\ncharge on the object. In metals, the electrons are able to move freely within the\nmetal. The electrons are not associated with a particular atom in the metal. We\nsay electrons in a metal are delocalised. Have a look at the following diagram\nwhich shows this.\nConducting wire in an electric circuit is made of metal. If we supply it with a\nsource of energy and a complete circuit, then the electrons will all move in the\nsame general direction through the wire. This movement of electrons through a\nconductor is electric current.\n.\nNEW WORDS\n• delocalised\n• component\n• conductor\n• electric circuit\n• electric current\n• qualitative\n• resistor\n• switch\n\nDo you remember what you learnt in Grade 6 and 7 about circuits? Let's revise\nbriefly:\n• An electric circuit needs a source of energy (a cell or battery).\n• Cells have positive and negative terminals.\n• A circuit is a complete pathway for electricity.\n• The circuit must be closed in order for a device to work, such as a bulb\nwhich lights up.\n• We can say that an electric circuit is a closed system which transfers\nelectrical energy.\n• A circuit is made up of various components, which we will look at in more\ndetail.\n.\nTAKE NOTE\nAn ion is an atom that\nhas a charge due to the\nloss or gain of electrons.\nHere the metal ions are\npositive as the electrons\nare delocalised.\n.\nACTIVITY: A simple circuit\n.\nINSTRUCTIONS:\n1. Look at the example of a simple circuit.\n2. Answer the questions which follow.\nQUESTIONS:\n1. What are the parts that make up this system for transferring electrical\nenergy?\n.\n.\n21\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n2. Do you think this is an open or closed circuit? Explain your answer.\n3. Which part is providing the source of energy?\n.\nVISIT\nElectricity and circuits\nbit.ly/17ni2R4 and\nRevise a simple circuit.\n[video)\nbit.ly/1eWpN5k\n4. What is the conducting material?\n5. What type of energy does the battery have?\n6. What is this energy transferred to when the circuit is closed and the\nelectrons move through the wires?\n7. What is the output of this system?\n8. In most systems, the input energy is more than the useful output energy as\nsome of the input energy is transferred to wasted output energy. In this\nsimple circuit with a light bulb, what is the wasted output energy?\n.\nA complete circuit is a complete conducting pathway for electricity. It goes\nfrom one terminal of a cell along conducting material, through a device and\nback to the other terminal of the cell. Let's look at the components of a circuit.\n.\n2.2 Components of a circuit\nYou are probably already familiar with the components of an electric circuit\nfrom previous grades. Do you remember that we have a specific way of\ndrawing the components in a circuit in an electric circuit diagram? Each\ncomponent has a different symbol.\n.\nNEW WORDS\n• ammeter\n• cell\n..\n22\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Components in an electric circuit\n.\nComplete the following table. List the function of the component and draw the\ncircuit symbol. The last two rows have been filled in for you as you may not yet\nknow these symbols, but we will be using them in this chapter.\nComponent\nFunction\nSymbol\nCell\nTorch bulb\nOpen switch\nClosed switch\nElectrical wire\nResistor\nA component that\nopposes or inhibits\nelectrical current in a\ncircuit. It can also\nconvert electrical\nenergy to heat or light.\nor\nVariable resistor\nA resistor whose\nresistance can be\nadjusted higher or\nlower.\n.\n.\n23\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nLet's now practice drawing some simple circuit diagrams. Draw the following\ncircuit diagrams.\n1. A closed circuit with one cell, two light bulbs and a switch.\n.\n2. An open circuit with two cells, two light bulbs and a switch.\n.\n3. A closed circuit with 4 cells and one light bulb.\n.\n..\n24\n.\nEnergy and Change\n\n.\n4. Look at the following circuit diagram. Identify the number of bulbs,\nswitches and cells in this circuit.\n5. What is wrong with the following circuit diagram? Does it represent a\nclosed circuit? Explain your answer.\n.\nVISIT\nBuild you own electric\ncircuits with this\nsimulation.\nbit.ly/19eotZk\n6. Why do you think it is useful to have a switch in a circuit?\n7. Why are conducting wires made out of metal?\n.\nLet's take a closer look at the source of energy in electric circuits.\n.\n.\n25\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nCells\nElectrical cells are the source of energy for the electric circuit. Where does that\nenergy come from?\n.\nDID YOU KNOW?\nAll muscles in our\nbodies move in\nresponse to electrical\nimpulses generated\nnaturally in our bodies.\nInside the cell are a number of chemicals. These chemicals store potential\nenergy. When a cell is in a complete circuit, the chemicals react with each other.\nAs a result, electrons are given the potential energy they need to start moving\nthrough the circuit. When the electrons move they have both potential and\nkinetic energy. The electric current is the movement of electrons through the\nconducting wires.\nCells come in many different sizes. Different sized cells provide different\namounts of energy to the electrical circuit. The types of cells you would use in\ntoys, torches and other small appliances range in size from AAA, AA, C, D, and\n9-volt sizes. AAA, AA, C and D cells usually have a rating of 1,5V, but the larger\ncells have a larger capacity. This means that the larger cells will last longer\nbefore going 'flat'. A cell goes flat when it is no longer able to supply energy\nthrough its chemical reactions.\nWhen we buy cells in the shop they are\nusually referred to as batteries. This\ncan be a bit confusing because a\nbattery is really two or more cells\nconnected together. So when we refer\nto a battery in circuit diagrams we\nneed to draw two or more cells\nconnected together.\nDifferent sized batteries.\n.\nACTIVITY: Recycling of batteries\n.\nBatteries which no longer work must not be thrown away in dustbins. They\nneed to be recycled.\nINSTRUCTIONS:\n1. Work in small groups.\n2. Find out why batteries should not be thrown away in normal dustbins.\nWrite a paragraph to explain why.\n..\n26\n.\nEnergy and Change\n\n.\n3. Find out where you can recycle batteries in your community. Write down\nthe details of the centre(s) closest to where you live.\n.\nResistors\nWhat are resistors? In order to work out what they are, let's first remind\nourselves about conductors and insulators.\nWe are specifically looking at electricity so we can now talk about electrical\nconductors and insulators. An electrical conductor is a substance which allows\nelectric charge to move through it. An insulator is a substance which does not\nallow electric charge to move through it.\nThink back to our model of a metal wire and how the electrons are able to move\nthrough the wire. The metal wire is a conductor of electricity. Write down some\nmaterials which do not conduct electricity.\n.\nVISIT\nA guide to recycling in\nSouth Africa.\nbit.ly/19Sygzg\nWhy do you think most conducting wires are surrounded with plastic?\nResistors are a bit of both. They allow electrons to move through them, but do\nnot make it easy. They are said to resist the movement of electrons. Resistors\ntherefore influence the electric current in a circuit.\nBut, why would we want to resist the movement of electrons? Resistors can be\nextremely useful. Think about a kettle. If you look inside you will see a large\nmetal coil.\nLooking inside a kettle.\nThis metal coil is the heating element.\nIf you plug in and switch on the kettle,\nthe element heats up and heats the\nwater. The element is a large resistor.\nWhen the electrons move through the\nresistor they expend a lot of energy in\novercoming the resistance. This energy\nis transferred to the surroundings in\nthe form of heat. This heat is useful to\nus as it heats our water.\nA good example of where resistors are used is in light bulbs. Let's take a closer\nlook at the different parts of a light bulb to see how it works.\n.\nDID YOU KNOW?\nThe first electric light\nwas made by Humphry\nDavy in 1800. He\ninvented an electric\nbattery, and when he\nconnected wires to it\nand a piece of carbon,\nthe carbon glowed as\nthe carbon is a resistor,\nproducing light.\n.\n.\n27\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Resistance in a light bulb\n.\nAn incandescent light bulb.\nMATERIALS:\n• light bulb\n• lamp\nINSTRUCTIONS:\n1. If you have light bulbs available, have a close look at the different parts,\notherwise have a look at the photos provided here.\n2. Read the information about how a light bulb works and identify the parts\nthat have been numbered.\n3. Answer the questions that follow.\n.\nVISIT\nHow a light bulb works.\nbit.ly/18K0hd3\nDiagram of the parts of a light bulb.\nA light bulb consists of an air-tight enclosed glass case (number 1). At the base\nof the bulb are two metal contacts (numbers 7 and 10), which connect to the\nends of an electrical circuit. The metal contacts are attached to two stiff wires,\n(numbers 3 and 4).\n..\n28\n.\nEnergy and Change\n\n.\nThese wires are attached to a thin metal filament. Have a look at a light bulb.\nCan you identify the filament? This is number 2 in the diagram. The filament is\nmade from tungsten wire. This is an element with high resistance.\nQUESTIONS:\n.\nTAKE NOTE\nIncandescent means to\nemit light as a result of\nbeing heated.\n1. When the electrons move through the filament they experience high\nresistance. This means that they transfer a lot of their energy to the\nfilament when they pass through. The energy is transferred to the\nsurroundings in the form of heat and bright light. Describe the transfer of\nenergy in this light bulb.\n2. What is the useful energy output and what is the wasted energy output in\nthis light bulb?\n3. Can you see the filament is coiled? Why do you think this is so? Discuss\nthis with your class and teacher.\n.\nVISIT\nA fun game about electric\ncircuits.\nbit.ly/15Icr49\n4. The filament is mounted on a glass stem (number 5). There are two small\nsupport wires to hold the filament up (number 6). Why do you think the\nstem is made of glass?\n5. The inside of the base of the bulb is made from an insulating material.This\nis the yellow part labeled number 8. On the outside of this is a metal\nconducting cap to which the wire is attached at number 7. Why is the wire\nattached at 7 making contact with the metal conducting cap?\n6. If you have a lamp in the classroom, screw the bulb into the lamp and turn\nit on to observe the filament glow and also getting hot.\n.\nThe amount of resistance a substance offers to the circuit is measured in ohms\n(Ω). If we want to use resistors to control the current flow, then we need to\nknow the amount of resistance. There are some common resistors shown in the\n.\n.\n29\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nphoto.\nSome common resistors.\nCan you see that there are different coloured bands on the resistors? This isn't\njust to make them look pleasing to the eye. The coloured bands are actually a\ncode that tells us the resistance of the resistor. We also get resistors where we\ncan adjust the resistance ourselves. This is called a variable resistor. You have\nalready seen the symbol for drawing a resistor in a circuit diagram. Draw a\ncircuit diagram in the space below with two bulbs, two cells, an open switch and\na resistor.\n.\nDID YOU KNOW?\nThe inventor, Thomas\nEdison, experimented\nwith thousands of\ndifferent resistor\nmaterials until he\neventually found the\nright material so that\nthe bulb would glow for\nover 1500 hours.\n.\nAn electric current can have various effects. Let's find out more about what\nthese are.\n.\n2.3 Effects of an electric current\n.\nNEW WORDS\n• variable\n• fuse\n• electromagnet\n• electric current\nWe are going to look at the effects of an electric current, and specifically how\nwe use these effects. An electric current can:\n• generate heat in a resistor;\n• generate a magnetic field; and\n..\n30\n.\nEnergy and Change\n\n• cause a chemical reaction in a solution.\nHeating effect\nAs electrons move through a resistor they encounter resistance and they\ntransfer some of their energy to the resistor itself. We saw this in the last section\nwhere we looked at the filament in a light bulb and the element in a kettle.\n.\nACTIVITY: Heating a wire in a circuit\n.\nMATERIALS:\n• 1,5 V cell\n• conducting wires\n• switch\n• block of wood\n• 2 nails\n• hammer\n• 10 cm of nichrome wire\n.\nTAKE NOTE\nYou can easily make\nyour own switch by\nsticking two metal\ndrawing pins into a\npiece of wood with a\nmetal paper clip in\nbetween, as shown in\nthe diagram.\nINSTRUCTIONS:\n1. Hammer the two nails into the block of wood and attach the nichrome wire\nbetween the nails.\n2. Build the following circuit and keep the switch open.\n3. Feel the nichrome wire. Is it hot or cold?\n4. Close the switch. Leave it on for a minute.\n5. Open the switch again.\n6. Feel the wire, briefly. Is it hot or cold?\n.\n.\n31\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nQUESTIONS:\n1. When you felt the nichrome wire after the circuit had been on for a while,\nyou felt an increase in temperature in your skin as thermal energy, which\nwas transferred from the wire to your skin. Explain the heating effect of\nthe electric current in the resistance wire.\n2. List 2 useful applications of the heating effect of an electric current.\n.\nTAKE NOTE\nRemember that heat\nand temperature are\nnot the same thing.\nTemperature is a\nmeasure of how hot or\ncold something is\n(measured inoC)\nwhereas heat is the\ntransfer of thermal\nenergy from a hotter\nobject to a colder object\n(measured in J).\n3. Choose one of the applications you listed in question 2 and explain how\nthe heating effect of the electric current is used.\n4. Look at the following photo of a toaster.\nAn electric toaster.\nCan you see the glowing filament inside? Why does the element glow?\n.\nSo now we know that an electric current can cause objects to heat up. Let's\nlook at a useful application of the heating effect.\n..\n32\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Melting metal\n.\nMATERIALS:\n• three 1,5 V cells\n• copper conducting wires with crocodile clips\n• steel wool\n• heat resistant mat or piece of wood\n• torch light bulb\n• variable resistor\n• ammeter\nINSTRUCTIONS\n1. Set up a circuit according to the following picture.\n2. Twist a few strands of steel wool into a wire.\n.\nTAKE NOTE\nAn ammeter is used to\nmeasure the electric\ncurrent in a circuit.\n3. Use the steel wool to complete the circuit.\n4. Set the variable resistor to its highest resistance.\n5. Close the switch. What do you observe?\n6. Take note of the reading on the ammeter which measures the current in\nthe circuit.\n7. Open the switch.\n8. Set the variable resistance to its lowest resistance.\n9. Close the switch. What do you observe?\nQUESTIONS:\n1. Draw a circuit diagram for your circuit.\nThis is the symbol for an ammeter.\n.\n.\n33\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\n2. Why is the light bulb included in the circuit?\n3. When you decreased the resistance, what happened to the current? In\nother words, what happened to the reading on the ammeter?\n4. What do you think happens to the electric current when the steel wool has\nburnt? Explain your answer.\n.\nIn this activity, we just demonstrated how a fuse works. The steel wool acted as\na fuse. When the current was too high, the steel wool melted and prevented any\nfurther current in the circuit.\nWhat are fuses?\nThe heating effect of an electric current can be dangerous. If a circuit overheats\nit could cause a fire. To avoid overheating, circuits often contain a fuse. Fuses\ncontain a low resistance wire made of a metal with a low melting point.\nTherefore, the piece of wire melt if it gets too hot, just like the steel wool in our\nactivity.\n..\n34\n.\nEnergy and Change\n\nAn example of a fuse. Can you see the low melting point wire inside?\nDifferent circuits need different strength currents and so we need different\ntypes of fuses. Some fuses can only handle a little bit of heat, some can handle a\nlot. We choose the fuse that suits the safety needs of our circuit. If the circuit\noverheats, the fuse will melt and break the circuit to reduce the danger of fire as\nwell as protect electronic equipment.\nHow did you draw the fuse that we made using steel wool in the last activity?\nThe conventional symbol for drawing a fuse in a circuit diagram is shown here:\nA fuse.\n.\nTAKE NOTE\nIt is important to never\nremove a fuse from a\ncircuit without first\nswitching offthe\ncurrent. You could get a\nnasty shock if you do.\nWhat is a short circuit?\nHave you ever heard that something broke because it short circuited? A short\ncircuit happens when another, easier path is accidently made in an electric\ncircuit. What do we mean by easier?\nWe mean that the path offers very little resistance to the electric current. As\nthere is so little resistance the current flows along the short circuit and doesn't\npass through the main circuit. Short circuits can be dangerous and cause a lot\nof damage to appliances.\nHave you ever had a piece of toast get stuck in a toaster? It's a real nuisance.\nLots of people are tempted to use their butter knife to unhook the bread. Don't\nbe tempted. Your knife is a conductor and can act as a short circuit. All the\nelectric current will flow through your knife and, because you are touching it,\nthrough you. What would be the safe way to unhook your toast?\n.\nTAKE NOTE\nThere are different\ntypes of fuses. The ones\nwe have investigated so\nfar require you to\nreplace the fuse if the\nwire melts. However,\nsome fuses work\ndifferently to break the\ncircuit and can just be\nreset once the problem\nin the circuit is fixed.\n.\n.\n35\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: How are fuses used in everyday\ncircuits?\n.\nINSTRUCTIONS:\n1. Find out about common household appliances which use fuses. Choose\none of these appliances on which to focus your research.\n2. Write a short paragraph describing the appliance and explaining why a\nfuse is necessary for that appliance.\n.\nMost modern homes have circuit breakers instead of fuses. A circuit breaker is\nsimilar to a fuse in that it is designed to protect an electric circuit from damage,\ndue to overload or a short circuit, by stopping the current flow. However, unlike\na fuse which melts and must then be replaced, a circuit breaker can be reset to\nstart operating again. This can be done manually or take place automatically.\nMagnetic effect\nBefore we look at how a current produces a magnetic field, let us first learn\nmore about magnets. A magnet is a piece of material which produces a\nmagnetic field. A magnet has a north pole and a south pole. Opposite poles will\nattract each other and the same poles will repel each other. A magnet has a\nmagnetic field around it.\n.\nVISIT\nSome fun tricks with\nmagnets. (video)\nbit.ly/1c01QsA\n..\n36\n.\nEnergy and Change\n\nA bar magnet.\nDid you know that the Earth is like a bar magnet with a North and a South Pole?\nThe Earth has a magnetic field. This is why we can use compasses to tell\ndirection. A plotting compass has a needle with a small magnet. The needle\npoints to magnetic north because the small magnet is attracted to the opposite\nmagnetic pole and can be used to determine direction.\nEarth has a magnetic field, as though there\nis a big bar magnet running through the\ncore, with its South Pole under Earth's\nmagnetic North pole.\nA compass with the needle pointing North.\n.\nVISIT\nWhat is the magnetic\nfield?\nbit.ly/GzwPyx\n.\nACTIVITY: Playing with plotting compasses and\nmagnets\n.\nMATERIALS:\n• plotting compasses\n• bar magnets\n• piece of white paper\n• iron filings\nINSTRUCTIONS:\n1. Hold the plotting compass in your hand. The north end of the needle\nshould point to magnetic north.\n2. Put the bar magnet flat on the desk. Make sure you know which end is\nnorth and which is south. If you are not sure, ask your teacher.\n3. Put plotting compasses in a circle around the bar magnet.\n.\n.\n37\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nDraw what you see.\n.\n4. Next, place a white sheet of paper over the bar magnet and sprinkle iron\nfilings over the sheet of paper over the magnet.\nObserve what happens to the iron filings. Did you see something similar to\nwhat is shown in the photograph below? Describe what you see.\nIron filings on a piece of paper over a bar magnet.\n.\nSo now we know that there is a magnetic field around a magnet and that\nplotting compasses and iron filings can be used to visualise that field. Is there\nanything else that has a magnetic field around it?\n.\nVISIT\nExplore the interactions\nbetween a compass and\nbar magnet with this\nsimulation.\nbit.ly/19etlNQ\n..\n38\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magnetic field around a conductor\n.\nMATERIALS:\n• plotting compasses\n• three 1,5 V cells\n• insulated copper conducting wires\n• switch\nINSTRUCTIONS:\n1. Construct a circuit which contains the batteries, copper wires and the\nswitch.\n2. Put the plotting compasses on either side of the conducting wire as shown\nin the diagram, as well as below and above the conducting wire.\nPlotting compasses placed around a conducting wire.\n3. Keep the switch open. What do you notice about the needles of the\nplotting compasses?\n4. Close the switch and observe what happens to the needles.\n5. Draw a picture of the wire and plotting compasses in the space below:\n6. What does the pattern of the compasses tell us?\n.\nWe saw from our first activity that plotting compasses react to magnetic fields.\nThe plotting compasses changed direction when the current was switched on.\nThis means there is a magnetic field around the wire. Was it there when the\ncurrent was switched off? No, it was not. That means that the presence of the\nelectric current in the wire must have produced a magnetic field.\n.\nVISIT\nDiscover how the Earth is\na magnet that protects us\nfrom damaging radiation\nfrom the sun!\nbit.ly/GCCtjK\nThe magnetic effect of an electric current has many useful applications.\n.\n.\n39\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Making an electromagnet\n.\nMATERIALS:\n• one iron nail (approximately 15 cm long)\n• 3 metres of 22 gauge insulated copper wire\n• two D cell batteries\n• paper clips\n• iron filings\nINSTRUCTIONS:\n1. Wrap the insulated copper wire tightly around the nail. Make sure that you\nwrap the wire in the same direction.\n2. Strip some of the insulation off each end of the insulated copper wire.\n3. Attach the ends of the insulated copper wire to the terminals of the\nbattery.\n4. Hold the wrapped nail above the paper clips.\n5. Disconnect the wire from the battery.\n6. Hold the wrapped nail above the paper clips.\n7. If you have iron filings, place some on a piece of paper around the\nelectromagnet you have made and observe the magnetic field.\nThe magnetic field around an electromagnet.\nQUESTIONS:\n.\nVISIT\nHow to make an\nelectromagnet (video)\nbit.ly/1bpHh61\n1. What happened when you held the nail over the paper clips?\n2. Why were the paper clips attracted to the nail?\n3. Did the disconnected nail attract the paper clips? Why?\n.\n..\n40\n.\nEnergy and Change\n\nElectromagnets can be used in all sorts\nof practical applications, including\nspeaker and electric bells, as you can\nsee in the photo.\nAn electromagnet in a bell.\n.\nVISIT\nElectromagnets in a\nspeaker.\nbit.ly/19jU1XL\n.\nACTIVITY: Research the use of electromagnets\n.\nINSTRUCTIONS:\n1. Work in groups of 2 or 3.\n2. Research one of the following applications of the magnetic effect of an\nelectric current to explain how the device works:\na) speakers\nb) electric bells\nc) telephones\nd) magnetic trains\ne) industrial lifters and separators\n3. Write a short paragraph showing what you've learnt. Remember to note\ndown from where you got your information.\n4. Share your paragraph with the rest of the class.\n.\nChemical effect\nThe last effect of an electric current that we are going to look at is how an\nelectric current can cause a chemical reaction in a solution.\n.\nVISIT\nDiscover how to generate\nelectricity using bar\nmagnets with this\nsimulation.\nbit.ly/15Guo8x and\nlearn how to build a\nsimple electric motor.\nbit.ly/1c02xCb\n.\n.\n41\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Electrolysis\n.\nYou might already have done this activity in Matter and Materials when we\ninvestigated the decomposition of copper chloride. We are going to perform it\nagain, this time focussing on the effects of an electric current.\nMATERIALS\n• 250 ml beaker\n• 2 carbon electrodes\n• sandpaper\n• 3 copper conducting wires (with crocodile clips)\n• copper chloride solution\n• torch bulb\n• power pack\nINSTRUCTIONS\n1. Sand down the electrodes with the sandpaper to make sure they are clean.\n2. Connect the conducting wire from one electrode to the torch bulb and\nanother wire from the torch bulb to the negative terminal of the power\nsource.\n3. Connect the crocodile clip from the second electrode to the positive\nterminal of the power source.\n4. Pour 100 ml copper chloride solution into the beaker.\n5. Put the electrodes into the beaker. Make sure that they do not touch each\nother.\n6. Look at the electrodes. What do you observe?\n7. Turn on the power source. Leave it on for a few minutes.\nThe setup might look something like this, which you have seen before. You might\nalso have a light bulb connected in the circuit.\n..\n42\n.\nEnergy and Change\n\n.\nQUESTIONS\n1. When you switch on the power source, does the torch bulb glow?\n.\nVISIT\nLearn more about silver\nrefining through\nelectrolysis.\nbit.ly/1fZQ5SW and the\nprocess of electroplating\n(video)\nbit.ly/GzH851\n2. What do you observe happening at the two different electrodes?\n3. Can you smell anything? What do you think this is?\n4. What is happening to the copper chloride solution when the electric\ncurrent is passed through it?\n5. If you switch off the power source, what happens?\n6. What is causing the separation of the copper chloride?\n7. Why is it important that you do not let the carbon electrodes touch each\nother while the current is flowing?\n.\nThe separation of the copper chloride means that an electric current can cause\nchemical reactions to occur. There are many ways in which we can harness this\nchemical effect for practical uses.\nElectrolysis is the breaking down of a substance into its component elements\nby passing an electric current through a liquid or solution. We can also use\nelectrolysis to purify substances.\nImpure copper can be purified using electrolysis. Instead of using carbon\nelectrodes in a copper sulphate solution we can use copper electrodes. If one of\nthe copper electrodes is pure copper and the other is impure copper, then the\nimpure electrode will break down and deposit pure copper on to the already\npure copper electrode.\n.\nNEW WORDS\n• electrolysis\n• electrodes\n• electroplating\n.\n.\n43\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nOne of the most important uses of electrolysis is electroplating.\nElectrolysis is used to electroplate metals. In the last activity, one of the carbon\nelectrodes was coated with an even layer of pure copper. We say that the\ncarbon electrode was electroplated with copper.\nWhy do we electroplate? An example is in the making of jewellery where an\ninexpensive metal is made into a ring, for example, and then coated with gold\nby electroplating. This makes it less expensive than if it were made from pure\ngold. Iron rusts easily and so it is useful to coat it with a layer of a zinc to\nprotect it from corrosion. Many car parts, bathroom taps and wheel rims are\nelectroplated with chromium.\n..\nSUMMARY:\n.\nKey Concepts\n• A circuit is a system for transferring electrical energy.\n• For a circuit to function there must be a complete, unbroken pathway\nfor the electrons to follow, a source of energy (cell or cells) and a load\n(lightbulb or any other resistor).\n• We use symbols to represent components of an electric circuit so that\neveryone can interpret the diagrams.\n• A resistor is a component in a circuit which resists the movement of\nelectrons through the circuit.\n• An electric current can heat a resistance wire. This heating effect is used\nin many everyday appliances, such as kettles and irons.\n• An electric current causes a magnetic field. This magnetic effect is used\nin electromagnets.\n• An electric current can cause a chemical reaction in solutions. This is\ncalled electrolysis, and is used to electroplate objects.\n.\nConcept Map\nComplete the concept map to summarise what you have learned about\nelectric circuits and the effects of an electric current in this chapter.\n..\n44\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Write your own definition for an electric circuit. [2 marks]\n2. What type of energy does a battery have? [1 mark]\n3. When a battery is connected to a circuit, it causes an electric current in the\ncircuit. Explain what an electric current is and why it is possible in metals.\nUse the word 'delocalised' in your explanation. [3 marks]\n4. List 3 materials which conduct electricity. [3 marks]\n5. List 3 materials that do not conduct electricity. [3 marks]\n6. You have a battery, insulated copper conducting wires and a light bulb.\nDraw a setup which would allow you to test whether the materials you\nlisted in questions 1 and 2 are conductors or not. [4 marks]\n.\n..\n46\n.\nEnergy and Change\n\n.\n7. Draw the symbols for the following components. [6 marks]\nA cell\nA light bulb\nA conducting wire\nAn open switch\nA resistor\nA variable resistor\n8. Look at the circuits below. If the bulb(s) will glow, place a tick next to the\npicture and explain why it will glow. If the bulb(s) will not glow, place a\ncross next to the picture and explain why it will not glow. [10 marks]\nCircuit\nGlow/Not Glow\nExplanation\n.\n.\n47\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nCircuit\nGlow/Not Glow\nExplanation\n9. Which of the following setups shows the correct way to connect a light\nbulb to a battery? Explain your answer. [2 marks]\n..\n48\n.\nEnergy and Change\n\n.\n10. Draw a circuit diagram to illustrate the following circuit: (3 marks)\nImage\nCircuit diagram\n11. An electrician wants to replace a faulty fuse with a normal piece of\nconducting wire. Should you let him? Why or why not? [3 marks]\n12. A child, while inserting an electric plug into the socket, did not see that\nthere was a thin piece of aluminium foil stuck between the pins of the plug.\nWhen he turned the switch on, he noticed a spark at the plug, and at the\nsame time, the lights went out. What could have happened to cause the\nspark and to make the lights go out? [4 marks]\n13. What is the benefit of using a circuit breaker rather than a fuse? [2 marks]\n14. Look at the following photo of a light bulb. Label the filament and explain\nwhy it glows. [4 marks]\n.\n.\n49\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n15. You place some plotting compasses around an electric wire and observe\nthe following.\na) Is there are current in the conducting wire? [1 mark]\nb) Explain your answer. [2 marks]\n16. Give two advantages of electroplating iron metal. [2 marks]\nTotal [55 marks]\n.\n..\n50\n.\nEnergy and Change\n\nCurious? Discover the possibilities with a magnifying glass.\n.\n.\n51\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n. .\n3\n.\nSeries and parallel circuits\n..\n52\n..\nKEY QUESTIONS:\n• Are there different types of electric circuits?\n• If all the light bulbs in a house are part of the same circuit, how can you\nswitch one light off without the rest also turning off?\n• What is a series circuit?\n• What is a parallel circuit?\n• What happens when you connect more components in series or in\nparallel?\nIn the last chapter, and in Gr 6 and 7, we have been looking at electric circuits.\nThese have mostly been series circuits. What does this mean? And how else can\na circuit be arranged?\n.\n3.1 Series circuits\nA series circuit is one in which there is only one pathway for the electric current\nto follow. The components are arranged one after another in a single pathway.\nWhen we connect the components we say that they are connected in series.\nWe have already seen examples of series circuits in the last chapter.\nA series circuit with one pathway for the current, from the negative to the positive\nterminal of the battery.\n.\nNEW WORDS\n• series\n• ammeter\n• ampere\n• resistance\nAmmeter\nAn ammeter is a measuring device used to measure the electric current in the\ncircuit. It is connected into the circuit in series. The current is measured in\namperes (A).\n\nAn ammeter.\nWhat is the symbol for an ammeter? Draw it here.\n.\n.\nDID YOU KNOW?\nThe ampere is named\nafter André-Marie\nAmpère (1775-1836), a\nFrench mathematician\nand physicist. He is\nconsidered the father of\nelectrodynamics, which\nis the study of the effect\nof electromagnetic\nforces between electric\ncharges and currents.\nDo you think that an ammeter would have a high resistance or a low resistance\nto the current? Explain your choice.\n.\nTAKE NOTE\nThe ampere is often\nshortened to 'amp'.\nA series circuit only provides one pathway for the electrons to follow. Let's\ninvestigate what happens when we increase the resistance in a series circuit.\n.\nINVESTIGATION:\nWhat happens when we add more\nresistors in series?\n.\nAIM: To investigate the effect of adding resistors to a series circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\n.\n.\n53\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cells\n• 3 torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, the ammeter, 1 bulb and the switch in\nseries.\nA photo showing the setup.\n2. Close the switch, or the circuit if you are not using a switch.\n3. Note how brightly the bulb is shining and write down the ammeter reading.\nDraw a circuit diagram.\n.\n4. Open the switch.\n5. Add another light bulb into the circuit.\n6. Close the switch.\n..\n54\n.\nEnergy and Change\n\n.\n7. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram.\n.\n8. Open the switch.\n9. Add the third light bulb into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram for the last circuit you built.\n.\n.\n.\n55\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nseries\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness, or was\none brighter than the other?\n..\n56\n.\nEnergy and Change\n\n.\n3. When you had three bulbs, did they glow the same as each other or was\none brighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the series circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin series?\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in series?\n2. Is your hypothesis accepted or rejected?\n.\nAs more resistors are added in series, the total resistance of the circuit\nincreases. As the total resistance increases, the current strength decreases.\nWhat would happen if we increased the number of cells connected in series?\nWould the current become larger or smaller? Let's investigate.\n.\nINVESTIGATION:\nHow does adding more cells in\nseries affect the current?\n.\nAIM: To investigate the effect of increasing the number of cells connected in\nseries on the electric current strength.\nHYPOTHESIS: Write a hypothesis for this investigation. Remember to mention\nhow the increase in the number of cells will affect the current strength.\n.\n.\n57\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS\n• three 1,5 V cells\n• insulated copper conducting wires\n• ammeter\n• 2 torch light bulbs (or 1 torch light bulb and one resistor)\nMETHOD:\n1. Construct a circuit with 1 cell, the ammeter and the two torch light bulbs.\n2. Observe the brightness of the bulbs and record the ammeter reading in the\ntable of results. Draw a circuit diagram.\n.\n3. Add a second cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n4. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\n5. Add a third cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n..\n58\n.\nEnergy and Change\n\n.\n6. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nseries\nBrightness of bulbs\nReading on a mmeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What can you conclude from the shape of the graph?\n2. Is your hypothesis true or false?\n.\nWe have seen that increasing the number of cells in series increases the current,\nbut increasing the number of resistors decreases the current.\nWe will now investigate the current strength at different points in a series circuit.\n.\n.\n59\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION:Is the current strength the same at all points in a\nseries circuit?\nHYPOTHESIS: Write a hypothesis for this investigation. What do you think will\nhappen in this investigation?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• two torch light bulbs\n• ammeter\nMETHOD:\n1. Set up a series circuit with two cells and two torch light bulbs in series with\neach other.\n2. Insert an ammeter in series between the positive terminal of the batteries\nand the first torch bulb.\n3. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series between the two torch bulbs.\n6. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n..\n60\n.\nEnergy and Change\n\n.\n.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series between the last torch bulb and the negative\nterminal of the batteries.\n9. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\nRESULTS:\nComplete the following table:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nBetween positive terminal\nof cell and first bulb\nBetween two bulbs\nBetween negative terminal\nof cell and last bulb\n.\n.\n61\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nCONCLUSIONS:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\nIn a series circuit, there is only one pathway for the electrons to move through.\nThe current strength is the same everywhere in that pathway.\nWhat have we learned about series circuits?\n• There is only one pathway for the electrons to follow.\n• The current flows at the same strength everywhere in a series circuit,\nbecause there is only one pathway. We say that the current is the same at\nall points in the circuit.\n• If you add more resistors in series, the current in the whole circuit\ndecreases.\nWhy does the current stay the same at all points? Let's think about how electric\ncurrent moves through a circuit. Do you remember that we spoke about the\ndelocalised electrons in metals in the last chapter?\n.\nVISIT\nAnimation showing the\nmovement of electrons.\nbit.ly/19Ww8pW\nThe electrons in a conductor normally drift in various different directions within\na metal, as shown in the diagram.\nDelocalised electrons move freely in a\nconducting wire.\nWhen the wire is connected in a closed\ncircuit, the electrons move towards the\npositive terminal of the battery.\nWhen we build a closed circuit with a cell as an energy source, the electrons will\nall begin to move towards the positive side of the cell. The rate at which the\nelectrons move, is determined by the resistance of the conductor.\nThere are electrons everywhere in the conducting wires and electrical\ncomponents. When the circuit is closed, all the electrons start moving in the\nsame general direction at the same time. This is why a light bulb turns on\nimmediately when you close the switch.\n.\nVISIT\nFlip the switch and watch\nthe electrons with this\nsimulation.\nbit.ly/15NlqBd\nIn a series circuit, all the electrons travel through every component and wire as\nthey travel through the circuit. All the electrons experience the same resistance\n..\n62\n.\nEnergy and Change\n\nand so they all move at the same rate.\nThis means that in the diagram below, the readings on all three ammeters will\nbe the same, so: A1= A2= A3\n.\n3.2 Parallel circuits\n.\nNEW WORDS\n• parallel circuit\nParallel circuits offer more than one pathway for the electrons to follow. When\nconstructing a parallel circuit, we say that components are connected in\nparallel.\nLook at the diagram which shows how two light bulbs are connected in parallel.\nThere are two paths for the current in this parallel circuit, one path through each of the\nbulbs.\nHow can you tell whether or not a circuit is connected in series or in parallel?\nLet's look at some circuit diagrams to tell the difference.\n.\nVISIT\nWatch a video that\nexplains the difference\nbetween series and\nparallel circuits\nbit.ly/1f5hZ0W\n.\nACTIVITY: Series or parallel?\n.\nINSTRUCTIONS:\nLook at the following circuits and write down which are in series and which are\nin parallel. The series circuits will only offer one pathway, but the parallel\ncircuits will have more than one pathway for the electrons to follow.\n.\n.\n63\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nLet's investigate how parallel circuits work.\n.\nINVESTIGATION:\nHow does adding resistors in\nparallel affect the current strength?\n.\nAIM: To investigate the effect of adding resistors in parallel on the current\nstrength.\nHYPOTHESIS: Write a hypothesis for this investigation.\n..\n64\n.\nEnergy and Change\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cell\n• three identical torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, ammeter, one bulb and the switch in\nseries.\n2. Close the switch.\n3. Note how brightly the bulb is shining and record the ammeter reading.\nDraw a diagram of your circuit.\n.\n4. Open the switch.\n5. Add another light bulb, in parallel to the first, into the circuit.\n6. Close the switch.\n7. Note how brightly the bulbs are shining and record the ammeter reading.\n8. Open the switch.\n9. Add the third light bulb, in parallel to the first two, into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and record the ammeter reading.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nparallel\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\n.\n.\n65\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness or was\none brighter than the other?\n3. When you had three bulbs, did they glow the same brightness or was one\nbrighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the parallel branches of the circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin parallel?\n..\n66\n.\nEnergy and Change\n\n.\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in parallel?\n2. Is your hypothesis true or false?\n.\nAs more resistors are added in parallel, the total current strength increases. The\noverall resistance of the circuit must therefore have decreased. The current in\neach light bulb was the same because all the bulbs glowed with the same\nbrightness. This tells us that the current of electrons must have split up and\nmoved through each of the branches.\nWe can also connect cells in parallel. What would happen if we increased the\nnumber of cells connected in parallel? Would the current get stronger or\nweaker?\n.\nINVESTIGATION:\nWhat happens to the current\nstrength when cells are connected\nin parallel?\n.\nAIM: To investigate how increasing the number of cells connected in parallel\naffects the current strength in a circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS\n• three 1,5V cells\n• one torch light bulb\n• insulated copper conducting wires\n• ammeter\nMETHOD:\n1. Set up a circuit which has one cell, the ammeter and the torch light bulb in\nseries with each other. Draw a circuit diagram of your circuit.\n.\n.\n67\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\n2. Observe the brightness of the bulb and record the ammeter reading.\n3. Connect another cell in parallel with the first cell. To connect the second\ncell in parallel, connect a wire from the positive terminal of the first cell to\nthe positive terminal of the second cell. Connect another wire between the\nnegative terminal of the first battery and the negative terminal of the\nsecond battery. Draw a circuit diagram of your circuit.\n.\n4. Observe the brightness of the bulb and record the ammeter reading.\n5. Connect a third cell in parallel to the other two cells. Draw a circuit\ndiagram of your circuit.\n.\n6. Observe the brightness of the bulb and record the ammeter reading.\n..\n68\n.\nEnergy and Change\n\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nparallel\nBrightness of bulb\nReading on ammeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What did you notice about the brightness of the bulbs?\n2. What did you notice about the ammeter readings?\n3. What conclusion can you draw from your results?\n.\nAdding cells in parallel has no overall effect on the current strength. The current\nstrength stays the same if you add cells in parallel.\nWe saw that the current strength increased when bulbs were connected in\nparallel. However, we were only testing the current strength at one point in the\nparallel circuit. How does the current compare in the different pathways of the\ncircuit? Let's do an investigation to find out.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION: Is the current strength equal at all points in a\nparallel circuit?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• three identical torch light bulbs\n• ammeter\n.\n.\n69\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMETHOD:\n1. Set up a parallel circuit with two cells in series with each other and three\ntorch light bulbs in parallel with each other.\n2. Insert an ammeter in series between the cells and the first pathway, as\nshown in the diagram.\n3. Measure the current strength using the ammeter.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series in the first pathway.\n6. Measure the current strength using the ammeter.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series in the second pathway.\n9. Measure the current strength using the ammeter.\n10. Remove the ammeter and close the circuit again.\n11. Insert the ammeter, in series, in the third pathway.\n..\n70\n.\nEnergy and Change\n\n.\n12. Measure the current strength using the ammeter.\n13. Remove the ammeter and close the circuit again.\n14. Insert the ammeter in series between the first pathway and the cells on the\nopposite side to the first reading.\n15. Measure the current strength using the ammeter.\nRESULTS:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nbetween the cell and first\npathway\nin the first pathway\nin the second pathway\nin the third pathway\nbetween the cell and the\nfirst pathway\nCONCLUSION:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\n.\n.\n71\n.\nChapter 3.\nSeries and parallel circuits\n\nWhat have we learned about parallel circuits?\n• There is more than one pathway for the current to follow.\n• The current divides between the different branches so that each branch\ngets some of the current. As the torch bulbs in each branch in our example\nwere identical, the current divided equally between them.\n• If you add more resistors in parallel, the total current supplied by the cell in\nthe circuit increases.\nWhy does the current divide when offered an alternative pathway?\nImagine that you are sitting in a school hall during assembly. You are bored and\nwaiting for it to end so that you can go out to break to chat to your friends.\nThere is only one exit from the hall. When you are dismissed, everyone has to\nexit through the same door. It takes a while because only some learners can\nleave at a time.\nNow imagine that there is a second door that is the same as the first door. Now\nyou and your friends have a choice of which door to go through. The speed at\nwhich the learners exit the hall will increase and some of you will exit through\nthe first door while others will exit through the second door. No one can go\nthrough both doors at the same time.\nThis is similar to the way current behaves when in a parallel circuit. As the\nelectrons approach the branch in the circuit, some electrons will take the first\npath and others will take the other path. The current is divided between the two\npathways.\nIn the following circuit A1 = A4 and A1 = A2 + A3 and A4 = A2 + A3\nWe have looked at how resistors and cells behave in series and parallel circuits.\nLet's look at how different metals conduct electricity. All conductors have some\nresistance in a circuit. Are some metals better conductors of electricity than\nothers?\nLet's have a look at which metals offer more resistance than others to the flow\nof charge (current) through an electric circuit .\n..\n72\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Which metals offer the most\nresistance?\n.\nMATERIALS:\n• a cell\n• torch light bulb\n• insulated copper wires\n• lengths of copper, aluminium, zinc and nichrome wire\n• crocodile clips (if available)\nINSTRUCTIONS\n1. Build a circuit with the cell and the torch light bulb and leave a gap for the\nmetal to be tested. You can use crocodile clips at the end of each piece of\nmetal for easy insertion.\n2. Insert each metal into the circuit (one at a time).\nAn example circuit with a cell, a light bulb and the piece of metal being tested.\nObserve the brightness of the bulb.\nQUESTIONS:\n1. Draw a circuit diagram of your apparatus.\n.\n.\n.\n73\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n2. Why can we use the brightness of the bulb to qualitatively measure\nresistance?\n3. List the metals in order of increasing resistance.\n4. Why do you think copper is used for connecting wires in electrical circuits?\n.\nThere are several factors which influence the amount of resistance a material\noffers to an electric current. We have seen that the type of material is one of\nthose factors.\n.\nTAKE NOTE\nIn Gr. 9 we will look at\nthe other factors that\ninfluence resistance. If\nyou want to see the\ncontent in other grades,\nremember that you can\nvisit\nhttp://www.\ncurious.org.za\n.\n3.3 Other output devices\nLight bulbs are not the only devices used in electrical circuits. Devices that use\nelectrical energy to function, including light bulbs, are called output devices.\nLet's look at some other common examples of output devices.\nLEDs (Light-Emitting Diodes)\nLEDs are widely used electronic devices. They are small lights but they do not\nhave a filament like an incandescent bulb has. They therefore cannot burn out,\nas there is no filament to wear out, and they do not get as hot. LEDs are used in\nelectronic timepieces, high definition televisions and many other applications.\nLarger LEDs are also replacing traditional light bulbs in many homes because\nthey do not use as much electricity. They last longer than incandescent bulbs\nand are more efficient.\n.\nVISIT\nWatch this video about\nthe history of the LED\nbit.ly/1bC5qKc\n..\n74\n.\nEnergy and Change\n\nDifferent LED bulbs.\nIn the last chapter, we looked at the energy transfers in an electrical system. We\nwill now represent energy transfer within electrical systems in a different way.\nWe will apply this new representation to the difference between energy outputs\nin an LED and an incandescent light bulb.\n.\nVISIT\nVideo on drawing a basic\nSankey diagram.\nbit.ly/19Wwxsu\n.\nACTIVITY: Sankey diagrams\n.\nYou might have drawn Sankey diagrams in Grade 7. If not, here is some quick\nrevision.\nIn an energy system, input energy is transferred to useful output energy and\nwasted output energy. A Sankey diagram is a visual and proportional\nrepresentation of the energy transfers that happen in a system.\nFor example, a kettle uses about 2000 J of input energy, but only about 1400 J\nis used to heat the water. The remaining 600 J is wasted as sound. Here is the\nSankey diagram to represent the energy transfer.\n.\nTAKE NOTE\nRemember that energy\nis measured in joules\n(J).\n.\n.\n75\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nQUESTIONS:\nWe will now compare an LED with an incandescent light bulb.\n1. Draw a Sankey diagram for an LED if the input energy is 100 J, 75 J of\nenergy is used to produce light and the rest is lost as heat.\n.\n.\nVISIT\nAn electricity timeline\nanimation.\nbit.ly/1fKZb8E\n2. Draw a Sankey diagram for a filament light bulb if the input energy is 100 J,\nthe wasted heat energy is 80 J and the rest produces light.\n.\n3. Which bulb do you think is more efficient? Explain your answer.\n.\nCan you think of any other output devices? Make a list of as many as you can.\n..\n76\n.\nEnergy and Change\n\n.\n.\nACTIVITY: History of electricity production\n.\nINSTRUCTIONS:\n1. Work in groups of three or four.\n2. Research the history of electricity production: How was electricity\ndiscovered and how did electricity become widely used?\n3. Create a basic timeline for the discovery of electricity and it's production.\n.\n.\nACTIVITY: Careers\n.\nINSTRUCTIONS:\n1. Choose a career related to electricity production.\n2. Write a short paragraph describing the career. Include information on how\none can study or prepare for your chosen career.\n.\n.\n.\n77\n.\nChapter 3.\nSeries and parallel circuits\n\n..\nSUMMARY:\n.\nKey Concepts\n• A series circuit has only one pathway for the electrons to travel through.\n• A parallel circuit has more than one pathway for the electrons to travel\nthrough.\n• In a series circuit, the current is the same at all points in the circuit.\n• In a series circuit, the resistance increases as more resistors are added\nin series.\n• In a parallel circuit, the current splits between the available paths.\n• In a parallel circuit, the resistance decreases as more resistors are added\nin parallel.\n.\nConcept Map\nComplete the concept map on the following page to summarise what you\nhave learned about series and parallel circuits.\n..\n78\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Look at the following circuit diagrams and decide whether they are series\ncircuits or parallel circuits. Write the correct answer in the space below\neach diagram. [6 marks]\n2. Look at the three circuit diagrams. Rank the circuits from brightest bulb to\ndimmest bulbs. [3 marks]\n..\n80\n.\nEnergy and Change\n\n.\n3. Explain your choices in the previous question. [5 marks]\n4. Look at the three circuit diagrams. Rank the circuits from brightest bulb(s)\nto dimmest bulb(s). [3 marks]\n5. Explain your choices in the previous question. [5 marks]\n6. Look at the circuit diagram below. Each light bulb is identical.\na) Is this a series or parallel circuit? Explain your answer. [2 mark]\nb) How do the brightness of bulbs A, B and C compare? (which is the\nbrightest?) [3 marks]\n.\n.\n81\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nc) What would happen to the brightness of the bulbs if the switch was\nopened? Explain your answer. [5 marks]\n7. Study the following diagram.\na) What is the relationship between the ammeter readings on A1 and A4?\nIn other words, how do the current strengths compare at these points\nin the circuit? Explain your answer. [3 marks]\nb) What is the relationship between the ammeter readings on A1, A2 and\nA3? In other words, how do the current strengths compare at these\npoints in the circuit? Explain your answer. [3 marks]\nTotal [38 marks]\n.\n..\n82\n.\nEnergy and Change\n\nDraw and discover the possibilities of what a slinky can be.\n.\n.\n83\n.\nChapter 3.\nSeries and parallel circuits\n\n. .\n4\n.\nVisible light\n..\n84\n..\nKEY QUESTIONS:\n• Where does light come from?\n• How does light travel?\n• How do we see?\n• Why do leaves look green?\n• How do mirrors work?\n• Why do my legs look crooked underwater?\nIn this chapter we will learn about visible light. We call it visible light because\nwe can see it with our own eyes. There are different forms of light which we\ncannot see with our naked eyes. Ultraviolet light is an example of a form of light\nwhich we cannot see with just our eyes. We will focus our attention on the\nvisible light spectrum and investigate how we are able to see different colours\nand how light behaves.\n.\n4.1 Radiation of light\nWhere does light come from? Natural light comes from luminous objects such\nas the Sun and light bulbs. We say that these objects emit light.\nThe Sun is our main source of light on Earth.\nA light bulb is a luminous object as it emits\nlight.\n.\nNEW WORDS\n• luminous\n• radiation\n• rectilinear\n• propagation\n.\nVISIT\nThe speed of light (video)\nbit.ly/GAMgFW\n\nThis image from NASA shows the Earth's lights at night. You can see how much we rely\non light nowadays.\n.\nDID YOU KNOW?\nIf you could travel at the\nspeed of light you could\ntravel around the\nequator 7,5 times in 1\nsecond!\n.\nTAKE NOTE\nThe Moon is NOT a\nluminous object as it\ndoes not emit its own\nlight light. It reflects the\nlight from the Sun.\nLight travels through space at a speed of 300 000 kilometers per second. We\nsay that energy is transferred by radiation. The energy of the light is transferred\nthrough space as electromagnetic waves in straight lines.\nLight and heat are transferred to Earth through space from the Sun by radiation.\n.\nDID YOU KNOW?\nIt takes light 8 minutes\nto travel from the Sun to\nthe Earth.\nLet's look at how light travels. We will make a simple camera to investigate how\nlight travels.\n.\n.\n85\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Make a pinhole camera\n.\nMATERIALS:\n• Pringles chip can\n• craft knife\n• aluminium foil\n• tape\n• ruler\n• drawing pin\nINSTRUCTIONS:\n.\nTAKE NOTE\nThe Sun emits radiation\nin all directions, but in\nthe diagram here, only\nthe radiation which\nreaches Earth has been\nshown.\n1. Measure 5 cm from the bottom of the can (opposite end to the plastic lid)\nand make a mark all around the can.\n2. Cut through the can along the line\nso that you have cut the can into 2\npieces.\n3. If you have a clear lid, put a piece of\nwax paper on top of the lid before\nsticking everything together.\n..\n86\n.\nEnergy and Change\n\n.\n4. Place the lid between the 2 pieces\nand stick it all together using tape.\n5. Wrap the aluminium foil around the\ncan to prevent any light from\ncoming in from the sides.\n6. Use a drawing pin to make a hole in the centre of the metal base of the can.\n7. Go outside with your pinhole camera.\n8. Point the metal end with the hole at an object which is in bright sunlight.\n9. Cup your hands around the other end and look through the open end.\nQUESTIONS:\n.\nVISIT\nLight travels in a straight\nline? (video)\nbit.ly/19n4T7g and\nbit.ly/174q6mx\n1. What did you see when you looked through the open end of the tube?\n2. What happens when you move closer or further away from an object?\n.\nDid you see an upside down image? Why is it upside down?\nWe see objects because light reflects off them and enters our eyes. If the image\nis upside down it means that the light from the bottom of the object has arrived\nat the top of the screen and the light from the top of the object has reached the\nbottom of the screen, as shown in the following diagram.\n.\n.\n87\n.\nChapter 4.\nVisible light\n\nWhen you moved closer to the object, the image appeared bigger, as shown in\nthe following diagram.\nWhat does this mean? It means that light must be travelling in straight lines.\nThis is called the rectilinear propagation of light.\n.\nVISIT\nCan you use what you\nhave learnt to understand\nhow this shadow illusion\nworks?\nbit.ly/156mx1y\nRay diagrams\nA ray diagram is a drawing that shows the path of light. Light rays are drawn\nusing straight lines and arrowheads, because light travels in straight lines. The\nfigure below shows some examples of ray diagrams.\n..\n88\n.\nEnergy and Change\n\nA ray diagram showing how you see\nanother person.\nA ray diagram showing how you see a\nreflection in a mirror.\n.\n4.2 Spectrum of visible light\n.\nNEW WORDS\n• composition\n• visible spectrum\n• dispersion\nThe visible light spectrum is the light that we are able to see with our naked\neyes. Have you ever wondered why everything is colourful and not just black\nand white? Have you ever seen a rainbow and wondered where the colours\nhave come from? The colours that we see everyday are part of the visible light\nspectrum. Let's investigate the visible light spectrum.\n.\nACTIVITY: Splitting white light\n.\nMATERIALS:\n• triangular perspex prism\n• ray box and power source\nINSTRUCTIONS:\n1. Connect the ray box to the power source. If you do not have a ray box,\nyour teacher will show you how to use a piece of cardboard with a slit cut\ninto it.\n2. Place the triangular prism on a white background.\n3. Shine a beam of white light through the side of the prism.\nQUESTIONS:\n1. Draw a picture showing what you observe.\n.\n.\n89\n.\nChapter 4.\nVisible light\n\n.\n.\n2. Write a description of what you observed.\n3. Write down the order in which the colours appear.\n4. If you repeat the experiment, does the order of the colours change?\n5. What do the different colours we see tell us about the composition of\nwhite light?\n.\n..\n90\n.\nEnergy and Change\n\nSo, what have we learned so far? Light radiates from luminous objects and\nalways travels in straight lines. The white light that we see is made up of the 7\ndifferent colours of the spectrum. When the 7 colours are travelling together we\nsee them as white light.\nThe 7 colours of the visible spectrum are Red, Orange, Yellow, Green, Blue,\nIndigo and Violet. Each colour has a different wavelength and frequency. Have\na look at the following image which shows the spectrum of visible light.\n.\nTAKE NOTE\nYou can use the\nabbreviation ROYGBIV\nto remember the order\nof the colours.\nThe colours combine to form white light.\n.\nTAKE NOTE\nThe primary colours of\nlight are red, green and\nblue.\n.\nACTIVITY: Colour spinning wheels\n.\nMATERIALS:\n• white cardboard\n• coloured pens or pencils (red, orange, yellow, green, blue, indigo, violet)\n• string\n• scissors\n• round object\nINSTRUCTIONS:\n1. Draw a circle on the cardboard. You can trace around a round object such\nas a cup or saucer to do this. Cut out the circle.\n.\n.\n91\n.\nChapter 4.\nVisible light\n\n.\n2. Now divide the circle into 7 equal segments. If you do not have indigo and\nviolet colours, but just one purple pen or crayon, then you can divide the\ncircle into 6 equal segments rather.\n3. Shade in each segment a different colour, in the order red, orange, yellow,\ngreen, blue, indigo, violet (or just purple if you do not have indigo and\nviolet).\n.\nDID YOU KNOW?\nAn artist might tell you\nthat the primary colours\nof paint are red, yellow\nand blue. This is\ndifferent to the primary\ncolours of light. This is\nbecause the pigments\nyellow, blue and red\ncannot be mixed from\nother pigments. In\nprinting, the primary\ncolours are magenta,\nyellow and cyan.\n4. Next, make two holes, one on either side of the centre as shown below.\n5. Thread the string through the holes and tie it in a loop.\n6. You are now ready to spin the wheel. Holding the ends of the loop in each\nhand, twirl the string over, like you would a skipping rope, so that the\nstring twists. Once the string is tightly twisted, pull your hands apart, then\nbring them back together. Continue bringing your hands in and out and\nwatch the circle spin.\n.\nVISIT\nThere is no pink light.\nbit.ly/1b2gFXU\n7. What do you observe about the colour of the wheel as it spins faster?\n.\n..\n92\n.\nEnergy and Change\n\nSo far we have been talking about the visible light spectrum. As we mentioned\nin the beginning, this is the light that we can see. We also spoke about how light\ntravels in electromagnetic waves. We can only see light with a certain range of\nwavelengths. What does this mean?\n.\nDID YOU KNOW?\nWavelengths can be as\nsmall as one billionth of\na meter, as with gamma\nrays. Wavelengths can\neven be as long as\nmeters, for example in\nradio waves.\nThe size of a wave is measured in wavelengths. A wavelength is the distance\nbetween two corresponding points on two consecutive waves. Normally this is\ndone by measuring from peak to peak or from trough to trough. Have a look at\nthe following diagram which illustrates a wavelength.\n.\nDID YOU KNOW?\nIn police forensics,\nultraviolet light can be\nused along with a\nspecial powder to\ndetect finger and shoe\nprints that can help\nsolve crimes.\nThe wavelengths of the different colours of visible light are different lengths, as\nshown in the following diagram.\nWe can also talk about the frequency of a wave. If a wave has a long\nwavelength, then it has a low frequency; if it has a short wavelength, then it has\na high frequency.\nOf visible light, orange and red light have the longest wavelengths (and lowest frequency)\nand violet, indigo and blue have the shorter wavelengths (and highest frequency).\n.\n.\n93\n.\nChapter 4.\nVisible light\n\nWhen it comes to visible light, we only see wavelengths of 400 to 700 billionths\nof a meter. This is called the visible spectrum. But, light waves are just part of\nthe wave spectrum. There is invisible light with shorter wavelengths, such as\nultraviolet light, and there are longer wavelengths, such as infrared light.\nHave you ever looked through a window and wondered why it is made of glass?\nLet's find out how light behaves when it strikes the surface of different types of\nmaterials in the next section.\n.\n4.3 Opaque and transparent substances\n.\nNEW WORDS\n• opaque\n• transparent\n• translucent\n• transmit\nThree different things happen when light hits a surface, it can be reflected\n(bounce off), absorbed or transmitted (pass through). Glass reflects some light\nbut most of the light is transmitted straight through. That's why we can see\nobjects on the other side of a closed window.\nWe say that glass is transparent. Let's find out more about what this means. If a\nsubstance is not transparent, it is opaque.\n.\nACTIVITY: Shadow Play\n.\nMATERIALS:\n• cardboard\n• clear plastic\n• plastic shopping bag\n• scissors\n• light source (ray box or light bulb)\nINSTRUCTIONS:\n1. Cut out three shapes from your cardboard. All of the shapes should be\nsimilar but three different sizes: small, medium and large.\n2. Switch on the light source.\n3. Hold your first shape a short distance in front of the light source.\n4. Look at the shadow that forms. Write down what you observe.\n5. Hold your second shape the same distance in front of the light source.\n6. Look at the shadow that forms. Write down what you observe.\n7. Hold your third shape the same distance in front of the light source.\n8. Look at the shadow that forms. Write down what you observe.\n9. The shadow is formed on the side furthest from the light source. It is dark\n..\n94\n.\nEnergy and Change\n\n.\nin colour and larger than the first and second shadows.\n10. Use your first cardboard shape as a template and cut the shape from the\nclear plastic and the plastic shopping bag.\n11. Hold the clear plastic shape the same distance from the light source. Write\ndown what you observe.\n12. Hold the plastic shopping bag shape the same distance from the light\nsource. Write down what you observe.\nQUESTIONS\n1. When you held the cardboard up to the light, did it allow light to pass\nthrough it? How do you know this?\n2. Is the cardboard shape opaque or transparent?\n3. What did you notice about the shadows formed by the different size\ncardboard shapes?\n4. Draw a diagram to show how the shadow is formed behind the opaque\nshape. Use straight lines with arrowheads to represent the rays of light.\n.\n.\n.\n95\n.\nChapter 4.\nVisible light\n\n.\n5. The distance between the shape and the light source was kept the same.\nWhat do you think would have happened to the shadow if the distance\nwas increased?\n6. Test your idea from question 5 by moving your cardboard shapes closer to\nand further away from the light source. What do you see? Were you\ncorrect in your prediction?\n7. Is the clear plastic shape opaque or transparent?\n8. Did the clear plastic cast a shadow?\n9. Explain why the cardboard casts a shadow but the clear plastic does not.\n10. Is the plastic shopping bag shape opaque or transparent?\n11. Explain why the shopping bag casts a lighter shadow.\n.\n..\n96\n.\nEnergy and Change\n\nWhat have we learned? Shadows are formed because light travels in straight\nlines and cannot pass through opaque objects.\nSubstances which transmit most of the light and only absorb or reflect a little bit\nare called transparent. Can you list some everyday objects which are\ntransparent?\nSubstances which completely reflect or absorb light without transmitting any\nare called opaque. Can you list some everyday objects which are opaque?\nSome substances, such as the plastic shopping bag, allow some light to pass\nthrough, but not all of it. This substance is translucent, or semi-transparent.\nShadows can be useful. Sundials have\nbeen used since ancient times as a\ntime-keeping device, like a watch or a\nclock. As the position of the Sun\nchanges in the sky, the shadow cast by\nthe style moves across the surface of\nthe sundial. The surface is marked with\nnumbers, allowing the shadow to\nindicate time of day.\nWe can use transparent objects to make filters. If we want red light we use a\nred glass bulb or a red plastic film placed in front of the light. Only red light is\nable to transmit through the red glass or plastic. The other colours are absorbed\nby the filter.\nThese are different colour filters for a camera. The red filter will only allow red light\nthrough and so the photograph will have a red effect applied to it. The other colours of\nlight are absorbed by the filter.\nNow that we have seen some examples of transparent and opaque substances,\nlet's take a closer look at what it means to absorb or reflect light.\n.\n.\n97\n.\nChapter 4.\nVisible light\n\n.\n4.4 Absorption of light\nLook at this picture of a ladybird. Why\nis it red and black? And why is the leaf\nso green? How do we see the different\ncolours? It all has to do with what\nhappens when light hits a surface.\nWhen light hits a surface, some of the\nlight is absorbed and the rest is\nreflected. It is the reflected light that\nreaches our eyes and allows us to see\nthe object.\nA ladybird.\nPreviously, we learned that white light is a mixture of different colours. When\nwhite light from the Sun hits the red shell of the ladybird all of the colours are\nabsorbed, except red. Red light is reflected back to our eyes and so we see a\nred ladybird.\nWe see the red shell of the ladybird as red light is reflected and the other colours are\nabsorbed.\nThe green leaf absorbs all the colours except green which it reflects back into\nour eyes.\n..\n98\n.\nEnergy and Change\n\nWe see a green leaf as green light is reflected and the other colours are absorbed by the\nleaf's surface.\nWhat about the black spots of the ladybird? Is black a colour? The black spots\non the ladybird absorb all the colours and no light is reflected. That is why they\nappear black.\n.\nTAKE NOTE\nAlthough we can get\nblack paint as a\npigment, black is not a\ncolour of light. Black is\nthe result of the\ncomplete absorption of\nlight.\nDo you remember learning about heat as energy transfer in Gr 7? We looked at\nthe absorption of heat. We saw that black, matt objects absorbed all of the light\nenergy, while white objects reflected all of it. Black, matt (not shiny) objects\nabsorb all of the colours of light and reflect none and so appear black to our\neyes.\nWhat about a white object? Why do you think white objects look white? Have a\nlook at the following diagram for a clue.\n.\n.\n99\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Why do objects look red under red\nlight?\n.\nMATERIALS:\n• piece of red plastic to act as a filter\n• light source (light bulb or torch)\n• white object\nINSTRUCTIONS:\n1. Place a white object on the desk.\n2. Switch on your light source and place the red plastic in front of the light.\n3. Shine the light (with the red plastic in front) onto the piece of white paper.\nQUESTIONS:\n1. What colour was the page under normal light?\n2. Why does the page appear white in normal light?\n3. What did you see when the red plastic filter shone on the white page?\n4. Explain why the paper changed colour.\n.\nLet's now look more at what we mean by reflection of light.\n..\n100\n.\nEnergy and Change\n\n.\n4.5 Reflection of light\n.\nNEW WORDS\n• reflect\n• incident ray\n• reflected ray\n• normal line\n• angle of\nincidence\n• angle of\nreflection\n• perpendicular\nWhen light hits a surface it is\noften reflected off the surface.\nThis photograph shows how\nlight is reflected off a still lake,\ncreating a mirror image of the\ntree. The still, flat surface of the\nlake has acted as a mirror.\nA tree reflection.\nHave some fun with these photos of reflections in water. One photograph is the\nright way up and the other one is upside down! Which one is which?\nReflections on the Negro River in the\nAmazon.\nReflections in the Arno River in Italy.\nMost surfaces reflect light. When light strikes a reflective surface, it can change\ndirection. Let's look at how this happens.\nWhen light reflects off a surface the ray which hits the surface, it is called the\nincident ray. The ray of light which is reflected from the surface is called the\nreflected ray. When we draw diagrams of reflection we also draw in an\nimaginary line to help us measure different angles. This line is called the normal.\nThe normal line is always drawn perpendicular to the surface.\nBetween the normal line and the incident and reflected rays, there are two\nangles. These are:\n• angle of incidence - the angle between the incident ray and normal line\n• angle of reflection - the angle between the reflected ray and normal line\nThe following diagram explains these concepts.\n.\n.\n101\n.\nChapter 4.\nVisible light\n\nLet's investigate the relationship between the angle of incidence and the angle\nof reflection.\n.\nINVESTIGATION:\nIs there a relationship between the\nangles of incidence and reflections?\n.\nAIM: To investigate the reflection of light from a surface.\nINVESTIGATIVE QUESTION:\nLook at the diagram above and try to formulate an investigative question for\nthis investigation.\nHYPOTHESIS: The angle of incidence is equal to the angle of reflection\nMATERIALS AND APPARATUS:\n• mirror\n• white paper\n• pencil\n• protractor\n• ruler\n• ray box\nMETHOD:\n1. Put a white piece of paper on the desk.\n2. Use your ruler to draw a straight line near the top of the white paper.\n..\n102\n.\nEnergy and Change\n\n.\n3. Use your protractor to make a right\nangle in the middle of your pencil\nline. This is the normal line.\nMarking a right angle with a protractor.\n4. Place your mirror upright along the\nfirst line.\n5. Shine a light from the ray box along\nthe paper so that it \"hits\" the mirror\nwhere your normal line and your\nmirror meet.\nA mirror is placed on the line and a ray\nshone to strike the mirror at the normal\nline.\n6. Use a pencil to mark the incident\nlight ray.\nMarking the incident light ray.\n7. Use a pencil to mark the reflected\nlight ray.\nMarking the reflected ray.\n8. Remove the mirror and switch off\nthe ray box.\n9. Use a ruler and pencil to draw a line\nfrom the points you have marked on\neach ray to the normal line.\nDrawing in the rays.\n.\n.\n103\n.\nChapter 4.\nVisible light\n\n.\n10. Mark the angle of incidence (i) and\nangle of reflection (r).\nYour ray diagram should look similar to\nthis.\n11. Turn the ray box on again to confirm\nthat your pencil lines follow the rays.\nThe ray diagram overlaps the actual rays.\n12. Use a protractor and measure the\nangle of incidence and the angle of\nreflection and record your results in\nthe table.\n13. Repeat this method 3 more times,\neach time using a different angle of\nincidence.\nA different angle of incidence.\n.\nTAKE NOTE\nKeep one of the sheets\nwith your drawn ray\ndiagram for the next\nactivity.\nRESULTS:\nFill your results into the following table.\nRepeat\nAngle of Incidence\nAngle of Reflection\n1\n2\n3\n4\nANALYSIS:\n1. Has your investigation provided everything you need to answer your\ninvestigative question?\n..\n104\n.\nEnergy and Change\n\n.\n2. How could you improve this investigation to get more accurate results?\nCONCLUSION:\nWhat can you conclude based on your results?\n.\nWhenever light is reflected from a surface, the angle of incidence to equal to\nthe angle of reflection. On a smooth surface all the light rays are reflected in the\nsame way and so the image is clear and focused.\nA mirror is an example of a smooth surface. The image you see is focused and\nclear. As you can see in the photograph, the scientists and engineers are clear\nand focused in the mirror image.\nA mirror segment from one of NASA's telescopes provides a clear and focused reflection.\n.\nTAKE NOTE\nIn reflection, not only is\nthe angle of incidence\nequal to the angle of\nreflection, but the\nincident ray and\nreflection ray are also in\nthe same plane.\n.\nVISIT\nWhat colour is a mirror?\n(video)\nbit.ly/GABdNZ\nWhat happens when we do not have a smooth surface? Have a look at the\nphoto.\n.\n.\n105\n.\nChapter 4.\nVisible light\n\nWhy is the reflection of the grass and reeds not clear, but rather blurred?\n.\nACTIVITY: Light reflection off aluminium foil\n.\nMATERIALS:\n• aluminium foil\n• white paper\n• ray box\nINSTRUCTIONS:\n1. If possible, use the white sheets of paper from the last investigation where\nyou drew your ray diagrams.\n2. Similar to what you did in the last investigation, set up a ray box and direct\nthe ray along the line of incidence which you drew.\n3. Crumple a piece of aluminium foil and place this in the spot instead of the\nmirror.\n4. Observe the reflected ray.\nQUESTIONS:\n1. Describe the reflected ray off the aluminium foil and how this compares to\nthe reflected ray off the mirror.\n.\nVISIT\nWatch a video about the\ncreative way that\nscientists have tried to\nanswer the question:\n\"What is light?\"\nbit.ly/GAMvAL\n2. Why do you think you observed these differences?\n.\n..\n106\n.\nEnergy and Change\n\nCan you now see why reflections off rippled water are not clear, but rather\nblurred? This is because the light rays have not reflected parallel to each other\nas they do from a smooth surface, but have scattered in different directions.\nThe following table shows the difference between a smooth surface and a rough\nsurface. Straight parallel rays are approaching the surface. You need to draw in\nthe reflected rays to show specular (clear) reflection from a smooth surface and\ndiffuse (unclear) reflection from a rough surface.\n.\nTAKE NOTE\n'Diffuse' can mean\nunclear as well as\nspread out. In this\nexample, the reflection\nis unclear because the\nrays are spread out or\ndiffuse.\nSpecular diffusion from a smooth\nsurface\nDiffuse reflection from a rough\nsurface.\nVisible light is the range of frequencies of light that are visible to the human eye,\nand is responsible for the sense of sight. Are you curious to find out how we\nactually see light? Let's discover more in the next section.\n.\n4.6 How do we see light?\n.\nNEW WORDS\n• retina\n• stimulate\nHow is it that we are able to see light? Light that is absorbed by objects does\nnot enter the eye. Only reflected light or direct light from luminous objects can\nenter the eye and be interpreted. Have a look at the following image which\nshows the outer structure of the eye.\nWe can see the iris, the pupil and the sclera. The sclera is a the tough white,\nouter part of the eye, which acts as protection. The iris is the coloured part of\nthe eye which differs from person to person. It is circular and surrounds the\npupil. Light enters the eye through the pupil.\n.\nVISIT\n2012 Nobel Prize: How do\nwe see light?\nbit.ly/1a4zs2D\n.\n.\n107\n.\nChapter 4.\nVisible light\n\nThe size of your pupil changes in different light conditions. In bright light, the pupil\ncontracts (gets smaller) to let less light through (as on the left), and in low light your\npupil dilates (gets bigger) to let more light through (as on the right).\nLet's take a look at the internal structure of the human eye. The following\ndiagram shows a cross section through the eye. The eye is actually a large ball,\nand only a small part is visible on the outside. Covering the iris is a tough,\ntransparent layer called the cornea. Behind the iris is the lens. Both the cornea\nand the lens help you to focus the light entering your eyes, as we will learn\nabout in the next section.\n.\nTAKE NOTE\nThe fovea is the part of\nthe eye located in the\ncentre of the retina\nwhere the clearest\nimage is formed.\nA diagram of the eye.\nThe light travels through the eye and hits the retina at the back of the eyeball.\nThe retina is a layer of tissue lining the back of the eyeball, as indicated in the\ndiagram, it is the yellow layer. The retina consists of cells which are sensitive to\nlight. Light enters the eye and forms an image on the back of the eyeball. The\nway in which light hits the back of the eye, is similar to what happens in a\npinhole camera. The receptor cells convert the light energy into electrical nerve\nimpulses. These impulses travel out of the eye through the optic nerve and to\nthe brain where they are interpreted as sight.\n.\nTAKE NOTE\nThe cell is the basic\nstructural and\nfunctional unit of all\nliving things. We will be\nlearning more about the\ncell next year in Gr 9\nLife and Living.\n.\nVISIT\nFind your blind spot with\nthis optical illusion.\nbit.ly/19jumEr\nSo how do we see colour? Do you remember when we spoke about why the\nladybird appears red and black? Look at the following diagram again.\n..\n108\n.\nEnergy and Change\n\nThe white light hits the ladybird's surface. The white light has all the colours of\nlight, but when it hits the red surface, only the red light is reflected. The other\ncolours are absorbed by the red surface. This means that when we look at the\nred parts of the ladybird, we only get red light reflected into our eyes.\nTherefore, when this reflected light hits our retina and the electrical impulse is\nsent to our brains, we see the red colour.\n.\nDID YOU KNOW?\nEach of your eyes has a\nsmall blind spot at the\nback of the retina where\nthe optic nerve\nattaches. You do not\nnormally notice the hole\nin your vision because\nyour eyes work together\nto fill in each other's\nblind spot.\n.\nACTIVITY: Seeing colours\n.\nMATERIALS:\n• coloured pens or pencils\nINSTRUCTIONS:\n.\nDID YOU KNOW?\nThe cells in your eye\ncome in different\nshapes. Rod-shaped\ncells allow you to see\nshapes, and\ncone-shaped cells allow\nyou to see colour.\n1. Answer the following questions about how we see objects.\n2. Draw a ray diagram to accompany your written answer.\n3. An example has been done for you.\nLook at the picture of a sunflower.\nA black and yellow sunflower.\n.\n.\n109\n.\nChapter 4.\nVisible light\n\n.\nWe can draw a ray diagram to show why we see the green leaves as green, as\nshown below. The green surface of the leaves absorb all the colours of white\nlight except green light which is reflected into our eyes.\nNow explain why the petals appear yellow and the centre appears black. Use\nthe concepts of absorption and reflection in your explanation. Draw diagrams\nto support your answer.\n.\nHeath has bought himself a blue car.\nExplain why we see the car as blue by\nusing the absorption and reflection of\nlight. Draw a diagram to support your\nanswer.\nHeath's blue car.\n..\n110\n.\nEnergy and Change\n\n.\n.\n.\n.\nVISIT\nA simulation on colour\nvision.\nbit.ly/18TbpEA\nWe have looked at opaque and transparent substances, absorption of light,\nreflection of light and how we see light. We are now going to go back to\ntransparent substances and see how light can interact with these materials.\n.\n4.7 Refraction of light\nDo you remember the last time you drank a cold drink with a straw? Did you\nnotice that the straw did not look straight anymore once it was in the water or\ncool drink?\n.\nNEW WORDS\n• refraction\n• medium\n• optical density\nWhy does the pencil in this glass of water look bent?\nLet's investigate this by examining what happens to light when it passes\nthrough a glass block.\n.\n.\n111\n.\nChapter 4.\nVisible light\n\n.\n.\nINVESTIGATION:\nWhat happens to light when it\npasses through a glass block\n.\nWe are going to investigate what happens to a ray of light when it passes from\nair and into a glass block and then from the glass block back into air. We are\ngoing to use a glass block with parallel sides.\nBefore we start the investigation, we need to think about how we are going to\ndetermine if light changes direction or not. Do you remember in the\ninvestigation on reflection where we measured the angle of incidence and the\nangle of reflection? What did we find in this investigation?\nWhen light passes through a transparent substance, we can also measure the\nangles. Look at the following diagram. The angle of incidence (i) is measured\nbetween the incident light ray and the normal line. As the light passes through\nthe transparent substance, the angle of refraction (r) is the angle between the\nrefracted light ray and the normal.\nA light ray passing from one medium to another.\nIn the diagram above, you can see that the angle of refraction is smaller than\nthe angle of incidence. Therefore, the refracted light ray changed direction\nwhen it entered the transparent medium. We can also say something about\nwhich direction it bent towards. Did the light ray bend towards or away from\nthe normal line?\nThe next diagram shows another outcome.\n..\n112\n.\nEnergy and Change\n\n.\nA light ray passing from one medium to another.\nIn the diagram above, does the refracted ray change direction when it enters\nthe transparent medium? Give a reason for your answer.\nIn which direction did the refracted ray change?\nWe are now ready to start our investigation.\nAIM: To determine whether light changes direction when it passes through a\nparallel-sided glass block.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS:\n• glass block\n• ray box, laser pointer or other light source\n• protractor\nMETHOD:\n.\nTAKE NOTE\nThe emergent ray from\na parallel sided block is\nparallel to the incident\nray.\n1. Put the glass block in the centre of a piece of white paper and trace around\nit.\n2. Shine a ray of light into the glass block. The ray should be at an angle to\nthe surface of the block.\n.\n.\n113\n.\nChapter 4.\nVisible light\n\n.\n3. Trace the light ray with pencil and mark the point at which it enters the\nglass block.\n4. The light ray emerges on the other side of the glass block. Mark the point\nat which it emerges with a pencil and trace the emergent ray.\n5. Remove the glass block. Your diagram should look similar to the one\nabove.\n6. Draw a line joining the incident ray and emergent ray. You have traced the\nrefracted ray through the glass block.\n7. Draw the normal lines where the incident ray meets the block and where\nthe emergent ray leaves the block.\n8. Measure the angles labelled 1, 2, 3 and 4 as shown on the diagram with a\nprotractor.\n9. Fill in the measurements in the table.\n10. Repeat the steps above three times using different angles of incidence\n(angle 1).\n..\n114\n.\nEnergy and Change\n\n.\nRESULTS AND OBSERVATIONS:\nFill your results into the following table.\nExperimental\nrepeat\nAngle 1\nAngle 2\nAngle 3\nAngle 4\n1\n2\n3\n4\n1. Which pairs of angles are equal in the measurements you have taken?\n2. Which of the angles you measured are the angles of incidence and which\nare the angles of refraction? Write this down below and mark them on the\ndiagram above.\n3. What do you notice about the angle of incidence and angle of refraction\nfor each of your sets of measurements?\n4. Did the light entering the glass block bend towards or away from the\nnormal line?\n5. Make the angle of incidence zero (make the light ray enter the block\nperpendicular to the surface). What is the angle of refraction?\nCONCLUSION:\nWhat can you conclude from your results?\n.\n.\nVISIT\nLearn more about\nrefraction with this\nsimulation.\nbit.ly/GAxLmc\nThe angle of incidence is not equal to the angle of refraction because the light\nhas changed direction as it enters the glass. Therefore, when light travels from\none medium to another, it bends, or changes direction. This is called refraction.\n.\n.\n115\n.\nChapter 4.\nVisible light\n\nWhen light enters a different medium at right angles then it does not change\ndirection.\nSo why does the light refract? Light behaves as a wave does and waves travel\nat different speeds in different media. For example, light travels faster in air\nthan it does in water. When light enters a different medium, it changes speed,\nand if it entered at an angle other than 90o, then it also changes direction. The\nmore dense the medium, the slower the light moves.\nDo you remember learning about density last term in Matter and Materials?\nWrite down your own definition for density in the space below.\n.\nTAKE NOTE\nRemember that\nalthough we learn\nabout Natural Sciences\nin 4 strands throughout\nthe year, there are many\nconnections and links\nbetween the strands.\nIf light moves from a less dense medium, like air, into a denser medium, like\nglass, then the light slows down. The light will bend towards the normal line.\n.\nVISIT\nThe speed of light in glass.\nbit.ly/1fcfJVZ\nIf light moves from a more dense medium to a less dense medium then the light\nspeeds up and moves away from the normal.\nWhen light refracts and changes direction as it passes through different\nmediums, it can distort what we see. Think back to the pencil or straw in a glass\nof water at the start of the section. We can now explain why a drinking straw or\npencil in a glass of water looks bent. The light bends when it moves from one\nmedium to another. Light moves from the air to glass to water, and therefore\nchanges direction.\nIf you have stood in a pool of water before and looked down, have you noticed\nhow short your legs appear to be? Let's have a look at this a bit more in the\nnext activity.\n..\n116\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magic coin trick\n.\nMATERIALS:\n• coin\n• prestik\n• opaque bowl or cup\n• water\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Put a small amount of prestik onto the bottom of the bowl.\n3. Stick the coin to the bottom of the bowl.\n4. Take small steps back from the desk/table until you cannot see the coin\nover the lip of the bowl.\n5. Ask your partner to slowly pour water into the bowl and observe.\nQUESTIONS:\n.\nVISIT\nWatch a video that shows\nand explains the coin\nactivity.\nbit.ly/15NmXXO\n1. What happened when your partner poured the water into the bowl?\n2. Where does the coin appear to be?\n3. Explain why the coin can be seen when the water is added, but not before.\nThe diagrams below will help you explain what is happening in words.\n.\nTAKE NOTE\nThe diagrams used here\nshow the container as\ntransparent so that you\ncan see the coin inside,\nwhereas you will\nactually be using an\nopaque container.\nEmpty container.\nContainer with water.\n.\n.\n.\n117\n.\nChapter 4.\nVisible light\n\nRefraction can be used to explain why images appear to be distorted when we\nview them through transparent mediums. For example, if you are looking at\nyour legs or hands through some water, they will appear closer than they\nactually are as the light is refracted. Look at the photograph of the glass with\nwater in it in front of diagonal lines. Can you see how the lines are distorted\nwhen the light travels through the water and glass compared to when it does\nnot?\nLight refraction through glass and water.\nCan you remember how we split white light into the separate colours of the\nvisible spectrum in the beginning of this chapter? What did we use to do this in\nthe activity?\nWe can do this because the different\ncolours of light bend by different\namounts when the light enters a\ndifferent medium. Different colours of\nlight will slow down to different\nspeeds, causing them to bend by\ndifferent amounts.\nRefraction through a triangular prism.\nWhen the white light entered the prism it refracted. The different colours of\nlight travel at different speeds in the prism so they refracted at different angles\nand split up. Red light refracts the least and the violet light refracts the most as\nyou can see in the following diagram.\n..\n118\n.\nEnergy and Change\n\nPrisms are not the only objects that can split white light into separate colours.\nIn fact, a rainbow is a good example of white light splitting up.\nA rainbow.\nLight from the Sun enters the raindrops and refracts. The light is then reflected\noff the back of the raindrop. When the light passes out of the raindrop it is\nrefracted again and the colours split up even more as shown in the diagram.\nA raindrop refracts and reflects light, dispersing white light into the colours of the visible\nspectrum.\n.\n.\n119\n.\nChapter 4.\nVisible light\n\nWhat colour is at the top of a rainbow and which colour is at the bottom?\nDoes this match the order which we see in the diagram showing how light is\nrefracted and reflected in a raindrop?\nHow does this happen? When we see a rainbow, we see a combination of\nmillions of raindrops. Although each raindrop refracts and reflects all 7 colours,\nwe only see only colour of light reflected from each particular raindrop. This\ndepends on the angle of the raindrop from our position. Therefore, the\nraindrops higher up in the sky reflect red light to us and the rain drops lower\ndown reflect violet light to us. This is shown in the following diagram.\nWe see rainbows with red at the top and violet at the bottom due to the combination of\nmillions of raindrops. We only see one colour reflected from a particular raindrop,\ndepending on its position in the sky.\nWe are now going to look at an application of the refraction of light.\nLenses\n.\nNEW WORDS\n• diverge\n• converge\n• focus\nDo you remember when we spoke about how we see light and the structure of\nthe eye, we mentioned that there is a lens just behind the iris? Another place\nwhere you may have seen lenses before are in reading glasses which some\npeople wear to correct their vision. Or, have you seen how a magnifying glass\nmakes things appear bigger. What are lenses and how do they work?\nA magnifying glass makes things look bigger.\n..\n120\n.\nEnergy and Change\n\nA lens is a transparent object which focuses or refracts light. When light is\nspread out, we say it has diverged. Some lenses will diverge light while others\nwill converge light, bringing the light rays together. When light rays are all\nbrought to the same point, we say they have been focused. Let's have a look at\nthis more closely.\n.\nACTIVITY: Diverging and converging light with\nlenses\n.\nMATERIALS:\n• ray box or light source\n• concave lens\n• convex lens\n• piece of paper\n• pencil\nBefore we start, it is important that you know the difference between a convex\nand a concave lens.\nConvex lens\nConcave lens\nA convex lens has one\nside which curves or\nbulges outwards. A\nconvex lens converges\nlight.\nA concave lens has one\nside which curves or is\nhollowed inwards. A\nconcave lens diverges\nlight.\n.\nTAKE NOTE\nA lens can have two\nsides which are concave\nand it is then called a\nbiconcave lens or two\nsides which are convex\nand it is then called a\nbiconvex lens.\n.\n.\n121\n.\nChapter 4.\nVisible light\n\n.\nINSTRUCTIONS:\n1. Place a ray box or light source on one side of a piece of paper and turn it\non. Observe the light rays. You might see something as shown in the\nphotograph here.\nThree rays coming out of a ray box.\n2. Turn the ray box off.\n3. Place the convex lens (with the rounded surface) on the piece of paper\nwhere the light rays will pass through it. Trace around it.\n4. Turn on the ray box or light source and observe what happens to the rays\nwhen they pass through the lens.\nLight rays passing through a convex lens.\n5. Trace the path of the light rays on your piece of paper.\n6. Describe what has happened to the light rays.\n7. Mark the point where the light rays cross. This is called the focal point of a\nconvex lens.\n8. Turn off the ray box or light source and place a new piece of paper in front\nof it.\n9. Now place the concave lens in the path of the light rays and trace around\nthe lens.\n10. Turn on the light source and observe what happens to the rays.\n..\n122\n.\nEnergy and Change\n\n.\n11. Trace the path of the rays on the piece of paper.\nA concave lens in front of the rays of light.\n12. Describe what has happened to the light rays.\n13. Turn off the light rays and extend the rays you have drawn until they meet\nat a point in front of the lens. This is the focal point of a concave lens.\n14. If you still have your pin hole cameras, place a convex and concave lens in\nfront of the camera and observe the image that forms.\nViewing a light source through a pinhole camera with different lenses.\n15. Is the image larger or smaller when you observe through a concave lens?\n16. Is the image larger or smaller when you observe through a convex lens?\n.\n.\n.\n123\n.\nChapter 4.\nVisible light\n\nWe have now seen how lenses can disperse or focus light. Have a look at the\nfollowing diagrams which show how a biconvex lens converges light and a\nbiconcave lens diverges light.\n..\n124\n.\nEnergy and Change\n\nConverging lens\nDiverging lens\nA converging lens refracts the light\nentering it and bends the light rays\nto a focal point on the other side of\nthe lens.\nA diverging lens refracts the light\nentering it and bends the light rays\naway from each other. The light\nrays can be traced back to a focal\npoint in front of the lens.\nWhat do we use lenses for? Think of a magnifying glass. If you hold a\nmagnifying glass over a picture or words then it enlarges the image. Is a\nmagnifying glass an example of a diverging or converging lens?\nLet's think about how this works. Imagine you are looking at the ladybird from\nthe beginning of the chapter through a magnifying glass. The ladybird looks\nbigger than what it actually is. When the object you are viewing is closer to the\nlens than the focal point, you see a virtual image of the ladybird that is larger\nthan the object.\nHave a look at the first diagram below. Can you see that the ladybird is between\nthe focal point and the lens? The rays reflected from the ladybird are refracted\nby the magnifying glass and enter the person's eye.\n.\n.\n125\n.\nChapter 4.\nVisible light\n\nIn the next diagram you can see how your eyes see a virtual image of the\nladybird which is bigger than the object. The more curved the convex lens is in\na magnifying glass, the greater its ability to magnify objects.\n.\nTAKE NOTE\nWhen you hold a\nmagnifying glass up\nand view a distant\nobject, the object\nappears smaller and\nupside down. Unlike\nwhen viewing the\nladybird close up, the\ndistant object is beyond\nthe focal point of the\nlens, which results in\nthis effect.\n.\nVISIT\nHow do lenses work?\nbit.ly/GABjoO\nDo you remember what the human eye looks like? We have lenses in our eyes\nto allow us to see. The light enters the eye and passes through the lens. The\nlens focuses the light onto the back of our retina so that a clear image is formed.\nWhat type of lens do we have in our eyes? Give a reason for your answer.\nIn order for a clear image to form, the lens in our eye needs to focus the light\nrays coming into our eyes so that the focal point falls on the retina. This\ndepends on the shape of the lens in our eyes. Sometimes, people have lenses in\ntheir eyes that cannot focus properly. Have a look at the following diagram\nwhich shows a normal eye and then an eye which focuses before the retina\n(near-sighted) and behind the retina (far-sighted).\n..\n126\n.\nEnergy and Change\n\nOptical glasses, or spectacles, are used to correct near or far-sightedness.\nIf you are near-sighted you need a diverging lens. Would this be a biconcave or\nbiconvex lens?\n.\nDID YOU KNOW?\nA contact lens is\ndesigned to rest on the\ncornea of the eye and\ncorrect vision. Leonardo\nda Vinci was the first to\ncome up with the idea\nin the 16th century to\nhelp prevent eye\ninfection.\n.\nDID YOU KNOW?\nA microscope makes a\ntiny, nearby object look\nmuch bigger. A\ntelescope makes a\nlarge, distant object\nlook much closer and\nbrighter. In both, light\nfrom the object passes\nthrough two or more\nlenses to form an\nimage. The lens shapes\nand distances between\nthem determine how\nthe image is produced.\nIf you are far-sighted you need a converging lens. Would this be a biconcave or\nbiconvex lens?\nAn optometrist holds a lens in front of a patient's eye to correct her vision.\nThe following image shows how lenses can be used to correct far and\nnear-sightedness.\n.\n.\n127\n.\nChapter 4.\nVisible light\n\n.\nTAKE NOTE\nNext term in Planet\nEarth and Beyond we\nwill look at how lenses\nare used in optical\ntelescopes to view\nobjects in space.\n.\nACTIVITY: Research careers in optics\n.\n.\nVISIT\nAn interview conducted\nwith an optometrist.\nbit.ly/19WxYYa\nThere are many different careers in the field of geometric optics.\nINSTRUCTIONS:\n1. Work in groups of 3.\n2. Interview someone in the field of geometric optics and find out how they\nchose their career and what and where they studied.\n3. Write a paragraph explaining the career and the study options available in\norder to qualify for that career.\n4. Here are some examples of careers in geometric optics.\na) Optometry\nb) Ophthalmology\nc) Optoelectronics\nd) Illumination engineering\n.\n..\n128\n.\nEnergy and Change\n\n.\nVISIT\nWant to take part in some\nreal science research?\nCheck out these citizen\nscience projects to get\ninvolved easily.\nbit.ly/15KjnmD\nRemember to discover more online by visiting http://www.curious.org.za and\nby typing the links in the Visit margin boxes into your internet browser to watch\nany videos, play with simulations or read an interesting article.\nType the bit.ly link for the video or site that you want to visit into the address bar of your\nbrowser on your computer, tablet or mobile phone.\n. .\nSUMMARY:\n.\nKey Concepts\n• Light travels in straight lines.\n• White light consists of all the colours of the visible spectrum.\n• The colour spectrum can be seen when white light is dispersed by a\nprism or a raindrop (rainbow).\n• Light cannot pass through opaque objects.\n• Light can pass through transparent objects.\n• Light is absorbed by some materials.\n• A material appears to be a certain colour because it reflects that part of\nthe colour spectrum. Other wavelengths of light are absorbed.\n• In reflection, the angle of incidence is equal to the angle of reflection.\n• On a smooth surface, parallel rays of light are all reflected at the same\nangle.\n• On rough surfaces, the light is scattered and the image produced is not\nclear.\n• The human eye has specialised cells in the retina which convert light\ninto electrical nerve impulses. The nerve impulses are transmitted to\nthe brain via the optic nerve, where they are interpreted.\n• Light travels at different speeds in different media.\n• When light enters a different medium at an angle, the light is refracted.\n• If the light slows down, the light bends towards the normal line.\n• If the light speeds up, the light bends away from the normal line.\n• Converging lenses refract and focus light.\n• Diverging lenses and triangular prisms refract and disperse light.\n• Lenses have many applications, for example, in glasses to correct vision,\nmicroscopes, telescopes and magnifying glasses.\n.\nConcept Map\nThe concept map on the next page shows how all the concepts relating to\nvisible light link together.\nComplete the map to reinforce what you have\nlearned in this chapter.\n.\n.\n129\n.\nChapter 4.\nVisible light\n\n.\n\n.\n.\nREVISION:\n.\n1. Match the correct definitions to the terms in the following table. Write the\nletter of the definition next to the correct number below. [12 marks]\nTerm\nDefinition\n1. Radiation\nA. Light cannot pass\nthrough.\n2. Visible light\nB. The angle of incidence\nequals the angle of\nreflection when a ray is\nreflected off a smooth\nsurface.\n3. Opaque\nC. One of the ways in\nwhich energy is\ntransferred, specifically\nthrough a vacuum\n4. Transparent\nD. When light enters a\ntransparent medium it\ncan change direction.\n5. Absorption\nE. Curved inwards.\n6. Reflection\nF. The spectrum of light\nwhich we are able to see.\n7. Retina\nG. Bulging outwards.\n8. Refraction\nH. A transparent object\nable to refract and focus\nlight.\n.\n.\n131\n.\nChapter 4.\nVisible light\n\n.\nTerm\nDefinition\n9. Diverging\nI. Light can pass through.\n10. Lens\nJ. When light rays are\nspread out from a point.\n11. Concave\nK. A layer of tissue at the\nback of the eye which is\nsensitive to light.\n12. Convex\nL. When the surface of a\nsubstance absorbs\ncertain colours of light.\nAnswers:\n1:\n2:\n3:\n4:\n5:\n6:\n7:\n8:\n9:\n10:\n11:\n12:\n..\n132\n.\nEnergy and Change\n\n.\n2. A beam of white light is shone through a glass prism. It splits up into seven\ncolours which are shone on a screen. A learner took a photograph which is\nshown below and drew a ray diagram to show the prism. The colours are\nmarked 1 to 7 in the diagram.\nA photograph of the prism.\nA diagram drawn by the learner.\na) What does this tell us about white light? [1 mark]\nb) Why does the light do this when it passes through the prism? [3\nmarks]\nc) What colour is at label 1 and what colour is at label 7? Explain your\nanswer. [3 marks]\nd) What label corresponds to the colour of grass? [1 mark]\ne) Can you see there are two other lighter, white rays emerging from the\nprism? What do you think this is the result of? [2 marks]\n3. Why does an opaque object cast a shadow? [2 marks]\n.\n.\n133\n.\nChapter 4.\nVisible light\n\n.\n4. Look at the following photograph of water in a pond and answer the\nquestions.\nWater in a pond.\na) How are we able to see the image of the wooden poles sticking up on\nthe edge of the pond? [2 marks]\nb) Why is the image not clear, but blurred? [2 marks]\n5. Two learners are discussing the colours of light. They decide that white\nand black are not really colours of light. If they are not colours, then how\ncan we see them? [5 marks]\n6. Explain how we are able to see the different colours on the South African\nflag. [6 marks]\n..\n134\n.\nEnergy and Change\n\n.\n7. Draw a ray diagram in the space provided to show how we see the green\npart of the flag. [5 marks]\n.\n8. Which diagram shown below correctly shows the path of a ray of light\nthrough a triangular piece of glass? [2 marks]\n.\n.\n135\n.\nChapter 4.\nVisible light\n\n.\n9. Complete the following sentence and write it out in full on the lines\nprovided: When light travels from a less dense into a more dense\ntransparent medium, it refracts and bends\nthe normal line.\nWhen light travels from more dense to a less dense medium, it refracts and\nbends\nfrom the normal line. [2 marks]\n10. Draw a diagram to show what is meant by 'when the refracted ray bends\ntowards the normal'. Mark the angle of incidence and angle of refraction.\nIndicate which medium is denser [4 marks]\n.\n11. Study the following diagram and answer the questions that follow.\na) This diagram is a drawing that a learner made during an investigation\ninto the refraction of light. What does the red line represent in this\ndiagram? [1 mark]\n..\n136\n.\nEnergy and Change\n\n.\nb) What do the blue lines represent? Label this on the diagram. [1 mark]\nc) The light passes from the air and into a block of another medium. Is\nthis medium more or less dense than air? Give a reason for your\nanswer. [2 marks]\nd) What type of medium could the block be made from? [1 mark]\ne) Label the incident ray and the emergent ray on the diagram. [2 marks]\nf) Label the angles of incidence (i) and angles of refraction (r) on the\ndiagram. [2 marks]\n12. Which diagram shown below shows the path of a light beam passing\nthrough a rectangular glass prism correctly? [2 marks]\n13. Why does it look like the tree trunk in the photograph is skew? [2 marks]\n.\n.\n137\n.\nChapter 4.\nVisible light\n\n.\n14. What shape does a lens have to have in order to focus the light? [1 mark]\n15. Draw a ray diagram to show how a converging lens focuses light to a point.\n[4 marks]\n.\n16. Which eyesight defect can be fixed by using a converging lens? Explain\nwhat this defect is and why it can be corrected. [4 mark]\nTotal [74 marks]\n.\n..\n138\n.\nEnergy and Change\n\n.\n.\n.\nGLOSSARY\nammeter:\ndevice that measures the strength of an electric\ncurrent\nampere:\nthe standard unit for measuring electric current\nangle of incidence:\nthe angle between the incident ray and the normal\nline\nangle of reflection:\nthe angle between the reflected ray and the normal\nline\nattract:\nto pull something closer\ncell:\na source of energy for an electric circuit\ncomponent:\na part of a larger system\ncomposition:\nthe parts of a mixture\nconductor:\na substance which easily transmits electricity, heat,\nsound or light\nconverge:\nlight rays that come together and focus on a point\ndelocalised:\nnot limited to a particular place, free to move\ndischarge:\nthe sudden flow of charged particles between two\nelectrically charged objects\ndispersion:\nspreading of something over an area\ndiverge:\nlight rays that spread apart as they move further\nand further away from a point\nearth:\n(or ground) to connect with a conductor to the\nground, or the earth\nearthing:\na way to prevent electrical charge from building up\non an object, or to neutralise an electric charge, by\nallowing the excess charge to flow into the Earth\nelectric circuit:\na complete path through which electrons can move\nelectric current:\nthe movement of charge in an electric circuit\nelectrodes:\na conductor which allows electricity to enter a\nsubstance\nelectrolysis:\nthe use of electricity to separate chemicals in a\nsolution\nelectromagnet:\na device which becomes a magnet when electric\ncurrent passes through it\nelectroplating:\ncovering an object with a thin layer of metal using\nelectrolysis\nelectrostatic charge:\nthe electric charge resulting from static electricity\ncaused by an excess or deficiency of electrons on\nthe surface of an object\nflammable:\nsomething is easily set on fire\nfocus:\nbring together to the same point\nfriction:\nthe resistance that results when two surfaces are\nrubbed or moved against each other\nfuse:\na safety device designed to melt and break the\ncircuit if an electric current reaches too high a level\n.\n.\n139\n.\nChapter 4.\nVisible light\n\n.\nignite:\nto light something\nincident ray:\nthe ray of light which hits a surface\nluminous:\nbright or shining\nmedium:\nsubstance through which waves (such as light) can\ntravel\nneutral:\nwhen the number of positive charges (from the\nprotons) is equal to the number of negative\ncharges (from the electrons); the (positive and\nnegative) charges balance each other so that the\nobject is neither positively nor negatively charged\nnormal line:\nthis is an imaginary line which is drawn at 90o to\nthe surface\nopaque:\nsomething that you cannot see through; no light\npasses through the object\noptical density:\na measure of how well a medium allows light to\ntravel through it\noptics:\nthe scientific study of sight and the behaviour of\nlight\nparallel circuit:\na circuit that provides more than one pathway for\nthe current to pass through it\nperpendicular:\nat right angles\npropagation:\nspreading into new areas\nqualitative:\ndescribing something in terms of its properties or\ncharacteristics rather than by a number or\nmeasurement\nradiation:\nthe emission of energy as electromagnetic waves\nrectilinear:\nstraight lines\nreflect:\nthrow back without absorbing\nreflected ray:\nthe ray of light which leaves a surface\nrefraction:\nthe change in direction of a wave passing from one\nmedium to another caused by its change in speed\nrepel:\nto push something away\nresistance:\nthe opposition to the movement of charge in a\nconductor\nresistor:\na component in an electrical circuit which slows the\nmovement of charge\nretina:\na layer at the back of the eyeball which is made up\nof light sensitive cells\nseries:\ncomponents connected in series provide only one\npathway for electrical current; they are connected\none after another\nstatic electricity:\nthe build-up of a stationary electric charge (either\npositive or negative) on the surface of an object\nstimulate:\nto cause activity\nswitch:\na control component in an electrical circuit which\nopens or closes the circuit\ntranslucent:\nsemi-transparent; some light is able to pass through\nbut not enough for details to be seen clearly\ntransmit:\nto cause light to pass through space or medium\n..\n140\n.\nEnergy and Change\n\n.\ntransparent:\nsomething that you can see through; light passes\nthrough the object\nvariable:\nsomething that can vary or change\nvisible spectrum:\nthe portion of the wave spectrum that is visible to\nthe human eye\n.\n.\n141\n.\nChapter 4.\nVisible light\n\n\n\n. .\n1\n.\nThe solar system\n..\n144\n..\nKEY QUESTIONS:\n• How does the Sun produce its energy?\n• How can we observe the Sun without damaging our eyes?\n• What objects are in orbit around the Sun in our solar system?\n• Why are there two types of planets?\n• How do the planets in our solar system differ?\n• What are asteroids and comets?\n• What is the difference between a planet and a dwarf planet?\n• Why is life possible on Earth?\nOur solar system includes the Sun and all the objects that orbit around the Sun.\nAs you will find out, a variety of objects are in orbit around the Sun: eight\nplanets, many dwarf planets, asteroids, Kuiper Belt objects and comets.\n.\n1.1 The Sun\n.\nNEW WORDS\n• solar system\n• star\n• nuclear fusion\n• convection\n• sunspot\n• solar wind\nBefore we look at the Sun close up, let's summarise what you learned about the\nSun in Grades 6 and 7:\n1. The Sun is our closest star and is very important for life on Earth as it\nprovides us with light and heat.\n2. The Sun is located at the very centre of our solar system.\n3. The Earth and other planets all orbit around the Sun, held in orbit by the\nforce of gravity.\n.\nVISIT\nSecrets of a dynamic Sun\n(video)\nbit.ly/1h0io4b\nWhat do you think the Sun would look like if it was further away, like the other\nstars we see at night?\nLet's look at the Sun in more detail.\n\nAn image of the Sun taken with the SOHO space satellite.\n.\nTAKE NOTE\nIt is very important that\nyou do not look at the\nSun directly! The Sun\ncan damage your eyes\npermanently!\n.\nVISIT\nThe birth of the solar\nsystem (video)\nbit.ly/1i8Bfrx\n.\nVISIT\nHow the Sun works.\nbit.ly/1gy769C\nDo you know what the Sun is made of? The Sun is mostly made up of hydrogen\ngas (about 71%), and also helium gas (about 27%) with a tiny amount of other\ngases. The temperature at the Sun's surface is very high, around 5500 oC.\nHowever, that is nothing compared to deep inside the Sun. At the Sun's centre,\nor core, it is about 15 million oC. It is so hot at the Sun's centre that nuclear\nreactions can occur, which change atoms from one element to another. In the\nSun's case, four hydrogen nuclei are squeezed or fused together to form a new\nhelium nucleus. This process is called nuclear fusion.\nThis nuclear fusion reaction releases energy because the new helium nuclei\nproduced have very slightly less mass than the four hydrogen nuclei used to\nmake them. How can this be? Well, according to the famous scientist Albert\nEinstein, energy and mass are equivalent. Some of the mass in the hydrogen\nnuclei is converted and released as energy when the nuclei fuse to make helium.\nA very large amount of energy is released. This energy travels outwards from\nthe Sun's core towards its surface. The energy eventually reaches the Sun's\nsurface somewhere between 17,000 and 100,000 years later! The Sun's energy\nthen spreads out into the solar system in the form of heat and light.\nYou are now going to observe the Sun to look at its surface features.\nRemember, you should never look directly at the Sun as it can permanently\ndamage your eyes. You can use either a telescope with a filter on it or a pinhole\nto project an image of the Sun onto a screen to safely view the Sun's image.\n.\n.\n145\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing the Sun using a telescope\n.\nMATERIALS:\n• telescope\n• white card\n• chair to rest the card on\n• cardboard to make a shade collar\n• pair of scissors\n• pencil\n.\nVISIT\nInteract with this\nsimulation to visualize the\neffects of gravity on\norbital paths of the Sun,\nEarth and Moon.\nbit.ly/1a2mJCL\n.\nTAKE NOTE\nNEVER look directly at\nthe Sun, even with\nsunglasses on as you\ncan permanently\ndamage your eyes.\nINSTRUCTIONS:\n1. Take a piece of cardboard and place it up against the narrowest end of the\ntelescope.\n2. Draw an outline around the edge of the telescope on the card to use as a\nguide for cutting to make the collar.\n3. Cut out inside the circle you just drew so that the cardboard can fit over\nthe telescope as shown in the figure above. You can cut a single slit into\nthe circle from the edge of the card as shown in the diagram\n4. Place the collar on the telescope. Adjust the size of the cut out circle if\nnecessary (for example if your telescope is slightly wider in the middle\nthan at the end, you may want to make your circle slightly larger). This\ncollar shades the area, where the image will fall, from stray light.\n5. Select the lowest magnification eyepiece lens you have and insert it into\nthe telescope's eyepiece.\n6. Focus the telescope by looking at a distant object (NOT the Sun).\n7. Point the telescope at the Sun (do NOT look through the telescope to do\nthis).\n8. Place a chair behind the telescope and rest a white piece of card on it. The\ncard should be tilted towards the telescope.\n9. Adjust the direction in which the telescope is pointing until the image of\nthe Sun appears on the white paper card. This may take some time.\n10. Keeping the telescope still, move the white card toward or away from the\neyepiece until the image of the Sun fits neatly in the middle of the card.\n..\n146\n.\nPlanet Earth and Beyond\n\n.\nAdjust the chair's position as needed.\n11. Adjust the tilt of the white card until the Sun's image is circular.\nQUESTIONS:\n1. Looking carefully you should see that the Sun's image moves slowly across\nthe white card. What causes this motion?\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n.\n.\nTAKE NOTE\nRevise the model of the\natom that you learned\nabout in Matter and\nMaterials if you are\nunsure of some of the\nterms used here, such\nas nucleus, which is at\nthe centre of an atom,\nand consists of protons\nand neutrons.\nAlternatively, if you do not have access to a telescope or binoculars, you can\nperform the following activity to view the Sun.\n.\nACTIVITY: Observing the Sun with a pinhole\ncamera\n.\nIn this activity you will reflect an image of the Sun onto a white card or screen\nfor your learners to observe. This method has the advantage of not needing a\ntelescope or binoculars, however, the solar image produced will be a bit fuzzy.\nHowever, it should be good enough to show large sunspots. This activity is\ndesigned as a teacher-led demonstration. If you have a sunlit window or door to\nyour class you can do this activity in the classroom. If you do not have a\nclassroom with a sunlit window, or if your class is very small, you can do the\nactivity outdoors, reflecting the Sun's image onto a shaded wall or back into a\ndarkened classroom.\n.\n.\n147\n.\nChapter 1.\nThe solar system\n\n.\n.\nVISIT\nThree years of the Sun in\nthree minutes.\nbit.ly/19nCfGu\nAs a rough guide, begin with a distance of around 8 m between the white card\nand the mirror. The further away you place the mirror from the white screen the\nfainter and larger the image will appear. At closer distances the image will be\nbrighter but it may not be in very good focus.\n.\nVISIT\nWhere does the Sun get\nits energy?\nbit.ly/1azFmsM\nAs mentioned in the previous activity, sunspots are sometimes (not always)\nvisible on the Sun's surface. Therefore, you could repeat this activity over the\ncourse of several days to see if any sunspots or sunspot groups change shape,\nsize, or position over time.\nMATERIALS:\n• small pocket mirror or hand mirror\n• piece of plain cardboard (or paper) to fit over the mirror (or alternatively\ntape)\n• white cardboard screen\n• bin bags or curtains for darkening the classroom\n.\nVISIT\nE = mc2 explained (video).\nbit.ly/16mVFNI\nMETHOD:\n1. Cut the plain cardboard or paper so it fits over the mirror.\n2. Cut or punch a very small hole, about 5 mm, in the middle of the plain\ncardboard.\n3. If you do not have cardboard, you can use tape to cover all but a small\nportion of the surface of the mirror.\n4. Place the mirror on a window sill in the Sun and tilt it so that it catches the\nsunlight and reflects it into the classroom. If your classroom is very small,\nplacing the mirror outside on a chair may be a better option in order to get\na larger image.\n5. Darken the classroom using curtains or bin bags, excluding where the\nmirror is.\n6. Reflect the sunlight from the mirror onto a wall of the darkened room.\n7. Put the white cardboard or paper on the wall where the reflected light\nshowing the Sun's image falls.\n8. Observe the image of the Sun.\n..\n148\n.\nPlanet Earth and Beyond\n\n.\n9. Remove the white cardboard from the wall and take three steps towards\nthe mirror with the cardboard still facing the mirror. Note what happens to\nthe image of the Sun on the cardboard.\nQUESTIONS:\n1. As you moved the white cardboard screen closer towards the mirror, what\ndid you notice happened to the image of the Sun?\n.\nDID YOU KNOW?\nAlbert Einstein\nexplained the\nmass-energy\nequivalence with the\nfamous equation\nE = mc2.\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n3. When the Sun reflects off the surface of the mirror, what can you say about\nthe angle of incidence and the angle of reflection of the ray?\n.\nDid you notice any features on the Sun's surface when you viewed it in class?\nLet's find out what some of these surface features could have been in the next\nactivity.\n.\nVISIT\nFiery looping rain on the\nSun (video)\nbit.ly/16qmriQ\n.\n.\n149\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing sunspots on the Sun's\nsurface\n.\nINSTRUCTIONS:\n1. Look at the images of the Sun which were taken in June 2013.\n2. Answer the questions that follow.\nA: DATE: 02.06.2013\n.\nVISIT\nLearn more about the\nresearch that NASA is\ndoing about our Sun with\nthe Solar and Heliospheric\nObservatory (SOHO).\nbit.ly/1fQhd8u\nB: DATE: 03.06.2013\n..\n150\n.\nPlanet Earth and Beyond\n\n.\nC: DATE: 04.06.2013\nQUESTIONS:\n.\nTAKE NOTE\nThis information about\nthe Sun's surface and\nsunspots is additional\ninformation for your\ninterest. Be curious and\ndiscover more!\n1. How many groups of dark spots do you see in each image?\n2. What do you notice about the positions of the spots in each image?\n3. Why do you think the spots have moved?\n4. What do you think these spots are?\n.\nSunspots and the Sun's surface\nThe Sun's surface often has little blemishes on it. These dark spots on the Sun\nare called sunspots. They are areas that are slightly cooler than the rest of the\nSun's surface. The Sun's surface is typically about 5500 oC and a typical\nsunspot has a temperature about 3900 oC.\n.\n.\n151\n.\nChapter 1.\nThe solar system\n\nImage of a sunspot. For perspective, take note of the size of the Earth in the lower left.\n.\nVISIT\nView real time images of\nthe Sun and track\nsunspots.\nbit.ly/19ZoU6c\nAs the Sun is made up of gas, there is no solid surface like on Earth. So when\none says that you are looking at the Sun's surface what are you actually looking\nat? Imagine that you are standing in thick fog (mist) with a friend. You can see\nthings close to you, like your hand in front of you and your friend standing next\nto you. However, because the fog is so thick you cannot see far into the\ndistance. Similarly, when we look at the Sun, we cannot see right into the centre\nof the Sun. As you go deeper and deeper in towards the centre of the Sun the\ngas begins to get thicker and thicker so that we cannot see through it. The\ndeepest depth that we can see into the Sun's gas is what we call the Sun's\nsurface.\nSunspots are areas that are slightly cooler, and therefore darker, than the rest of\nthe Sun's surface. A typical sunspot only lasts a few days. When a sunspot lasts\nfor several days you can observe it move across the Sun's disc. The sunspot\nappears to move across the Sun because the Sun is spinning slowly on its own\naxis.\n.\nDID YOU KNOW?\nThe number of sunspots\non the Sun increases\nand decreases in a\nregular pattern which\nrepeats every 11 years.\nWhen there are more\nsunspots the Sun is\nmore active and there\nare more solar storms\nand more of the Sun's\nenergy reaches the\nEarth.\nThe outer atmosphere of the Sun is called the corona. Gas particles from the\ncorona are constantly escaping into space, forming the solar wind. When the\nSun is very active, violent eruptions called solar flares occur on its surface.\n..\n152\n.\nPlanet Earth and Beyond\n\nA large loop of gas extending over 35 Earth diameters out from the Sun's surface.\n.\n1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.\n1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.\nChapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "2" }, { "title": "Friction and static electricity", "content": "", "chapter_id": "1.1" }, { "title": "Energy transfer in electrical systems", "content": "Chapter 2.\nEnergy transfer in electrical systems\n\n.\n2. Do you think this is an open or closed circuit? Explain your answer.\n3. Which part is providing the source of energy?\n.\nVISIT\nElectricity and circuits\nbit.ly/17ni2R4 and\nRevise a simple circuit.\n[video)\nbit.ly/1eWpN5k\n4. What is the conducting material?\n5. What type of energy does the battery have?\n6. What is this energy transferred to when the circuit is closed and the\nelectrons move through the wires?\n7. What is the output of this system?\n8. In most systems, the input energy is more than the useful output energy as\nsome of the input energy is transferred to wasted output energy. In this\nsimple circuit with a light bulb, what is the wasted output energy?\n.\nA complete circuit is a complete conducting pathway for electricity. It goes\nfrom one terminal of a cell along conducting material, through a device and\nback to the other terminal of the cell. Let's look at the components of a circuit.\n.\n2.2 Components of a circuit\nYou are probably already familiar with the components of an electric circuit\nfrom previous grades. Do you remember that we have a specific way of\ndrawing the components in a circuit in an electric circuit diagram? Each\ncomponent has a different symbol.\n.\nNEW WORDS\n• ammeter\n• cell\n..\n22\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Components in an electric circuit\n.\nComplete the following table. List the function of the component and draw the\ncircuit symbol. The last two rows have been filled in for you as you may not yet\nknow these symbols, but we will be using them in this chapter.\nComponent\nFunction\nSymbol\nCell\nTorch bulb\nOpen switch\nClosed switch\nElectrical wire\nResistor\nA component that\nopposes or inhibits\nelectrical current in a\ncircuit. It can also\nconvert electrical\nenergy to heat or light.\nor\nVariable resistor\nA resistor whose\nresistance can be\nadjusted higher or\nlower.\n.\n.\n23\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nLet's now practice drawing some simple circuit diagrams. Draw the following\ncircuit diagrams.\n1. A closed circuit with one cell, two light bulbs and a switch.\n.\n2. An open circuit with two cells, two light bulbs and a switch.\n.\n3. A closed circuit with 4 cells and one light bulb.\n.\n..\n24\n.\nEnergy and Change\n\n.\n4. Look at the following circuit diagram. Identify the number of bulbs,\nswitches and cells in this circuit.\n5. What is wrong with the following circuit diagram? Does it represent a\nclosed circuit? Explain your answer.\n.\nVISIT\nBuild you own electric\ncircuits with this\nsimulation.\nbit.ly/19eotZk\n6. Why do you think it is useful to have a switch in a circuit?\n7. Why are conducting wires made out of metal?\n.\nLet's take a closer look at the source of energy in electric circuits.\n.\n.\n25\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nCells\nElectrical cells are the source of energy for the electric circuit. Where does that\nenergy come from?\n.\nDID YOU KNOW?\nAll muscles in our\nbodies move in\nresponse to electrical\nimpulses generated\nnaturally in our bodies.\nInside the cell are a number of chemicals. These chemicals store potential\nenergy. When a cell is in a complete circuit, the chemicals react with each other.\nAs a result, electrons are given the potential energy they need to start moving\nthrough the circuit. When the electrons move they have both potential and\nkinetic energy. The electric current is the movement of electrons through the\nconducting wires.\nCells come in many different sizes. Different sized cells provide different\namounts of energy to the electrical circuit. The types of cells you would use in\ntoys, torches and other small appliances range in size from AAA, AA, C, D, and\n9-volt sizes. AAA, AA, C and D cells usually have a rating of 1,5V, but the larger\ncells have a larger capacity. This means that the larger cells will last longer\nbefore going 'flat'. A cell goes flat when it is no longer able to supply energy\nthrough its chemical reactions.\nWhen we buy cells in the shop they are\nusually referred to as batteries. This\ncan be a bit confusing because a\nbattery is really two or more cells\nconnected together. So when we refer\nto a battery in circuit diagrams we\nneed to draw two or more cells\nconnected together.\nDifferent sized batteries.\n.\nACTIVITY: Recycling of batteries\n.\nBatteries which no longer work must not be thrown away in dustbins. They\nneed to be recycled.\nINSTRUCTIONS:\n1. Work in small groups.\n2. Find out why batteries should not be thrown away in normal dustbins.\nWrite a paragraph to explain why.\n..\n26\n.\nEnergy and Change\n\n.\n3. Find out where you can recycle batteries in your community. Write down\nthe details of the centre(s) closest to where you live.\n.\nResistors\nWhat are resistors? In order to work out what they are, let's first remind\nourselves about conductors and insulators.\nWe are specifically looking at electricity so we can now talk about electrical\nconductors and insulators. An electrical conductor is a substance which allows\nelectric charge to move through it. An insulator is a substance which does not\nallow electric charge to move through it.\nThink back to our model of a metal wire and how the electrons are able to move\nthrough the wire. The metal wire is a conductor of electricity. Write down some\nmaterials which do not conduct electricity.\n.\nVISIT\nA guide to recycling in\nSouth Africa.\nbit.ly/19Sygzg\nWhy do you think most conducting wires are surrounded with plastic?\nResistors are a bit of both. They allow electrons to move through them, but do\nnot make it easy. They are said to resist the movement of electrons. Resistors\ntherefore influence the electric current in a circuit.\nBut, why would we want to resist the movement of electrons? Resistors can be\nextremely useful. Think about a kettle. If you look inside you will see a large\nmetal coil.\nLooking inside a kettle.\nThis metal coil is the heating element.\nIf you plug in and switch on the kettle,\nthe element heats up and heats the\nwater. The element is a large resistor.\nWhen the electrons move through the\nresistor they expend a lot of energy in\novercoming the resistance. This energy\nis transferred to the surroundings in\nthe form of heat. This heat is useful to\nus as it heats our water.\nA good example of where resistors are used is in light bulbs. Let's take a closer\nlook at the different parts of a light bulb to see how it works.\n.\nDID YOU KNOW?\nThe first electric light\nwas made by Humphry\nDavy in 1800. He\ninvented an electric\nbattery, and when he\nconnected wires to it\nand a piece of carbon,\nthe carbon glowed as\nthe carbon is a resistor,\nproducing light.\n.\n.\n27\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Resistance in a light bulb\n.\nAn incandescent light bulb.\nMATERIALS:\n• light bulb\n• lamp\nINSTRUCTIONS:\n1. If you have light bulbs available, have a close look at the different parts,\notherwise have a look at the photos provided here.\n2. Read the information about how a light bulb works and identify the parts\nthat have been numbered.\n3. Answer the questions that follow.\n.\nVISIT\nHow a light bulb works.\nbit.ly/18K0hd3\nDiagram of the parts of a light bulb.\nA light bulb consists of an air-tight enclosed glass case (number 1). At the base\nof the bulb are two metal contacts (numbers 7 and 10), which connect to the\nends of an electrical circuit. The metal contacts are attached to two stiff wires,\n(numbers 3 and 4).\n..\n28\n.\nEnergy and Change\n\n.\nThese wires are attached to a thin metal filament. Have a look at a light bulb.\nCan you identify the filament? This is number 2 in the diagram. The filament is\nmade from tungsten wire. This is an element with high resistance.\nQUESTIONS:\n.\nTAKE NOTE\nIncandescent means to\nemit light as a result of\nbeing heated.\n1. When the electrons move through the filament they experience high\nresistance. This means that they transfer a lot of their energy to the\nfilament when they pass through. The energy is transferred to the\nsurroundings in the form of heat and bright light. Describe the transfer of\nenergy in this light bulb.\n2. What is the useful energy output and what is the wasted energy output in\nthis light bulb?\n3. Can you see the filament is coiled? Why do you think this is so? Discuss\nthis with your class and teacher.\n.\nVISIT\nA fun game about electric\ncircuits.\nbit.ly/15Icr49\n4. The filament is mounted on a glass stem (number 5). There are two small\nsupport wires to hold the filament up (number 6). Why do you think the\nstem is made of glass?\n5. The inside of the base of the bulb is made from an insulating material.This\nis the yellow part labeled number 8. On the outside of this is a metal\nconducting cap to which the wire is attached at number 7. Why is the wire\nattached at 7 making contact with the metal conducting cap?\n6. If you have a lamp in the classroom, screw the bulb into the lamp and turn\nit on to observe the filament glow and also getting hot.\n.\nThe amount of resistance a substance offers to the circuit is measured in ohms\n(Ω). If we want to use resistors to control the current flow, then we need to\nknow the amount of resistance. There are some common resistors shown in the\n.\n.\n29\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nphoto.\nSome common resistors.\nCan you see that there are different coloured bands on the resistors? This isn't\njust to make them look pleasing to the eye. The coloured bands are actually a\ncode that tells us the resistance of the resistor. We also get resistors where we\ncan adjust the resistance ourselves. This is called a variable resistor. You have\nalready seen the symbol for drawing a resistor in a circuit diagram. Draw a\ncircuit diagram in the space below with two bulbs, two cells, an open switch and\na resistor.\n.\nDID YOU KNOW?\nThe inventor, Thomas\nEdison, experimented\nwith thousands of\ndifferent resistor\nmaterials until he\neventually found the\nright material so that\nthe bulb would glow for\nover 1500 hours.\n.\nAn electric current can have various effects. Let's find out more about what\nthese are.\n.\n2.3 Effects of an electric current\n.\nNEW WORDS\n• variable\n• fuse\n• electromagnet\n• electric current\nWe are going to look at the effects of an electric current, and specifically how\nwe use these effects. An electric current can:\n• generate heat in a resistor;\n• generate a magnetic field; and\n..\n30\n.\nEnergy and Change\n\n• cause a chemical reaction in a solution.\nHeating effect\nAs electrons move through a resistor they encounter resistance and they\ntransfer some of their energy to the resistor itself. We saw this in the last section\nwhere we looked at the filament in a light bulb and the element in a kettle.\n.\nACTIVITY: Heating a wire in a circuit\n.\nMATERIALS:\n• 1,5 V cell\n• conducting wires\n• switch\n• block of wood\n• 2 nails\n• hammer\n• 10 cm of nichrome wire\n.\nTAKE NOTE\nYou can easily make\nyour own switch by\nsticking two metal\ndrawing pins into a\npiece of wood with a\nmetal paper clip in\nbetween, as shown in\nthe diagram.\nINSTRUCTIONS:\n1. Hammer the two nails into the block of wood and attach the nichrome wire\nbetween the nails.\n2. Build the following circuit and keep the switch open.\n3. Feel the nichrome wire. Is it hot or cold?\n4. Close the switch. Leave it on for a minute.\n5. Open the switch again.\n6. Feel the wire, briefly. Is it hot or cold?\n.\n.\n31\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nQUESTIONS:\n1. When you felt the nichrome wire after the circuit had been on for a while,\nyou felt an increase in temperature in your skin as thermal energy, which\nwas transferred from the wire to your skin. Explain the heating effect of\nthe electric current in the resistance wire.\n2. List 2 useful applications of the heating effect of an electric current.\n.\nTAKE NOTE\nRemember that heat\nand temperature are\nnot the same thing.\nTemperature is a\nmeasure of how hot or\ncold something is\n(measured inoC)\nwhereas heat is the\ntransfer of thermal\nenergy from a hotter\nobject to a colder object\n(measured in J).\n3. Choose one of the applications you listed in question 2 and explain how\nthe heating effect of the electric current is used.\n4. Look at the following photo of a toaster.\nAn electric toaster.\nCan you see the glowing filament inside? Why does the element glow?\n.\nSo now we know that an electric current can cause objects to heat up. Let's\nlook at a useful application of the heating effect.\n..\n32\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Melting metal\n.\nMATERIALS:\n• three 1,5 V cells\n• copper conducting wires with crocodile clips\n• steel wool\n• heat resistant mat or piece of wood\n• torch light bulb\n• variable resistor\n• ammeter\nINSTRUCTIONS\n1. Set up a circuit according to the following picture.\n2. Twist a few strands of steel wool into a wire.\n.\nTAKE NOTE\nAn ammeter is used to\nmeasure the electric\ncurrent in a circuit.\n3. Use the steel wool to complete the circuit.\n4. Set the variable resistor to its highest resistance.\n5. Close the switch. What do you observe?\n6. Take note of the reading on the ammeter which measures the current in\nthe circuit.\n7. Open the switch.\n8. Set the variable resistance to its lowest resistance.\n9. Close the switch. What do you observe?\nQUESTIONS:\n1. Draw a circuit diagram for your circuit.\nThis is the symbol for an ammeter.\n.\n.\n33\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\n2. Why is the light bulb included in the circuit?\n3. When you decreased the resistance, what happened to the current? In\nother words, what happened to the reading on the ammeter?\n4. What do you think happens to the electric current when the steel wool has\nburnt? Explain your answer.\n.\nIn this activity, we just demonstrated how a fuse works. The steel wool acted as\na fuse. When the current was too high, the steel wool melted and prevented any\nfurther current in the circuit.\nWhat are fuses?\nThe heating effect of an electric current can be dangerous. If a circuit overheats\nit could cause a fire. To avoid overheating, circuits often contain a fuse. Fuses\ncontain a low resistance wire made of a metal with a low melting point.\nTherefore, the piece of wire melt if it gets too hot, just like the steel wool in our\nactivity.\n..\n34\n.\nEnergy and Change\n\nAn example of a fuse. Can you see the low melting point wire inside?\nDifferent circuits need different strength currents and so we need different\ntypes of fuses. Some fuses can only handle a little bit of heat, some can handle a\nlot. We choose the fuse that suits the safety needs of our circuit. If the circuit\noverheats, the fuse will melt and break the circuit to reduce the danger of fire as\nwell as protect electronic equipment.\nHow did you draw the fuse that we made using steel wool in the last activity?\nThe conventional symbol for drawing a fuse in a circuit diagram is shown here:\nA fuse.\n.\nTAKE NOTE\nIt is important to never\nremove a fuse from a\ncircuit without first\nswitching offthe\ncurrent. You could get a\nnasty shock if you do.\nWhat is a short circuit?\nHave you ever heard that something broke because it short circuited? A short\ncircuit happens when another, easier path is accidently made in an electric\ncircuit. What do we mean by easier?\nWe mean that the path offers very little resistance to the electric current. As\nthere is so little resistance the current flows along the short circuit and doesn't\npass through the main circuit. Short circuits can be dangerous and cause a lot\nof damage to appliances.\nHave you ever had a piece of toast get stuck in a toaster? It's a real nuisance.\nLots of people are tempted to use their butter knife to unhook the bread. Don't\nbe tempted. Your knife is a conductor and can act as a short circuit. All the\nelectric current will flow through your knife and, because you are touching it,\nthrough you. What would be the safe way to unhook your toast?\n.\nTAKE NOTE\nThere are different\ntypes of fuses. The ones\nwe have investigated so\nfar require you to\nreplace the fuse if the\nwire melts. However,\nsome fuses work\ndifferently to break the\ncircuit and can just be\nreset once the problem\nin the circuit is fixed.\n.\n.\n35\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: How are fuses used in everyday\ncircuits?\n.\nINSTRUCTIONS:\n1. Find out about common household appliances which use fuses. Choose\none of these appliances on which to focus your research.\n2. Write a short paragraph describing the appliance and explaining why a\nfuse is necessary for that appliance.\n.\nMost modern homes have circuit breakers instead of fuses. A circuit breaker is\nsimilar to a fuse in that it is designed to protect an electric circuit from damage,\ndue to overload or a short circuit, by stopping the current flow. However, unlike\na fuse which melts and must then be replaced, a circuit breaker can be reset to\nstart operating again. This can be done manually or take place automatically.\nMagnetic effect\nBefore we look at how a current produces a magnetic field, let us first learn\nmore about magnets. A magnet is a piece of material which produces a\nmagnetic field. A magnet has a north pole and a south pole. Opposite poles will\nattract each other and the same poles will repel each other. A magnet has a\nmagnetic field around it.\n.\nVISIT\nSome fun tricks with\nmagnets. (video)\nbit.ly/1c01QsA\n..\n36\n.\nEnergy and Change\n\nA bar magnet.\nDid you know that the Earth is like a bar magnet with a North and a South Pole?\nThe Earth has a magnetic field. This is why we can use compasses to tell\ndirection. A plotting compass has a needle with a small magnet. The needle\npoints to magnetic north because the small magnet is attracted to the opposite\nmagnetic pole and can be used to determine direction.\nEarth has a magnetic field, as though there\nis a big bar magnet running through the\ncore, with its South Pole under Earth's\nmagnetic North pole.\nA compass with the needle pointing North.\n.\nVISIT\nWhat is the magnetic\nfield?\nbit.ly/GzwPyx\n.\nACTIVITY: Playing with plotting compasses and\nmagnets\n.\nMATERIALS:\n• plotting compasses\n• bar magnets\n• piece of white paper\n• iron filings\nINSTRUCTIONS:\n1. Hold the plotting compass in your hand. The north end of the needle\nshould point to magnetic north.\n2. Put the bar magnet flat on the desk. Make sure you know which end is\nnorth and which is south. If you are not sure, ask your teacher.\n3. Put plotting compasses in a circle around the bar magnet.\n.\n.\n37\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nDraw what you see.\n.\n4. Next, place a white sheet of paper over the bar magnet and sprinkle iron\nfilings over the sheet of paper over the magnet.\nObserve what happens to the iron filings. Did you see something similar to\nwhat is shown in the photograph below? Describe what you see.\nIron filings on a piece of paper over a bar magnet.\n.\nSo now we know that there is a magnetic field around a magnet and that\nplotting compasses and iron filings can be used to visualise that field. Is there\nanything else that has a magnetic field around it?\n.\nVISIT\nExplore the interactions\nbetween a compass and\nbar magnet with this\nsimulation.\nbit.ly/19etlNQ\n..\n38\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magnetic field around a conductor\n.\nMATERIALS:\n• plotting compasses\n• three 1,5 V cells\n• insulated copper conducting wires\n• switch\nINSTRUCTIONS:\n1. Construct a circuit which contains the batteries, copper wires and the\nswitch.\n2. Put the plotting compasses on either side of the conducting wire as shown\nin the diagram, as well as below and above the conducting wire.\nPlotting compasses placed around a conducting wire.\n3. Keep the switch open. What do you notice about the needles of the\nplotting compasses?\n4. Close the switch and observe what happens to the needles.\n5. Draw a picture of the wire and plotting compasses in the space below:\n6. What does the pattern of the compasses tell us?\n.\nWe saw from our first activity that plotting compasses react to magnetic fields.\nThe plotting compasses changed direction when the current was switched on.\nThis means there is a magnetic field around the wire. Was it there when the\ncurrent was switched off? No, it was not. That means that the presence of the\nelectric current in the wire must have produced a magnetic field.\n.\nVISIT\nDiscover how the Earth is\na magnet that protects us\nfrom damaging radiation\nfrom the sun!\nbit.ly/GCCtjK\nThe magnetic effect of an electric current has many useful applications.\n.\n.\n39\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Making an electromagnet\n.\nMATERIALS:\n• one iron nail (approximately 15 cm long)\n• 3 metres of 22 gauge insulated copper wire\n• two D cell batteries\n• paper clips\n• iron filings\nINSTRUCTIONS:\n1. Wrap the insulated copper wire tightly around the nail. Make sure that you\nwrap the wire in the same direction.\n2. Strip some of the insulation off each end of the insulated copper wire.\n3. Attach the ends of the insulated copper wire to the terminals of the\nbattery.\n4. Hold the wrapped nail above the paper clips.\n5. Disconnect the wire from the battery.\n6. Hold the wrapped nail above the paper clips.\n7. If you have iron filings, place some on a piece of paper around the\nelectromagnet you have made and observe the magnetic field.\nThe magnetic field around an electromagnet.\nQUESTIONS:\n.\nVISIT\nHow to make an\nelectromagnet (video)\nbit.ly/1bpHh61\n1. What happened when you held the nail over the paper clips?\n2. Why were the paper clips attracted to the nail?\n3. Did the disconnected nail attract the paper clips? Why?\n.\n..\n40\n.\nEnergy and Change\n\nElectromagnets can be used in all sorts\nof practical applications, including\nspeaker and electric bells, as you can\nsee in the photo.\nAn electromagnet in a bell.\n.\nVISIT\nElectromagnets in a\nspeaker.\nbit.ly/19jU1XL\n.\nACTIVITY: Research the use of electromagnets\n.\nINSTRUCTIONS:\n1. Work in groups of 2 or 3.\n2. Research one of the following applications of the magnetic effect of an\nelectric current to explain how the device works:\na) speakers\nb) electric bells\nc) telephones\nd) magnetic trains\ne) industrial lifters and separators\n3. Write a short paragraph showing what you've learnt. Remember to note\ndown from where you got your information.\n4. Share your paragraph with the rest of the class.\n.\nChemical effect\nThe last effect of an electric current that we are going to look at is how an\nelectric current can cause a chemical reaction in a solution.\n.\nVISIT\nDiscover how to generate\nelectricity using bar\nmagnets with this\nsimulation.\nbit.ly/15Guo8x and\nlearn how to build a\nsimple electric motor.\nbit.ly/1c02xCb\n.\n.\n41\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Electrolysis\n.\nYou might already have done this activity in Matter and Materials when we\ninvestigated the decomposition of copper chloride. We are going to perform it\nagain, this time focussing on the effects of an electric current.\nMATERIALS\n• 250 ml beaker\n• 2 carbon electrodes\n• sandpaper\n• 3 copper conducting wires (with crocodile clips)\n• copper chloride solution\n• torch bulb\n• power pack\nINSTRUCTIONS\n1. Sand down the electrodes with the sandpaper to make sure they are clean.\n2. Connect the conducting wire from one electrode to the torch bulb and\nanother wire from the torch bulb to the negative terminal of the power\nsource.\n3. Connect the crocodile clip from the second electrode to the positive\nterminal of the power source.\n4. Pour 100 ml copper chloride solution into the beaker.\n5. Put the electrodes into the beaker. Make sure that they do not touch each\nother.\n6. Look at the electrodes. What do you observe?\n7. Turn on the power source. Leave it on for a few minutes.\nThe setup might look something like this, which you have seen before. You might\nalso have a light bulb connected in the circuit.\n..\n42\n.\nEnergy and Change\n\n.\nQUESTIONS\n1. When you switch on the power source, does the torch bulb glow?\n.\nVISIT\nLearn more about silver\nrefining through\nelectrolysis.\nbit.ly/1fZQ5SW and the\nprocess of electroplating\n(video)\nbit.ly/GzH851\n2. What do you observe happening at the two different electrodes?\n3. Can you smell anything? What do you think this is?\n4. What is happening to the copper chloride solution when the electric\ncurrent is passed through it?\n5. If you switch off the power source, what happens?\n6. What is causing the separation of the copper chloride?\n7. Why is it important that you do not let the carbon electrodes touch each\nother while the current is flowing?\n.\nThe separation of the copper chloride means that an electric current can cause\nchemical reactions to occur. There are many ways in which we can harness this\nchemical effect for practical uses.\nElectrolysis is the breaking down of a substance into its component elements\nby passing an electric current through a liquid or solution. We can also use\nelectrolysis to purify substances.\nImpure copper can be purified using electrolysis. Instead of using carbon\nelectrodes in a copper sulphate solution we can use copper electrodes. If one of\nthe copper electrodes is pure copper and the other is impure copper, then the\nimpure electrode will break down and deposit pure copper on to the already\npure copper electrode.\n.\nNEW WORDS\n• electrolysis\n• electrodes\n• electroplating\n.\n.\n43\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nOne of the most important uses of electrolysis is electroplating.\nElectrolysis is used to electroplate metals. In the last activity, one of the carbon\nelectrodes was coated with an even layer of pure copper. We say that the\ncarbon electrode was electroplated with copper.\nWhy do we electroplate? An example is in the making of jewellery where an\ninexpensive metal is made into a ring, for example, and then coated with gold\nby electroplating. This makes it less expensive than if it were made from pure\ngold. Iron rusts easily and so it is useful to coat it with a layer of a zinc to\nprotect it from corrosion. Many car parts, bathroom taps and wheel rims are\nelectroplated with chromium.\n..\nSUMMARY:\n.\nKey Concepts\n• A circuit is a system for transferring electrical energy.\n• For a circuit to function there must be a complete, unbroken pathway\nfor the electrons to follow, a source of energy (cell or cells) and a load\n(lightbulb or any other resistor).\n• We use symbols to represent components of an electric circuit so that\neveryone can interpret the diagrams.\n• A resistor is a component in a circuit which resists the movement of\nelectrons through the circuit.\n• An electric current can heat a resistance wire. This heating effect is used\nin many everyday appliances, such as kettles and irons.\n• An electric current causes a magnetic field. This magnetic effect is used\nin electromagnets.\n• An electric current can cause a chemical reaction in solutions. This is\ncalled electrolysis, and is used to electroplate objects.\n.\nConcept Map\nComplete the concept map to summarise what you have learned about\nelectric circuits and the effects of an electric current in this chapter.\n..\n44\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Write your own definition for an electric circuit. [2 marks]\n2. What type of energy does a battery have? [1 mark]\n3. When a battery is connected to a circuit, it causes an electric current in the\ncircuit. Explain what an electric current is and why it is possible in metals.\nUse the word 'delocalised' in your explanation. [3 marks]\n4. List 3 materials which conduct electricity. [3 marks]\n5. List 3 materials that do not conduct electricity. [3 marks]\n6. You have a battery, insulated copper conducting wires and a light bulb.\nDraw a setup which would allow you to test whether the materials you\nlisted in questions 1 and 2 are conductors or not. [4 marks]\n.\n..\n46\n.\nEnergy and Change\n\n.\n7. Draw the symbols for the following components. [6 marks]\nA cell\nA light bulb\nA conducting wire\nAn open switch\nA resistor\nA variable resistor\n8. Look at the circuits below. If the bulb(s) will glow, place a tick next to the\npicture and explain why it will glow. If the bulb(s) will not glow, place a\ncross next to the picture and explain why it will not glow. [10 marks]\nCircuit\nGlow/Not Glow\nExplanation\n.\n.\n47\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nCircuit\nGlow/Not Glow\nExplanation\n9. Which of the following setups shows the correct way to connect a light\nbulb to a battery? Explain your answer. [2 marks]\n..\n48\n.\nEnergy and Change\n\n.\n10. Draw a circuit diagram to illustrate the following circuit: (3 marks)\nImage\nCircuit diagram\n11. An electrician wants to replace a faulty fuse with a normal piece of\nconducting wire. Should you let him? Why or why not? [3 marks]\n12. A child, while inserting an electric plug into the socket, did not see that\nthere was a thin piece of aluminium foil stuck between the pins of the plug.\nWhen he turned the switch on, he noticed a spark at the plug, and at the\nsame time, the lights went out. What could have happened to cause the\nspark and to make the lights go out? [4 marks]\n13. What is the benefit of using a circuit breaker rather than a fuse? [2 marks]\n14. Look at the following photo of a light bulb. Label the filament and explain\nwhy it glows. [4 marks]\n.\n.\n49\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n15. You place some plotting compasses around an electric wire and observe\nthe following.\na) Is there are current in the conducting wire? [1 mark]\nb) Explain your answer. [2 marks]\n16. Give two advantages of electroplating iron metal. [2 marks]\nTotal [55 marks]\n.\n..\n50\n.\nEnergy and Change\n\nCurious? Discover the possibilities with a magnifying glass.\n.\n.\n51\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n. .\n3\n.\nSeries and parallel circuits\n..\n52\n..\nKEY QUESTIONS:\n• Are there different types of electric circuits?\n• If all the light bulbs in a house are part of the same circuit, how can you\nswitch one light off without the rest also turning off?\n• What is a series circuit?\n• What is a parallel circuit?\n• What happens when you connect more components in series or in\nparallel?\nIn the last chapter, and in Gr 6 and 7, we have been looking at electric circuits.\nThese have mostly been series circuits. What does this mean? And how else can\na circuit be arranged?\n.\n3.1 Series circuits\nA series circuit is one in which there is only one pathway for the electric current\nto follow. The components are arranged one after another in a single pathway.\nWhen we connect the components we say that they are connected in series.\nWe have already seen examples of series circuits in the last chapter.\nA series circuit with one pathway for the current, from the negative to the positive\nterminal of the battery.\n.\nNEW WORDS\n• series\n• ammeter\n• ampere\n• resistance\nAmmeter\nAn ammeter is a measuring device used to measure the electric current in the\ncircuit. It is connected into the circuit in series. The current is measured in\namperes (A).\n\nAn ammeter.\nWhat is the symbol for an ammeter? Draw it here.\n.\n.\nDID YOU KNOW?\nThe ampere is named\nafter André-Marie\nAmpère (1775-1836), a\nFrench mathematician\nand physicist. He is\nconsidered the father of\nelectrodynamics, which\nis the study of the effect\nof electromagnetic\nforces between electric\ncharges and currents.\nDo you think that an ammeter would have a high resistance or a low resistance\nto the current? Explain your choice.\n.\nTAKE NOTE\nThe ampere is often\nshortened to 'amp'.\nA series circuit only provides one pathway for the electrons to follow. Let's\ninvestigate what happens when we increase the resistance in a series circuit.\n.\nINVESTIGATION:\nWhat happens when we add more\nresistors in series?\n.\nAIM: To investigate the effect of adding resistors to a series circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\n.\n.\n53\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cells\n• 3 torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, the ammeter, 1 bulb and the switch in\nseries.\nA photo showing the setup.\n2. Close the switch, or the circuit if you are not using a switch.\n3. Note how brightly the bulb is shining and write down the ammeter reading.\nDraw a circuit diagram.\n.\n4. Open the switch.\n5. Add another light bulb into the circuit.\n6. Close the switch.\n..\n54\n.\nEnergy and Change\n\n.\n7. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram.\n.\n8. Open the switch.\n9. Add the third light bulb into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram for the last circuit you built.\n.\n.\n.\n55\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nseries\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness, or was\none brighter than the other?\n..\n56\n.\nEnergy and Change\n\n.\n3. When you had three bulbs, did they glow the same as each other or was\none brighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the series circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin series?\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in series?\n2. Is your hypothesis accepted or rejected?\n.\nAs more resistors are added in series, the total resistance of the circuit\nincreases. As the total resistance increases, the current strength decreases.\nWhat would happen if we increased the number of cells connected in series?\nWould the current become larger or smaller? Let's investigate.\n.\nINVESTIGATION:\nHow does adding more cells in\nseries affect the current?\n.\nAIM: To investigate the effect of increasing the number of cells connected in\nseries on the electric current strength.\nHYPOTHESIS: Write a hypothesis for this investigation. Remember to mention\nhow the increase in the number of cells will affect the current strength.\n.\n.\n57\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS\n• three 1,5 V cells\n• insulated copper conducting wires\n• ammeter\n• 2 torch light bulbs (or 1 torch light bulb and one resistor)\nMETHOD:\n1. Construct a circuit with 1 cell, the ammeter and the two torch light bulbs.\n2. Observe the brightness of the bulbs and record the ammeter reading in the\ntable of results. Draw a circuit diagram.\n.\n3. Add a second cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n4. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\n5. Add a third cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n..\n58\n.\nEnergy and Change\n\n.\n6. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nseries\nBrightness of bulbs\nReading on a mmeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What can you conclude from the shape of the graph?\n2. Is your hypothesis true or false?\n.\nWe have seen that increasing the number of cells in series increases the current,\nbut increasing the number of resistors decreases the current.\nWe will now investigate the current strength at different points in a series circuit.\n.\n.\n59\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION:Is the current strength the same at all points in a\nseries circuit?\nHYPOTHESIS: Write a hypothesis for this investigation. What do you think will\nhappen in this investigation?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• two torch light bulbs\n• ammeter\nMETHOD:\n1. Set up a series circuit with two cells and two torch light bulbs in series with\neach other.\n2. Insert an ammeter in series between the positive terminal of the batteries\nand the first torch bulb.\n3. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series between the two torch bulbs.\n6. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n..\n60\n.\nEnergy and Change\n\n.\n.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series between the last torch bulb and the negative\nterminal of the batteries.\n9. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\nRESULTS:\nComplete the following table:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nBetween positive terminal\nof cell and first bulb\nBetween two bulbs\nBetween negative terminal\nof cell and last bulb\n.\n.\n61\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nCONCLUSIONS:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\nIn a series circuit, there is only one pathway for the electrons to move through.\nThe current strength is the same everywhere in that pathway.\nWhat have we learned about series circuits?\n• There is only one pathway for the electrons to follow.\n• The current flows at the same strength everywhere in a series circuit,\nbecause there is only one pathway. We say that the current is the same at\nall points in the circuit.\n• If you add more resistors in series, the current in the whole circuit\ndecreases.\nWhy does the current stay the same at all points? Let's think about how electric\ncurrent moves through a circuit. Do you remember that we spoke about the\ndelocalised electrons in metals in the last chapter?\n.\nVISIT\nAnimation showing the\nmovement of electrons.\nbit.ly/19Ww8pW\nThe electrons in a conductor normally drift in various different directions within\na metal, as shown in the diagram.\nDelocalised electrons move freely in a\nconducting wire.\nWhen the wire is connected in a closed\ncircuit, the electrons move towards the\npositive terminal of the battery.\nWhen we build a closed circuit with a cell as an energy source, the electrons will\nall begin to move towards the positive side of the cell. The rate at which the\nelectrons move, is determined by the resistance of the conductor.\nThere are electrons everywhere in the conducting wires and electrical\ncomponents. When the circuit is closed, all the electrons start moving in the\nsame general direction at the same time. This is why a light bulb turns on\nimmediately when you close the switch.\n.\nVISIT\nFlip the switch and watch\nthe electrons with this\nsimulation.\nbit.ly/15NlqBd\nIn a series circuit, all the electrons travel through every component and wire as\nthey travel through the circuit. All the electrons experience the same resistance\n..\n62\n.\nEnergy and Change\n\nand so they all move at the same rate.\nThis means that in the diagram below, the readings on all three ammeters will\nbe the same, so: A1= A2= A3\n.\n3.2 Parallel circuits\n.\nNEW WORDS\n• parallel circuit\nParallel circuits offer more than one pathway for the electrons to follow. When\nconstructing a parallel circuit, we say that components are connected in\nparallel.\nLook at the diagram which shows how two light bulbs are connected in parallel.\nThere are two paths for the current in this parallel circuit, one path through each of the\nbulbs.\nHow can you tell whether or not a circuit is connected in series or in parallel?\nLet's look at some circuit diagrams to tell the difference.\n.\nVISIT\nWatch a video that\nexplains the difference\nbetween series and\nparallel circuits\nbit.ly/1f5hZ0W\n.\nACTIVITY: Series or parallel?\n.\nINSTRUCTIONS:\nLook at the following circuits and write down which are in series and which are\nin parallel. The series circuits will only offer one pathway, but the parallel\ncircuits will have more than one pathway for the electrons to follow.\n.\n.\n63\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nLet's investigate how parallel circuits work.\n.\nINVESTIGATION:\nHow does adding resistors in\nparallel affect the current strength?\n.\nAIM: To investigate the effect of adding resistors in parallel on the current\nstrength.\nHYPOTHESIS: Write a hypothesis for this investigation.\n..\n64\n.\nEnergy and Change\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cell\n• three identical torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, ammeter, one bulb and the switch in\nseries.\n2. Close the switch.\n3. Note how brightly the bulb is shining and record the ammeter reading.\nDraw a diagram of your circuit.\n.\n4. Open the switch.\n5. Add another light bulb, in parallel to the first, into the circuit.\n6. Close the switch.\n7. Note how brightly the bulbs are shining and record the ammeter reading.\n8. Open the switch.\n9. Add the third light bulb, in parallel to the first two, into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and record the ammeter reading.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nparallel\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\n.\n.\n65\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness or was\none brighter than the other?\n3. When you had three bulbs, did they glow the same brightness or was one\nbrighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the parallel branches of the circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin parallel?\n..\n66\n.\nEnergy and Change\n\n.\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in parallel?\n2. Is your hypothesis true or false?\n.\nAs more resistors are added in parallel, the total current strength increases. The\noverall resistance of the circuit must therefore have decreased. The current in\neach light bulb was the same because all the bulbs glowed with the same\nbrightness. This tells us that the current of electrons must have split up and\nmoved through each of the branches.\nWe can also connect cells in parallel. What would happen if we increased the\nnumber of cells connected in parallel? Would the current get stronger or\nweaker?\n.\nINVESTIGATION:\nWhat happens to the current\nstrength when cells are connected\nin parallel?\n.\nAIM: To investigate how increasing the number of cells connected in parallel\naffects the current strength in a circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS\n• three 1,5V cells\n• one torch light bulb\n• insulated copper conducting wires\n• ammeter\nMETHOD:\n1. Set up a circuit which has one cell, the ammeter and the torch light bulb in\nseries with each other. Draw a circuit diagram of your circuit.\n.\n.\n67\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\n2. Observe the brightness of the bulb and record the ammeter reading.\n3. Connect another cell in parallel with the first cell. To connect the second\ncell in parallel, connect a wire from the positive terminal of the first cell to\nthe positive terminal of the second cell. Connect another wire between the\nnegative terminal of the first battery and the negative terminal of the\nsecond battery. Draw a circuit diagram of your circuit.\n.\n4. Observe the brightness of the bulb and record the ammeter reading.\n5. Connect a third cell in parallel to the other two cells. Draw a circuit\ndiagram of your circuit.\n.\n6. Observe the brightness of the bulb and record the ammeter reading.\n..\n68\n.\nEnergy and Change\n\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nparallel\nBrightness of bulb\nReading on ammeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What did you notice about the brightness of the bulbs?\n2. What did you notice about the ammeter readings?\n3. What conclusion can you draw from your results?\n.\nAdding cells in parallel has no overall effect on the current strength. The current\nstrength stays the same if you add cells in parallel.\nWe saw that the current strength increased when bulbs were connected in\nparallel. However, we were only testing the current strength at one point in the\nparallel circuit. How does the current compare in the different pathways of the\ncircuit? Let's do an investigation to find out.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION: Is the current strength equal at all points in a\nparallel circuit?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• three identical torch light bulbs\n• ammeter\n.\n.\n69\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMETHOD:\n1. Set up a parallel circuit with two cells in series with each other and three\ntorch light bulbs in parallel with each other.\n2. Insert an ammeter in series between the cells and the first pathway, as\nshown in the diagram.\n3. Measure the current strength using the ammeter.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series in the first pathway.\n6. Measure the current strength using the ammeter.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series in the second pathway.\n9. Measure the current strength using the ammeter.\n10. Remove the ammeter and close the circuit again.\n11. Insert the ammeter, in series, in the third pathway.\n..\n70\n.\nEnergy and Change\n\n.\n12. Measure the current strength using the ammeter.\n13. Remove the ammeter and close the circuit again.\n14. Insert the ammeter in series between the first pathway and the cells on the\nopposite side to the first reading.\n15. Measure the current strength using the ammeter.\nRESULTS:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nbetween the cell and first\npathway\nin the first pathway\nin the second pathway\nin the third pathway\nbetween the cell and the\nfirst pathway\nCONCLUSION:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\n.\n.\n71\n.\nChapter 3.\nSeries and parallel circuits\n\nWhat have we learned about parallel circuits?\n• There is more than one pathway for the current to follow.\n• The current divides between the different branches so that each branch\ngets some of the current. As the torch bulbs in each branch in our example\nwere identical, the current divided equally between them.\n• If you add more resistors in parallel, the total current supplied by the cell in\nthe circuit increases.\nWhy does the current divide when offered an alternative pathway?\nImagine that you are sitting in a school hall during assembly. You are bored and\nwaiting for it to end so that you can go out to break to chat to your friends.\nThere is only one exit from the hall. When you are dismissed, everyone has to\nexit through the same door. It takes a while because only some learners can\nleave at a time.\nNow imagine that there is a second door that is the same as the first door. Now\nyou and your friends have a choice of which door to go through. The speed at\nwhich the learners exit the hall will increase and some of you will exit through\nthe first door while others will exit through the second door. No one can go\nthrough both doors at the same time.\nThis is similar to the way current behaves when in a parallel circuit. As the\nelectrons approach the branch in the circuit, some electrons will take the first\npath and others will take the other path. The current is divided between the two\npathways.\nIn the following circuit A1 = A4 and A1 = A2 + A3 and A4 = A2 + A3\nWe have looked at how resistors and cells behave in series and parallel circuits.\nLet's look at how different metals conduct electricity. All conductors have some\nresistance in a circuit. Are some metals better conductors of electricity than\nothers?\nLet's have a look at which metals offer more resistance than others to the flow\nof charge (current) through an electric circuit .\n..\n72\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Which metals offer the most\nresistance?\n.\nMATERIALS:\n• a cell\n• torch light bulb\n• insulated copper wires\n• lengths of copper, aluminium, zinc and nichrome wire\n• crocodile clips (if available)\nINSTRUCTIONS\n1. Build a circuit with the cell and the torch light bulb and leave a gap for the\nmetal to be tested. You can use crocodile clips at the end of each piece of\nmetal for easy insertion.\n2. Insert each metal into the circuit (one at a time).\nAn example circuit with a cell, a light bulb and the piece of metal being tested.\nObserve the brightness of the bulb.\nQUESTIONS:\n1. Draw a circuit diagram of your apparatus.\n.\n.\n.\n73\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n2. Why can we use the brightness of the bulb to qualitatively measure\nresistance?\n3. List the metals in order of increasing resistance.\n4. Why do you think copper is used for connecting wires in electrical circuits?\n.\nThere are several factors which influence the amount of resistance a material\noffers to an electric current. We have seen that the type of material is one of\nthose factors.\n.\nTAKE NOTE\nIn Gr. 9 we will look at\nthe other factors that\ninfluence resistance. If\nyou want to see the\ncontent in other grades,\nremember that you can\nvisit\nhttp://www.\ncurious.org.za\n.\n3.3 Other output devices\nLight bulbs are not the only devices used in electrical circuits. Devices that use\nelectrical energy to function, including light bulbs, are called output devices.\nLet's look at some other common examples of output devices.\nLEDs (Light-Emitting Diodes)\nLEDs are widely used electronic devices. They are small lights but they do not\nhave a filament like an incandescent bulb has. They therefore cannot burn out,\nas there is no filament to wear out, and they do not get as hot. LEDs are used in\nelectronic timepieces, high definition televisions and many other applications.\nLarger LEDs are also replacing traditional light bulbs in many homes because\nthey do not use as much electricity. They last longer than incandescent bulbs\nand are more efficient.\n.\nVISIT\nWatch this video about\nthe history of the LED\nbit.ly/1bC5qKc\n..\n74\n.\nEnergy and Change\n\nDifferent LED bulbs.\nIn the last chapter, we looked at the energy transfers in an electrical system. We\nwill now represent energy transfer within electrical systems in a different way.\nWe will apply this new representation to the difference between energy outputs\nin an LED and an incandescent light bulb.\n.\nVISIT\nVideo on drawing a basic\nSankey diagram.\nbit.ly/19Wwxsu\n.\nACTIVITY: Sankey diagrams\n.\nYou might have drawn Sankey diagrams in Grade 7. If not, here is some quick\nrevision.\nIn an energy system, input energy is transferred to useful output energy and\nwasted output energy. A Sankey diagram is a visual and proportional\nrepresentation of the energy transfers that happen in a system.\nFor example, a kettle uses about 2000 J of input energy, but only about 1400 J\nis used to heat the water. The remaining 600 J is wasted as sound. Here is the\nSankey diagram to represent the energy transfer.\n.\nTAKE NOTE\nRemember that energy\nis measured in joules\n(J).\n.\n.\n75\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nQUESTIONS:\nWe will now compare an LED with an incandescent light bulb.\n1. Draw a Sankey diagram for an LED if the input energy is 100 J, 75 J of\nenergy is used to produce light and the rest is lost as heat.\n.\n.\nVISIT\nAn electricity timeline\nanimation.\nbit.ly/1fKZb8E\n2. Draw a Sankey diagram for a filament light bulb if the input energy is 100 J,\nthe wasted heat energy is 80 J and the rest produces light.\n.\n3. Which bulb do you think is more efficient? Explain your answer.\n.\nCan you think of any other output devices? Make a list of as many as you can.\n..\n76\n.\nEnergy and Change\n\n.\n.\nACTIVITY: History of electricity production\n.\nINSTRUCTIONS:\n1. Work in groups of three or four.\n2. Research the history of electricity production: How was electricity\ndiscovered and how did electricity become widely used?\n3. Create a basic timeline for the discovery of electricity and it's production.\n.\n.\nACTIVITY: Careers\n.\nINSTRUCTIONS:\n1. Choose a career related to electricity production.\n2. Write a short paragraph describing the career. Include information on how\none can study or prepare for your chosen career.\n.\n.\n.\n77\n.\nChapter 3.\nSeries and parallel circuits\n\n..\nSUMMARY:\n.\nKey Concepts\n• A series circuit has only one pathway for the electrons to travel through.\n• A parallel circuit has more than one pathway for the electrons to travel\nthrough.\n• In a series circuit, the current is the same at all points in the circuit.\n• In a series circuit, the resistance increases as more resistors are added\nin series.\n• In a parallel circuit, the current splits between the available paths.\n• In a parallel circuit, the resistance decreases as more resistors are added\nin parallel.\n.\nConcept Map\nComplete the concept map on the following page to summarise what you\nhave learned about series and parallel circuits.\n..\n78\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Look at the following circuit diagrams and decide whether they are series\ncircuits or parallel circuits. Write the correct answer in the space below\neach diagram. [6 marks]\n2. Look at the three circuit diagrams. Rank the circuits from brightest bulb to\ndimmest bulbs. [3 marks]\n..\n80\n.\nEnergy and Change\n\n.\n3. Explain your choices in the previous question. [5 marks]\n4. Look at the three circuit diagrams. Rank the circuits from brightest bulb(s)\nto dimmest bulb(s). [3 marks]\n5. Explain your choices in the previous question. [5 marks]\n6. Look at the circuit diagram below. Each light bulb is identical.\na) Is this a series or parallel circuit? Explain your answer. [2 mark]\nb) How do the brightness of bulbs A, B and C compare? (which is the\nbrightest?) [3 marks]\n.\n.\n81\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nc) What would happen to the brightness of the bulbs if the switch was\nopened? Explain your answer. [5 marks]\n7. Study the following diagram.\na) What is the relationship between the ammeter readings on A1 and A4?\nIn other words, how do the current strengths compare at these points\nin the circuit? Explain your answer. [3 marks]\nb) What is the relationship between the ammeter readings on A1, A2 and\nA3? In other words, how do the current strengths compare at these\npoints in the circuit? Explain your answer. [3 marks]\nTotal [38 marks]\n.\n..\n82\n.\nEnergy and Change\n\nDraw and discover the possibilities of what a slinky can be.\n.\n.\n83\n.\nChapter 3.\nSeries and parallel circuits\n\n. .\n4\n.\nVisible light\n..\n84\n..\nKEY QUESTIONS:\n• Where does light come from?\n• How does light travel?\n• How do we see?\n• Why do leaves look green?\n• How do mirrors work?\n• Why do my legs look crooked underwater?\nIn this chapter we will learn about visible light. We call it visible light because\nwe can see it with our own eyes. There are different forms of light which we\ncannot see with our naked eyes. Ultraviolet light is an example of a form of light\nwhich we cannot see with just our eyes. We will focus our attention on the\nvisible light spectrum and investigate how we are able to see different colours\nand how light behaves.\n.\n4.1 Radiation of light\nWhere does light come from? Natural light comes from luminous objects such\nas the Sun and light bulbs. We say that these objects emit light.\nThe Sun is our main source of light on Earth.\nA light bulb is a luminous object as it emits\nlight.\n.\nNEW WORDS\n• luminous\n• radiation\n• rectilinear\n• propagation\n.\nVISIT\nThe speed of light (video)\nbit.ly/GAMgFW\n\nThis image from NASA shows the Earth's lights at night. You can see how much we rely\non light nowadays.\n.\nDID YOU KNOW?\nIf you could travel at the\nspeed of light you could\ntravel around the\nequator 7,5 times in 1\nsecond!\n.\nTAKE NOTE\nThe Moon is NOT a\nluminous object as it\ndoes not emit its own\nlight light. It reflects the\nlight from the Sun.\nLight travels through space at a speed of 300 000 kilometers per second. We\nsay that energy is transferred by radiation. The energy of the light is transferred\nthrough space as electromagnetic waves in straight lines.\nLight and heat are transferred to Earth through space from the Sun by radiation.\n.\nDID YOU KNOW?\nIt takes light 8 minutes\nto travel from the Sun to\nthe Earth.\nLet's look at how light travels. We will make a simple camera to investigate how\nlight travels.\n.\n.\n85\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Make a pinhole camera\n.\nMATERIALS:\n• Pringles chip can\n• craft knife\n• aluminium foil\n• tape\n• ruler\n• drawing pin\nINSTRUCTIONS:\n.\nTAKE NOTE\nThe Sun emits radiation\nin all directions, but in\nthe diagram here, only\nthe radiation which\nreaches Earth has been\nshown.\n1. Measure 5 cm from the bottom of the can (opposite end to the plastic lid)\nand make a mark all around the can.\n2. Cut through the can along the line\nso that you have cut the can into 2\npieces.\n3. If you have a clear lid, put a piece of\nwax paper on top of the lid before\nsticking everything together.\n..\n86\n.\nEnergy and Change\n\n.\n4. Place the lid between the 2 pieces\nand stick it all together using tape.\n5. Wrap the aluminium foil around the\ncan to prevent any light from\ncoming in from the sides.\n6. Use a drawing pin to make a hole in the centre of the metal base of the can.\n7. Go outside with your pinhole camera.\n8. Point the metal end with the hole at an object which is in bright sunlight.\n9. Cup your hands around the other end and look through the open end.\nQUESTIONS:\n.\nVISIT\nLight travels in a straight\nline? (video)\nbit.ly/19n4T7g and\nbit.ly/174q6mx\n1. What did you see when you looked through the open end of the tube?\n2. What happens when you move closer or further away from an object?\n.\nDid you see an upside down image? Why is it upside down?\nWe see objects because light reflects off them and enters our eyes. If the image\nis upside down it means that the light from the bottom of the object has arrived\nat the top of the screen and the light from the top of the object has reached the\nbottom of the screen, as shown in the following diagram.\n.\n.\n87\n.\nChapter 4.\nVisible light\n\nWhen you moved closer to the object, the image appeared bigger, as shown in\nthe following diagram.\nWhat does this mean? It means that light must be travelling in straight lines.\nThis is called the rectilinear propagation of light.\n.\nVISIT\nCan you use what you\nhave learnt to understand\nhow this shadow illusion\nworks?\nbit.ly/156mx1y\nRay diagrams\nA ray diagram is a drawing that shows the path of light. Light rays are drawn\nusing straight lines and arrowheads, because light travels in straight lines. The\nfigure below shows some examples of ray diagrams.\n..\n88\n.\nEnergy and Change\n\nA ray diagram showing how you see\nanother person.\nA ray diagram showing how you see a\nreflection in a mirror.\n.\n4.2 Spectrum of visible light\n.\nNEW WORDS\n• composition\n• visible spectrum\n• dispersion\nThe visible light spectrum is the light that we are able to see with our naked\neyes. Have you ever wondered why everything is colourful and not just black\nand white? Have you ever seen a rainbow and wondered where the colours\nhave come from? The colours that we see everyday are part of the visible light\nspectrum. Let's investigate the visible light spectrum.\n.\nACTIVITY: Splitting white light\n.\nMATERIALS:\n• triangular perspex prism\n• ray box and power source\nINSTRUCTIONS:\n1. Connect the ray box to the power source. If you do not have a ray box,\nyour teacher will show you how to use a piece of cardboard with a slit cut\ninto it.\n2. Place the triangular prism on a white background.\n3. Shine a beam of white light through the side of the prism.\nQUESTIONS:\n1. Draw a picture showing what you observe.\n.\n.\n89\n.\nChapter 4.\nVisible light\n\n.\n.\n2. Write a description of what you observed.\n3. Write down the order in which the colours appear.\n4. If you repeat the experiment, does the order of the colours change?\n5. What do the different colours we see tell us about the composition of\nwhite light?\n.\n..\n90\n.\nEnergy and Change\n\nSo, what have we learned so far? Light radiates from luminous objects and\nalways travels in straight lines. The white light that we see is made up of the 7\ndifferent colours of the spectrum. When the 7 colours are travelling together we\nsee them as white light.\nThe 7 colours of the visible spectrum are Red, Orange, Yellow, Green, Blue,\nIndigo and Violet. Each colour has a different wavelength and frequency. Have\na look at the following image which shows the spectrum of visible light.\n.\nTAKE NOTE\nYou can use the\nabbreviation ROYGBIV\nto remember the order\nof the colours.\nThe colours combine to form white light.\n.\nTAKE NOTE\nThe primary colours of\nlight are red, green and\nblue.\n.\nACTIVITY: Colour spinning wheels\n.\nMATERIALS:\n• white cardboard\n• coloured pens or pencils (red, orange, yellow, green, blue, indigo, violet)\n• string\n• scissors\n• round object\nINSTRUCTIONS:\n1. Draw a circle on the cardboard. You can trace around a round object such\nas a cup or saucer to do this. Cut out the circle.\n.\n.\n91\n.\nChapter 4.\nVisible light\n\n.\n2. Now divide the circle into 7 equal segments. If you do not have indigo and\nviolet colours, but just one purple pen or crayon, then you can divide the\ncircle into 6 equal segments rather.\n3. Shade in each segment a different colour, in the order red, orange, yellow,\ngreen, blue, indigo, violet (or just purple if you do not have indigo and\nviolet).\n.\nDID YOU KNOW?\nAn artist might tell you\nthat the primary colours\nof paint are red, yellow\nand blue. This is\ndifferent to the primary\ncolours of light. This is\nbecause the pigments\nyellow, blue and red\ncannot be mixed from\nother pigments. In\nprinting, the primary\ncolours are magenta,\nyellow and cyan.\n4. Next, make two holes, one on either side of the centre as shown below.\n5. Thread the string through the holes and tie it in a loop.\n6. You are now ready to spin the wheel. Holding the ends of the loop in each\nhand, twirl the string over, like you would a skipping rope, so that the\nstring twists. Once the string is tightly twisted, pull your hands apart, then\nbring them back together. Continue bringing your hands in and out and\nwatch the circle spin.\n.\nVISIT\nThere is no pink light.\nbit.ly/1b2gFXU\n7. What do you observe about the colour of the wheel as it spins faster?\n.\n..\n92\n.\nEnergy and Change\n\nSo far we have been talking about the visible light spectrum. As we mentioned\nin the beginning, this is the light that we can see. We also spoke about how light\ntravels in electromagnetic waves. We can only see light with a certain range of\nwavelengths. What does this mean?\n.\nDID YOU KNOW?\nWavelengths can be as\nsmall as one billionth of\na meter, as with gamma\nrays. Wavelengths can\neven be as long as\nmeters, for example in\nradio waves.\nThe size of a wave is measured in wavelengths. A wavelength is the distance\nbetween two corresponding points on two consecutive waves. Normally this is\ndone by measuring from peak to peak or from trough to trough. Have a look at\nthe following diagram which illustrates a wavelength.\n.\nDID YOU KNOW?\nIn police forensics,\nultraviolet light can be\nused along with a\nspecial powder to\ndetect finger and shoe\nprints that can help\nsolve crimes.\nThe wavelengths of the different colours of visible light are different lengths, as\nshown in the following diagram.\nWe can also talk about the frequency of a wave. If a wave has a long\nwavelength, then it has a low frequency; if it has a short wavelength, then it has\na high frequency.\nOf visible light, orange and red light have the longest wavelengths (and lowest frequency)\nand violet, indigo and blue have the shorter wavelengths (and highest frequency).\n.\n.\n93\n.\nChapter 4.\nVisible light\n\nWhen it comes to visible light, we only see wavelengths of 400 to 700 billionths\nof a meter. This is called the visible spectrum. But, light waves are just part of\nthe wave spectrum. There is invisible light with shorter wavelengths, such as\nultraviolet light, and there are longer wavelengths, such as infrared light.\nHave you ever looked through a window and wondered why it is made of glass?\nLet's find out how light behaves when it strikes the surface of different types of\nmaterials in the next section.\n.\n4.3 Opaque and transparent substances\n.\nNEW WORDS\n• opaque\n• transparent\n• translucent\n• transmit\nThree different things happen when light hits a surface, it can be reflected\n(bounce off), absorbed or transmitted (pass through). Glass reflects some light\nbut most of the light is transmitted straight through. That's why we can see\nobjects on the other side of a closed window.\nWe say that glass is transparent. Let's find out more about what this means. If a\nsubstance is not transparent, it is opaque.\n.\nACTIVITY: Shadow Play\n.\nMATERIALS:\n• cardboard\n• clear plastic\n• plastic shopping bag\n• scissors\n• light source (ray box or light bulb)\nINSTRUCTIONS:\n1. Cut out three shapes from your cardboard. All of the shapes should be\nsimilar but three different sizes: small, medium and large.\n2. Switch on the light source.\n3. Hold your first shape a short distance in front of the light source.\n4. Look at the shadow that forms. Write down what you observe.\n5. Hold your second shape the same distance in front of the light source.\n6. Look at the shadow that forms. Write down what you observe.\n7. Hold your third shape the same distance in front of the light source.\n8. Look at the shadow that forms. Write down what you observe.\n9. The shadow is formed on the side furthest from the light source. It is dark\n..\n94\n.\nEnergy and Change\n\n.\nin colour and larger than the first and second shadows.\n10. Use your first cardboard shape as a template and cut the shape from the\nclear plastic and the plastic shopping bag.\n11. Hold the clear plastic shape the same distance from the light source. Write\ndown what you observe.\n12. Hold the plastic shopping bag shape the same distance from the light\nsource. Write down what you observe.\nQUESTIONS\n1. When you held the cardboard up to the light, did it allow light to pass\nthrough it? How do you know this?\n2. Is the cardboard shape opaque or transparent?\n3. What did you notice about the shadows formed by the different size\ncardboard shapes?\n4. Draw a diagram to show how the shadow is formed behind the opaque\nshape. Use straight lines with arrowheads to represent the rays of light.\n.\n.\n.\n95\n.\nChapter 4.\nVisible light\n\n.\n5. The distance between the shape and the light source was kept the same.\nWhat do you think would have happened to the shadow if the distance\nwas increased?\n6. Test your idea from question 5 by moving your cardboard shapes closer to\nand further away from the light source. What do you see? Were you\ncorrect in your prediction?\n7. Is the clear plastic shape opaque or transparent?\n8. Did the clear plastic cast a shadow?\n9. Explain why the cardboard casts a shadow but the clear plastic does not.\n10. Is the plastic shopping bag shape opaque or transparent?\n11. Explain why the shopping bag casts a lighter shadow.\n.\n..\n96\n.\nEnergy and Change\n\nWhat have we learned? Shadows are formed because light travels in straight\nlines and cannot pass through opaque objects.\nSubstances which transmit most of the light and only absorb or reflect a little bit\nare called transparent. Can you list some everyday objects which are\ntransparent?\nSubstances which completely reflect or absorb light without transmitting any\nare called opaque. Can you list some everyday objects which are opaque?\nSome substances, such as the plastic shopping bag, allow some light to pass\nthrough, but not all of it. This substance is translucent, or semi-transparent.\nShadows can be useful. Sundials have\nbeen used since ancient times as a\ntime-keeping device, like a watch or a\nclock. As the position of the Sun\nchanges in the sky, the shadow cast by\nthe style moves across the surface of\nthe sundial. The surface is marked with\nnumbers, allowing the shadow to\nindicate time of day.\nWe can use transparent objects to make filters. If we want red light we use a\nred glass bulb or a red plastic film placed in front of the light. Only red light is\nable to transmit through the red glass or plastic. The other colours are absorbed\nby the filter.\nThese are different colour filters for a camera. The red filter will only allow red light\nthrough and so the photograph will have a red effect applied to it. The other colours of\nlight are absorbed by the filter.\nNow that we have seen some examples of transparent and opaque substances,\nlet's take a closer look at what it means to absorb or reflect light.\n.\n.\n97\n.\nChapter 4.\nVisible light\n\n.\n4.4 Absorption of light\nLook at this picture of a ladybird. Why\nis it red and black? And why is the leaf\nso green? How do we see the different\ncolours? It all has to do with what\nhappens when light hits a surface.\nWhen light hits a surface, some of the\nlight is absorbed and the rest is\nreflected. It is the reflected light that\nreaches our eyes and allows us to see\nthe object.\nA ladybird.\nPreviously, we learned that white light is a mixture of different colours. When\nwhite light from the Sun hits the red shell of the ladybird all of the colours are\nabsorbed, except red. Red light is reflected back to our eyes and so we see a\nred ladybird.\nWe see the red shell of the ladybird as red light is reflected and the other colours are\nabsorbed.\nThe green leaf absorbs all the colours except green which it reflects back into\nour eyes.\n..\n98\n.\nEnergy and Change\n\nWe see a green leaf as green light is reflected and the other colours are absorbed by the\nleaf's surface.\nWhat about the black spots of the ladybird? Is black a colour? The black spots\non the ladybird absorb all the colours and no light is reflected. That is why they\nappear black.\n.\nTAKE NOTE\nAlthough we can get\nblack paint as a\npigment, black is not a\ncolour of light. Black is\nthe result of the\ncomplete absorption of\nlight.\nDo you remember learning about heat as energy transfer in Gr 7? We looked at\nthe absorption of heat. We saw that black, matt objects absorbed all of the light\nenergy, while white objects reflected all of it. Black, matt (not shiny) objects\nabsorb all of the colours of light and reflect none and so appear black to our\neyes.\nWhat about a white object? Why do you think white objects look white? Have a\nlook at the following diagram for a clue.\n.\n.\n99\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Why do objects look red under red\nlight?\n.\nMATERIALS:\n• piece of red plastic to act as a filter\n• light source (light bulb or torch)\n• white object\nINSTRUCTIONS:\n1. Place a white object on the desk.\n2. Switch on your light source and place the red plastic in front of the light.\n3. Shine the light (with the red plastic in front) onto the piece of white paper.\nQUESTIONS:\n1. What colour was the page under normal light?\n2. Why does the page appear white in normal light?\n3. What did you see when the red plastic filter shone on the white page?\n4. Explain why the paper changed colour.\n.\nLet's now look more at what we mean by reflection of light.\n..\n100\n.\nEnergy and Change\n\n.\n4.5 Reflection of light\n.\nNEW WORDS\n• reflect\n• incident ray\n• reflected ray\n• normal line\n• angle of\nincidence\n• angle of\nreflection\n• perpendicular\nWhen light hits a surface it is\noften reflected off the surface.\nThis photograph shows how\nlight is reflected off a still lake,\ncreating a mirror image of the\ntree. The still, flat surface of the\nlake has acted as a mirror.\nA tree reflection.\nHave some fun with these photos of reflections in water. One photograph is the\nright way up and the other one is upside down! Which one is which?\nReflections on the Negro River in the\nAmazon.\nReflections in the Arno River in Italy.\nMost surfaces reflect light. When light strikes a reflective surface, it can change\ndirection. Let's look at how this happens.\nWhen light reflects off a surface the ray which hits the surface, it is called the\nincident ray. The ray of light which is reflected from the surface is called the\nreflected ray. When we draw diagrams of reflection we also draw in an\nimaginary line to help us measure different angles. This line is called the normal.\nThe normal line is always drawn perpendicular to the surface.\nBetween the normal line and the incident and reflected rays, there are two\nangles. These are:\n• angle of incidence - the angle between the incident ray and normal line\n• angle of reflection - the angle between the reflected ray and normal line\nThe following diagram explains these concepts.\n.\n.\n101\n.\nChapter 4.\nVisible light\n\nLet's investigate the relationship between the angle of incidence and the angle\nof reflection.\n.\nINVESTIGATION:\nIs there a relationship between the\nangles of incidence and reflections?\n.\nAIM: To investigate the reflection of light from a surface.\nINVESTIGATIVE QUESTION:\nLook at the diagram above and try to formulate an investigative question for\nthis investigation.\nHYPOTHESIS: The angle of incidence is equal to the angle of reflection\nMATERIALS AND APPARATUS:\n• mirror\n• white paper\n• pencil\n• protractor\n• ruler\n• ray box\nMETHOD:\n1. Put a white piece of paper on the desk.\n2. Use your ruler to draw a straight line near the top of the white paper.\n..\n102\n.\nEnergy and Change\n\n.\n3. Use your protractor to make a right\nangle in the middle of your pencil\nline. This is the normal line.\nMarking a right angle with a protractor.\n4. Place your mirror upright along the\nfirst line.\n5. Shine a light from the ray box along\nthe paper so that it \"hits\" the mirror\nwhere your normal line and your\nmirror meet.\nA mirror is placed on the line and a ray\nshone to strike the mirror at the normal\nline.\n6. Use a pencil to mark the incident\nlight ray.\nMarking the incident light ray.\n7. Use a pencil to mark the reflected\nlight ray.\nMarking the reflected ray.\n8. Remove the mirror and switch off\nthe ray box.\n9. Use a ruler and pencil to draw a line\nfrom the points you have marked on\neach ray to the normal line.\nDrawing in the rays.\n.\n.\n103\n.\nChapter 4.\nVisible light\n\n.\n10. Mark the angle of incidence (i) and\nangle of reflection (r).\nYour ray diagram should look similar to\nthis.\n11. Turn the ray box on again to confirm\nthat your pencil lines follow the rays.\nThe ray diagram overlaps the actual rays.\n12. Use a protractor and measure the\nangle of incidence and the angle of\nreflection and record your results in\nthe table.\n13. Repeat this method 3 more times,\neach time using a different angle of\nincidence.\nA different angle of incidence.\n.\nTAKE NOTE\nKeep one of the sheets\nwith your drawn ray\ndiagram for the next\nactivity.\nRESULTS:\nFill your results into the following table.\nRepeat\nAngle of Incidence\nAngle of Reflection\n1\n2\n3\n4\nANALYSIS:\n1. Has your investigation provided everything you need to answer your\ninvestigative question?\n..\n104\n.\nEnergy and Change\n\n.\n2. How could you improve this investigation to get more accurate results?\nCONCLUSION:\nWhat can you conclude based on your results?\n.\nWhenever light is reflected from a surface, the angle of incidence to equal to\nthe angle of reflection. On a smooth surface all the light rays are reflected in the\nsame way and so the image is clear and focused.\nA mirror is an example of a smooth surface. The image you see is focused and\nclear. As you can see in the photograph, the scientists and engineers are clear\nand focused in the mirror image.\nA mirror segment from one of NASA's telescopes provides a clear and focused reflection.\n.\nTAKE NOTE\nIn reflection, not only is\nthe angle of incidence\nequal to the angle of\nreflection, but the\nincident ray and\nreflection ray are also in\nthe same plane.\n.\nVISIT\nWhat colour is a mirror?\n(video)\nbit.ly/GABdNZ\nWhat happens when we do not have a smooth surface? Have a look at the\nphoto.\n.\n.\n105\n.\nChapter 4.\nVisible light\n\nWhy is the reflection of the grass and reeds not clear, but rather blurred?\n.\nACTIVITY: Light reflection off aluminium foil\n.\nMATERIALS:\n• aluminium foil\n• white paper\n• ray box\nINSTRUCTIONS:\n1. If possible, use the white sheets of paper from the last investigation where\nyou drew your ray diagrams.\n2. Similar to what you did in the last investigation, set up a ray box and direct\nthe ray along the line of incidence which you drew.\n3. Crumple a piece of aluminium foil and place this in the spot instead of the\nmirror.\n4. Observe the reflected ray.\nQUESTIONS:\n1. Describe the reflected ray off the aluminium foil and how this compares to\nthe reflected ray off the mirror.\n.\nVISIT\nWatch a video about the\ncreative way that\nscientists have tried to\nanswer the question:\n\"What is light?\"\nbit.ly/GAMvAL\n2. Why do you think you observed these differences?\n.\n..\n106\n.\nEnergy and Change\n\nCan you now see why reflections off rippled water are not clear, but rather\nblurred? This is because the light rays have not reflected parallel to each other\nas they do from a smooth surface, but have scattered in different directions.\nThe following table shows the difference between a smooth surface and a rough\nsurface. Straight parallel rays are approaching the surface. You need to draw in\nthe reflected rays to show specular (clear) reflection from a smooth surface and\ndiffuse (unclear) reflection from a rough surface.\n.\nTAKE NOTE\n'Diffuse' can mean\nunclear as well as\nspread out. In this\nexample, the reflection\nis unclear because the\nrays are spread out or\ndiffuse.\nSpecular diffusion from a smooth\nsurface\nDiffuse reflection from a rough\nsurface.\nVisible light is the range of frequencies of light that are visible to the human eye,\nand is responsible for the sense of sight. Are you curious to find out how we\nactually see light? Let's discover more in the next section.\n.\n4.6 How do we see light?\n.\nNEW WORDS\n• retina\n• stimulate\nHow is it that we are able to see light? Light that is absorbed by objects does\nnot enter the eye. Only reflected light or direct light from luminous objects can\nenter the eye and be interpreted. Have a look at the following image which\nshows the outer structure of the eye.\nWe can see the iris, the pupil and the sclera. The sclera is a the tough white,\nouter part of the eye, which acts as protection. The iris is the coloured part of\nthe eye which differs from person to person. It is circular and surrounds the\npupil. Light enters the eye through the pupil.\n.\nVISIT\n2012 Nobel Prize: How do\nwe see light?\nbit.ly/1a4zs2D\n.\n.\n107\n.\nChapter 4.\nVisible light\n\nThe size of your pupil changes in different light conditions. In bright light, the pupil\ncontracts (gets smaller) to let less light through (as on the left), and in low light your\npupil dilates (gets bigger) to let more light through (as on the right).\nLet's take a look at the internal structure of the human eye. The following\ndiagram shows a cross section through the eye. The eye is actually a large ball,\nand only a small part is visible on the outside. Covering the iris is a tough,\ntransparent layer called the cornea. Behind the iris is the lens. Both the cornea\nand the lens help you to focus the light entering your eyes, as we will learn\nabout in the next section.\n.\nTAKE NOTE\nThe fovea is the part of\nthe eye located in the\ncentre of the retina\nwhere the clearest\nimage is formed.\nA diagram of the eye.\nThe light travels through the eye and hits the retina at the back of the eyeball.\nThe retina is a layer of tissue lining the back of the eyeball, as indicated in the\ndiagram, it is the yellow layer. The retina consists of cells which are sensitive to\nlight. Light enters the eye and forms an image on the back of the eyeball. The\nway in which light hits the back of the eye, is similar to what happens in a\npinhole camera. The receptor cells convert the light energy into electrical nerve\nimpulses. These impulses travel out of the eye through the optic nerve and to\nthe brain where they are interpreted as sight.\n.\nTAKE NOTE\nThe cell is the basic\nstructural and\nfunctional unit of all\nliving things. We will be\nlearning more about the\ncell next year in Gr 9\nLife and Living.\n.\nVISIT\nFind your blind spot with\nthis optical illusion.\nbit.ly/19jumEr\nSo how do we see colour? Do you remember when we spoke about why the\nladybird appears red and black? Look at the following diagram again.\n..\n108\n.\nEnergy and Change\n\nThe white light hits the ladybird's surface. The white light has all the colours of\nlight, but when it hits the red surface, only the red light is reflected. The other\ncolours are absorbed by the red surface. This means that when we look at the\nred parts of the ladybird, we only get red light reflected into our eyes.\nTherefore, when this reflected light hits our retina and the electrical impulse is\nsent to our brains, we see the red colour.\n.\nDID YOU KNOW?\nEach of your eyes has a\nsmall blind spot at the\nback of the retina where\nthe optic nerve\nattaches. You do not\nnormally notice the hole\nin your vision because\nyour eyes work together\nto fill in each other's\nblind spot.\n.\nACTIVITY: Seeing colours\n.\nMATERIALS:\n• coloured pens or pencils\nINSTRUCTIONS:\n.\nDID YOU KNOW?\nThe cells in your eye\ncome in different\nshapes. Rod-shaped\ncells allow you to see\nshapes, and\ncone-shaped cells allow\nyou to see colour.\n1. Answer the following questions about how we see objects.\n2. Draw a ray diagram to accompany your written answer.\n3. An example has been done for you.\nLook at the picture of a sunflower.\nA black and yellow sunflower.\n.\n.\n109\n.\nChapter 4.\nVisible light\n\n.\nWe can draw a ray diagram to show why we see the green leaves as green, as\nshown below. The green surface of the leaves absorb all the colours of white\nlight except green light which is reflected into our eyes.\nNow explain why the petals appear yellow and the centre appears black. Use\nthe concepts of absorption and reflection in your explanation. Draw diagrams\nto support your answer.\n.\nHeath has bought himself a blue car.\nExplain why we see the car as blue by\nusing the absorption and reflection of\nlight. Draw a diagram to support your\nanswer.\nHeath's blue car.\n..\n110\n.\nEnergy and Change\n\n.\n.\n.\n.\nVISIT\nA simulation on colour\nvision.\nbit.ly/18TbpEA\nWe have looked at opaque and transparent substances, absorption of light,\nreflection of light and how we see light. We are now going to go back to\ntransparent substances and see how light can interact with these materials.\n.\n4.7 Refraction of light\nDo you remember the last time you drank a cold drink with a straw? Did you\nnotice that the straw did not look straight anymore once it was in the water or\ncool drink?\n.\nNEW WORDS\n• refraction\n• medium\n• optical density\nWhy does the pencil in this glass of water look bent?\nLet's investigate this by examining what happens to light when it passes\nthrough a glass block.\n.\n.\n111\n.\nChapter 4.\nVisible light\n\n.\n.\nINVESTIGATION:\nWhat happens to light when it\npasses through a glass block\n.\nWe are going to investigate what happens to a ray of light when it passes from\nair and into a glass block and then from the glass block back into air. We are\ngoing to use a glass block with parallel sides.\nBefore we start the investigation, we need to think about how we are going to\ndetermine if light changes direction or not. Do you remember in the\ninvestigation on reflection where we measured the angle of incidence and the\nangle of reflection? What did we find in this investigation?\nWhen light passes through a transparent substance, we can also measure the\nangles. Look at the following diagram. The angle of incidence (i) is measured\nbetween the incident light ray and the normal line. As the light passes through\nthe transparent substance, the angle of refraction (r) is the angle between the\nrefracted light ray and the normal.\nA light ray passing from one medium to another.\nIn the diagram above, you can see that the angle of refraction is smaller than\nthe angle of incidence. Therefore, the refracted light ray changed direction\nwhen it entered the transparent medium. We can also say something about\nwhich direction it bent towards. Did the light ray bend towards or away from\nthe normal line?\nThe next diagram shows another outcome.\n..\n112\n.\nEnergy and Change\n\n.\nA light ray passing from one medium to another.\nIn the diagram above, does the refracted ray change direction when it enters\nthe transparent medium? Give a reason for your answer.\nIn which direction did the refracted ray change?\nWe are now ready to start our investigation.\nAIM: To determine whether light changes direction when it passes through a\nparallel-sided glass block.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS:\n• glass block\n• ray box, laser pointer or other light source\n• protractor\nMETHOD:\n.\nTAKE NOTE\nThe emergent ray from\na parallel sided block is\nparallel to the incident\nray.\n1. Put the glass block in the centre of a piece of white paper and trace around\nit.\n2. Shine a ray of light into the glass block. The ray should be at an angle to\nthe surface of the block.\n.\n.\n113\n.\nChapter 4.\nVisible light\n\n.\n3. Trace the light ray with pencil and mark the point at which it enters the\nglass block.\n4. The light ray emerges on the other side of the glass block. Mark the point\nat which it emerges with a pencil and trace the emergent ray.\n5. Remove the glass block. Your diagram should look similar to the one\nabove.\n6. Draw a line joining the incident ray and emergent ray. You have traced the\nrefracted ray through the glass block.\n7. Draw the normal lines where the incident ray meets the block and where\nthe emergent ray leaves the block.\n8. Measure the angles labelled 1, 2, 3 and 4 as shown on the diagram with a\nprotractor.\n9. Fill in the measurements in the table.\n10. Repeat the steps above three times using different angles of incidence\n(angle 1).\n..\n114\n.\nEnergy and Change\n\n.\nRESULTS AND OBSERVATIONS:\nFill your results into the following table.\nExperimental\nrepeat\nAngle 1\nAngle 2\nAngle 3\nAngle 4\n1\n2\n3\n4\n1. Which pairs of angles are equal in the measurements you have taken?\n2. Which of the angles you measured are the angles of incidence and which\nare the angles of refraction? Write this down below and mark them on the\ndiagram above.\n3. What do you notice about the angle of incidence and angle of refraction\nfor each of your sets of measurements?\n4. Did the light entering the glass block bend towards or away from the\nnormal line?\n5. Make the angle of incidence zero (make the light ray enter the block\nperpendicular to the surface). What is the angle of refraction?\nCONCLUSION:\nWhat can you conclude from your results?\n.\n.\nVISIT\nLearn more about\nrefraction with this\nsimulation.\nbit.ly/GAxLmc\nThe angle of incidence is not equal to the angle of refraction because the light\nhas changed direction as it enters the glass. Therefore, when light travels from\none medium to another, it bends, or changes direction. This is called refraction.\n.\n.\n115\n.\nChapter 4.\nVisible light\n\nWhen light enters a different medium at right angles then it does not change\ndirection.\nSo why does the light refract? Light behaves as a wave does and waves travel\nat different speeds in different media. For example, light travels faster in air\nthan it does in water. When light enters a different medium, it changes speed,\nand if it entered at an angle other than 90o, then it also changes direction. The\nmore dense the medium, the slower the light moves.\nDo you remember learning about density last term in Matter and Materials?\nWrite down your own definition for density in the space below.\n.\nTAKE NOTE\nRemember that\nalthough we learn\nabout Natural Sciences\nin 4 strands throughout\nthe year, there are many\nconnections and links\nbetween the strands.\nIf light moves from a less dense medium, like air, into a denser medium, like\nglass, then the light slows down. The light will bend towards the normal line.\n.\nVISIT\nThe speed of light in glass.\nbit.ly/1fcfJVZ\nIf light moves from a more dense medium to a less dense medium then the light\nspeeds up and moves away from the normal.\nWhen light refracts and changes direction as it passes through different\nmediums, it can distort what we see. Think back to the pencil or straw in a glass\nof water at the start of the section. We can now explain why a drinking straw or\npencil in a glass of water looks bent. The light bends when it moves from one\nmedium to another. Light moves from the air to glass to water, and therefore\nchanges direction.\nIf you have stood in a pool of water before and looked down, have you noticed\nhow short your legs appear to be? Let's have a look at this a bit more in the\nnext activity.\n..\n116\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magic coin trick\n.\nMATERIALS:\n• coin\n• prestik\n• opaque bowl or cup\n• water\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Put a small amount of prestik onto the bottom of the bowl.\n3. Stick the coin to the bottom of the bowl.\n4. Take small steps back from the desk/table until you cannot see the coin\nover the lip of the bowl.\n5. Ask your partner to slowly pour water into the bowl and observe.\nQUESTIONS:\n.\nVISIT\nWatch a video that shows\nand explains the coin\nactivity.\nbit.ly/15NmXXO\n1. What happened when your partner poured the water into the bowl?\n2. Where does the coin appear to be?\n3. Explain why the coin can be seen when the water is added, but not before.\nThe diagrams below will help you explain what is happening in words.\n.\nTAKE NOTE\nThe diagrams used here\nshow the container as\ntransparent so that you\ncan see the coin inside,\nwhereas you will\nactually be using an\nopaque container.\nEmpty container.\nContainer with water.\n.\n.\n.\n117\n.\nChapter 4.\nVisible light\n\nRefraction can be used to explain why images appear to be distorted when we\nview them through transparent mediums. For example, if you are looking at\nyour legs or hands through some water, they will appear closer than they\nactually are as the light is refracted. Look at the photograph of the glass with\nwater in it in front of diagonal lines. Can you see how the lines are distorted\nwhen the light travels through the water and glass compared to when it does\nnot?\nLight refraction through glass and water.\nCan you remember how we split white light into the separate colours of the\nvisible spectrum in the beginning of this chapter? What did we use to do this in\nthe activity?\nWe can do this because the different\ncolours of light bend by different\namounts when the light enters a\ndifferent medium. Different colours of\nlight will slow down to different\nspeeds, causing them to bend by\ndifferent amounts.\nRefraction through a triangular prism.\nWhen the white light entered the prism it refracted. The different colours of\nlight travel at different speeds in the prism so they refracted at different angles\nand split up. Red light refracts the least and the violet light refracts the most as\nyou can see in the following diagram.\n..\n118\n.\nEnergy and Change\n\nPrisms are not the only objects that can split white light into separate colours.\nIn fact, a rainbow is a good example of white light splitting up.\nA rainbow.\nLight from the Sun enters the raindrops and refracts. The light is then reflected\noff the back of the raindrop. When the light passes out of the raindrop it is\nrefracted again and the colours split up even more as shown in the diagram.\nA raindrop refracts and reflects light, dispersing white light into the colours of the visible\nspectrum.\n.\n.\n119\n.\nChapter 4.\nVisible light\n\nWhat colour is at the top of a rainbow and which colour is at the bottom?\nDoes this match the order which we see in the diagram showing how light is\nrefracted and reflected in a raindrop?\nHow does this happen? When we see a rainbow, we see a combination of\nmillions of raindrops. Although each raindrop refracts and reflects all 7 colours,\nwe only see only colour of light reflected from each particular raindrop. This\ndepends on the angle of the raindrop from our position. Therefore, the\nraindrops higher up in the sky reflect red light to us and the rain drops lower\ndown reflect violet light to us. This is shown in the following diagram.\nWe see rainbows with red at the top and violet at the bottom due to the combination of\nmillions of raindrops. We only see one colour reflected from a particular raindrop,\ndepending on its position in the sky.\nWe are now going to look at an application of the refraction of light.\nLenses\n.\nNEW WORDS\n• diverge\n• converge\n• focus\nDo you remember when we spoke about how we see light and the structure of\nthe eye, we mentioned that there is a lens just behind the iris? Another place\nwhere you may have seen lenses before are in reading glasses which some\npeople wear to correct their vision. Or, have you seen how a magnifying glass\nmakes things appear bigger. What are lenses and how do they work?\nA magnifying glass makes things look bigger.\n..\n120\n.\nEnergy and Change\n\nA lens is a transparent object which focuses or refracts light. When light is\nspread out, we say it has diverged. Some lenses will diverge light while others\nwill converge light, bringing the light rays together. When light rays are all\nbrought to the same point, we say they have been focused. Let's have a look at\nthis more closely.\n.\nACTIVITY: Diverging and converging light with\nlenses\n.\nMATERIALS:\n• ray box or light source\n• concave lens\n• convex lens\n• piece of paper\n• pencil\nBefore we start, it is important that you know the difference between a convex\nand a concave lens.\nConvex lens\nConcave lens\nA convex lens has one\nside which curves or\nbulges outwards. A\nconvex lens converges\nlight.\nA concave lens has one\nside which curves or is\nhollowed inwards. A\nconcave lens diverges\nlight.\n.\nTAKE NOTE\nA lens can have two\nsides which are concave\nand it is then called a\nbiconcave lens or two\nsides which are convex\nand it is then called a\nbiconvex lens.\n.\n.\n121\n.\nChapter 4.\nVisible light\n\n.\nINSTRUCTIONS:\n1. Place a ray box or light source on one side of a piece of paper and turn it\non. Observe the light rays. You might see something as shown in the\nphotograph here.\nThree rays coming out of a ray box.\n2. Turn the ray box off.\n3. Place the convex lens (with the rounded surface) on the piece of paper\nwhere the light rays will pass through it. Trace around it.\n4. Turn on the ray box or light source and observe what happens to the rays\nwhen they pass through the lens.\nLight rays passing through a convex lens.\n5. Trace the path of the light rays on your piece of paper.\n6. Describe what has happened to the light rays.\n7. Mark the point where the light rays cross. This is called the focal point of a\nconvex lens.\n8. Turn off the ray box or light source and place a new piece of paper in front\nof it.\n9. Now place the concave lens in the path of the light rays and trace around\nthe lens.\n10. Turn on the light source and observe what happens to the rays.\n..\n122\n.\nEnergy and Change\n\n.\n11. Trace the path of the rays on the piece of paper.\nA concave lens in front of the rays of light.\n12. Describe what has happened to the light rays.\n13. Turn off the light rays and extend the rays you have drawn until they meet\nat a point in front of the lens. This is the focal point of a concave lens.\n14. If you still have your pin hole cameras, place a convex and concave lens in\nfront of the camera and observe the image that forms.\nViewing a light source through a pinhole camera with different lenses.\n15. Is the image larger or smaller when you observe through a concave lens?\n16. Is the image larger or smaller when you observe through a convex lens?\n.\n.\n.\n123\n.\nChapter 4.\nVisible light\n\nWe have now seen how lenses can disperse or focus light. Have a look at the\nfollowing diagrams which show how a biconvex lens converges light and a\nbiconcave lens diverges light.\n..\n124\n.\nEnergy and Change\n\nConverging lens\nDiverging lens\nA converging lens refracts the light\nentering it and bends the light rays\nto a focal point on the other side of\nthe lens.\nA diverging lens refracts the light\nentering it and bends the light rays\naway from each other. The light\nrays can be traced back to a focal\npoint in front of the lens.\nWhat do we use lenses for? Think of a magnifying glass. If you hold a\nmagnifying glass over a picture or words then it enlarges the image. Is a\nmagnifying glass an example of a diverging or converging lens?\nLet's think about how this works. Imagine you are looking at the ladybird from\nthe beginning of the chapter through a magnifying glass. The ladybird looks\nbigger than what it actually is. When the object you are viewing is closer to the\nlens than the focal point, you see a virtual image of the ladybird that is larger\nthan the object.\nHave a look at the first diagram below. Can you see that the ladybird is between\nthe focal point and the lens? The rays reflected from the ladybird are refracted\nby the magnifying glass and enter the person's eye.\n.\n.\n125\n.\nChapter 4.\nVisible light\n\nIn the next diagram you can see how your eyes see a virtual image of the\nladybird which is bigger than the object. The more curved the convex lens is in\na magnifying glass, the greater its ability to magnify objects.\n.\nTAKE NOTE\nWhen you hold a\nmagnifying glass up\nand view a distant\nobject, the object\nappears smaller and\nupside down. Unlike\nwhen viewing the\nladybird close up, the\ndistant object is beyond\nthe focal point of the\nlens, which results in\nthis effect.\n.\nVISIT\nHow do lenses work?\nbit.ly/GABjoO\nDo you remember what the human eye looks like? We have lenses in our eyes\nto allow us to see. The light enters the eye and passes through the lens. The\nlens focuses the light onto the back of our retina so that a clear image is formed.\nWhat type of lens do we have in our eyes? Give a reason for your answer.\nIn order for a clear image to form, the lens in our eye needs to focus the light\nrays coming into our eyes so that the focal point falls on the retina. This\ndepends on the shape of the lens in our eyes. Sometimes, people have lenses in\ntheir eyes that cannot focus properly. Have a look at the following diagram\nwhich shows a normal eye and then an eye which focuses before the retina\n(near-sighted) and behind the retina (far-sighted).\n..\n126\n.\nEnergy and Change\n\nOptical glasses, or spectacles, are used to correct near or far-sightedness.\nIf you are near-sighted you need a diverging lens. Would this be a biconcave or\nbiconvex lens?\n.\nDID YOU KNOW?\nA contact lens is\ndesigned to rest on the\ncornea of the eye and\ncorrect vision. Leonardo\nda Vinci was the first to\ncome up with the idea\nin the 16th century to\nhelp prevent eye\ninfection.\n.\nDID YOU KNOW?\nA microscope makes a\ntiny, nearby object look\nmuch bigger. A\ntelescope makes a\nlarge, distant object\nlook much closer and\nbrighter. In both, light\nfrom the object passes\nthrough two or more\nlenses to form an\nimage. The lens shapes\nand distances between\nthem determine how\nthe image is produced.\nIf you are far-sighted you need a converging lens. Would this be a biconcave or\nbiconvex lens?\nAn optometrist holds a lens in front of a patient's eye to correct her vision.\nThe following image shows how lenses can be used to correct far and\nnear-sightedness.\n.\n.\n127\n.\nChapter 4.\nVisible light\n\n.\nTAKE NOTE\nNext term in Planet\nEarth and Beyond we\nwill look at how lenses\nare used in optical\ntelescopes to view\nobjects in space.\n.\nACTIVITY: Research careers in optics\n.\n.\nVISIT\nAn interview conducted\nwith an optometrist.\nbit.ly/19WxYYa\nThere are many different careers in the field of geometric optics.\nINSTRUCTIONS:\n1. Work in groups of 3.\n2. Interview someone in the field of geometric optics and find out how they\nchose their career and what and where they studied.\n3. Write a paragraph explaining the career and the study options available in\norder to qualify for that career.\n4. Here are some examples of careers in geometric optics.\na) Optometry\nb) Ophthalmology\nc) Optoelectronics\nd) Illumination engineering\n.\n..\n128\n.\nEnergy and Change\n\n.\nVISIT\nWant to take part in some\nreal science research?\nCheck out these citizen\nscience projects to get\ninvolved easily.\nbit.ly/15KjnmD\nRemember to discover more online by visiting http://www.curious.org.za and\nby typing the links in the Visit margin boxes into your internet browser to watch\nany videos, play with simulations or read an interesting article.\nType the bit.ly link for the video or site that you want to visit into the address bar of your\nbrowser on your computer, tablet or mobile phone.\n. .\nSUMMARY:\n.\nKey Concepts\n• Light travels in straight lines.\n• White light consists of all the colours of the visible spectrum.\n• The colour spectrum can be seen when white light is dispersed by a\nprism or a raindrop (rainbow).\n• Light cannot pass through opaque objects.\n• Light can pass through transparent objects.\n• Light is absorbed by some materials.\n• A material appears to be a certain colour because it reflects that part of\nthe colour spectrum. Other wavelengths of light are absorbed.\n• In reflection, the angle of incidence is equal to the angle of reflection.\n• On a smooth surface, parallel rays of light are all reflected at the same\nangle.\n• On rough surfaces, the light is scattered and the image produced is not\nclear.\n• The human eye has specialised cells in the retina which convert light\ninto electrical nerve impulses. The nerve impulses are transmitted to\nthe brain via the optic nerve, where they are interpreted.\n• Light travels at different speeds in different media.\n• When light enters a different medium at an angle, the light is refracted.\n• If the light slows down, the light bends towards the normal line.\n• If the light speeds up, the light bends away from the normal line.\n• Converging lenses refract and focus light.\n• Diverging lenses and triangular prisms refract and disperse light.\n• Lenses have many applications, for example, in glasses to correct vision,\nmicroscopes, telescopes and magnifying glasses.\n.\nConcept Map\nThe concept map on the next page shows how all the concepts relating to\nvisible light link together.\nComplete the map to reinforce what you have\nlearned in this chapter.\n.\n.\n129\n.\nChapter 4.\nVisible light\n\n.\n\n.\n.\nREVISION:\n.\n1. Match the correct definitions to the terms in the following table. Write the\nletter of the definition next to the correct number below. [12 marks]\nTerm\nDefinition\n1. Radiation\nA. Light cannot pass\nthrough.\n2. Visible light\nB. The angle of incidence\nequals the angle of\nreflection when a ray is\nreflected off a smooth\nsurface.\n3. Opaque\nC. One of the ways in\nwhich energy is\ntransferred, specifically\nthrough a vacuum\n4. Transparent\nD. When light enters a\ntransparent medium it\ncan change direction.\n5. Absorption\nE. Curved inwards.\n6. Reflection\nF. The spectrum of light\nwhich we are able to see.\n7. Retina\nG. Bulging outwards.\n8. Refraction\nH. A transparent object\nable to refract and focus\nlight.\n.\n.\n131\n.\nChapter 4.\nVisible light\n\n.\nTerm\nDefinition\n9. Diverging\nI. Light can pass through.\n10. Lens\nJ. When light rays are\nspread out from a point.\n11. Concave\nK. A layer of tissue at the\nback of the eye which is\nsensitive to light.\n12. Convex\nL. When the surface of a\nsubstance absorbs\ncertain colours of light.\nAnswers:\n1:\n2:\n3:\n4:\n5:\n6:\n7:\n8:\n9:\n10:\n11:\n12:\n..\n132\n.\nEnergy and Change\n\n.\n2. A beam of white light is shone through a glass prism. It splits up into seven\ncolours which are shone on a screen. A learner took a photograph which is\nshown below and drew a ray diagram to show the prism. The colours are\nmarked 1 to 7 in the diagram.\nA photograph of the prism.\nA diagram drawn by the learner.\na) What does this tell us about white light? [1 mark]\nb) Why does the light do this when it passes through the prism? [3\nmarks]\nc) What colour is at label 1 and what colour is at label 7? Explain your\nanswer. [3 marks]\nd) What label corresponds to the colour of grass? [1 mark]\ne) Can you see there are two other lighter, white rays emerging from the\nprism? What do you think this is the result of? [2 marks]\n3. Why does an opaque object cast a shadow? [2 marks]\n.\n.\n133\n.\nChapter 4.\nVisible light\n\n.\n4. Look at the following photograph of water in a pond and answer the\nquestions.\nWater in a pond.\na) How are we able to see the image of the wooden poles sticking up on\nthe edge of the pond? [2 marks]\nb) Why is the image not clear, but blurred? [2 marks]\n5. Two learners are discussing the colours of light. They decide that white\nand black are not really colours of light. If they are not colours, then how\ncan we see them? [5 marks]\n6. Explain how we are able to see the different colours on the South African\nflag. [6 marks]\n..\n134\n.\nEnergy and Change\n\n.\n7. Draw a ray diagram in the space provided to show how we see the green\npart of the flag. [5 marks]\n.\n8. Which diagram shown below correctly shows the path of a ray of light\nthrough a triangular piece of glass? [2 marks]\n.\n.\n135\n.\nChapter 4.\nVisible light\n\n.\n9. Complete the following sentence and write it out in full on the lines\nprovided: When light travels from a less dense into a more dense\ntransparent medium, it refracts and bends\nthe normal line.\nWhen light travels from more dense to a less dense medium, it refracts and\nbends\nfrom the normal line. [2 marks]\n10. Draw a diagram to show what is meant by 'when the refracted ray bends\ntowards the normal'. Mark the angle of incidence and angle of refraction.\nIndicate which medium is denser [4 marks]\n.\n11. Study the following diagram and answer the questions that follow.\na) This diagram is a drawing that a learner made during an investigation\ninto the refraction of light. What does the red line represent in this\ndiagram? [1 mark]\n..\n136\n.\nEnergy and Change\n\n.\nb) What do the blue lines represent? Label this on the diagram. [1 mark]\nc) The light passes from the air and into a block of another medium. Is\nthis medium more or less dense than air? Give a reason for your\nanswer. [2 marks]\nd) What type of medium could the block be made from? [1 mark]\ne) Label the incident ray and the emergent ray on the diagram. [2 marks]\nf) Label the angles of incidence (i) and angles of refraction (r) on the\ndiagram. [2 marks]\n12. Which diagram shown below shows the path of a light beam passing\nthrough a rectangular glass prism correctly? [2 marks]\n13. Why does it look like the tree trunk in the photograph is skew? [2 marks]\n.\n.\n137\n.\nChapter 4.\nVisible light\n\n.\n14. What shape does a lens have to have in order to focus the light? [1 mark]\n15. Draw a ray diagram to show how a converging lens focuses light to a point.\n[4 marks]\n.\n16. Which eyesight defect can be fixed by using a converging lens? Explain\nwhat this defect is and why it can be corrected. [4 mark]\nTotal [74 marks]\n.\n..\n138\n.\nEnergy and Change\n\n.\n.\n.\nGLOSSARY\nammeter:\ndevice that measures the strength of an electric\ncurrent\nampere:\nthe standard unit for measuring electric current\nangle of incidence:\nthe angle between the incident ray and the normal\nline\nangle of reflection:\nthe angle between the reflected ray and the normal\nline\nattract:\nto pull something closer\ncell:\na source of energy for an electric circuit\ncomponent:\na part of a larger system\ncomposition:\nthe parts of a mixture\nconductor:\na substance which easily transmits electricity, heat,\nsound or light\nconverge:\nlight rays that come together and focus on a point\ndelocalised:\nnot limited to a particular place, free to move\ndischarge:\nthe sudden flow of charged particles between two\nelectrically charged objects\ndispersion:\nspreading of something over an area\ndiverge:\nlight rays that spread apart as they move further\nand further away from a point\nearth:\n(or ground) to connect with a conductor to the\nground, or the earth\nearthing:\na way to prevent electrical charge from building up\non an object, or to neutralise an electric charge, by\nallowing the excess charge to flow into the Earth\nelectric circuit:\na complete path through which electrons can move\nelectric current:\nthe movement of charge in an electric circuit\nelectrodes:\na conductor which allows electricity to enter a\nsubstance\nelectrolysis:\nthe use of electricity to separate chemicals in a\nsolution\nelectromagnet:\na device which becomes a magnet when electric\ncurrent passes through it\nelectroplating:\ncovering an object with a thin layer of metal using\nelectrolysis\nelectrostatic charge:\nthe electric charge resulting from static electricity\ncaused by an excess or deficiency of electrons on\nthe surface of an object\nflammable:\nsomething is easily set on fire\nfocus:\nbring together to the same point\nfriction:\nthe resistance that results when two surfaces are\nrubbed or moved against each other\nfuse:\na safety device designed to melt and break the\ncircuit if an electric current reaches too high a level\n.\n.\n139\n.\nChapter 4.\nVisible light\n\n.\nignite:\nto light something\nincident ray:\nthe ray of light which hits a surface\nluminous:\nbright or shining\nmedium:\nsubstance through which waves (such as light) can\ntravel\nneutral:\nwhen the number of positive charges (from the\nprotons) is equal to the number of negative\ncharges (from the electrons); the (positive and\nnegative) charges balance each other so that the\nobject is neither positively nor negatively charged\nnormal line:\nthis is an imaginary line which is drawn at 90o to\nthe surface\nopaque:\nsomething that you cannot see through; no light\npasses through the object\noptical density:\na measure of how well a medium allows light to\ntravel through it\noptics:\nthe scientific study of sight and the behaviour of\nlight\nparallel circuit:\na circuit that provides more than one pathway for\nthe current to pass through it\nperpendicular:\nat right angles\npropagation:\nspreading into new areas\nqualitative:\ndescribing something in terms of its properties or\ncharacteristics rather than by a number or\nmeasurement\nradiation:\nthe emission of energy as electromagnetic waves\nrectilinear:\nstraight lines\nreflect:\nthrow back without absorbing\nreflected ray:\nthe ray of light which leaves a surface\nrefraction:\nthe change in direction of a wave passing from one\nmedium to another caused by its change in speed\nrepel:\nto push something away\nresistance:\nthe opposition to the movement of charge in a\nconductor\nresistor:\na component in an electrical circuit which slows the\nmovement of charge\nretina:\na layer at the back of the eyeball which is made up\nof light sensitive cells\nseries:\ncomponents connected in series provide only one\npathway for electrical current; they are connected\none after another\nstatic electricity:\nthe build-up of a stationary electric charge (either\npositive or negative) on the surface of an object\nstimulate:\nto cause activity\nswitch:\na control component in an electrical circuit which\nopens or closes the circuit\ntranslucent:\nsemi-transparent; some light is able to pass through\nbut not enough for details to be seen clearly\ntransmit:\nto cause light to pass through space or medium\n..\n140\n.\nEnergy and Change\n\n.\ntransparent:\nsomething that you can see through; light passes\nthrough the object\nvariable:\nsomething that can vary or change\nvisible spectrum:\nthe portion of the wave spectrum that is visible to\nthe human eye\n.\n.\n141\n.\nChapter 4.\nVisible light\n\n\n\n. .\n1\n.\nThe solar system\n..\n144\n..\nKEY QUESTIONS:\n• How does the Sun produce its energy?\n• How can we observe the Sun without damaging our eyes?\n• What objects are in orbit around the Sun in our solar system?\n• Why are there two types of planets?\n• How do the planets in our solar system differ?\n• What are asteroids and comets?\n• What is the difference between a planet and a dwarf planet?\n• Why is life possible on Earth?\nOur solar system includes the Sun and all the objects that orbit around the Sun.\nAs you will find out, a variety of objects are in orbit around the Sun: eight\nplanets, many dwarf planets, asteroids, Kuiper Belt objects and comets.\n.\n1.1 The Sun\n.\nNEW WORDS\n• solar system\n• star\n• nuclear fusion\n• convection\n• sunspot\n• solar wind\nBefore we look at the Sun close up, let's summarise what you learned about the\nSun in Grades 6 and 7:\n1. The Sun is our closest star and is very important for life on Earth as it\nprovides us with light and heat.\n2. The Sun is located at the very centre of our solar system.\n3. The Earth and other planets all orbit around the Sun, held in orbit by the\nforce of gravity.\n.\nVISIT\nSecrets of a dynamic Sun\n(video)\nbit.ly/1h0io4b\nWhat do you think the Sun would look like if it was further away, like the other\nstars we see at night?\nLet's look at the Sun in more detail.\n\nAn image of the Sun taken with the SOHO space satellite.\n.\nTAKE NOTE\nIt is very important that\nyou do not look at the\nSun directly! The Sun\ncan damage your eyes\npermanently!\n.\nVISIT\nThe birth of the solar\nsystem (video)\nbit.ly/1i8Bfrx\n.\nVISIT\nHow the Sun works.\nbit.ly/1gy769C\nDo you know what the Sun is made of? The Sun is mostly made up of hydrogen\ngas (about 71%), and also helium gas (about 27%) with a tiny amount of other\ngases. The temperature at the Sun's surface is very high, around 5500 oC.\nHowever, that is nothing compared to deep inside the Sun. At the Sun's centre,\nor core, it is about 15 million oC. It is so hot at the Sun's centre that nuclear\nreactions can occur, which change atoms from one element to another. In the\nSun's case, four hydrogen nuclei are squeezed or fused together to form a new\nhelium nucleus. This process is called nuclear fusion.\nThis nuclear fusion reaction releases energy because the new helium nuclei\nproduced have very slightly less mass than the four hydrogen nuclei used to\nmake them. How can this be? Well, according to the famous scientist Albert\nEinstein, energy and mass are equivalent. Some of the mass in the hydrogen\nnuclei is converted and released as energy when the nuclei fuse to make helium.\nA very large amount of energy is released. This energy travels outwards from\nthe Sun's core towards its surface. The energy eventually reaches the Sun's\nsurface somewhere between 17,000 and 100,000 years later! The Sun's energy\nthen spreads out into the solar system in the form of heat and light.\nYou are now going to observe the Sun to look at its surface features.\nRemember, you should never look directly at the Sun as it can permanently\ndamage your eyes. You can use either a telescope with a filter on it or a pinhole\nto project an image of the Sun onto a screen to safely view the Sun's image.\n.\n.\n145\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing the Sun using a telescope\n.\nMATERIALS:\n• telescope\n• white card\n• chair to rest the card on\n• cardboard to make a shade collar\n• pair of scissors\n• pencil\n.\nVISIT\nInteract with this\nsimulation to visualize the\neffects of gravity on\norbital paths of the Sun,\nEarth and Moon.\nbit.ly/1a2mJCL\n.\nTAKE NOTE\nNEVER look directly at\nthe Sun, even with\nsunglasses on as you\ncan permanently\ndamage your eyes.\nINSTRUCTIONS:\n1. Take a piece of cardboard and place it up against the narrowest end of the\ntelescope.\n2. Draw an outline around the edge of the telescope on the card to use as a\nguide for cutting to make the collar.\n3. Cut out inside the circle you just drew so that the cardboard can fit over\nthe telescope as shown in the figure above. You can cut a single slit into\nthe circle from the edge of the card as shown in the diagram\n4. Place the collar on the telescope. Adjust the size of the cut out circle if\nnecessary (for example if your telescope is slightly wider in the middle\nthan at the end, you may want to make your circle slightly larger). This\ncollar shades the area, where the image will fall, from stray light.\n5. Select the lowest magnification eyepiece lens you have and insert it into\nthe telescope's eyepiece.\n6. Focus the telescope by looking at a distant object (NOT the Sun).\n7. Point the telescope at the Sun (do NOT look through the telescope to do\nthis).\n8. Place a chair behind the telescope and rest a white piece of card on it. The\ncard should be tilted towards the telescope.\n9. Adjust the direction in which the telescope is pointing until the image of\nthe Sun appears on the white paper card. This may take some time.\n10. Keeping the telescope still, move the white card toward or away from the\neyepiece until the image of the Sun fits neatly in the middle of the card.\n..\n146\n.\nPlanet Earth and Beyond\n\n.\nAdjust the chair's position as needed.\n11. Adjust the tilt of the white card until the Sun's image is circular.\nQUESTIONS:\n1. Looking carefully you should see that the Sun's image moves slowly across\nthe white card. What causes this motion?\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n.\n.\nTAKE NOTE\nRevise the model of the\natom that you learned\nabout in Matter and\nMaterials if you are\nunsure of some of the\nterms used here, such\nas nucleus, which is at\nthe centre of an atom,\nand consists of protons\nand neutrons.\nAlternatively, if you do not have access to a telescope or binoculars, you can\nperform the following activity to view the Sun.\n.\nACTIVITY: Observing the Sun with a pinhole\ncamera\n.\nIn this activity you will reflect an image of the Sun onto a white card or screen\nfor your learners to observe. This method has the advantage of not needing a\ntelescope or binoculars, however, the solar image produced will be a bit fuzzy.\nHowever, it should be good enough to show large sunspots. This activity is\ndesigned as a teacher-led demonstration. If you have a sunlit window or door to\nyour class you can do this activity in the classroom. If you do not have a\nclassroom with a sunlit window, or if your class is very small, you can do the\nactivity outdoors, reflecting the Sun's image onto a shaded wall or back into a\ndarkened classroom.\n.\n.\n147\n.\nChapter 1.\nThe solar system\n\n.\n.\nVISIT\nThree years of the Sun in\nthree minutes.\nbit.ly/19nCfGu\nAs a rough guide, begin with a distance of around 8 m between the white card\nand the mirror. The further away you place the mirror from the white screen the\nfainter and larger the image will appear. At closer distances the image will be\nbrighter but it may not be in very good focus.\n.\nVISIT\nWhere does the Sun get\nits energy?\nbit.ly/1azFmsM\nAs mentioned in the previous activity, sunspots are sometimes (not always)\nvisible on the Sun's surface. Therefore, you could repeat this activity over the\ncourse of several days to see if any sunspots or sunspot groups change shape,\nsize, or position over time.\nMATERIALS:\n• small pocket mirror or hand mirror\n• piece of plain cardboard (or paper) to fit over the mirror (or alternatively\ntape)\n• white cardboard screen\n• bin bags or curtains for darkening the classroom\n.\nVISIT\nE = mc2 explained (video).\nbit.ly/16mVFNI\nMETHOD:\n1. Cut the plain cardboard or paper so it fits over the mirror.\n2. Cut or punch a very small hole, about 5 mm, in the middle of the plain\ncardboard.\n3. If you do not have cardboard, you can use tape to cover all but a small\nportion of the surface of the mirror.\n4. Place the mirror on a window sill in the Sun and tilt it so that it catches the\nsunlight and reflects it into the classroom. If your classroom is very small,\nplacing the mirror outside on a chair may be a better option in order to get\na larger image.\n5. Darken the classroom using curtains or bin bags, excluding where the\nmirror is.\n6. Reflect the sunlight from the mirror onto a wall of the darkened room.\n7. Put the white cardboard or paper on the wall where the reflected light\nshowing the Sun's image falls.\n8. Observe the image of the Sun.\n..\n148\n.\nPlanet Earth and Beyond\n\n.\n9. Remove the white cardboard from the wall and take three steps towards\nthe mirror with the cardboard still facing the mirror. Note what happens to\nthe image of the Sun on the cardboard.\nQUESTIONS:\n1. As you moved the white cardboard screen closer towards the mirror, what\ndid you notice happened to the image of the Sun?\n.\nDID YOU KNOW?\nAlbert Einstein\nexplained the\nmass-energy\nequivalence with the\nfamous equation\nE = mc2.\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n3. When the Sun reflects off the surface of the mirror, what can you say about\nthe angle of incidence and the angle of reflection of the ray?\n.\nDid you notice any features on the Sun's surface when you viewed it in class?\nLet's find out what some of these surface features could have been in the next\nactivity.\n.\nVISIT\nFiery looping rain on the\nSun (video)\nbit.ly/16qmriQ\n.\n.\n149\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing sunspots on the Sun's\nsurface\n.\nINSTRUCTIONS:\n1. Look at the images of the Sun which were taken in June 2013.\n2. Answer the questions that follow.\nA: DATE: 02.06.2013\n.\nVISIT\nLearn more about the\nresearch that NASA is\ndoing about our Sun with\nthe Solar and Heliospheric\nObservatory (SOHO).\nbit.ly/1fQhd8u\nB: DATE: 03.06.2013\n..\n150\n.\nPlanet Earth and Beyond\n\n.\nC: DATE: 04.06.2013\nQUESTIONS:\n.\nTAKE NOTE\nThis information about\nthe Sun's surface and\nsunspots is additional\ninformation for your\ninterest. Be curious and\ndiscover more!\n1. How many groups of dark spots do you see in each image?\n2. What do you notice about the positions of the spots in each image?\n3. Why do you think the spots have moved?\n4. What do you think these spots are?\n.\nSunspots and the Sun's surface\nThe Sun's surface often has little blemishes on it. These dark spots on the Sun\nare called sunspots. They are areas that are slightly cooler than the rest of the\nSun's surface. The Sun's surface is typically about 5500 oC and a typical\nsunspot has a temperature about 3900 oC.\n.\n.\n151\n.\nChapter 1.\nThe solar system\n\nImage of a sunspot. For perspective, take note of the size of the Earth in the lower left.\n.\nVISIT\nView real time images of\nthe Sun and track\nsunspots.\nbit.ly/19ZoU6c\nAs the Sun is made up of gas, there is no solid surface like on Earth. So when\none says that you are looking at the Sun's surface what are you actually looking\nat? Imagine that you are standing in thick fog (mist) with a friend. You can see\nthings close to you, like your hand in front of you and your friend standing next\nto you. However, because the fog is so thick you cannot see far into the\ndistance. Similarly, when we look at the Sun, we cannot see right into the centre\nof the Sun. As you go deeper and deeper in towards the centre of the Sun the\ngas begins to get thicker and thicker so that we cannot see through it. The\ndeepest depth that we can see into the Sun's gas is what we call the Sun's\nsurface.\nSunspots are areas that are slightly cooler, and therefore darker, than the rest of\nthe Sun's surface. A typical sunspot only lasts a few days. When a sunspot lasts\nfor several days you can observe it move across the Sun's disc. The sunspot\nappears to move across the Sun because the Sun is spinning slowly on its own\naxis.\n.\nDID YOU KNOW?\nThe number of sunspots\non the Sun increases\nand decreases in a\nregular pattern which\nrepeats every 11 years.\nWhen there are more\nsunspots the Sun is\nmore active and there\nare more solar storms\nand more of the Sun's\nenergy reaches the\nEarth.\nThe outer atmosphere of the Sun is called the corona. Gas particles from the\ncorona are constantly escaping into space, forming the solar wind. When the\nSun is very active, violent eruptions called solar flares occur on its surface.\n..\n152\n.\nPlanet Earth and Beyond\n\nA large loop of gas extending over 35 Earth diameters out from the Sun's surface.\n.\n1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.\n1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.\nChapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "4" }, { "title": "Circuits and current electricity", "content": "", "chapter_id": "2.1" }, { "title": "Components of a circuit", "content": "2.2 Components of a circuit\nYou are probably already familiar with the components of an electric circuit\nfrom previous grades. Do you remember that we have a specific way of\ndrawing the components in a circuit in an electric circuit diagram? Each\ncomponent has a different symbol.\n.\nNEW WORDS\n• ammeter\n• cell\n..\n22\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Components in an electric circuit\n.\nComplete the following table. List the function of the component and draw the\ncircuit symbol. The last two rows have been filled in for you as you may not yet\nknow these symbols, but we will be using them in this chapter.\nComponent\nFunction\nSymbol\nCell\nTorch bulb\nOpen switch\nClosed switch\nElectrical wire\nResistor\nA component that\nopposes or inhibits\nelectrical current in a\ncircuit. It can also\nconvert electrical\nenergy to heat or light.\nor\nVariable resistor\nA resistor whose\nresistance can be\nadjusted higher or\nlower.\n.\n.\n23\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nLet's now practice drawing some simple circuit diagrams. Draw the following\ncircuit diagrams.\n1. A closed circuit with one cell, two light bulbs and a switch.\n.\n2. An open circuit with two cells, two light bulbs and a switch.\n.\n3. A closed circuit with 4 cells and one light bulb.\n.\n..\n24\n.\nEnergy and Change\n\n.\n4. Look at the following circuit diagram. Identify the number of bulbs,\nswitches and cells in this circuit.\n5. What is wrong with the following circuit diagram? Does it represent a\nclosed circuit? Explain your answer.\n.\nVISIT\nBuild you own electric\ncircuits with this\nsimulation.\nbit.ly/19eotZk\n6. Why do you think it is useful to have a switch in a circuit?\n7. Why are conducting wires made out of metal?\n.\nLet's take a closer look at the source of energy in electric circuits.\n.\n.\n25\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nCells\nElectrical cells are the source of energy for the electric circuit. Where does that\nenergy come from?\n.\nDID YOU KNOW?\nAll muscles in our\nbodies move in\nresponse to electrical\nimpulses generated\nnaturally in our bodies.\nInside the cell are a number of chemicals. These chemicals store potential\nenergy. When a cell is in a complete circuit, the chemicals react with each other.\nAs a result, electrons are given the potential energy they need to start moving\nthrough the circuit. When the electrons move they have both potential and\nkinetic energy. The electric current is the movement of electrons through the\nconducting wires.\nCells come in many different sizes. Different sized cells provide different\namounts of energy to the electrical circuit. The types of cells you would use in\ntoys, torches and other small appliances range in size from AAA, AA, C, D, and\n9-volt sizes. AAA, AA, C and D cells usually have a rating of 1,5V, but the larger\ncells have a larger capacity. This means that the larger cells will last longer\nbefore going 'flat'. A cell goes flat when it is no longer able to supply energy\nthrough its chemical reactions.\nWhen we buy cells in the shop they are\nusually referred to as batteries. This\ncan be a bit confusing because a\nbattery is really two or more cells\nconnected together. So when we refer\nto a battery in circuit diagrams we\nneed to draw two or more cells\nconnected together.\nDifferent sized batteries.\n.\nACTIVITY: Recycling of batteries\n.\nBatteries which no longer work must not be thrown away in dustbins. They\nneed to be recycled.\nINSTRUCTIONS:\n1. Work in small groups.\n2. Find out why batteries should not be thrown away in normal dustbins.\nWrite a paragraph to explain why.\n..\n26\n.\nEnergy and Change\n\n.\n3. Find out where you can recycle batteries in your community. Write down\nthe details of the centre(s) closest to where you live.\n.\nResistors\nWhat are resistors? In order to work out what they are, let's first remind\nourselves about conductors and insulators.\nWe are specifically looking at electricity so we can now talk about electrical\nconductors and insulators. An electrical conductor is a substance which allows\nelectric charge to move through it. An insulator is a substance which does not\nallow electric charge to move through it.\nThink back to our model of a metal wire and how the electrons are able to move\nthrough the wire. The metal wire is a conductor of electricity. Write down some\nmaterials which do not conduct electricity.\n.\nVISIT\nA guide to recycling in\nSouth Africa.\nbit.ly/19Sygzg\nWhy do you think most conducting wires are surrounded with plastic?\nResistors are a bit of both. They allow electrons to move through them, but do\nnot make it easy. They are said to resist the movement of electrons. Resistors\ntherefore influence the electric current in a circuit.\nBut, why would we want to resist the movement of electrons? Resistors can be\nextremely useful. Think about a kettle. If you look inside you will see a large\nmetal coil.\nLooking inside a kettle.\nThis metal coil is the heating element.\nIf you plug in and switch on the kettle,\nthe element heats up and heats the\nwater. The element is a large resistor.\nWhen the electrons move through the\nresistor they expend a lot of energy in\novercoming the resistance. This energy\nis transferred to the surroundings in\nthe form of heat. This heat is useful to\nus as it heats our water.\nA good example of where resistors are used is in light bulbs. Let's take a closer\nlook at the different parts of a light bulb to see how it works.\n.\nDID YOU KNOW?\nThe first electric light\nwas made by Humphry\nDavy in 1800. He\ninvented an electric\nbattery, and when he\nconnected wires to it\nand a piece of carbon,\nthe carbon glowed as\nthe carbon is a resistor,\nproducing light.\n.\n.\n27\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Resistance in a light bulb\n.\nAn incandescent light bulb.\nMATERIALS:\n• light bulb\n• lamp\nINSTRUCTIONS:\n1. If you have light bulbs available, have a close look at the different parts,\notherwise have a look at the photos provided here.\n2. Read the information about how a light bulb works and identify the parts\nthat have been numbered.\n3. Answer the questions that follow.\n.\nVISIT\nHow a light bulb works.\nbit.ly/18K0hd3\nDiagram of the parts of a light bulb.\nA light bulb consists of an air-tight enclosed glass case (number 1). At the base\nof the bulb are two metal contacts (numbers 7 and 10), which connect to the\nends of an electrical circuit. The metal contacts are attached to two stiff wires,\n(numbers 3 and 4).\n..\n28\n.\nEnergy and Change\n\n.\nThese wires are attached to a thin metal filament. Have a look at a light bulb.\nCan you identify the filament? This is number 2 in the diagram. The filament is\nmade from tungsten wire. This is an element with high resistance.\nQUESTIONS:\n.\nTAKE NOTE\nIncandescent means to\nemit light as a result of\nbeing heated.\n1. When the electrons move through the filament they experience high\nresistance. This means that they transfer a lot of their energy to the\nfilament when they pass through. The energy is transferred to the\nsurroundings in the form of heat and bright light. Describe the transfer of\nenergy in this light bulb.\n2. What is the useful energy output and what is the wasted energy output in\nthis light bulb?\n3. Can you see the filament is coiled? Why do you think this is so? Discuss\nthis with your class and teacher.\n.\nVISIT\nA fun game about electric\ncircuits.\nbit.ly/15Icr49\n4. The filament is mounted on a glass stem (number 5). There are two small\nsupport wires to hold the filament up (number 6). Why do you think the\nstem is made of glass?\n5. The inside of the base of the bulb is made from an insulating material.This\nis the yellow part labeled number 8. On the outside of this is a metal\nconducting cap to which the wire is attached at number 7. Why is the wire\nattached at 7 making contact with the metal conducting cap?\n6. If you have a lamp in the classroom, screw the bulb into the lamp and turn\nit on to observe the filament glow and also getting hot.\n.\nThe amount of resistance a substance offers to the circuit is measured in ohms\n(Ω). If we want to use resistors to control the current flow, then we need to\nknow the amount of resistance. There are some common resistors shown in the\n.\n.\n29\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nphoto.\nSome common resistors.\nCan you see that there are different coloured bands on the resistors? This isn't\njust to make them look pleasing to the eye. The coloured bands are actually a\ncode that tells us the resistance of the resistor. We also get resistors where we\ncan adjust the resistance ourselves. This is called a variable resistor. You have\nalready seen the symbol for drawing a resistor in a circuit diagram. Draw a\ncircuit diagram in the space below with two bulbs, two cells, an open switch and\na resistor.\n.\nDID YOU KNOW?\nThe inventor, Thomas\nEdison, experimented\nwith thousands of\ndifferent resistor\nmaterials until he\neventually found the\nright material so that\nthe bulb would glow for\nover 1500 hours.\n.\nAn electric current can have various effects. Let's find out more about what\nthese are.\n.", "chapter_id": "2.2" }, { "title": "Effects of an electric current", "content": "2.3 Effects of an electric current\n.\nNEW WORDS\n• variable\n• fuse\n• electromagnet\n• electric current\nWe are going to look at the effects of an electric current, and specifically how\nwe use these effects. An electric current can:\n• generate heat in a resistor;\n• generate a magnetic field; and\n..\n30\n.\nEnergy and Change\n\n• cause a chemical reaction in a solution.\nHeating effect\nAs electrons move through a resistor they encounter resistance and they\ntransfer some of their energy to the resistor itself. We saw this in the last section\nwhere we looked at the filament in a light bulb and the element in a kettle.\n.\nACTIVITY: Heating a wire in a circuit\n.\nMATERIALS:\n• 1,5 V cell\n• conducting wires\n• switch\n• block of wood\n• 2 nails\n• hammer\n• 10 cm of nichrome wire\n.\nTAKE NOTE\nYou can easily make\nyour own switch by\nsticking two metal\ndrawing pins into a\npiece of wood with a\nmetal paper clip in\nbetween, as shown in\nthe diagram.\nINSTRUCTIONS:\n1. Hammer the two nails into the block of wood and attach the nichrome wire\nbetween the nails.\n2. Build the following circuit and keep the switch open.\n3. Feel the nichrome wire. Is it hot or cold?\n4. Close the switch. Leave it on for a minute.\n5. Open the switch again.\n6. Feel the wire, briefly. Is it hot or cold?\n.\n.\n31\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nQUESTIONS:\n1. When you felt the nichrome wire after the circuit had been on for a while,\nyou felt an increase in temperature in your skin as thermal energy, which\nwas transferred from the wire to your skin. Explain the heating effect of\nthe electric current in the resistance wire.\n2. List 2 useful applications of the heating effect of an electric current.\n.\nTAKE NOTE\nRemember that heat\nand temperature are\nnot the same thing.\nTemperature is a\nmeasure of how hot or\ncold something is\n(measured inoC)\nwhereas heat is the\ntransfer of thermal\nenergy from a hotter\nobject to a colder object\n(measured in J).\n3. Choose one of the applications you listed in question 2 and explain how\nthe heating effect of the electric current is used.\n4. Look at the following photo of a toaster.\nAn electric toaster.\nCan you see the glowing filament inside? Why does the element glow?\n.\nSo now we know that an electric current can cause objects to heat up. Let's\nlook at a useful application of the heating effect.\n..\n32\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Melting metal\n.\nMATERIALS:\n• three 1,5 V cells\n• copper conducting wires with crocodile clips\n• steel wool\n• heat resistant mat or piece of wood\n• torch light bulb\n• variable resistor\n• ammeter\nINSTRUCTIONS\n1. Set up a circuit according to the following picture.\n2. Twist a few strands of steel wool into a wire.\n.\nTAKE NOTE\nAn ammeter is used to\nmeasure the electric\ncurrent in a circuit.\n3. Use the steel wool to complete the circuit.\n4. Set the variable resistor to its highest resistance.\n5. Close the switch. What do you observe?\n6. Take note of the reading on the ammeter which measures the current in\nthe circuit.\n7. Open the switch.\n8. Set the variable resistance to its lowest resistance.\n9. Close the switch. What do you observe?\nQUESTIONS:\n1. Draw a circuit diagram for your circuit.\nThis is the symbol for an ammeter.\n.\n.\n33\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\n2. Why is the light bulb included in the circuit?\n3. When you decreased the resistance, what happened to the current? In\nother words, what happened to the reading on the ammeter?\n4. What do you think happens to the electric current when the steel wool has\nburnt? Explain your answer.\n.\nIn this activity, we just demonstrated how a fuse works. The steel wool acted as\na fuse. When the current was too high, the steel wool melted and prevented any\nfurther current in the circuit.\nWhat are fuses?\nThe heating effect of an electric current can be dangerous. If a circuit overheats\nit could cause a fire. To avoid overheating, circuits often contain a fuse. Fuses\ncontain a low resistance wire made of a metal with a low melting point.\nTherefore, the piece of wire melt if it gets too hot, just like the steel wool in our\nactivity.\n..\n34\n.\nEnergy and Change\n\nAn example of a fuse. Can you see the low melting point wire inside?\nDifferent circuits need different strength currents and so we need different\ntypes of fuses. Some fuses can only handle a little bit of heat, some can handle a\nlot. We choose the fuse that suits the safety needs of our circuit. If the circuit\noverheats, the fuse will melt and break the circuit to reduce the danger of fire as\nwell as protect electronic equipment.\nHow did you draw the fuse that we made using steel wool in the last activity?\nThe conventional symbol for drawing a fuse in a circuit diagram is shown here:\nA fuse.\n.\nTAKE NOTE\nIt is important to never\nremove a fuse from a\ncircuit without first\nswitching offthe\ncurrent. You could get a\nnasty shock if you do.\nWhat is a short circuit?\nHave you ever heard that something broke because it short circuited? A short\ncircuit happens when another, easier path is accidently made in an electric\ncircuit. What do we mean by easier?\nWe mean that the path offers very little resistance to the electric current. As\nthere is so little resistance the current flows along the short circuit and doesn't\npass through the main circuit. Short circuits can be dangerous and cause a lot\nof damage to appliances.\nHave you ever had a piece of toast get stuck in a toaster? It's a real nuisance.\nLots of people are tempted to use their butter knife to unhook the bread. Don't\nbe tempted. Your knife is a conductor and can act as a short circuit. All the\nelectric current will flow through your knife and, because you are touching it,\nthrough you. What would be the safe way to unhook your toast?\n.\nTAKE NOTE\nThere are different\ntypes of fuses. The ones\nwe have investigated so\nfar require you to\nreplace the fuse if the\nwire melts. However,\nsome fuses work\ndifferently to break the\ncircuit and can just be\nreset once the problem\nin the circuit is fixed.\n.\n.\n35\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: How are fuses used in everyday\ncircuits?\n.\nINSTRUCTIONS:\n1. Find out about common household appliances which use fuses. Choose\none of these appliances on which to focus your research.\n2. Write a short paragraph describing the appliance and explaining why a\nfuse is necessary for that appliance.\n.\nMost modern homes have circuit breakers instead of fuses. A circuit breaker is\nsimilar to a fuse in that it is designed to protect an electric circuit from damage,\ndue to overload or a short circuit, by stopping the current flow. However, unlike\na fuse which melts and must then be replaced, a circuit breaker can be reset to\nstart operating again. This can be done manually or take place automatically.\nMagnetic effect\nBefore we look at how a current produces a magnetic field, let us first learn\nmore about magnets. A magnet is a piece of material which produces a\nmagnetic field. A magnet has a north pole and a south pole. Opposite poles will\nattract each other and the same poles will repel each other. A magnet has a\nmagnetic field around it.\n.\nVISIT\nSome fun tricks with\nmagnets. (video)\nbit.ly/1c01QsA\n..\n36\n.\nEnergy and Change\n\nA bar magnet.\nDid you know that the Earth is like a bar magnet with a North and a South Pole?\nThe Earth has a magnetic field. This is why we can use compasses to tell\ndirection. A plotting compass has a needle with a small magnet. The needle\npoints to magnetic north because the small magnet is attracted to the opposite\nmagnetic pole and can be used to determine direction.\nEarth has a magnetic field, as though there\nis a big bar magnet running through the\ncore, with its South Pole under Earth's\nmagnetic North pole.\nA compass with the needle pointing North.\n.\nVISIT\nWhat is the magnetic\nfield?\nbit.ly/GzwPyx\n.\nACTIVITY: Playing with plotting compasses and\nmagnets\n.\nMATERIALS:\n• plotting compasses\n• bar magnets\n• piece of white paper\n• iron filings\nINSTRUCTIONS:\n1. Hold the plotting compass in your hand. The north end of the needle\nshould point to magnetic north.\n2. Put the bar magnet flat on the desk. Make sure you know which end is\nnorth and which is south. If you are not sure, ask your teacher.\n3. Put plotting compasses in a circle around the bar magnet.\n.\n.\n37\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nDraw what you see.\n.\n4. Next, place a white sheet of paper over the bar magnet and sprinkle iron\nfilings over the sheet of paper over the magnet.\nObserve what happens to the iron filings. Did you see something similar to\nwhat is shown in the photograph below? Describe what you see.\nIron filings on a piece of paper over a bar magnet.\n.\nSo now we know that there is a magnetic field around a magnet and that\nplotting compasses and iron filings can be used to visualise that field. Is there\nanything else that has a magnetic field around it?\n.\nVISIT\nExplore the interactions\nbetween a compass and\nbar magnet with this\nsimulation.\nbit.ly/19etlNQ\n..\n38\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magnetic field around a conductor\n.\nMATERIALS:\n• plotting compasses\n• three 1,5 V cells\n• insulated copper conducting wires\n• switch\nINSTRUCTIONS:\n1. Construct a circuit which contains the batteries, copper wires and the\nswitch.\n2. Put the plotting compasses on either side of the conducting wire as shown\nin the diagram, as well as below and above the conducting wire.\nPlotting compasses placed around a conducting wire.\n3. Keep the switch open. What do you notice about the needles of the\nplotting compasses?\n4. Close the switch and observe what happens to the needles.\n5. Draw a picture of the wire and plotting compasses in the space below:\n6. What does the pattern of the compasses tell us?\n.\nWe saw from our first activity that plotting compasses react to magnetic fields.\nThe plotting compasses changed direction when the current was switched on.\nThis means there is a magnetic field around the wire. Was it there when the\ncurrent was switched off? No, it was not. That means that the presence of the\nelectric current in the wire must have produced a magnetic field.\n.\nVISIT\nDiscover how the Earth is\na magnet that protects us\nfrom damaging radiation\nfrom the sun!\nbit.ly/GCCtjK\nThe magnetic effect of an electric current has many useful applications.\n.\n.\n39\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Making an electromagnet\n.\nMATERIALS:\n• one iron nail (approximately 15 cm long)\n• 3 metres of 22 gauge insulated copper wire\n• two D cell batteries\n• paper clips\n• iron filings\nINSTRUCTIONS:\n1. Wrap the insulated copper wire tightly around the nail. Make sure that you\nwrap the wire in the same direction.\n2. Strip some of the insulation off each end of the insulated copper wire.\n3. Attach the ends of the insulated copper wire to the terminals of the\nbattery.\n4. Hold the wrapped nail above the paper clips.\n5. Disconnect the wire from the battery.\n6. Hold the wrapped nail above the paper clips.\n7. If you have iron filings, place some on a piece of paper around the\nelectromagnet you have made and observe the magnetic field.\nThe magnetic field around an electromagnet.\nQUESTIONS:\n.\nVISIT\nHow to make an\nelectromagnet (video)\nbit.ly/1bpHh61\n1. What happened when you held the nail over the paper clips?\n2. Why were the paper clips attracted to the nail?\n3. Did the disconnected nail attract the paper clips? Why?\n.\n..\n40\n.\nEnergy and Change\n\nElectromagnets can be used in all sorts\nof practical applications, including\nspeaker and electric bells, as you can\nsee in the photo.\nAn electromagnet in a bell.\n.\nVISIT\nElectromagnets in a\nspeaker.\nbit.ly/19jU1XL\n.\nACTIVITY: Research the use of electromagnets\n.\nINSTRUCTIONS:\n1. Work in groups of 2 or 3.\n2. Research one of the following applications of the magnetic effect of an\nelectric current to explain how the device works:\na) speakers\nb) electric bells\nc) telephones\nd) magnetic trains\ne) industrial lifters and separators\n3. Write a short paragraph showing what you've learnt. Remember to note\ndown from where you got your information.\n4. Share your paragraph with the rest of the class.\n.\nChemical effect\nThe last effect of an electric current that we are going to look at is how an\nelectric current can cause a chemical reaction in a solution.\n.\nVISIT\nDiscover how to generate\nelectricity using bar\nmagnets with this\nsimulation.\nbit.ly/15Guo8x and\nlearn how to build a\nsimple electric motor.\nbit.ly/1c02xCb\n.\n.\n41\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n.\nACTIVITY: Electrolysis\n.\nYou might already have done this activity in Matter and Materials when we\ninvestigated the decomposition of copper chloride. We are going to perform it\nagain, this time focussing on the effects of an electric current.\nMATERIALS\n• 250 ml beaker\n• 2 carbon electrodes\n• sandpaper\n• 3 copper conducting wires (with crocodile clips)\n• copper chloride solution\n• torch bulb\n• power pack\nINSTRUCTIONS\n1. Sand down the electrodes with the sandpaper to make sure they are clean.\n2. Connect the conducting wire from one electrode to the torch bulb and\nanother wire from the torch bulb to the negative terminal of the power\nsource.\n3. Connect the crocodile clip from the second electrode to the positive\nterminal of the power source.\n4. Pour 100 ml copper chloride solution into the beaker.\n5. Put the electrodes into the beaker. Make sure that they do not touch each\nother.\n6. Look at the electrodes. What do you observe?\n7. Turn on the power source. Leave it on for a few minutes.\nThe setup might look something like this, which you have seen before. You might\nalso have a light bulb connected in the circuit.\n..\n42\n.\nEnergy and Change\n\n.\nQUESTIONS\n1. When you switch on the power source, does the torch bulb glow?\n.\nVISIT\nLearn more about silver\nrefining through\nelectrolysis.\nbit.ly/1fZQ5SW and the\nprocess of electroplating\n(video)\nbit.ly/GzH851\n2. What do you observe happening at the two different electrodes?\n3. Can you smell anything? What do you think this is?\n4. What is happening to the copper chloride solution when the electric\ncurrent is passed through it?\n5. If you switch off the power source, what happens?\n6. What is causing the separation of the copper chloride?\n7. Why is it important that you do not let the carbon electrodes touch each\nother while the current is flowing?\n.\nThe separation of the copper chloride means that an electric current can cause\nchemical reactions to occur. There are many ways in which we can harness this\nchemical effect for practical uses.\nElectrolysis is the breaking down of a substance into its component elements\nby passing an electric current through a liquid or solution. We can also use\nelectrolysis to purify substances.\nImpure copper can be purified using electrolysis. Instead of using carbon\nelectrodes in a copper sulphate solution we can use copper electrodes. If one of\nthe copper electrodes is pure copper and the other is impure copper, then the\nimpure electrode will break down and deposit pure copper on to the already\npure copper electrode.\n.\nNEW WORDS\n• electrolysis\n• electrodes\n• electroplating\n.\n.\n43\n.\nChapter 2.\nEnergy transfer in electrical systems\n\nOne of the most important uses of electrolysis is electroplating.\nElectrolysis is used to electroplate metals. In the last activity, one of the carbon\nelectrodes was coated with an even layer of pure copper. We say that the\ncarbon electrode was electroplated with copper.\nWhy do we electroplate? An example is in the making of jewellery where an\ninexpensive metal is made into a ring, for example, and then coated with gold\nby electroplating. This makes it less expensive than if it were made from pure\ngold. Iron rusts easily and so it is useful to coat it with a layer of a zinc to\nprotect it from corrosion. Many car parts, bathroom taps and wheel rims are\nelectroplated with chromium.\n..\nSUMMARY:\n.\nKey Concepts\n• A circuit is a system for transferring electrical energy.\n• For a circuit to function there must be a complete, unbroken pathway\nfor the electrons to follow, a source of energy (cell or cells) and a load\n(lightbulb or any other resistor).\n• We use symbols to represent components of an electric circuit so that\neveryone can interpret the diagrams.\n• A resistor is a component in a circuit which resists the movement of\nelectrons through the circuit.\n• An electric current can heat a resistance wire. This heating effect is used\nin many everyday appliances, such as kettles and irons.\n• An electric current causes a magnetic field. This magnetic effect is used\nin electromagnets.\n• An electric current can cause a chemical reaction in solutions. This is\ncalled electrolysis, and is used to electroplate objects.\n.\nConcept Map\nComplete the concept map to summarise what you have learned about\nelectric circuits and the effects of an electric current in this chapter.\n..\n44\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Write your own definition for an electric circuit. [2 marks]\n2. What type of energy does a battery have? [1 mark]\n3. When a battery is connected to a circuit, it causes an electric current in the\ncircuit. Explain what an electric current is and why it is possible in metals.\nUse the word 'delocalised' in your explanation. [3 marks]\n4. List 3 materials which conduct electricity. [3 marks]\n5. List 3 materials that do not conduct electricity. [3 marks]\n6. You have a battery, insulated copper conducting wires and a light bulb.\nDraw a setup which would allow you to test whether the materials you\nlisted in questions 1 and 2 are conductors or not. [4 marks]\n.\n..\n46\n.\nEnergy and Change\n\n.\n7. Draw the symbols for the following components. [6 marks]\nA cell\nA light bulb\nA conducting wire\nAn open switch\nA resistor\nA variable resistor\n8. Look at the circuits below. If the bulb(s) will glow, place a tick next to the\npicture and explain why it will glow. If the bulb(s) will not glow, place a\ncross next to the picture and explain why it will not glow. [10 marks]\nCircuit\nGlow/Not Glow\nExplanation\n.\n.\n47\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\nCircuit\nGlow/Not Glow\nExplanation\n9. Which of the following setups shows the correct way to connect a light\nbulb to a battery? Explain your answer. [2 marks]\n..\n48\n.\nEnergy and Change\n\n.\n10. Draw a circuit diagram to illustrate the following circuit: (3 marks)\nImage\nCircuit diagram\n11. An electrician wants to replace a faulty fuse with a normal piece of\nconducting wire. Should you let him? Why or why not? [3 marks]\n12. A child, while inserting an electric plug into the socket, did not see that\nthere was a thin piece of aluminium foil stuck between the pins of the plug.\nWhen he turned the switch on, he noticed a spark at the plug, and at the\nsame time, the lights went out. What could have happened to cause the\nspark and to make the lights go out? [4 marks]\n13. What is the benefit of using a circuit breaker rather than a fuse? [2 marks]\n14. Look at the following photo of a light bulb. Label the filament and explain\nwhy it glows. [4 marks]\n.\n.\n49\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n.\n15. You place some plotting compasses around an electric wire and observe\nthe following.\na) Is there are current in the conducting wire? [1 mark]\nb) Explain your answer. [2 marks]\n16. Give two advantages of electroplating iron metal. [2 marks]\nTotal [55 marks]\n.\n..\n50\n.\nEnergy and Change\n\nCurious? Discover the possibilities with a magnifying glass.\n.\n.\n51\n.\nChapter 2.\nEnergy transfer in electrical systems\n\n. .\n3\n.\nSeries and parallel circuits\n..\n52\n..\nKEY QUESTIONS:\n• Are there different types of electric circuits?\n• If all the light bulbs in a house are part of the same circuit, how can you\nswitch one light off without the rest also turning off?\n• What is a series circuit?\n• What is a parallel circuit?\n• What happens when you connect more components in series or in\nparallel?\nIn the last chapter, and in Gr 6 and 7, we have been looking at electric circuits.\nThese have mostly been series circuits. What does this mean? And how else can\na circuit be arranged?\n.\n3.1 Series circuits\nA series circuit is one in which there is only one pathway for the electric current\nto follow. The components are arranged one after another in a single pathway.\nWhen we connect the components we say that they are connected in series.\nWe have already seen examples of series circuits in the last chapter.\nA series circuit with one pathway for the current, from the negative to the positive\nterminal of the battery.\n.\nNEW WORDS\n• series\n• ammeter\n• ampere\n• resistance\nAmmeter\nAn ammeter is a measuring device used to measure the electric current in the\ncircuit. It is connected into the circuit in series. The current is measured in\namperes (A).\n\nAn ammeter.\nWhat is the symbol for an ammeter? Draw it here.\n.\n.\nDID YOU KNOW?\nThe ampere is named\nafter André-Marie\nAmpère (1775-1836), a\nFrench mathematician\nand physicist. He is\nconsidered the father of\nelectrodynamics, which\nis the study of the effect\nof electromagnetic\nforces between electric\ncharges and currents.\nDo you think that an ammeter would have a high resistance or a low resistance\nto the current? Explain your choice.\n.\nTAKE NOTE\nThe ampere is often\nshortened to 'amp'.\nA series circuit only provides one pathway for the electrons to follow. Let's\ninvestigate what happens when we increase the resistance in a series circuit.\n.\nINVESTIGATION:\nWhat happens when we add more\nresistors in series?\n.\nAIM: To investigate the effect of adding resistors to a series circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\n.\n.\n53\n.", "chapter_id": "2.3" }, { "title": "Series and parallel circuits", "content": "Chapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cells\n• 3 torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, the ammeter, 1 bulb and the switch in\nseries.\nA photo showing the setup.\n2. Close the switch, or the circuit if you are not using a switch.\n3. Note how brightly the bulb is shining and write down the ammeter reading.\nDraw a circuit diagram.\n.\n4. Open the switch.\n5. Add another light bulb into the circuit.\n6. Close the switch.\n..\n54\n.\nEnergy and Change\n\n.\n7. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram.\n.\n8. Open the switch.\n9. Add the third light bulb into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and write down the ammeter\nreading. Draw a circuit diagram for the last circuit you built.\n.\n.\n.\n55\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nseries\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness, or was\none brighter than the other?\n..\n56\n.\nEnergy and Change\n\n.\n3. When you had three bulbs, did they glow the same as each other or was\none brighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the series circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin series?\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in series?\n2. Is your hypothesis accepted or rejected?\n.\nAs more resistors are added in series, the total resistance of the circuit\nincreases. As the total resistance increases, the current strength decreases.\nWhat would happen if we increased the number of cells connected in series?\nWould the current become larger or smaller? Let's investigate.\n.\nINVESTIGATION:\nHow does adding more cells in\nseries affect the current?\n.\nAIM: To investigate the effect of increasing the number of cells connected in\nseries on the electric current strength.\nHYPOTHESIS: Write a hypothesis for this investigation. Remember to mention\nhow the increase in the number of cells will affect the current strength.\n.\n.\n57\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMATERIALS AND APPARATUS\n• three 1,5 V cells\n• insulated copper conducting wires\n• ammeter\n• 2 torch light bulbs (or 1 torch light bulb and one resistor)\nMETHOD:\n1. Construct a circuit with 1 cell, the ammeter and the two torch light bulbs.\n2. Observe the brightness of the bulbs and record the ammeter reading in the\ntable of results. Draw a circuit diagram.\n.\n3. Add a second cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n4. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\n5. Add a third cell in series and observe the brightness of the bulbs. Draw a\ncircuit diagram of your circuit.\n..\n58\n.\nEnergy and Change\n\n.\n6. Record the ammeter reading in the table of results. Draw a circuit diagram.\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nseries\nBrightness of bulbs\nReading on a mmeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What can you conclude from the shape of the graph?\n2. Is your hypothesis true or false?\n.\nWe have seen that increasing the number of cells in series increases the current,\nbut increasing the number of resistors decreases the current.\nWe will now investigate the current strength at different points in a series circuit.\n.\n.\n59\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION:Is the current strength the same at all points in a\nseries circuit?\nHYPOTHESIS: Write a hypothesis for this investigation. What do you think will\nhappen in this investigation?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• two torch light bulbs\n• ammeter\nMETHOD:\n1. Set up a series circuit with two cells and two torch light bulbs in series with\neach other.\n2. Insert an ammeter in series between the positive terminal of the batteries\nand the first torch bulb.\n3. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series between the two torch bulbs.\n6. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n..\n60\n.\nEnergy and Change\n\n.\n.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series between the last torch bulb and the negative\nterminal of the batteries.\n9. Measure the current strength using the ammeter. Draw a circuit diagram of\nthis set up.\n.\nRESULTS:\nComplete the following table:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nBetween positive terminal\nof cell and first bulb\nBetween two bulbs\nBetween negative terminal\nof cell and last bulb\n.\n.\n61\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nCONCLUSIONS:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\nIn a series circuit, there is only one pathway for the electrons to move through.\nThe current strength is the same everywhere in that pathway.\nWhat have we learned about series circuits?\n• There is only one pathway for the electrons to follow.\n• The current flows at the same strength everywhere in a series circuit,\nbecause there is only one pathway. We say that the current is the same at\nall points in the circuit.\n• If you add more resistors in series, the current in the whole circuit\ndecreases.\nWhy does the current stay the same at all points? Let's think about how electric\ncurrent moves through a circuit. Do you remember that we spoke about the\ndelocalised electrons in metals in the last chapter?\n.\nVISIT\nAnimation showing the\nmovement of electrons.\nbit.ly/19Ww8pW\nThe electrons in a conductor normally drift in various different directions within\na metal, as shown in the diagram.\nDelocalised electrons move freely in a\nconducting wire.\nWhen the wire is connected in a closed\ncircuit, the electrons move towards the\npositive terminal of the battery.\nWhen we build a closed circuit with a cell as an energy source, the electrons will\nall begin to move towards the positive side of the cell. The rate at which the\nelectrons move, is determined by the resistance of the conductor.\nThere are electrons everywhere in the conducting wires and electrical\ncomponents. When the circuit is closed, all the electrons start moving in the\nsame general direction at the same time. This is why a light bulb turns on\nimmediately when you close the switch.\n.\nVISIT\nFlip the switch and watch\nthe electrons with this\nsimulation.\nbit.ly/15NlqBd\nIn a series circuit, all the electrons travel through every component and wire as\nthey travel through the circuit. All the electrons experience the same resistance\n..\n62\n.\nEnergy and Change\n\nand so they all move at the same rate.\nThis means that in the diagram below, the readings on all three ammeters will\nbe the same, so: A1= A2= A3\n.\n3.2 Parallel circuits\n.\nNEW WORDS\n• parallel circuit\nParallel circuits offer more than one pathway for the electrons to follow. When\nconstructing a parallel circuit, we say that components are connected in\nparallel.\nLook at the diagram which shows how two light bulbs are connected in parallel.\nThere are two paths for the current in this parallel circuit, one path through each of the\nbulbs.\nHow can you tell whether or not a circuit is connected in series or in parallel?\nLet's look at some circuit diagrams to tell the difference.\n.\nVISIT\nWatch a video that\nexplains the difference\nbetween series and\nparallel circuits\nbit.ly/1f5hZ0W\n.\nACTIVITY: Series or parallel?\n.\nINSTRUCTIONS:\nLook at the following circuits and write down which are in series and which are\nin parallel. The series circuits will only offer one pathway, but the parallel\ncircuits will have more than one pathway for the electrons to follow.\n.\n.\n63\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nLet's investigate how parallel circuits work.\n.\nINVESTIGATION:\nHow does adding resistors in\nparallel affect the current strength?\n.\nAIM: To investigate the effect of adding resistors in parallel on the current\nstrength.\nHYPOTHESIS: Write a hypothesis for this investigation.\n..\n64\n.\nEnergy and Change\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cell\n• three identical torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, ammeter, one bulb and the switch in\nseries.\n2. Close the switch.\n3. Note how brightly the bulb is shining and record the ammeter reading.\nDraw a diagram of your circuit.\n.\n4. Open the switch.\n5. Add another light bulb, in parallel to the first, into the circuit.\n6. Close the switch.\n7. Note how brightly the bulbs are shining and record the ammeter reading.\n8. Open the switch.\n9. Add the third light bulb, in parallel to the first two, into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and record the ammeter reading.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nparallel\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\n.\n.\n65\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness or was\none brighter than the other?\n3. When you had three bulbs, did they glow the same brightness or was one\nbrighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the parallel branches of the circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin parallel?\n..\n66\n.\nEnergy and Change\n\n.\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in parallel?\n2. Is your hypothesis true or false?\n.\nAs more resistors are added in parallel, the total current strength increases. The\noverall resistance of the circuit must therefore have decreased. The current in\neach light bulb was the same because all the bulbs glowed with the same\nbrightness. This tells us that the current of electrons must have split up and\nmoved through each of the branches.\nWe can also connect cells in parallel. What would happen if we increased the\nnumber of cells connected in parallel? Would the current get stronger or\nweaker?\n.\nINVESTIGATION:\nWhat happens to the current\nstrength when cells are connected\nin parallel?\n.\nAIM: To investigate how increasing the number of cells connected in parallel\naffects the current strength in a circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS\n• three 1,5V cells\n• one torch light bulb\n• insulated copper conducting wires\n• ammeter\nMETHOD:\n1. Set up a circuit which has one cell, the ammeter and the torch light bulb in\nseries with each other. Draw a circuit diagram of your circuit.\n.\n.\n67\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\n2. Observe the brightness of the bulb and record the ammeter reading.\n3. Connect another cell in parallel with the first cell. To connect the second\ncell in parallel, connect a wire from the positive terminal of the first cell to\nthe positive terminal of the second cell. Connect another wire between the\nnegative terminal of the first battery and the negative terminal of the\nsecond battery. Draw a circuit diagram of your circuit.\n.\n4. Observe the brightness of the bulb and record the ammeter reading.\n5. Connect a third cell in parallel to the other two cells. Draw a circuit\ndiagram of your circuit.\n.\n6. Observe the brightness of the bulb and record the ammeter reading.\n..\n68\n.\nEnergy and Change\n\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nparallel\nBrightness of bulb\nReading on ammeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What did you notice about the brightness of the bulbs?\n2. What did you notice about the ammeter readings?\n3. What conclusion can you draw from your results?\n.\nAdding cells in parallel has no overall effect on the current strength. The current\nstrength stays the same if you add cells in parallel.\nWe saw that the current strength increased when bulbs were connected in\nparallel. However, we were only testing the current strength at one point in the\nparallel circuit. How does the current compare in the different pathways of the\ncircuit? Let's do an investigation to find out.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION: Is the current strength equal at all points in a\nparallel circuit?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• three identical torch light bulbs\n• ammeter\n.\n.\n69\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMETHOD:\n1. Set up a parallel circuit with two cells in series with each other and three\ntorch light bulbs in parallel with each other.\n2. Insert an ammeter in series between the cells and the first pathway, as\nshown in the diagram.\n3. Measure the current strength using the ammeter.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series in the first pathway.\n6. Measure the current strength using the ammeter.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series in the second pathway.\n9. Measure the current strength using the ammeter.\n10. Remove the ammeter and close the circuit again.\n11. Insert the ammeter, in series, in the third pathway.\n..\n70\n.\nEnergy and Change\n\n.\n12. Measure the current strength using the ammeter.\n13. Remove the ammeter and close the circuit again.\n14. Insert the ammeter in series between the first pathway and the cells on the\nopposite side to the first reading.\n15. Measure the current strength using the ammeter.\nRESULTS:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nbetween the cell and first\npathway\nin the first pathway\nin the second pathway\nin the third pathway\nbetween the cell and the\nfirst pathway\nCONCLUSION:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\n.\n.\n71\n.\nChapter 3.\nSeries and parallel circuits\n\nWhat have we learned about parallel circuits?\n• There is more than one pathway for the current to follow.\n• The current divides between the different branches so that each branch\ngets some of the current. As the torch bulbs in each branch in our example\nwere identical, the current divided equally between them.\n• If you add more resistors in parallel, the total current supplied by the cell in\nthe circuit increases.\nWhy does the current divide when offered an alternative pathway?\nImagine that you are sitting in a school hall during assembly. You are bored and\nwaiting for it to end so that you can go out to break to chat to your friends.\nThere is only one exit from the hall. When you are dismissed, everyone has to\nexit through the same door. It takes a while because only some learners can\nleave at a time.\nNow imagine that there is a second door that is the same as the first door. Now\nyou and your friends have a choice of which door to go through. The speed at\nwhich the learners exit the hall will increase and some of you will exit through\nthe first door while others will exit through the second door. No one can go\nthrough both doors at the same time.\nThis is similar to the way current behaves when in a parallel circuit. As the\nelectrons approach the branch in the circuit, some electrons will take the first\npath and others will take the other path. The current is divided between the two\npathways.\nIn the following circuit A1 = A4 and A1 = A2 + A3 and A4 = A2 + A3\nWe have looked at how resistors and cells behave in series and parallel circuits.\nLet's look at how different metals conduct electricity. All conductors have some\nresistance in a circuit. Are some metals better conductors of electricity than\nothers?\nLet's have a look at which metals offer more resistance than others to the flow\nof charge (current) through an electric circuit .\n..\n72\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Which metals offer the most\nresistance?\n.\nMATERIALS:\n• a cell\n• torch light bulb\n• insulated copper wires\n• lengths of copper, aluminium, zinc and nichrome wire\n• crocodile clips (if available)\nINSTRUCTIONS\n1. Build a circuit with the cell and the torch light bulb and leave a gap for the\nmetal to be tested. You can use crocodile clips at the end of each piece of\nmetal for easy insertion.\n2. Insert each metal into the circuit (one at a time).\nAn example circuit with a cell, a light bulb and the piece of metal being tested.\nObserve the brightness of the bulb.\nQUESTIONS:\n1. Draw a circuit diagram of your apparatus.\n.\n.\n.\n73\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n2. Why can we use the brightness of the bulb to qualitatively measure\nresistance?\n3. List the metals in order of increasing resistance.\n4. Why do you think copper is used for connecting wires in electrical circuits?\n.\nThere are several factors which influence the amount of resistance a material\noffers to an electric current. We have seen that the type of material is one of\nthose factors.\n.\nTAKE NOTE\nIn Gr. 9 we will look at\nthe other factors that\ninfluence resistance. If\nyou want to see the\ncontent in other grades,\nremember that you can\nvisit\nhttp://www.\ncurious.org.za\n.\n3.3 Other output devices\nLight bulbs are not the only devices used in electrical circuits. Devices that use\nelectrical energy to function, including light bulbs, are called output devices.\nLet's look at some other common examples of output devices.\nLEDs (Light-Emitting Diodes)\nLEDs are widely used electronic devices. They are small lights but they do not\nhave a filament like an incandescent bulb has. They therefore cannot burn out,\nas there is no filament to wear out, and they do not get as hot. LEDs are used in\nelectronic timepieces, high definition televisions and many other applications.\nLarger LEDs are also replacing traditional light bulbs in many homes because\nthey do not use as much electricity. They last longer than incandescent bulbs\nand are more efficient.\n.\nVISIT\nWatch this video about\nthe history of the LED\nbit.ly/1bC5qKc\n..\n74\n.\nEnergy and Change\n\nDifferent LED bulbs.\nIn the last chapter, we looked at the energy transfers in an electrical system. We\nwill now represent energy transfer within electrical systems in a different way.\nWe will apply this new representation to the difference between energy outputs\nin an LED and an incandescent light bulb.\n.\nVISIT\nVideo on drawing a basic\nSankey diagram.\nbit.ly/19Wwxsu\n.\nACTIVITY: Sankey diagrams\n.\nYou might have drawn Sankey diagrams in Grade 7. If not, here is some quick\nrevision.\nIn an energy system, input energy is transferred to useful output energy and\nwasted output energy. A Sankey diagram is a visual and proportional\nrepresentation of the energy transfers that happen in a system.\nFor example, a kettle uses about 2000 J of input energy, but only about 1400 J\nis used to heat the water. The remaining 600 J is wasted as sound. Here is the\nSankey diagram to represent the energy transfer.\n.\nTAKE NOTE\nRemember that energy\nis measured in joules\n(J).\n.\n.\n75\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nQUESTIONS:\nWe will now compare an LED with an incandescent light bulb.\n1. Draw a Sankey diagram for an LED if the input energy is 100 J, 75 J of\nenergy is used to produce light and the rest is lost as heat.\n.\n.\nVISIT\nAn electricity timeline\nanimation.\nbit.ly/1fKZb8E\n2. Draw a Sankey diagram for a filament light bulb if the input energy is 100 J,\nthe wasted heat energy is 80 J and the rest produces light.\n.\n3. Which bulb do you think is more efficient? Explain your answer.\n.\nCan you think of any other output devices? Make a list of as many as you can.\n..\n76\n.\nEnergy and Change\n\n.\n.\nACTIVITY: History of electricity production\n.\nINSTRUCTIONS:\n1. Work in groups of three or four.\n2. Research the history of electricity production: How was electricity\ndiscovered and how did electricity become widely used?\n3. Create a basic timeline for the discovery of electricity and it's production.\n.\n.\nACTIVITY: Careers\n.\nINSTRUCTIONS:\n1. Choose a career related to electricity production.\n2. Write a short paragraph describing the career. Include information on how\none can study or prepare for your chosen career.\n.\n.\n.\n77\n.\nChapter 3.\nSeries and parallel circuits\n\n..\nSUMMARY:\n.\nKey Concepts\n• A series circuit has only one pathway for the electrons to travel through.\n• A parallel circuit has more than one pathway for the electrons to travel\nthrough.\n• In a series circuit, the current is the same at all points in the circuit.\n• In a series circuit, the resistance increases as more resistors are added\nin series.\n• In a parallel circuit, the current splits between the available paths.\n• In a parallel circuit, the resistance decreases as more resistors are added\nin parallel.\n.\nConcept Map\nComplete the concept map on the following page to summarise what you\nhave learned about series and parallel circuits.\n..\n78\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Look at the following circuit diagrams and decide whether they are series\ncircuits or parallel circuits. Write the correct answer in the space below\neach diagram. [6 marks]\n2. Look at the three circuit diagrams. Rank the circuits from brightest bulb to\ndimmest bulbs. [3 marks]\n..\n80\n.\nEnergy and Change\n\n.\n3. Explain your choices in the previous question. [5 marks]\n4. Look at the three circuit diagrams. Rank the circuits from brightest bulb(s)\nto dimmest bulb(s). [3 marks]\n5. Explain your choices in the previous question. [5 marks]\n6. Look at the circuit diagram below. Each light bulb is identical.\na) Is this a series or parallel circuit? Explain your answer. [2 mark]\nb) How do the brightness of bulbs A, B and C compare? (which is the\nbrightest?) [3 marks]\n.\n.\n81\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nc) What would happen to the brightness of the bulbs if the switch was\nopened? Explain your answer. [5 marks]\n7. Study the following diagram.\na) What is the relationship between the ammeter readings on A1 and A4?\nIn other words, how do the current strengths compare at these points\nin the circuit? Explain your answer. [3 marks]\nb) What is the relationship between the ammeter readings on A1, A2 and\nA3? In other words, how do the current strengths compare at these\npoints in the circuit? Explain your answer. [3 marks]\nTotal [38 marks]\n.\n..\n82\n.\nEnergy and Change\n\nDraw and discover the possibilities of what a slinky can be.\n.\n.\n83\n.\nChapter 3.\nSeries and parallel circuits\n\n. .\n4\n.\nVisible light\n..\n84\n..\nKEY QUESTIONS:\n• Where does light come from?\n• How does light travel?\n• How do we see?\n• Why do leaves look green?\n• How do mirrors work?\n• Why do my legs look crooked underwater?\nIn this chapter we will learn about visible light. We call it visible light because\nwe can see it with our own eyes. There are different forms of light which we\ncannot see with our naked eyes. Ultraviolet light is an example of a form of light\nwhich we cannot see with just our eyes. We will focus our attention on the\nvisible light spectrum and investigate how we are able to see different colours\nand how light behaves.\n.\n4.1 Radiation of light\nWhere does light come from? Natural light comes from luminous objects such\nas the Sun and light bulbs. We say that these objects emit light.\nThe Sun is our main source of light on Earth.\nA light bulb is a luminous object as it emits\nlight.\n.\nNEW WORDS\n• luminous\n• radiation\n• rectilinear\n• propagation\n.\nVISIT\nThe speed of light (video)\nbit.ly/GAMgFW\n\nThis image from NASA shows the Earth's lights at night. You can see how much we rely\non light nowadays.\n.\nDID YOU KNOW?\nIf you could travel at the\nspeed of light you could\ntravel around the\nequator 7,5 times in 1\nsecond!\n.\nTAKE NOTE\nThe Moon is NOT a\nluminous object as it\ndoes not emit its own\nlight light. It reflects the\nlight from the Sun.\nLight travels through space at a speed of 300 000 kilometers per second. We\nsay that energy is transferred by radiation. The energy of the light is transferred\nthrough space as electromagnetic waves in straight lines.\nLight and heat are transferred to Earth through space from the Sun by radiation.\n.\nDID YOU KNOW?\nIt takes light 8 minutes\nto travel from the Sun to\nthe Earth.\nLet's look at how light travels. We will make a simple camera to investigate how\nlight travels.\n.\n.\n85\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Make a pinhole camera\n.\nMATERIALS:\n• Pringles chip can\n• craft knife\n• aluminium foil\n• tape\n• ruler\n• drawing pin\nINSTRUCTIONS:\n.\nTAKE NOTE\nThe Sun emits radiation\nin all directions, but in\nthe diagram here, only\nthe radiation which\nreaches Earth has been\nshown.\n1. Measure 5 cm from the bottom of the can (opposite end to the plastic lid)\nand make a mark all around the can.\n2. Cut through the can along the line\nso that you have cut the can into 2\npieces.\n3. If you have a clear lid, put a piece of\nwax paper on top of the lid before\nsticking everything together.\n..\n86\n.\nEnergy and Change\n\n.\n4. Place the lid between the 2 pieces\nand stick it all together using tape.\n5. Wrap the aluminium foil around the\ncan to prevent any light from\ncoming in from the sides.\n6. Use a drawing pin to make a hole in the centre of the metal base of the can.\n7. Go outside with your pinhole camera.\n8. Point the metal end with the hole at an object which is in bright sunlight.\n9. Cup your hands around the other end and look through the open end.\nQUESTIONS:\n.\nVISIT\nLight travels in a straight\nline? (video)\nbit.ly/19n4T7g and\nbit.ly/174q6mx\n1. What did you see when you looked through the open end of the tube?\n2. What happens when you move closer or further away from an object?\n.\nDid you see an upside down image? Why is it upside down?\nWe see objects because light reflects off them and enters our eyes. If the image\nis upside down it means that the light from the bottom of the object has arrived\nat the top of the screen and the light from the top of the object has reached the\nbottom of the screen, as shown in the following diagram.\n.\n.\n87\n.\nChapter 4.\nVisible light\n\nWhen you moved closer to the object, the image appeared bigger, as shown in\nthe following diagram.\nWhat does this mean? It means that light must be travelling in straight lines.\nThis is called the rectilinear propagation of light.\n.\nVISIT\nCan you use what you\nhave learnt to understand\nhow this shadow illusion\nworks?\nbit.ly/156mx1y\nRay diagrams\nA ray diagram is a drawing that shows the path of light. Light rays are drawn\nusing straight lines and arrowheads, because light travels in straight lines. The\nfigure below shows some examples of ray diagrams.\n..\n88\n.\nEnergy and Change\n\nA ray diagram showing how you see\nanother person.\nA ray diagram showing how you see a\nreflection in a mirror.\n.\n4.2 Spectrum of visible light\n.\nNEW WORDS\n• composition\n• visible spectrum\n• dispersion\nThe visible light spectrum is the light that we are able to see with our naked\neyes. Have you ever wondered why everything is colourful and not just black\nand white? Have you ever seen a rainbow and wondered where the colours\nhave come from? The colours that we see everyday are part of the visible light\nspectrum. Let's investigate the visible light spectrum.\n.\nACTIVITY: Splitting white light\n.\nMATERIALS:\n• triangular perspex prism\n• ray box and power source\nINSTRUCTIONS:\n1. Connect the ray box to the power source. If you do not have a ray box,\nyour teacher will show you how to use a piece of cardboard with a slit cut\ninto it.\n2. Place the triangular prism on a white background.\n3. Shine a beam of white light through the side of the prism.\nQUESTIONS:\n1. Draw a picture showing what you observe.\n.\n.\n89\n.\nChapter 4.\nVisible light\n\n.\n.\n2. Write a description of what you observed.\n3. Write down the order in which the colours appear.\n4. If you repeat the experiment, does the order of the colours change?\n5. What do the different colours we see tell us about the composition of\nwhite light?\n.\n..\n90\n.\nEnergy and Change\n\nSo, what have we learned so far? Light radiates from luminous objects and\nalways travels in straight lines. The white light that we see is made up of the 7\ndifferent colours of the spectrum. When the 7 colours are travelling together we\nsee them as white light.\nThe 7 colours of the visible spectrum are Red, Orange, Yellow, Green, Blue,\nIndigo and Violet. Each colour has a different wavelength and frequency. Have\na look at the following image which shows the spectrum of visible light.\n.\nTAKE NOTE\nYou can use the\nabbreviation ROYGBIV\nto remember the order\nof the colours.\nThe colours combine to form white light.\n.\nTAKE NOTE\nThe primary colours of\nlight are red, green and\nblue.\n.\nACTIVITY: Colour spinning wheels\n.\nMATERIALS:\n• white cardboard\n• coloured pens or pencils (red, orange, yellow, green, blue, indigo, violet)\n• string\n• scissors\n• round object\nINSTRUCTIONS:\n1. Draw a circle on the cardboard. You can trace around a round object such\nas a cup or saucer to do this. Cut out the circle.\n.\n.\n91\n.\nChapter 4.\nVisible light\n\n.\n2. Now divide the circle into 7 equal segments. If you do not have indigo and\nviolet colours, but just one purple pen or crayon, then you can divide the\ncircle into 6 equal segments rather.\n3. Shade in each segment a different colour, in the order red, orange, yellow,\ngreen, blue, indigo, violet (or just purple if you do not have indigo and\nviolet).\n.\nDID YOU KNOW?\nAn artist might tell you\nthat the primary colours\nof paint are red, yellow\nand blue. This is\ndifferent to the primary\ncolours of light. This is\nbecause the pigments\nyellow, blue and red\ncannot be mixed from\nother pigments. In\nprinting, the primary\ncolours are magenta,\nyellow and cyan.\n4. Next, make two holes, one on either side of the centre as shown below.\n5. Thread the string through the holes and tie it in a loop.\n6. You are now ready to spin the wheel. Holding the ends of the loop in each\nhand, twirl the string over, like you would a skipping rope, so that the\nstring twists. Once the string is tightly twisted, pull your hands apart, then\nbring them back together. Continue bringing your hands in and out and\nwatch the circle spin.\n.\nVISIT\nThere is no pink light.\nbit.ly/1b2gFXU\n7. What do you observe about the colour of the wheel as it spins faster?\n.\n..\n92\n.\nEnergy and Change\n\nSo far we have been talking about the visible light spectrum. As we mentioned\nin the beginning, this is the light that we can see. We also spoke about how light\ntravels in electromagnetic waves. We can only see light with a certain range of\nwavelengths. What does this mean?\n.\nDID YOU KNOW?\nWavelengths can be as\nsmall as one billionth of\na meter, as with gamma\nrays. Wavelengths can\neven be as long as\nmeters, for example in\nradio waves.\nThe size of a wave is measured in wavelengths. A wavelength is the distance\nbetween two corresponding points on two consecutive waves. Normally this is\ndone by measuring from peak to peak or from trough to trough. Have a look at\nthe following diagram which illustrates a wavelength.\n.\nDID YOU KNOW?\nIn police forensics,\nultraviolet light can be\nused along with a\nspecial powder to\ndetect finger and shoe\nprints that can help\nsolve crimes.\nThe wavelengths of the different colours of visible light are different lengths, as\nshown in the following diagram.\nWe can also talk about the frequency of a wave. If a wave has a long\nwavelength, then it has a low frequency; if it has a short wavelength, then it has\na high frequency.\nOf visible light, orange and red light have the longest wavelengths (and lowest frequency)\nand violet, indigo and blue have the shorter wavelengths (and highest frequency).\n.\n.\n93\n.\nChapter 4.\nVisible light\n\nWhen it comes to visible light, we only see wavelengths of 400 to 700 billionths\nof a meter. This is called the visible spectrum. But, light waves are just part of\nthe wave spectrum. There is invisible light with shorter wavelengths, such as\nultraviolet light, and there are longer wavelengths, such as infrared light.\nHave you ever looked through a window and wondered why it is made of glass?\nLet's find out how light behaves when it strikes the surface of different types of\nmaterials in the next section.\n.\n4.3 Opaque and transparent substances\n.\nNEW WORDS\n• opaque\n• transparent\n• translucent\n• transmit\nThree different things happen when light hits a surface, it can be reflected\n(bounce off), absorbed or transmitted (pass through). Glass reflects some light\nbut most of the light is transmitted straight through. That's why we can see\nobjects on the other side of a closed window.\nWe say that glass is transparent. Let's find out more about what this means. If a\nsubstance is not transparent, it is opaque.\n.\nACTIVITY: Shadow Play\n.\nMATERIALS:\n• cardboard\n• clear plastic\n• plastic shopping bag\n• scissors\n• light source (ray box or light bulb)\nINSTRUCTIONS:\n1. Cut out three shapes from your cardboard. All of the shapes should be\nsimilar but three different sizes: small, medium and large.\n2. Switch on the light source.\n3. Hold your first shape a short distance in front of the light source.\n4. Look at the shadow that forms. Write down what you observe.\n5. Hold your second shape the same distance in front of the light source.\n6. Look at the shadow that forms. Write down what you observe.\n7. Hold your third shape the same distance in front of the light source.\n8. Look at the shadow that forms. Write down what you observe.\n9. The shadow is formed on the side furthest from the light source. It is dark\n..\n94\n.\nEnergy and Change\n\n.\nin colour and larger than the first and second shadows.\n10. Use your first cardboard shape as a template and cut the shape from the\nclear plastic and the plastic shopping bag.\n11. Hold the clear plastic shape the same distance from the light source. Write\ndown what you observe.\n12. Hold the plastic shopping bag shape the same distance from the light\nsource. Write down what you observe.\nQUESTIONS\n1. When you held the cardboard up to the light, did it allow light to pass\nthrough it? How do you know this?\n2. Is the cardboard shape opaque or transparent?\n3. What did you notice about the shadows formed by the different size\ncardboard shapes?\n4. Draw a diagram to show how the shadow is formed behind the opaque\nshape. Use straight lines with arrowheads to represent the rays of light.\n.\n.\n.\n95\n.\nChapter 4.\nVisible light\n\n.\n5. The distance between the shape and the light source was kept the same.\nWhat do you think would have happened to the shadow if the distance\nwas increased?\n6. Test your idea from question 5 by moving your cardboard shapes closer to\nand further away from the light source. What do you see? Were you\ncorrect in your prediction?\n7. Is the clear plastic shape opaque or transparent?\n8. Did the clear plastic cast a shadow?\n9. Explain why the cardboard casts a shadow but the clear plastic does not.\n10. Is the plastic shopping bag shape opaque or transparent?\n11. Explain why the shopping bag casts a lighter shadow.\n.\n..\n96\n.\nEnergy and Change\n\nWhat have we learned? Shadows are formed because light travels in straight\nlines and cannot pass through opaque objects.\nSubstances which transmit most of the light and only absorb or reflect a little bit\nare called transparent. Can you list some everyday objects which are\ntransparent?\nSubstances which completely reflect or absorb light without transmitting any\nare called opaque. Can you list some everyday objects which are opaque?\nSome substances, such as the plastic shopping bag, allow some light to pass\nthrough, but not all of it. This substance is translucent, or semi-transparent.\nShadows can be useful. Sundials have\nbeen used since ancient times as a\ntime-keeping device, like a watch or a\nclock. As the position of the Sun\nchanges in the sky, the shadow cast by\nthe style moves across the surface of\nthe sundial. The surface is marked with\nnumbers, allowing the shadow to\nindicate time of day.\nWe can use transparent objects to make filters. If we want red light we use a\nred glass bulb or a red plastic film placed in front of the light. Only red light is\nable to transmit through the red glass or plastic. The other colours are absorbed\nby the filter.\nThese are different colour filters for a camera. The red filter will only allow red light\nthrough and so the photograph will have a red effect applied to it. The other colours of\nlight are absorbed by the filter.\nNow that we have seen some examples of transparent and opaque substances,\nlet's take a closer look at what it means to absorb or reflect light.\n.\n.\n97\n.\nChapter 4.\nVisible light\n\n.\n4.4 Absorption of light\nLook at this picture of a ladybird. Why\nis it red and black? And why is the leaf\nso green? How do we see the different\ncolours? It all has to do with what\nhappens when light hits a surface.\nWhen light hits a surface, some of the\nlight is absorbed and the rest is\nreflected. It is the reflected light that\nreaches our eyes and allows us to see\nthe object.\nA ladybird.\nPreviously, we learned that white light is a mixture of different colours. When\nwhite light from the Sun hits the red shell of the ladybird all of the colours are\nabsorbed, except red. Red light is reflected back to our eyes and so we see a\nred ladybird.\nWe see the red shell of the ladybird as red light is reflected and the other colours are\nabsorbed.\nThe green leaf absorbs all the colours except green which it reflects back into\nour eyes.\n..\n98\n.\nEnergy and Change\n\nWe see a green leaf as green light is reflected and the other colours are absorbed by the\nleaf's surface.\nWhat about the black spots of the ladybird? Is black a colour? The black spots\non the ladybird absorb all the colours and no light is reflected. That is why they\nappear black.\n.\nTAKE NOTE\nAlthough we can get\nblack paint as a\npigment, black is not a\ncolour of light. Black is\nthe result of the\ncomplete absorption of\nlight.\nDo you remember learning about heat as energy transfer in Gr 7? We looked at\nthe absorption of heat. We saw that black, matt objects absorbed all of the light\nenergy, while white objects reflected all of it. Black, matt (not shiny) objects\nabsorb all of the colours of light and reflect none and so appear black to our\neyes.\nWhat about a white object? Why do you think white objects look white? Have a\nlook at the following diagram for a clue.\n.\n.\n99\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Why do objects look red under red\nlight?\n.\nMATERIALS:\n• piece of red plastic to act as a filter\n• light source (light bulb or torch)\n• white object\nINSTRUCTIONS:\n1. Place a white object on the desk.\n2. Switch on your light source and place the red plastic in front of the light.\n3. Shine the light (with the red plastic in front) onto the piece of white paper.\nQUESTIONS:\n1. What colour was the page under normal light?\n2. Why does the page appear white in normal light?\n3. What did you see when the red plastic filter shone on the white page?\n4. Explain why the paper changed colour.\n.\nLet's now look more at what we mean by reflection of light.\n..\n100\n.\nEnergy and Change\n\n.\n4.5 Reflection of light\n.\nNEW WORDS\n• reflect\n• incident ray\n• reflected ray\n• normal line\n• angle of\nincidence\n• angle of\nreflection\n• perpendicular\nWhen light hits a surface it is\noften reflected off the surface.\nThis photograph shows how\nlight is reflected off a still lake,\ncreating a mirror image of the\ntree. The still, flat surface of the\nlake has acted as a mirror.\nA tree reflection.\nHave some fun with these photos of reflections in water. One photograph is the\nright way up and the other one is upside down! Which one is which?\nReflections on the Negro River in the\nAmazon.\nReflections in the Arno River in Italy.\nMost surfaces reflect light. When light strikes a reflective surface, it can change\ndirection. Let's look at how this happens.\nWhen light reflects off a surface the ray which hits the surface, it is called the\nincident ray. The ray of light which is reflected from the surface is called the\nreflected ray. When we draw diagrams of reflection we also draw in an\nimaginary line to help us measure different angles. This line is called the normal.\nThe normal line is always drawn perpendicular to the surface.\nBetween the normal line and the incident and reflected rays, there are two\nangles. These are:\n• angle of incidence - the angle between the incident ray and normal line\n• angle of reflection - the angle between the reflected ray and normal line\nThe following diagram explains these concepts.\n.\n.\n101\n.\nChapter 4.\nVisible light\n\nLet's investigate the relationship between the angle of incidence and the angle\nof reflection.\n.\nINVESTIGATION:\nIs there a relationship between the\nangles of incidence and reflections?\n.\nAIM: To investigate the reflection of light from a surface.\nINVESTIGATIVE QUESTION:\nLook at the diagram above and try to formulate an investigative question for\nthis investigation.\nHYPOTHESIS: The angle of incidence is equal to the angle of reflection\nMATERIALS AND APPARATUS:\n• mirror\n• white paper\n• pencil\n• protractor\n• ruler\n• ray box\nMETHOD:\n1. Put a white piece of paper on the desk.\n2. Use your ruler to draw a straight line near the top of the white paper.\n..\n102\n.\nEnergy and Change\n\n.\n3. Use your protractor to make a right\nangle in the middle of your pencil\nline. This is the normal line.\nMarking a right angle with a protractor.\n4. Place your mirror upright along the\nfirst line.\n5. Shine a light from the ray box along\nthe paper so that it \"hits\" the mirror\nwhere your normal line and your\nmirror meet.\nA mirror is placed on the line and a ray\nshone to strike the mirror at the normal\nline.\n6. Use a pencil to mark the incident\nlight ray.\nMarking the incident light ray.\n7. Use a pencil to mark the reflected\nlight ray.\nMarking the reflected ray.\n8. Remove the mirror and switch off\nthe ray box.\n9. Use a ruler and pencil to draw a line\nfrom the points you have marked on\neach ray to the normal line.\nDrawing in the rays.\n.\n.\n103\n.\nChapter 4.\nVisible light\n\n.\n10. Mark the angle of incidence (i) and\nangle of reflection (r).\nYour ray diagram should look similar to\nthis.\n11. Turn the ray box on again to confirm\nthat your pencil lines follow the rays.\nThe ray diagram overlaps the actual rays.\n12. Use a protractor and measure the\nangle of incidence and the angle of\nreflection and record your results in\nthe table.\n13. Repeat this method 3 more times,\neach time using a different angle of\nincidence.\nA different angle of incidence.\n.\nTAKE NOTE\nKeep one of the sheets\nwith your drawn ray\ndiagram for the next\nactivity.\nRESULTS:\nFill your results into the following table.\nRepeat\nAngle of Incidence\nAngle of Reflection\n1\n2\n3\n4\nANALYSIS:\n1. Has your investigation provided everything you need to answer your\ninvestigative question?\n..\n104\n.\nEnergy and Change\n\n.\n2. How could you improve this investigation to get more accurate results?\nCONCLUSION:\nWhat can you conclude based on your results?\n.\nWhenever light is reflected from a surface, the angle of incidence to equal to\nthe angle of reflection. On a smooth surface all the light rays are reflected in the\nsame way and so the image is clear and focused.\nA mirror is an example of a smooth surface. The image you see is focused and\nclear. As you can see in the photograph, the scientists and engineers are clear\nand focused in the mirror image.\nA mirror segment from one of NASA's telescopes provides a clear and focused reflection.\n.\nTAKE NOTE\nIn reflection, not only is\nthe angle of incidence\nequal to the angle of\nreflection, but the\nincident ray and\nreflection ray are also in\nthe same plane.\n.\nVISIT\nWhat colour is a mirror?\n(video)\nbit.ly/GABdNZ\nWhat happens when we do not have a smooth surface? Have a look at the\nphoto.\n.\n.\n105\n.\nChapter 4.\nVisible light\n\nWhy is the reflection of the grass and reeds not clear, but rather blurred?\n.\nACTIVITY: Light reflection off aluminium foil\n.\nMATERIALS:\n• aluminium foil\n• white paper\n• ray box\nINSTRUCTIONS:\n1. If possible, use the white sheets of paper from the last investigation where\nyou drew your ray diagrams.\n2. Similar to what you did in the last investigation, set up a ray box and direct\nthe ray along the line of incidence which you drew.\n3. Crumple a piece of aluminium foil and place this in the spot instead of the\nmirror.\n4. Observe the reflected ray.\nQUESTIONS:\n1. Describe the reflected ray off the aluminium foil and how this compares to\nthe reflected ray off the mirror.\n.\nVISIT\nWatch a video about the\ncreative way that\nscientists have tried to\nanswer the question:\n\"What is light?\"\nbit.ly/GAMvAL\n2. Why do you think you observed these differences?\n.\n..\n106\n.\nEnergy and Change\n\nCan you now see why reflections off rippled water are not clear, but rather\nblurred? This is because the light rays have not reflected parallel to each other\nas they do from a smooth surface, but have scattered in different directions.\nThe following table shows the difference between a smooth surface and a rough\nsurface. Straight parallel rays are approaching the surface. You need to draw in\nthe reflected rays to show specular (clear) reflection from a smooth surface and\ndiffuse (unclear) reflection from a rough surface.\n.\nTAKE NOTE\n'Diffuse' can mean\nunclear as well as\nspread out. In this\nexample, the reflection\nis unclear because the\nrays are spread out or\ndiffuse.\nSpecular diffusion from a smooth\nsurface\nDiffuse reflection from a rough\nsurface.\nVisible light is the range of frequencies of light that are visible to the human eye,\nand is responsible for the sense of sight. Are you curious to find out how we\nactually see light? Let's discover more in the next section.\n.\n4.6 How do we see light?\n.\nNEW WORDS\n• retina\n• stimulate\nHow is it that we are able to see light? Light that is absorbed by objects does\nnot enter the eye. Only reflected light or direct light from luminous objects can\nenter the eye and be interpreted. Have a look at the following image which\nshows the outer structure of the eye.\nWe can see the iris, the pupil and the sclera. The sclera is a the tough white,\nouter part of the eye, which acts as protection. The iris is the coloured part of\nthe eye which differs from person to person. It is circular and surrounds the\npupil. Light enters the eye through the pupil.\n.\nVISIT\n2012 Nobel Prize: How do\nwe see light?\nbit.ly/1a4zs2D\n.\n.\n107\n.\nChapter 4.\nVisible light\n\nThe size of your pupil changes in different light conditions. In bright light, the pupil\ncontracts (gets smaller) to let less light through (as on the left), and in low light your\npupil dilates (gets bigger) to let more light through (as on the right).\nLet's take a look at the internal structure of the human eye. The following\ndiagram shows a cross section through the eye. The eye is actually a large ball,\nand only a small part is visible on the outside. Covering the iris is a tough,\ntransparent layer called the cornea. Behind the iris is the lens. Both the cornea\nand the lens help you to focus the light entering your eyes, as we will learn\nabout in the next section.\n.\nTAKE NOTE\nThe fovea is the part of\nthe eye located in the\ncentre of the retina\nwhere the clearest\nimage is formed.\nA diagram of the eye.\nThe light travels through the eye and hits the retina at the back of the eyeball.\nThe retina is a layer of tissue lining the back of the eyeball, as indicated in the\ndiagram, it is the yellow layer. The retina consists of cells which are sensitive to\nlight. Light enters the eye and forms an image on the back of the eyeball. The\nway in which light hits the back of the eye, is similar to what happens in a\npinhole camera. The receptor cells convert the light energy into electrical nerve\nimpulses. These impulses travel out of the eye through the optic nerve and to\nthe brain where they are interpreted as sight.\n.\nTAKE NOTE\nThe cell is the basic\nstructural and\nfunctional unit of all\nliving things. We will be\nlearning more about the\ncell next year in Gr 9\nLife and Living.\n.\nVISIT\nFind your blind spot with\nthis optical illusion.\nbit.ly/19jumEr\nSo how do we see colour? Do you remember when we spoke about why the\nladybird appears red and black? Look at the following diagram again.\n..\n108\n.\nEnergy and Change\n\nThe white light hits the ladybird's surface. The white light has all the colours of\nlight, but when it hits the red surface, only the red light is reflected. The other\ncolours are absorbed by the red surface. This means that when we look at the\nred parts of the ladybird, we only get red light reflected into our eyes.\nTherefore, when this reflected light hits our retina and the electrical impulse is\nsent to our brains, we see the red colour.\n.\nDID YOU KNOW?\nEach of your eyes has a\nsmall blind spot at the\nback of the retina where\nthe optic nerve\nattaches. You do not\nnormally notice the hole\nin your vision because\nyour eyes work together\nto fill in each other's\nblind spot.\n.\nACTIVITY: Seeing colours\n.\nMATERIALS:\n• coloured pens or pencils\nINSTRUCTIONS:\n.\nDID YOU KNOW?\nThe cells in your eye\ncome in different\nshapes. Rod-shaped\ncells allow you to see\nshapes, and\ncone-shaped cells allow\nyou to see colour.\n1. Answer the following questions about how we see objects.\n2. Draw a ray diagram to accompany your written answer.\n3. An example has been done for you.\nLook at the picture of a sunflower.\nA black and yellow sunflower.\n.\n.\n109\n.\nChapter 4.\nVisible light\n\n.\nWe can draw a ray diagram to show why we see the green leaves as green, as\nshown below. The green surface of the leaves absorb all the colours of white\nlight except green light which is reflected into our eyes.\nNow explain why the petals appear yellow and the centre appears black. Use\nthe concepts of absorption and reflection in your explanation. Draw diagrams\nto support your answer.\n.\nHeath has bought himself a blue car.\nExplain why we see the car as blue by\nusing the absorption and reflection of\nlight. Draw a diagram to support your\nanswer.\nHeath's blue car.\n..\n110\n.\nEnergy and Change\n\n.\n.\n.\n.\nVISIT\nA simulation on colour\nvision.\nbit.ly/18TbpEA\nWe have looked at opaque and transparent substances, absorption of light,\nreflection of light and how we see light. We are now going to go back to\ntransparent substances and see how light can interact with these materials.\n.\n4.7 Refraction of light\nDo you remember the last time you drank a cold drink with a straw? Did you\nnotice that the straw did not look straight anymore once it was in the water or\ncool drink?\n.\nNEW WORDS\n• refraction\n• medium\n• optical density\nWhy does the pencil in this glass of water look bent?\nLet's investigate this by examining what happens to light when it passes\nthrough a glass block.\n.\n.\n111\n.\nChapter 4.\nVisible light\n\n.\n.\nINVESTIGATION:\nWhat happens to light when it\npasses through a glass block\n.\nWe are going to investigate what happens to a ray of light when it passes from\nair and into a glass block and then from the glass block back into air. We are\ngoing to use a glass block with parallel sides.\nBefore we start the investigation, we need to think about how we are going to\ndetermine if light changes direction or not. Do you remember in the\ninvestigation on reflection where we measured the angle of incidence and the\nangle of reflection? What did we find in this investigation?\nWhen light passes through a transparent substance, we can also measure the\nangles. Look at the following diagram. The angle of incidence (i) is measured\nbetween the incident light ray and the normal line. As the light passes through\nthe transparent substance, the angle of refraction (r) is the angle between the\nrefracted light ray and the normal.\nA light ray passing from one medium to another.\nIn the diagram above, you can see that the angle of refraction is smaller than\nthe angle of incidence. Therefore, the refracted light ray changed direction\nwhen it entered the transparent medium. We can also say something about\nwhich direction it bent towards. Did the light ray bend towards or away from\nthe normal line?\nThe next diagram shows another outcome.\n..\n112\n.\nEnergy and Change\n\n.\nA light ray passing from one medium to another.\nIn the diagram above, does the refracted ray change direction when it enters\nthe transparent medium? Give a reason for your answer.\nIn which direction did the refracted ray change?\nWe are now ready to start our investigation.\nAIM: To determine whether light changes direction when it passes through a\nparallel-sided glass block.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS:\n• glass block\n• ray box, laser pointer or other light source\n• protractor\nMETHOD:\n.\nTAKE NOTE\nThe emergent ray from\na parallel sided block is\nparallel to the incident\nray.\n1. Put the glass block in the centre of a piece of white paper and trace around\nit.\n2. Shine a ray of light into the glass block. The ray should be at an angle to\nthe surface of the block.\n.\n.\n113\n.\nChapter 4.\nVisible light\n\n.\n3. Trace the light ray with pencil and mark the point at which it enters the\nglass block.\n4. The light ray emerges on the other side of the glass block. Mark the point\nat which it emerges with a pencil and trace the emergent ray.\n5. Remove the glass block. Your diagram should look similar to the one\nabove.\n6. Draw a line joining the incident ray and emergent ray. You have traced the\nrefracted ray through the glass block.\n7. Draw the normal lines where the incident ray meets the block and where\nthe emergent ray leaves the block.\n8. Measure the angles labelled 1, 2, 3 and 4 as shown on the diagram with a\nprotractor.\n9. Fill in the measurements in the table.\n10. Repeat the steps above three times using different angles of incidence\n(angle 1).\n..\n114\n.\nEnergy and Change\n\n.\nRESULTS AND OBSERVATIONS:\nFill your results into the following table.\nExperimental\nrepeat\nAngle 1\nAngle 2\nAngle 3\nAngle 4\n1\n2\n3\n4\n1. Which pairs of angles are equal in the measurements you have taken?\n2. Which of the angles you measured are the angles of incidence and which\nare the angles of refraction? Write this down below and mark them on the\ndiagram above.\n3. What do you notice about the angle of incidence and angle of refraction\nfor each of your sets of measurements?\n4. Did the light entering the glass block bend towards or away from the\nnormal line?\n5. Make the angle of incidence zero (make the light ray enter the block\nperpendicular to the surface). What is the angle of refraction?\nCONCLUSION:\nWhat can you conclude from your results?\n.\n.\nVISIT\nLearn more about\nrefraction with this\nsimulation.\nbit.ly/GAxLmc\nThe angle of incidence is not equal to the angle of refraction because the light\nhas changed direction as it enters the glass. Therefore, when light travels from\none medium to another, it bends, or changes direction. This is called refraction.\n.\n.\n115\n.\nChapter 4.\nVisible light\n\nWhen light enters a different medium at right angles then it does not change\ndirection.\nSo why does the light refract? Light behaves as a wave does and waves travel\nat different speeds in different media. For example, light travels faster in air\nthan it does in water. When light enters a different medium, it changes speed,\nand if it entered at an angle other than 90o, then it also changes direction. The\nmore dense the medium, the slower the light moves.\nDo you remember learning about density last term in Matter and Materials?\nWrite down your own definition for density in the space below.\n.\nTAKE NOTE\nRemember that\nalthough we learn\nabout Natural Sciences\nin 4 strands throughout\nthe year, there are many\nconnections and links\nbetween the strands.\nIf light moves from a less dense medium, like air, into a denser medium, like\nglass, then the light slows down. The light will bend towards the normal line.\n.\nVISIT\nThe speed of light in glass.\nbit.ly/1fcfJVZ\nIf light moves from a more dense medium to a less dense medium then the light\nspeeds up and moves away from the normal.\nWhen light refracts and changes direction as it passes through different\nmediums, it can distort what we see. Think back to the pencil or straw in a glass\nof water at the start of the section. We can now explain why a drinking straw or\npencil in a glass of water looks bent. The light bends when it moves from one\nmedium to another. Light moves from the air to glass to water, and therefore\nchanges direction.\nIf you have stood in a pool of water before and looked down, have you noticed\nhow short your legs appear to be? Let's have a look at this a bit more in the\nnext activity.\n..\n116\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magic coin trick\n.\nMATERIALS:\n• coin\n• prestik\n• opaque bowl or cup\n• water\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Put a small amount of prestik onto the bottom of the bowl.\n3. Stick the coin to the bottom of the bowl.\n4. Take small steps back from the desk/table until you cannot see the coin\nover the lip of the bowl.\n5. Ask your partner to slowly pour water into the bowl and observe.\nQUESTIONS:\n.\nVISIT\nWatch a video that shows\nand explains the coin\nactivity.\nbit.ly/15NmXXO\n1. What happened when your partner poured the water into the bowl?\n2. Where does the coin appear to be?\n3. Explain why the coin can be seen when the water is added, but not before.\nThe diagrams below will help you explain what is happening in words.\n.\nTAKE NOTE\nThe diagrams used here\nshow the container as\ntransparent so that you\ncan see the coin inside,\nwhereas you will\nactually be using an\nopaque container.\nEmpty container.\nContainer with water.\n.\n.\n.\n117\n.\nChapter 4.\nVisible light\n\nRefraction can be used to explain why images appear to be distorted when we\nview them through transparent mediums. For example, if you are looking at\nyour legs or hands through some water, they will appear closer than they\nactually are as the light is refracted. Look at the photograph of the glass with\nwater in it in front of diagonal lines. Can you see how the lines are distorted\nwhen the light travels through the water and glass compared to when it does\nnot?\nLight refraction through glass and water.\nCan you remember how we split white light into the separate colours of the\nvisible spectrum in the beginning of this chapter? What did we use to do this in\nthe activity?\nWe can do this because the different\ncolours of light bend by different\namounts when the light enters a\ndifferent medium. Different colours of\nlight will slow down to different\nspeeds, causing them to bend by\ndifferent amounts.\nRefraction through a triangular prism.\nWhen the white light entered the prism it refracted. The different colours of\nlight travel at different speeds in the prism so they refracted at different angles\nand split up. Red light refracts the least and the violet light refracts the most as\nyou can see in the following diagram.\n..\n118\n.\nEnergy and Change\n\nPrisms are not the only objects that can split white light into separate colours.\nIn fact, a rainbow is a good example of white light splitting up.\nA rainbow.\nLight from the Sun enters the raindrops and refracts. The light is then reflected\noff the back of the raindrop. When the light passes out of the raindrop it is\nrefracted again and the colours split up even more as shown in the diagram.\nA raindrop refracts and reflects light, dispersing white light into the colours of the visible\nspectrum.\n.\n.\n119\n.\nChapter 4.\nVisible light\n\nWhat colour is at the top of a rainbow and which colour is at the bottom?\nDoes this match the order which we see in the diagram showing how light is\nrefracted and reflected in a raindrop?\nHow does this happen? When we see a rainbow, we see a combination of\nmillions of raindrops. Although each raindrop refracts and reflects all 7 colours,\nwe only see only colour of light reflected from each particular raindrop. This\ndepends on the angle of the raindrop from our position. Therefore, the\nraindrops higher up in the sky reflect red light to us and the rain drops lower\ndown reflect violet light to us. This is shown in the following diagram.\nWe see rainbows with red at the top and violet at the bottom due to the combination of\nmillions of raindrops. We only see one colour reflected from a particular raindrop,\ndepending on its position in the sky.\nWe are now going to look at an application of the refraction of light.\nLenses\n.\nNEW WORDS\n• diverge\n• converge\n• focus\nDo you remember when we spoke about how we see light and the structure of\nthe eye, we mentioned that there is a lens just behind the iris? Another place\nwhere you may have seen lenses before are in reading glasses which some\npeople wear to correct their vision. Or, have you seen how a magnifying glass\nmakes things appear bigger. What are lenses and how do they work?\nA magnifying glass makes things look bigger.\n..\n120\n.\nEnergy and Change\n\nA lens is a transparent object which focuses or refracts light. When light is\nspread out, we say it has diverged. Some lenses will diverge light while others\nwill converge light, bringing the light rays together. When light rays are all\nbrought to the same point, we say they have been focused. Let's have a look at\nthis more closely.\n.\nACTIVITY: Diverging and converging light with\nlenses\n.\nMATERIALS:\n• ray box or light source\n• concave lens\n• convex lens\n• piece of paper\n• pencil\nBefore we start, it is important that you know the difference between a convex\nand a concave lens.\nConvex lens\nConcave lens\nA convex lens has one\nside which curves or\nbulges outwards. A\nconvex lens converges\nlight.\nA concave lens has one\nside which curves or is\nhollowed inwards. A\nconcave lens diverges\nlight.\n.\nTAKE NOTE\nA lens can have two\nsides which are concave\nand it is then called a\nbiconcave lens or two\nsides which are convex\nand it is then called a\nbiconvex lens.\n.\n.\n121\n.\nChapter 4.\nVisible light\n\n.\nINSTRUCTIONS:\n1. Place a ray box or light source on one side of a piece of paper and turn it\non. Observe the light rays. You might see something as shown in the\nphotograph here.\nThree rays coming out of a ray box.\n2. Turn the ray box off.\n3. Place the convex lens (with the rounded surface) on the piece of paper\nwhere the light rays will pass through it. Trace around it.\n4. Turn on the ray box or light source and observe what happens to the rays\nwhen they pass through the lens.\nLight rays passing through a convex lens.\n5. Trace the path of the light rays on your piece of paper.\n6. Describe what has happened to the light rays.\n7. Mark the point where the light rays cross. This is called the focal point of a\nconvex lens.\n8. Turn off the ray box or light source and place a new piece of paper in front\nof it.\n9. Now place the concave lens in the path of the light rays and trace around\nthe lens.\n10. Turn on the light source and observe what happens to the rays.\n..\n122\n.\nEnergy and Change\n\n.\n11. Trace the path of the rays on the piece of paper.\nA concave lens in front of the rays of light.\n12. Describe what has happened to the light rays.\n13. Turn off the light rays and extend the rays you have drawn until they meet\nat a point in front of the lens. This is the focal point of a concave lens.\n14. If you still have your pin hole cameras, place a convex and concave lens in\nfront of the camera and observe the image that forms.\nViewing a light source through a pinhole camera with different lenses.\n15. Is the image larger or smaller when you observe through a concave lens?\n16. Is the image larger or smaller when you observe through a convex lens?\n.\n.\n.\n123\n.\nChapter 4.\nVisible light\n\nWe have now seen how lenses can disperse or focus light. Have a look at the\nfollowing diagrams which show how a biconvex lens converges light and a\nbiconcave lens diverges light.\n..\n124\n.\nEnergy and Change\n\nConverging lens\nDiverging lens\nA converging lens refracts the light\nentering it and bends the light rays\nto a focal point on the other side of\nthe lens.\nA diverging lens refracts the light\nentering it and bends the light rays\naway from each other. The light\nrays can be traced back to a focal\npoint in front of the lens.\nWhat do we use lenses for? Think of a magnifying glass. If you hold a\nmagnifying glass over a picture or words then it enlarges the image. Is a\nmagnifying glass an example of a diverging or converging lens?\nLet's think about how this works. Imagine you are looking at the ladybird from\nthe beginning of the chapter through a magnifying glass. The ladybird looks\nbigger than what it actually is. When the object you are viewing is closer to the\nlens than the focal point, you see a virtual image of the ladybird that is larger\nthan the object.\nHave a look at the first diagram below. Can you see that the ladybird is between\nthe focal point and the lens? The rays reflected from the ladybird are refracted\nby the magnifying glass and enter the person's eye.\n.\n.\n125\n.\nChapter 4.\nVisible light\n\nIn the next diagram you can see how your eyes see a virtual image of the\nladybird which is bigger than the object. The more curved the convex lens is in\na magnifying glass, the greater its ability to magnify objects.\n.\nTAKE NOTE\nWhen you hold a\nmagnifying glass up\nand view a distant\nobject, the object\nappears smaller and\nupside down. Unlike\nwhen viewing the\nladybird close up, the\ndistant object is beyond\nthe focal point of the\nlens, which results in\nthis effect.\n.\nVISIT\nHow do lenses work?\nbit.ly/GABjoO\nDo you remember what the human eye looks like? We have lenses in our eyes\nto allow us to see. The light enters the eye and passes through the lens. The\nlens focuses the light onto the back of our retina so that a clear image is formed.\nWhat type of lens do we have in our eyes? Give a reason for your answer.\nIn order for a clear image to form, the lens in our eye needs to focus the light\nrays coming into our eyes so that the focal point falls on the retina. This\ndepends on the shape of the lens in our eyes. Sometimes, people have lenses in\ntheir eyes that cannot focus properly. Have a look at the following diagram\nwhich shows a normal eye and then an eye which focuses before the retina\n(near-sighted) and behind the retina (far-sighted).\n..\n126\n.\nEnergy and Change\n\nOptical glasses, or spectacles, are used to correct near or far-sightedness.\nIf you are near-sighted you need a diverging lens. Would this be a biconcave or\nbiconvex lens?\n.\nDID YOU KNOW?\nA contact lens is\ndesigned to rest on the\ncornea of the eye and\ncorrect vision. Leonardo\nda Vinci was the first to\ncome up with the idea\nin the 16th century to\nhelp prevent eye\ninfection.\n.\nDID YOU KNOW?\nA microscope makes a\ntiny, nearby object look\nmuch bigger. A\ntelescope makes a\nlarge, distant object\nlook much closer and\nbrighter. In both, light\nfrom the object passes\nthrough two or more\nlenses to form an\nimage. The lens shapes\nand distances between\nthem determine how\nthe image is produced.\nIf you are far-sighted you need a converging lens. Would this be a biconcave or\nbiconvex lens?\nAn optometrist holds a lens in front of a patient's eye to correct her vision.\nThe following image shows how lenses can be used to correct far and\nnear-sightedness.\n.\n.\n127\n.\nChapter 4.\nVisible light\n\n.\nTAKE NOTE\nNext term in Planet\nEarth and Beyond we\nwill look at how lenses\nare used in optical\ntelescopes to view\nobjects in space.\n.\nACTIVITY: Research careers in optics\n.\n.\nVISIT\nAn interview conducted\nwith an optometrist.\nbit.ly/19WxYYa\nThere are many different careers in the field of geometric optics.\nINSTRUCTIONS:\n1. Work in groups of 3.\n2. Interview someone in the field of geometric optics and find out how they\nchose their career and what and where they studied.\n3. Write a paragraph explaining the career and the study options available in\norder to qualify for that career.\n4. Here are some examples of careers in geometric optics.\na) Optometry\nb) Ophthalmology\nc) Optoelectronics\nd) Illumination engineering\n.\n..\n128\n.\nEnergy and Change\n\n.\nVISIT\nWant to take part in some\nreal science research?\nCheck out these citizen\nscience projects to get\ninvolved easily.\nbit.ly/15KjnmD\nRemember to discover more online by visiting http://www.curious.org.za and\nby typing the links in the Visit margin boxes into your internet browser to watch\nany videos, play with simulations or read an interesting article.\nType the bit.ly link for the video or site that you want to visit into the address bar of your\nbrowser on your computer, tablet or mobile phone.\n. .\nSUMMARY:\n.\nKey Concepts\n• Light travels in straight lines.\n• White light consists of all the colours of the visible spectrum.\n• The colour spectrum can be seen when white light is dispersed by a\nprism or a raindrop (rainbow).\n• Light cannot pass through opaque objects.\n• Light can pass through transparent objects.\n• Light is absorbed by some materials.\n• A material appears to be a certain colour because it reflects that part of\nthe colour spectrum. Other wavelengths of light are absorbed.\n• In reflection, the angle of incidence is equal to the angle of reflection.\n• On a smooth surface, parallel rays of light are all reflected at the same\nangle.\n• On rough surfaces, the light is scattered and the image produced is not\nclear.\n• The human eye has specialised cells in the retina which convert light\ninto electrical nerve impulses. The nerve impulses are transmitted to\nthe brain via the optic nerve, where they are interpreted.\n• Light travels at different speeds in different media.\n• When light enters a different medium at an angle, the light is refracted.\n• If the light slows down, the light bends towards the normal line.\n• If the light speeds up, the light bends away from the normal line.\n• Converging lenses refract and focus light.\n• Diverging lenses and triangular prisms refract and disperse light.\n• Lenses have many applications, for example, in glasses to correct vision,\nmicroscopes, telescopes and magnifying glasses.\n.\nConcept Map\nThe concept map on the next page shows how all the concepts relating to\nvisible light link together.\nComplete the map to reinforce what you have\nlearned in this chapter.\n.\n.\n129\n.\nChapter 4.\nVisible light\n\n.\n\n.\n.\nREVISION:\n.\n1. Match the correct definitions to the terms in the following table. Write the\nletter of the definition next to the correct number below. [12 marks]\nTerm\nDefinition\n1. Radiation\nA. Light cannot pass\nthrough.\n2. Visible light\nB. The angle of incidence\nequals the angle of\nreflection when a ray is\nreflected off a smooth\nsurface.\n3. Opaque\nC. One of the ways in\nwhich energy is\ntransferred, specifically\nthrough a vacuum\n4. Transparent\nD. When light enters a\ntransparent medium it\ncan change direction.\n5. Absorption\nE. Curved inwards.\n6. Reflection\nF. The spectrum of light\nwhich we are able to see.\n7. Retina\nG. Bulging outwards.\n8. Refraction\nH. A transparent object\nable to refract and focus\nlight.\n.\n.\n131\n.\nChapter 4.\nVisible light\n\n.\nTerm\nDefinition\n9. Diverging\nI. Light can pass through.\n10. Lens\nJ. When light rays are\nspread out from a point.\n11. Concave\nK. A layer of tissue at the\nback of the eye which is\nsensitive to light.\n12. Convex\nL. When the surface of a\nsubstance absorbs\ncertain colours of light.\nAnswers:\n1:\n2:\n3:\n4:\n5:\n6:\n7:\n8:\n9:\n10:\n11:\n12:\n..\n132\n.\nEnergy and Change\n\n.\n2. A beam of white light is shone through a glass prism. It splits up into seven\ncolours which are shone on a screen. A learner took a photograph which is\nshown below and drew a ray diagram to show the prism. The colours are\nmarked 1 to 7 in the diagram.\nA photograph of the prism.\nA diagram drawn by the learner.\na) What does this tell us about white light? [1 mark]\nb) Why does the light do this when it passes through the prism? [3\nmarks]\nc) What colour is at label 1 and what colour is at label 7? Explain your\nanswer. [3 marks]\nd) What label corresponds to the colour of grass? [1 mark]\ne) Can you see there are two other lighter, white rays emerging from the\nprism? What do you think this is the result of? [2 marks]\n3. Why does an opaque object cast a shadow? [2 marks]\n.\n.\n133\n.\nChapter 4.\nVisible light\n\n.\n4. Look at the following photograph of water in a pond and answer the\nquestions.\nWater in a pond.\na) How are we able to see the image of the wooden poles sticking up on\nthe edge of the pond? [2 marks]\nb) Why is the image not clear, but blurred? [2 marks]\n5. Two learners are discussing the colours of light. They decide that white\nand black are not really colours of light. If they are not colours, then how\ncan we see them? [5 marks]\n6. Explain how we are able to see the different colours on the South African\nflag. [6 marks]\n..\n134\n.\nEnergy and Change\n\n.\n7. Draw a ray diagram in the space provided to show how we see the green\npart of the flag. [5 marks]\n.\n8. Which diagram shown below correctly shows the path of a ray of light\nthrough a triangular piece of glass? [2 marks]\n.\n.\n135\n.\nChapter 4.\nVisible light\n\n.\n9. Complete the following sentence and write it out in full on the lines\nprovided: When light travels from a less dense into a more dense\ntransparent medium, it refracts and bends\nthe normal line.\nWhen light travels from more dense to a less dense medium, it refracts and\nbends\nfrom the normal line. [2 marks]\n10. Draw a diagram to show what is meant by 'when the refracted ray bends\ntowards the normal'. Mark the angle of incidence and angle of refraction.\nIndicate which medium is denser [4 marks]\n.\n11. Study the following diagram and answer the questions that follow.\na) This diagram is a drawing that a learner made during an investigation\ninto the refraction of light. What does the red line represent in this\ndiagram? [1 mark]\n..\n136\n.\nEnergy and Change\n\n.\nb) What do the blue lines represent? Label this on the diagram. [1 mark]\nc) The light passes from the air and into a block of another medium. Is\nthis medium more or less dense than air? Give a reason for your\nanswer. [2 marks]\nd) What type of medium could the block be made from? [1 mark]\ne) Label the incident ray and the emergent ray on the diagram. [2 marks]\nf) Label the angles of incidence (i) and angles of refraction (r) on the\ndiagram. [2 marks]\n12. Which diagram shown below shows the path of a light beam passing\nthrough a rectangular glass prism correctly? [2 marks]\n13. Why does it look like the tree trunk in the photograph is skew? [2 marks]\n.\n.\n137\n.\nChapter 4.\nVisible light\n\n.\n14. What shape does a lens have to have in order to focus the light? [1 mark]\n15. Draw a ray diagram to show how a converging lens focuses light to a point.\n[4 marks]\n.\n16. Which eyesight defect can be fixed by using a converging lens? Explain\nwhat this defect is and why it can be corrected. [4 mark]\nTotal [74 marks]\n.\n..\n138\n.\nEnergy and Change\n\n.\n.\n.\nGLOSSARY\nammeter:\ndevice that measures the strength of an electric\ncurrent\nampere:\nthe standard unit for measuring electric current\nangle of incidence:\nthe angle between the incident ray and the normal\nline\nangle of reflection:\nthe angle between the reflected ray and the normal\nline\nattract:\nto pull something closer\ncell:\na source of energy for an electric circuit\ncomponent:\na part of a larger system\ncomposition:\nthe parts of a mixture\nconductor:\na substance which easily transmits electricity, heat,\nsound or light\nconverge:\nlight rays that come together and focus on a point\ndelocalised:\nnot limited to a particular place, free to move\ndischarge:\nthe sudden flow of charged particles between two\nelectrically charged objects\ndispersion:\nspreading of something over an area\ndiverge:\nlight rays that spread apart as they move further\nand further away from a point\nearth:\n(or ground) to connect with a conductor to the\nground, or the earth\nearthing:\na way to prevent electrical charge from building up\non an object, or to neutralise an electric charge, by\nallowing the excess charge to flow into the Earth\nelectric circuit:\na complete path through which electrons can move\nelectric current:\nthe movement of charge in an electric circuit\nelectrodes:\na conductor which allows electricity to enter a\nsubstance\nelectrolysis:\nthe use of electricity to separate chemicals in a\nsolution\nelectromagnet:\na device which becomes a magnet when electric\ncurrent passes through it\nelectroplating:\ncovering an object with a thin layer of metal using\nelectrolysis\nelectrostatic charge:\nthe electric charge resulting from static electricity\ncaused by an excess or deficiency of electrons on\nthe surface of an object\nflammable:\nsomething is easily set on fire\nfocus:\nbring together to the same point\nfriction:\nthe resistance that results when two surfaces are\nrubbed or moved against each other\nfuse:\na safety device designed to melt and break the\ncircuit if an electric current reaches too high a level\n.\n.\n139\n.\nChapter 4.\nVisible light\n\n.\nignite:\nto light something\nincident ray:\nthe ray of light which hits a surface\nluminous:\nbright or shining\nmedium:\nsubstance through which waves (such as light) can\ntravel\nneutral:\nwhen the number of positive charges (from the\nprotons) is equal to the number of negative\ncharges (from the electrons); the (positive and\nnegative) charges balance each other so that the\nobject is neither positively nor negatively charged\nnormal line:\nthis is an imaginary line which is drawn at 90o to\nthe surface\nopaque:\nsomething that you cannot see through; no light\npasses through the object\noptical density:\na measure of how well a medium allows light to\ntravel through it\noptics:\nthe scientific study of sight and the behaviour of\nlight\nparallel circuit:\na circuit that provides more than one pathway for\nthe current to pass through it\nperpendicular:\nat right angles\npropagation:\nspreading into new areas\nqualitative:\ndescribing something in terms of its properties or\ncharacteristics rather than by a number or\nmeasurement\nradiation:\nthe emission of energy as electromagnetic waves\nrectilinear:\nstraight lines\nreflect:\nthrow back without absorbing\nreflected ray:\nthe ray of light which leaves a surface\nrefraction:\nthe change in direction of a wave passing from one\nmedium to another caused by its change in speed\nrepel:\nto push something away\nresistance:\nthe opposition to the movement of charge in a\nconductor\nresistor:\na component in an electrical circuit which slows the\nmovement of charge\nretina:\na layer at the back of the eyeball which is made up\nof light sensitive cells\nseries:\ncomponents connected in series provide only one\npathway for electrical current; they are connected\none after another\nstatic electricity:\nthe build-up of a stationary electric charge (either\npositive or negative) on the surface of an object\nstimulate:\nto cause activity\nswitch:\na control component in an electrical circuit which\nopens or closes the circuit\ntranslucent:\nsemi-transparent; some light is able to pass through\nbut not enough for details to be seen clearly\ntransmit:\nto cause light to pass through space or medium\n..\n140\n.\nEnergy and Change\n\n.\ntransparent:\nsomething that you can see through; light passes\nthrough the object\nvariable:\nsomething that can vary or change\nvisible spectrum:\nthe portion of the wave spectrum that is visible to\nthe human eye\n.\n.\n141\n.\nChapter 4.\nVisible light\n\n\n\n. .\n1\n.\nThe solar system\n..\n144\n..\nKEY QUESTIONS:\n• How does the Sun produce its energy?\n• How can we observe the Sun without damaging our eyes?\n• What objects are in orbit around the Sun in our solar system?\n• Why are there two types of planets?\n• How do the planets in our solar system differ?\n• What are asteroids and comets?\n• What is the difference between a planet and a dwarf planet?\n• Why is life possible on Earth?\nOur solar system includes the Sun and all the objects that orbit around the Sun.\nAs you will find out, a variety of objects are in orbit around the Sun: eight\nplanets, many dwarf planets, asteroids, Kuiper Belt objects and comets.\n.\n1.1 The Sun\n.\nNEW WORDS\n• solar system\n• star\n• nuclear fusion\n• convection\n• sunspot\n• solar wind\nBefore we look at the Sun close up, let's summarise what you learned about the\nSun in Grades 6 and 7:\n1. The Sun is our closest star and is very important for life on Earth as it\nprovides us with light and heat.\n2. The Sun is located at the very centre of our solar system.\n3. The Earth and other planets all orbit around the Sun, held in orbit by the\nforce of gravity.\n.\nVISIT\nSecrets of a dynamic Sun\n(video)\nbit.ly/1h0io4b\nWhat do you think the Sun would look like if it was further away, like the other\nstars we see at night?\nLet's look at the Sun in more detail.\n\nAn image of the Sun taken with the SOHO space satellite.\n.\nTAKE NOTE\nIt is very important that\nyou do not look at the\nSun directly! The Sun\ncan damage your eyes\npermanently!\n.\nVISIT\nThe birth of the solar\nsystem (video)\nbit.ly/1i8Bfrx\n.\nVISIT\nHow the Sun works.\nbit.ly/1gy769C\nDo you know what the Sun is made of? The Sun is mostly made up of hydrogen\ngas (about 71%), and also helium gas (about 27%) with a tiny amount of other\ngases. The temperature at the Sun's surface is very high, around 5500 oC.\nHowever, that is nothing compared to deep inside the Sun. At the Sun's centre,\nor core, it is about 15 million oC. It is so hot at the Sun's centre that nuclear\nreactions can occur, which change atoms from one element to another. In the\nSun's case, four hydrogen nuclei are squeezed or fused together to form a new\nhelium nucleus. This process is called nuclear fusion.\nThis nuclear fusion reaction releases energy because the new helium nuclei\nproduced have very slightly less mass than the four hydrogen nuclei used to\nmake them. How can this be? Well, according to the famous scientist Albert\nEinstein, energy and mass are equivalent. Some of the mass in the hydrogen\nnuclei is converted and released as energy when the nuclei fuse to make helium.\nA very large amount of energy is released. This energy travels outwards from\nthe Sun's core towards its surface. The energy eventually reaches the Sun's\nsurface somewhere between 17,000 and 100,000 years later! The Sun's energy\nthen spreads out into the solar system in the form of heat and light.\nYou are now going to observe the Sun to look at its surface features.\nRemember, you should never look directly at the Sun as it can permanently\ndamage your eyes. You can use either a telescope with a filter on it or a pinhole\nto project an image of the Sun onto a screen to safely view the Sun's image.\n.\n.\n145\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing the Sun using a telescope\n.\nMATERIALS:\n• telescope\n• white card\n• chair to rest the card on\n• cardboard to make a shade collar\n• pair of scissors\n• pencil\n.\nVISIT\nInteract with this\nsimulation to visualize the\neffects of gravity on\norbital paths of the Sun,\nEarth and Moon.\nbit.ly/1a2mJCL\n.\nTAKE NOTE\nNEVER look directly at\nthe Sun, even with\nsunglasses on as you\ncan permanently\ndamage your eyes.\nINSTRUCTIONS:\n1. Take a piece of cardboard and place it up against the narrowest end of the\ntelescope.\n2. Draw an outline around the edge of the telescope on the card to use as a\nguide for cutting to make the collar.\n3. Cut out inside the circle you just drew so that the cardboard can fit over\nthe telescope as shown in the figure above. You can cut a single slit into\nthe circle from the edge of the card as shown in the diagram\n4. Place the collar on the telescope. Adjust the size of the cut out circle if\nnecessary (for example if your telescope is slightly wider in the middle\nthan at the end, you may want to make your circle slightly larger). This\ncollar shades the area, where the image will fall, from stray light.\n5. Select the lowest magnification eyepiece lens you have and insert it into\nthe telescope's eyepiece.\n6. Focus the telescope by looking at a distant object (NOT the Sun).\n7. Point the telescope at the Sun (do NOT look through the telescope to do\nthis).\n8. Place a chair behind the telescope and rest a white piece of card on it. The\ncard should be tilted towards the telescope.\n9. Adjust the direction in which the telescope is pointing until the image of\nthe Sun appears on the white paper card. This may take some time.\n10. Keeping the telescope still, move the white card toward or away from the\neyepiece until the image of the Sun fits neatly in the middle of the card.\n..\n146\n.\nPlanet Earth and Beyond\n\n.\nAdjust the chair's position as needed.\n11. Adjust the tilt of the white card until the Sun's image is circular.\nQUESTIONS:\n1. Looking carefully you should see that the Sun's image moves slowly across\nthe white card. What causes this motion?\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n.\n.\nTAKE NOTE\nRevise the model of the\natom that you learned\nabout in Matter and\nMaterials if you are\nunsure of some of the\nterms used here, such\nas nucleus, which is at\nthe centre of an atom,\nand consists of protons\nand neutrons.\nAlternatively, if you do not have access to a telescope or binoculars, you can\nperform the following activity to view the Sun.\n.\nACTIVITY: Observing the Sun with a pinhole\ncamera\n.\nIn this activity you will reflect an image of the Sun onto a white card or screen\nfor your learners to observe. This method has the advantage of not needing a\ntelescope or binoculars, however, the solar image produced will be a bit fuzzy.\nHowever, it should be good enough to show large sunspots. This activity is\ndesigned as a teacher-led demonstration. If you have a sunlit window or door to\nyour class you can do this activity in the classroom. If you do not have a\nclassroom with a sunlit window, or if your class is very small, you can do the\nactivity outdoors, reflecting the Sun's image onto a shaded wall or back into a\ndarkened classroom.\n.\n.\n147\n.\nChapter 1.\nThe solar system\n\n.\n.\nVISIT\nThree years of the Sun in\nthree minutes.\nbit.ly/19nCfGu\nAs a rough guide, begin with a distance of around 8 m between the white card\nand the mirror. The further away you place the mirror from the white screen the\nfainter and larger the image will appear. At closer distances the image will be\nbrighter but it may not be in very good focus.\n.\nVISIT\nWhere does the Sun get\nits energy?\nbit.ly/1azFmsM\nAs mentioned in the previous activity, sunspots are sometimes (not always)\nvisible on the Sun's surface. Therefore, you could repeat this activity over the\ncourse of several days to see if any sunspots or sunspot groups change shape,\nsize, or position over time.\nMATERIALS:\n• small pocket mirror or hand mirror\n• piece of plain cardboard (or paper) to fit over the mirror (or alternatively\ntape)\n• white cardboard screen\n• bin bags or curtains for darkening the classroom\n.\nVISIT\nE = mc2 explained (video).\nbit.ly/16mVFNI\nMETHOD:\n1. Cut the plain cardboard or paper so it fits over the mirror.\n2. Cut or punch a very small hole, about 5 mm, in the middle of the plain\ncardboard.\n3. If you do not have cardboard, you can use tape to cover all but a small\nportion of the surface of the mirror.\n4. Place the mirror on a window sill in the Sun and tilt it so that it catches the\nsunlight and reflects it into the classroom. If your classroom is very small,\nplacing the mirror outside on a chair may be a better option in order to get\na larger image.\n5. Darken the classroom using curtains or bin bags, excluding where the\nmirror is.\n6. Reflect the sunlight from the mirror onto a wall of the darkened room.\n7. Put the white cardboard or paper on the wall where the reflected light\nshowing the Sun's image falls.\n8. Observe the image of the Sun.\n..\n148\n.\nPlanet Earth and Beyond\n\n.\n9. Remove the white cardboard from the wall and take three steps towards\nthe mirror with the cardboard still facing the mirror. Note what happens to\nthe image of the Sun on the cardboard.\nQUESTIONS:\n1. As you moved the white cardboard screen closer towards the mirror, what\ndid you notice happened to the image of the Sun?\n.\nDID YOU KNOW?\nAlbert Einstein\nexplained the\nmass-energy\nequivalence with the\nfamous equation\nE = mc2.\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n3. When the Sun reflects off the surface of the mirror, what can you say about\nthe angle of incidence and the angle of reflection of the ray?\n.\nDid you notice any features on the Sun's surface when you viewed it in class?\nLet's find out what some of these surface features could have been in the next\nactivity.\n.\nVISIT\nFiery looping rain on the\nSun (video)\nbit.ly/16qmriQ\n.\n.\n149\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing sunspots on the Sun's\nsurface\n.\nINSTRUCTIONS:\n1. Look at the images of the Sun which were taken in June 2013.\n2. Answer the questions that follow.\nA: DATE: 02.06.2013\n.\nVISIT\nLearn more about the\nresearch that NASA is\ndoing about our Sun with\nthe Solar and Heliospheric\nObservatory (SOHO).\nbit.ly/1fQhd8u\nB: DATE: 03.06.2013\n..\n150\n.\nPlanet Earth and Beyond\n\n.\nC: DATE: 04.06.2013\nQUESTIONS:\n.\nTAKE NOTE\nThis information about\nthe Sun's surface and\nsunspots is additional\ninformation for your\ninterest. Be curious and\ndiscover more!\n1. How many groups of dark spots do you see in each image?\n2. What do you notice about the positions of the spots in each image?\n3. Why do you think the spots have moved?\n4. What do you think these spots are?\n.\nSunspots and the Sun's surface\nThe Sun's surface often has little blemishes on it. These dark spots on the Sun\nare called sunspots. They are areas that are slightly cooler than the rest of the\nSun's surface. The Sun's surface is typically about 5500 oC and a typical\nsunspot has a temperature about 3900 oC.\n.\n.\n151\n.\nChapter 1.\nThe solar system\n\nImage of a sunspot. For perspective, take note of the size of the Earth in the lower left.\n.\nVISIT\nView real time images of\nthe Sun and track\nsunspots.\nbit.ly/19ZoU6c\nAs the Sun is made up of gas, there is no solid surface like on Earth. So when\none says that you are looking at the Sun's surface what are you actually looking\nat? Imagine that you are standing in thick fog (mist) with a friend. You can see\nthings close to you, like your hand in front of you and your friend standing next\nto you. However, because the fog is so thick you cannot see far into the\ndistance. Similarly, when we look at the Sun, we cannot see right into the centre\nof the Sun. As you go deeper and deeper in towards the centre of the Sun the\ngas begins to get thicker and thicker so that we cannot see through it. The\ndeepest depth that we can see into the Sun's gas is what we call the Sun's\nsurface.\nSunspots are areas that are slightly cooler, and therefore darker, than the rest of\nthe Sun's surface. A typical sunspot only lasts a few days. When a sunspot lasts\nfor several days you can observe it move across the Sun's disc. The sunspot\nappears to move across the Sun because the Sun is spinning slowly on its own\naxis.\n.\nDID YOU KNOW?\nThe number of sunspots\non the Sun increases\nand decreases in a\nregular pattern which\nrepeats every 11 years.\nWhen there are more\nsunspots the Sun is\nmore active and there\nare more solar storms\nand more of the Sun's\nenergy reaches the\nEarth.\nThe outer atmosphere of the Sun is called the corona. Gas particles from the\ncorona are constantly escaping into space, forming the solar wind. When the\nSun is very active, violent eruptions called solar flares occur on its surface.\n..\n152\n.\nPlanet Earth and Beyond\n\nA large loop of gas extending over 35 Earth diameters out from the Sun's surface.\n.\n1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.\n1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.\nChapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "8" }, { "title": "Series circuits", "content": "", "chapter_id": "3.1" }, { "title": "Parallel circuits", "content": "3.2 Parallel circuits\n.\nNEW WORDS\n• parallel circuit\nParallel circuits offer more than one pathway for the electrons to follow. When\nconstructing a parallel circuit, we say that components are connected in\nparallel.\nLook at the diagram which shows how two light bulbs are connected in parallel.\nThere are two paths for the current in this parallel circuit, one path through each of the\nbulbs.\nHow can you tell whether or not a circuit is connected in series or in parallel?\nLet's look at some circuit diagrams to tell the difference.\n.\nVISIT\nWatch a video that\nexplains the difference\nbetween series and\nparallel circuits\nbit.ly/1f5hZ0W\n.\nACTIVITY: Series or parallel?\n.\nINSTRUCTIONS:\nLook at the following circuits and write down which are in series and which are\nin parallel. The series circuits will only offer one pathway, but the parallel\ncircuits will have more than one pathway for the electrons to follow.\n.\n.\n63\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\nLet's investigate how parallel circuits work.\n.\nINVESTIGATION:\nHow does adding resistors in\nparallel affect the current strength?\n.\nAIM: To investigate the effect of adding resistors in parallel on the current\nstrength.\nHYPOTHESIS: Write a hypothesis for this investigation.\n..\n64\n.\nEnergy and Change\n\n.\nMATERIALS AND APPARATUS:\n• 1,5 V cell\n• three identical torch bulbs\n• insulated copper conducting wires\n• switch\n• ammeter\nMETHOD:\n1. Construct the circuit with the cell, ammeter, one bulb and the switch in\nseries.\n2. Close the switch.\n3. Note how brightly the bulb is shining and record the ammeter reading.\nDraw a diagram of your circuit.\n.\n4. Open the switch.\n5. Add another light bulb, in parallel to the first, into the circuit.\n6. Close the switch.\n7. Note how brightly the bulbs are shining and record the ammeter reading.\n8. Open the switch.\n9. Add the third light bulb, in parallel to the first two, into the circuit.\n10. Close the switch.\n11. Note how brightly the bulbs are shining and record the ammeter reading.\nRESULTS:\nComplete the table:\nNumber of bulbs in\nparallel\nBrightness of bulbs\nReading on ammeter\n(A)\n1\n2\n3\n.\n.\n65\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nDraw a graph to show the relationship between the number of bulbs and the\ncurrent.\n.\nANALYSIS:\n1. What happened to the brightness of the bulbs as the number of bulbs\nincreased?\n2. When you had two bulbs, did they glow with the same brightness or was\none brighter than the other?\n3. When you had three bulbs, did they glow the same brightness or was one\nbrighter than the others?\n4. What do your answers to the previous questions tell you about the current\nin the parallel branches of the circuit?\n5. What happened to the reading on the ammeter as you added more bulbs\nin parallel?\n..\n66\n.\nEnergy and Change\n\n.\nCONCLUSION:\n1. Based on your answers, what happened to the current when more bulbs\nwere added in parallel?\n2. Is your hypothesis true or false?\n.\nAs more resistors are added in parallel, the total current strength increases. The\noverall resistance of the circuit must therefore have decreased. The current in\neach light bulb was the same because all the bulbs glowed with the same\nbrightness. This tells us that the current of electrons must have split up and\nmoved through each of the branches.\nWe can also connect cells in parallel. What would happen if we increased the\nnumber of cells connected in parallel? Would the current get stronger or\nweaker?\n.\nINVESTIGATION:\nWhat happens to the current\nstrength when cells are connected\nin parallel?\n.\nAIM: To investigate how increasing the number of cells connected in parallel\naffects the current strength in a circuit.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS\n• three 1,5V cells\n• one torch light bulb\n• insulated copper conducting wires\n• ammeter\nMETHOD:\n1. Set up a circuit which has one cell, the ammeter and the torch light bulb in\nseries with each other. Draw a circuit diagram of your circuit.\n.\n.\n67\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n.\n2. Observe the brightness of the bulb and record the ammeter reading.\n3. Connect another cell in parallel with the first cell. To connect the second\ncell in parallel, connect a wire from the positive terminal of the first cell to\nthe positive terminal of the second cell. Connect another wire between the\nnegative terminal of the first battery and the negative terminal of the\nsecond battery. Draw a circuit diagram of your circuit.\n.\n4. Observe the brightness of the bulb and record the ammeter reading.\n5. Connect a third cell in parallel to the other two cells. Draw a circuit\ndiagram of your circuit.\n.\n6. Observe the brightness of the bulb and record the ammeter reading.\n..\n68\n.\nEnergy and Change\n\n.\nRESULTS:\nComplete the table:\nNumber of cells in\nparallel\nBrightness of bulb\nReading on ammeter\n(A)\n1\n2\n3\nCONCLUSION:\n1. What did you notice about the brightness of the bulbs?\n2. What did you notice about the ammeter readings?\n3. What conclusion can you draw from your results?\n.\nAdding cells in parallel has no overall effect on the current strength. The current\nstrength stays the same if you add cells in parallel.\nWe saw that the current strength increased when bulbs were connected in\nparallel. However, we were only testing the current strength at one point in the\nparallel circuit. How does the current compare in the different pathways of the\ncircuit? Let's do an investigation to find out.\n.\nINVESTIGATION:\nTesting the current strength\n.\nINVESTIGATIVE QUESTION: Is the current strength equal at all points in a\nparallel circuit?\nMATERIALS AND APPARATUS:\n• insulated copper connecting wires.\n• two 1,5V cells\n• three identical torch light bulbs\n• ammeter\n.\n.\n69\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nMETHOD:\n1. Set up a parallel circuit with two cells in series with each other and three\ntorch light bulbs in parallel with each other.\n2. Insert an ammeter in series between the cells and the first pathway, as\nshown in the diagram.\n3. Measure the current strength using the ammeter.\n4. Remove the ammeter and close the circuit again.\n5. Insert the ammeter in series in the first pathway.\n6. Measure the current strength using the ammeter.\n7. Remove the ammeter and close the circuit again.\n8. Insert the ammeter in series in the second pathway.\n9. Measure the current strength using the ammeter.\n10. Remove the ammeter and close the circuit again.\n11. Insert the ammeter, in series, in the third pathway.\n..\n70\n.\nEnergy and Change\n\n.\n12. Measure the current strength using the ammeter.\n13. Remove the ammeter and close the circuit again.\n14. Insert the ammeter in series between the first pathway and the cells on the\nopposite side to the first reading.\n15. Measure the current strength using the ammeter.\nRESULTS:\nPosition of ammeter in\ncircuit\nAmmeter reading (A)\nbetween the cell and first\npathway\nin the first pathway\nin the second pathway\nin the third pathway\nbetween the cell and the\nfirst pathway\nCONCLUSION:\n1. Write a conclusion based on your results.\n2. Is your hypothesis true or false?\n.\n.\n.\n71\n.\nChapter 3.\nSeries and parallel circuits\n\nWhat have we learned about parallel circuits?\n• There is more than one pathway for the current to follow.\n• The current divides between the different branches so that each branch\ngets some of the current. As the torch bulbs in each branch in our example\nwere identical, the current divided equally between them.\n• If you add more resistors in parallel, the total current supplied by the cell in\nthe circuit increases.\nWhy does the current divide when offered an alternative pathway?\nImagine that you are sitting in a school hall during assembly. You are bored and\nwaiting for it to end so that you can go out to break to chat to your friends.\nThere is only one exit from the hall. When you are dismissed, everyone has to\nexit through the same door. It takes a while because only some learners can\nleave at a time.\nNow imagine that there is a second door that is the same as the first door. Now\nyou and your friends have a choice of which door to go through. The speed at\nwhich the learners exit the hall will increase and some of you will exit through\nthe first door while others will exit through the second door. No one can go\nthrough both doors at the same time.\nThis is similar to the way current behaves when in a parallel circuit. As the\nelectrons approach the branch in the circuit, some electrons will take the first\npath and others will take the other path. The current is divided between the two\npathways.\nIn the following circuit A1 = A4 and A1 = A2 + A3 and A4 = A2 + A3\nWe have looked at how resistors and cells behave in series and parallel circuits.\nLet's look at how different metals conduct electricity. All conductors have some\nresistance in a circuit. Are some metals better conductors of electricity than\nothers?\nLet's have a look at which metals offer more resistance than others to the flow\nof charge (current) through an electric circuit .\n..\n72\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Which metals offer the most\nresistance?\n.\nMATERIALS:\n• a cell\n• torch light bulb\n• insulated copper wires\n• lengths of copper, aluminium, zinc and nichrome wire\n• crocodile clips (if available)\nINSTRUCTIONS\n1. Build a circuit with the cell and the torch light bulb and leave a gap for the\nmetal to be tested. You can use crocodile clips at the end of each piece of\nmetal for easy insertion.\n2. Insert each metal into the circuit (one at a time).\nAn example circuit with a cell, a light bulb and the piece of metal being tested.\nObserve the brightness of the bulb.\nQUESTIONS:\n1. Draw a circuit diagram of your apparatus.\n.\n.\n.\n73\n.\nChapter 3.\nSeries and parallel circuits\n\n.\n2. Why can we use the brightness of the bulb to qualitatively measure\nresistance?\n3. List the metals in order of increasing resistance.\n4. Why do you think copper is used for connecting wires in electrical circuits?\n.\nThere are several factors which influence the amount of resistance a material\noffers to an electric current. We have seen that the type of material is one of\nthose factors.\n.\nTAKE NOTE\nIn Gr. 9 we will look at\nthe other factors that\ninfluence resistance. If\nyou want to see the\ncontent in other grades,\nremember that you can\nvisit\nhttp://www.\ncurious.org.za\n.", "chapter_id": "3.2" }, { "title": "Other output devices", "content": "3.3 Other output devices\nLight bulbs are not the only devices used in electrical circuits. Devices that use\nelectrical energy to function, including light bulbs, are called output devices.\nLet's look at some other common examples of output devices.\nLEDs (Light-Emitting Diodes)\nLEDs are widely used electronic devices. They are small lights but they do not\nhave a filament like an incandescent bulb has. They therefore cannot burn out,\nas there is no filament to wear out, and they do not get as hot. LEDs are used in\nelectronic timepieces, high definition televisions and many other applications.\nLarger LEDs are also replacing traditional light bulbs in many homes because\nthey do not use as much electricity. They last longer than incandescent bulbs\nand are more efficient.\n.\nVISIT\nWatch this video about\nthe history of the LED\nbit.ly/1bC5qKc\n..\n74\n.\nEnergy and Change\n\nDifferent LED bulbs.\nIn the last chapter, we looked at the energy transfers in an electrical system. We\nwill now represent energy transfer within electrical systems in a different way.\nWe will apply this new representation to the difference between energy outputs\nin an LED and an incandescent light bulb.\n.\nVISIT\nVideo on drawing a basic\nSankey diagram.\nbit.ly/19Wwxsu\n.\nACTIVITY: Sankey diagrams\n.\nYou might have drawn Sankey diagrams in Grade 7. If not, here is some quick\nrevision.\nIn an energy system, input energy is transferred to useful output energy and\nwasted output energy. A Sankey diagram is a visual and proportional\nrepresentation of the energy transfers that happen in a system.\nFor example, a kettle uses about 2000 J of input energy, but only about 1400 J\nis used to heat the water. The remaining 600 J is wasted as sound. Here is the\nSankey diagram to represent the energy transfer.\n.\nTAKE NOTE\nRemember that energy\nis measured in joules\n(J).\n.\n.\n75\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nQUESTIONS:\nWe will now compare an LED with an incandescent light bulb.\n1. Draw a Sankey diagram for an LED if the input energy is 100 J, 75 J of\nenergy is used to produce light and the rest is lost as heat.\n.\n.\nVISIT\nAn electricity timeline\nanimation.\nbit.ly/1fKZb8E\n2. Draw a Sankey diagram for a filament light bulb if the input energy is 100 J,\nthe wasted heat energy is 80 J and the rest produces light.\n.\n3. Which bulb do you think is more efficient? Explain your answer.\n.\nCan you think of any other output devices? Make a list of as many as you can.\n..\n76\n.\nEnergy and Change\n\n.\n.\nACTIVITY: History of electricity production\n.\nINSTRUCTIONS:\n1. Work in groups of three or four.\n2. Research the history of electricity production: How was electricity\ndiscovered and how did electricity become widely used?\n3. Create a basic timeline for the discovery of electricity and it's production.\n.\n.\nACTIVITY: Careers\n.\nINSTRUCTIONS:\n1. Choose a career related to electricity production.\n2. Write a short paragraph describing the career. Include information on how\none can study or prepare for your chosen career.\n.\n.\n.\n77\n.\nChapter 3.\nSeries and parallel circuits\n\n..\nSUMMARY:\n.\nKey Concepts\n• A series circuit has only one pathway for the electrons to travel through.\n• A parallel circuit has more than one pathway for the electrons to travel\nthrough.\n• In a series circuit, the current is the same at all points in the circuit.\n• In a series circuit, the resistance increases as more resistors are added\nin series.\n• In a parallel circuit, the current splits between the available paths.\n• In a parallel circuit, the resistance decreases as more resistors are added\nin parallel.\n.\nConcept Map\nComplete the concept map on the following page to summarise what you\nhave learned about series and parallel circuits.\n..\n78\n.\nEnergy and Change\n\n.\n\n.\n.\nREVISION:\n.\n1. Look at the following circuit diagrams and decide whether they are series\ncircuits or parallel circuits. Write the correct answer in the space below\neach diagram. [6 marks]\n2. Look at the three circuit diagrams. Rank the circuits from brightest bulb to\ndimmest bulbs. [3 marks]\n..\n80\n.\nEnergy and Change\n\n.\n3. Explain your choices in the previous question. [5 marks]\n4. Look at the three circuit diagrams. Rank the circuits from brightest bulb(s)\nto dimmest bulb(s). [3 marks]\n5. Explain your choices in the previous question. [5 marks]\n6. Look at the circuit diagram below. Each light bulb is identical.\na) Is this a series or parallel circuit? Explain your answer. [2 mark]\nb) How do the brightness of bulbs A, B and C compare? (which is the\nbrightest?) [3 marks]\n.\n.\n81\n.\nChapter 3.\nSeries and parallel circuits\n\n.\nc) What would happen to the brightness of the bulbs if the switch was\nopened? Explain your answer. [5 marks]\n7. Study the following diagram.\na) What is the relationship between the ammeter readings on A1 and A4?\nIn other words, how do the current strengths compare at these points\nin the circuit? Explain your answer. [3 marks]\nb) What is the relationship between the ammeter readings on A1, A2 and\nA3? In other words, how do the current strengths compare at these\npoints in the circuit? Explain your answer. [3 marks]\nTotal [38 marks]\n.\n..\n82\n.\nEnergy and Change\n\nDraw and discover the possibilities of what a slinky can be.\n.\n.\n83\n.\nChapter 3.\nSeries and parallel circuits\n\n. .\n4\n.\nVisible light\n..\n84\n..\nKEY QUESTIONS:\n• Where does light come from?\n• How does light travel?\n• How do we see?\n• Why do leaves look green?\n• How do mirrors work?\n• Why do my legs look crooked underwater?\nIn this chapter we will learn about visible light. We call it visible light because\nwe can see it with our own eyes. There are different forms of light which we\ncannot see with our naked eyes. Ultraviolet light is an example of a form of light\nwhich we cannot see with just our eyes. We will focus our attention on the\nvisible light spectrum and investigate how we are able to see different colours\nand how light behaves.\n.\n4.1 Radiation of light\nWhere does light come from? Natural light comes from luminous objects such\nas the Sun and light bulbs. We say that these objects emit light.\nThe Sun is our main source of light on Earth.\nA light bulb is a luminous object as it emits\nlight.\n.\nNEW WORDS\n• luminous\n• radiation\n• rectilinear\n• propagation\n.\nVISIT\nThe speed of light (video)\nbit.ly/GAMgFW\n\nThis image from NASA shows the Earth's lights at night. You can see how much we rely\non light nowadays.\n.\nDID YOU KNOW?\nIf you could travel at the\nspeed of light you could\ntravel around the\nequator 7,5 times in 1\nsecond!\n.\nTAKE NOTE\nThe Moon is NOT a\nluminous object as it\ndoes not emit its own\nlight light. It reflects the\nlight from the Sun.\nLight travels through space at a speed of 300 000 kilometers per second. We\nsay that energy is transferred by radiation. The energy of the light is transferred\nthrough space as electromagnetic waves in straight lines.\nLight and heat are transferred to Earth through space from the Sun by radiation.\n.\nDID YOU KNOW?\nIt takes light 8 minutes\nto travel from the Sun to\nthe Earth.\nLet's look at how light travels. We will make a simple camera to investigate how\nlight travels.\n.\n.\n85\n.", "chapter_id": "3.3" }, { "title": "Visible light", "content": "Chapter 4.\nVisible light\n\n.\n.\nACTIVITY: Make a pinhole camera\n.\nMATERIALS:\n• Pringles chip can\n• craft knife\n• aluminium foil\n• tape\n• ruler\n• drawing pin\nINSTRUCTIONS:\n.\nTAKE NOTE\nThe Sun emits radiation\nin all directions, but in\nthe diagram here, only\nthe radiation which\nreaches Earth has been\nshown.\n1. Measure 5 cm from the bottom of the can (opposite end to the plastic lid)\nand make a mark all around the can.\n2. Cut through the can along the line\nso that you have cut the can into 2\npieces.\n3. If you have a clear lid, put a piece of\nwax paper on top of the lid before\nsticking everything together.\n..\n86\n.\nEnergy and Change\n\n.\n4. Place the lid between the 2 pieces\nand stick it all together using tape.\n5. Wrap the aluminium foil around the\ncan to prevent any light from\ncoming in from the sides.\n6. Use a drawing pin to make a hole in the centre of the metal base of the can.\n7. Go outside with your pinhole camera.\n8. Point the metal end with the hole at an object which is in bright sunlight.\n9. Cup your hands around the other end and look through the open end.\nQUESTIONS:\n.\nVISIT\nLight travels in a straight\nline? (video)\nbit.ly/19n4T7g and\nbit.ly/174q6mx\n1. What did you see when you looked through the open end of the tube?\n2. What happens when you move closer or further away from an object?\n.\nDid you see an upside down image? Why is it upside down?\nWe see objects because light reflects off them and enters our eyes. If the image\nis upside down it means that the light from the bottom of the object has arrived\nat the top of the screen and the light from the top of the object has reached the\nbottom of the screen, as shown in the following diagram.\n.\n.\n87\n.\nChapter 4.\nVisible light\n\nWhen you moved closer to the object, the image appeared bigger, as shown in\nthe following diagram.\nWhat does this mean? It means that light must be travelling in straight lines.\nThis is called the rectilinear propagation of light.\n.\nVISIT\nCan you use what you\nhave learnt to understand\nhow this shadow illusion\nworks?\nbit.ly/156mx1y\nRay diagrams\nA ray diagram is a drawing that shows the path of light. Light rays are drawn\nusing straight lines and arrowheads, because light travels in straight lines. The\nfigure below shows some examples of ray diagrams.\n..\n88\n.\nEnergy and Change\n\nA ray diagram showing how you see\nanother person.\nA ray diagram showing how you see a\nreflection in a mirror.\n.\n4.2 Spectrum of visible light\n.\nNEW WORDS\n• composition\n• visible spectrum\n• dispersion\nThe visible light spectrum is the light that we are able to see with our naked\neyes. Have you ever wondered why everything is colourful and not just black\nand white? Have you ever seen a rainbow and wondered where the colours\nhave come from? The colours that we see everyday are part of the visible light\nspectrum. Let's investigate the visible light spectrum.\n.\nACTIVITY: Splitting white light\n.\nMATERIALS:\n• triangular perspex prism\n• ray box and power source\nINSTRUCTIONS:\n1. Connect the ray box to the power source. If you do not have a ray box,\nyour teacher will show you how to use a piece of cardboard with a slit cut\ninto it.\n2. Place the triangular prism on a white background.\n3. Shine a beam of white light through the side of the prism.\nQUESTIONS:\n1. Draw a picture showing what you observe.\n.\n.\n89\n.\nChapter 4.\nVisible light\n\n.\n.\n2. Write a description of what you observed.\n3. Write down the order in which the colours appear.\n4. If you repeat the experiment, does the order of the colours change?\n5. What do the different colours we see tell us about the composition of\nwhite light?\n.\n..\n90\n.\nEnergy and Change\n\nSo, what have we learned so far? Light radiates from luminous objects and\nalways travels in straight lines. The white light that we see is made up of the 7\ndifferent colours of the spectrum. When the 7 colours are travelling together we\nsee them as white light.\nThe 7 colours of the visible spectrum are Red, Orange, Yellow, Green, Blue,\nIndigo and Violet. Each colour has a different wavelength and frequency. Have\na look at the following image which shows the spectrum of visible light.\n.\nTAKE NOTE\nYou can use the\nabbreviation ROYGBIV\nto remember the order\nof the colours.\nThe colours combine to form white light.\n.\nTAKE NOTE\nThe primary colours of\nlight are red, green and\nblue.\n.\nACTIVITY: Colour spinning wheels\n.\nMATERIALS:\n• white cardboard\n• coloured pens or pencils (red, orange, yellow, green, blue, indigo, violet)\n• string\n• scissors\n• round object\nINSTRUCTIONS:\n1. Draw a circle on the cardboard. You can trace around a round object such\nas a cup or saucer to do this. Cut out the circle.\n.\n.\n91\n.\nChapter 4.\nVisible light\n\n.\n2. Now divide the circle into 7 equal segments. If you do not have indigo and\nviolet colours, but just one purple pen or crayon, then you can divide the\ncircle into 6 equal segments rather.\n3. Shade in each segment a different colour, in the order red, orange, yellow,\ngreen, blue, indigo, violet (or just purple if you do not have indigo and\nviolet).\n.\nDID YOU KNOW?\nAn artist might tell you\nthat the primary colours\nof paint are red, yellow\nand blue. This is\ndifferent to the primary\ncolours of light. This is\nbecause the pigments\nyellow, blue and red\ncannot be mixed from\nother pigments. In\nprinting, the primary\ncolours are magenta,\nyellow and cyan.\n4. Next, make two holes, one on either side of the centre as shown below.\n5. Thread the string through the holes and tie it in a loop.\n6. You are now ready to spin the wheel. Holding the ends of the loop in each\nhand, twirl the string over, like you would a skipping rope, so that the\nstring twists. Once the string is tightly twisted, pull your hands apart, then\nbring them back together. Continue bringing your hands in and out and\nwatch the circle spin.\n.\nVISIT\nThere is no pink light.\nbit.ly/1b2gFXU\n7. What do you observe about the colour of the wheel as it spins faster?\n.\n..\n92\n.\nEnergy and Change\n\nSo far we have been talking about the visible light spectrum. As we mentioned\nin the beginning, this is the light that we can see. We also spoke about how light\ntravels in electromagnetic waves. We can only see light with a certain range of\nwavelengths. What does this mean?\n.\nDID YOU KNOW?\nWavelengths can be as\nsmall as one billionth of\na meter, as with gamma\nrays. Wavelengths can\neven be as long as\nmeters, for example in\nradio waves.\nThe size of a wave is measured in wavelengths. A wavelength is the distance\nbetween two corresponding points on two consecutive waves. Normally this is\ndone by measuring from peak to peak or from trough to trough. Have a look at\nthe following diagram which illustrates a wavelength.\n.\nDID YOU KNOW?\nIn police forensics,\nultraviolet light can be\nused along with a\nspecial powder to\ndetect finger and shoe\nprints that can help\nsolve crimes.\nThe wavelengths of the different colours of visible light are different lengths, as\nshown in the following diagram.\nWe can also talk about the frequency of a wave. If a wave has a long\nwavelength, then it has a low frequency; if it has a short wavelength, then it has\na high frequency.\nOf visible light, orange and red light have the longest wavelengths (and lowest frequency)\nand violet, indigo and blue have the shorter wavelengths (and highest frequency).\n.\n.\n93\n.\nChapter 4.\nVisible light\n\nWhen it comes to visible light, we only see wavelengths of 400 to 700 billionths\nof a meter. This is called the visible spectrum. But, light waves are just part of\nthe wave spectrum. There is invisible light with shorter wavelengths, such as\nultraviolet light, and there are longer wavelengths, such as infrared light.\nHave you ever looked through a window and wondered why it is made of glass?\nLet's find out how light behaves when it strikes the surface of different types of\nmaterials in the next section.\n.\n4.3 Opaque and transparent substances\n.\nNEW WORDS\n• opaque\n• transparent\n• translucent\n• transmit\nThree different things happen when light hits a surface, it can be reflected\n(bounce off), absorbed or transmitted (pass through). Glass reflects some light\nbut most of the light is transmitted straight through. That's why we can see\nobjects on the other side of a closed window.\nWe say that glass is transparent. Let's find out more about what this means. If a\nsubstance is not transparent, it is opaque.\n.\nACTIVITY: Shadow Play\n.\nMATERIALS:\n• cardboard\n• clear plastic\n• plastic shopping bag\n• scissors\n• light source (ray box or light bulb)\nINSTRUCTIONS:\n1. Cut out three shapes from your cardboard. All of the shapes should be\nsimilar but three different sizes: small, medium and large.\n2. Switch on the light source.\n3. Hold your first shape a short distance in front of the light source.\n4. Look at the shadow that forms. Write down what you observe.\n5. Hold your second shape the same distance in front of the light source.\n6. Look at the shadow that forms. Write down what you observe.\n7. Hold your third shape the same distance in front of the light source.\n8. Look at the shadow that forms. Write down what you observe.\n9. The shadow is formed on the side furthest from the light source. It is dark\n..\n94\n.\nEnergy and Change\n\n.\nin colour and larger than the first and second shadows.\n10. Use your first cardboard shape as a template and cut the shape from the\nclear plastic and the plastic shopping bag.\n11. Hold the clear plastic shape the same distance from the light source. Write\ndown what you observe.\n12. Hold the plastic shopping bag shape the same distance from the light\nsource. Write down what you observe.\nQUESTIONS\n1. When you held the cardboard up to the light, did it allow light to pass\nthrough it? How do you know this?\n2. Is the cardboard shape opaque or transparent?\n3. What did you notice about the shadows formed by the different size\ncardboard shapes?\n4. Draw a diagram to show how the shadow is formed behind the opaque\nshape. Use straight lines with arrowheads to represent the rays of light.\n.\n.\n.\n95\n.\nChapter 4.\nVisible light\n\n.\n5. The distance between the shape and the light source was kept the same.\nWhat do you think would have happened to the shadow if the distance\nwas increased?\n6. Test your idea from question 5 by moving your cardboard shapes closer to\nand further away from the light source. What do you see? Were you\ncorrect in your prediction?\n7. Is the clear plastic shape opaque or transparent?\n8. Did the clear plastic cast a shadow?\n9. Explain why the cardboard casts a shadow but the clear plastic does not.\n10. Is the plastic shopping bag shape opaque or transparent?\n11. Explain why the shopping bag casts a lighter shadow.\n.\n..\n96\n.\nEnergy and Change\n\nWhat have we learned? Shadows are formed because light travels in straight\nlines and cannot pass through opaque objects.\nSubstances which transmit most of the light and only absorb or reflect a little bit\nare called transparent. Can you list some everyday objects which are\ntransparent?\nSubstances which completely reflect or absorb light without transmitting any\nare called opaque. Can you list some everyday objects which are opaque?\nSome substances, such as the plastic shopping bag, allow some light to pass\nthrough, but not all of it. This substance is translucent, or semi-transparent.\nShadows can be useful. Sundials have\nbeen used since ancient times as a\ntime-keeping device, like a watch or a\nclock. As the position of the Sun\nchanges in the sky, the shadow cast by\nthe style moves across the surface of\nthe sundial. The surface is marked with\nnumbers, allowing the shadow to\nindicate time of day.\nWe can use transparent objects to make filters. If we want red light we use a\nred glass bulb or a red plastic film placed in front of the light. Only red light is\nable to transmit through the red glass or plastic. The other colours are absorbed\nby the filter.\nThese are different colour filters for a camera. The red filter will only allow red light\nthrough and so the photograph will have a red effect applied to it. The other colours of\nlight are absorbed by the filter.\nNow that we have seen some examples of transparent and opaque substances,\nlet's take a closer look at what it means to absorb or reflect light.\n.\n.\n97\n.\nChapter 4.\nVisible light\n\n.\n4.4 Absorption of light\nLook at this picture of a ladybird. Why\nis it red and black? And why is the leaf\nso green? How do we see the different\ncolours? It all has to do with what\nhappens when light hits a surface.\nWhen light hits a surface, some of the\nlight is absorbed and the rest is\nreflected. It is the reflected light that\nreaches our eyes and allows us to see\nthe object.\nA ladybird.\nPreviously, we learned that white light is a mixture of different colours. When\nwhite light from the Sun hits the red shell of the ladybird all of the colours are\nabsorbed, except red. Red light is reflected back to our eyes and so we see a\nred ladybird.\nWe see the red shell of the ladybird as red light is reflected and the other colours are\nabsorbed.\nThe green leaf absorbs all the colours except green which it reflects back into\nour eyes.\n..\n98\n.\nEnergy and Change\n\nWe see a green leaf as green light is reflected and the other colours are absorbed by the\nleaf's surface.\nWhat about the black spots of the ladybird? Is black a colour? The black spots\non the ladybird absorb all the colours and no light is reflected. That is why they\nappear black.\n.\nTAKE NOTE\nAlthough we can get\nblack paint as a\npigment, black is not a\ncolour of light. Black is\nthe result of the\ncomplete absorption of\nlight.\nDo you remember learning about heat as energy transfer in Gr 7? We looked at\nthe absorption of heat. We saw that black, matt objects absorbed all of the light\nenergy, while white objects reflected all of it. Black, matt (not shiny) objects\nabsorb all of the colours of light and reflect none and so appear black to our\neyes.\nWhat about a white object? Why do you think white objects look white? Have a\nlook at the following diagram for a clue.\n.\n.\n99\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Why do objects look red under red\nlight?\n.\nMATERIALS:\n• piece of red plastic to act as a filter\n• light source (light bulb or torch)\n• white object\nINSTRUCTIONS:\n1. Place a white object on the desk.\n2. Switch on your light source and place the red plastic in front of the light.\n3. Shine the light (with the red plastic in front) onto the piece of white paper.\nQUESTIONS:\n1. What colour was the page under normal light?\n2. Why does the page appear white in normal light?\n3. What did you see when the red plastic filter shone on the white page?\n4. Explain why the paper changed colour.\n.\nLet's now look more at what we mean by reflection of light.\n..\n100\n.\nEnergy and Change\n\n.\n4.5 Reflection of light\n.\nNEW WORDS\n• reflect\n• incident ray\n• reflected ray\n• normal line\n• angle of\nincidence\n• angle of\nreflection\n• perpendicular\nWhen light hits a surface it is\noften reflected off the surface.\nThis photograph shows how\nlight is reflected off a still lake,\ncreating a mirror image of the\ntree. The still, flat surface of the\nlake has acted as a mirror.\nA tree reflection.\nHave some fun with these photos of reflections in water. One photograph is the\nright way up and the other one is upside down! Which one is which?\nReflections on the Negro River in the\nAmazon.\nReflections in the Arno River in Italy.\nMost surfaces reflect light. When light strikes a reflective surface, it can change\ndirection. Let's look at how this happens.\nWhen light reflects off a surface the ray which hits the surface, it is called the\nincident ray. The ray of light which is reflected from the surface is called the\nreflected ray. When we draw diagrams of reflection we also draw in an\nimaginary line to help us measure different angles. This line is called the normal.\nThe normal line is always drawn perpendicular to the surface.\nBetween the normal line and the incident and reflected rays, there are two\nangles. These are:\n• angle of incidence - the angle between the incident ray and normal line\n• angle of reflection - the angle between the reflected ray and normal line\nThe following diagram explains these concepts.\n.\n.\n101\n.\nChapter 4.\nVisible light\n\nLet's investigate the relationship between the angle of incidence and the angle\nof reflection.\n.\nINVESTIGATION:\nIs there a relationship between the\nangles of incidence and reflections?\n.\nAIM: To investigate the reflection of light from a surface.\nINVESTIGATIVE QUESTION:\nLook at the diagram above and try to formulate an investigative question for\nthis investigation.\nHYPOTHESIS: The angle of incidence is equal to the angle of reflection\nMATERIALS AND APPARATUS:\n• mirror\n• white paper\n• pencil\n• protractor\n• ruler\n• ray box\nMETHOD:\n1. Put a white piece of paper on the desk.\n2. Use your ruler to draw a straight line near the top of the white paper.\n..\n102\n.\nEnergy and Change\n\n.\n3. Use your protractor to make a right\nangle in the middle of your pencil\nline. This is the normal line.\nMarking a right angle with a protractor.\n4. Place your mirror upright along the\nfirst line.\n5. Shine a light from the ray box along\nthe paper so that it \"hits\" the mirror\nwhere your normal line and your\nmirror meet.\nA mirror is placed on the line and a ray\nshone to strike the mirror at the normal\nline.\n6. Use a pencil to mark the incident\nlight ray.\nMarking the incident light ray.\n7. Use a pencil to mark the reflected\nlight ray.\nMarking the reflected ray.\n8. Remove the mirror and switch off\nthe ray box.\n9. Use a ruler and pencil to draw a line\nfrom the points you have marked on\neach ray to the normal line.\nDrawing in the rays.\n.\n.\n103\n.\nChapter 4.\nVisible light\n\n.\n10. Mark the angle of incidence (i) and\nangle of reflection (r).\nYour ray diagram should look similar to\nthis.\n11. Turn the ray box on again to confirm\nthat your pencil lines follow the rays.\nThe ray diagram overlaps the actual rays.\n12. Use a protractor and measure the\nangle of incidence and the angle of\nreflection and record your results in\nthe table.\n13. Repeat this method 3 more times,\neach time using a different angle of\nincidence.\nA different angle of incidence.\n.\nTAKE NOTE\nKeep one of the sheets\nwith your drawn ray\ndiagram for the next\nactivity.\nRESULTS:\nFill your results into the following table.\nRepeat\nAngle of Incidence\nAngle of Reflection\n1\n2\n3\n4\nANALYSIS:\n1. Has your investigation provided everything you need to answer your\ninvestigative question?\n..\n104\n.\nEnergy and Change\n\n.\n2. How could you improve this investigation to get more accurate results?\nCONCLUSION:\nWhat can you conclude based on your results?\n.\nWhenever light is reflected from a surface, the angle of incidence to equal to\nthe angle of reflection. On a smooth surface all the light rays are reflected in the\nsame way and so the image is clear and focused.\nA mirror is an example of a smooth surface. The image you see is focused and\nclear. As you can see in the photograph, the scientists and engineers are clear\nand focused in the mirror image.\nA mirror segment from one of NASA's telescopes provides a clear and focused reflection.\n.\nTAKE NOTE\nIn reflection, not only is\nthe angle of incidence\nequal to the angle of\nreflection, but the\nincident ray and\nreflection ray are also in\nthe same plane.\n.\nVISIT\nWhat colour is a mirror?\n(video)\nbit.ly/GABdNZ\nWhat happens when we do not have a smooth surface? Have a look at the\nphoto.\n.\n.\n105\n.\nChapter 4.\nVisible light\n\nWhy is the reflection of the grass and reeds not clear, but rather blurred?\n.\nACTIVITY: Light reflection off aluminium foil\n.\nMATERIALS:\n• aluminium foil\n• white paper\n• ray box\nINSTRUCTIONS:\n1. If possible, use the white sheets of paper from the last investigation where\nyou drew your ray diagrams.\n2. Similar to what you did in the last investigation, set up a ray box and direct\nthe ray along the line of incidence which you drew.\n3. Crumple a piece of aluminium foil and place this in the spot instead of the\nmirror.\n4. Observe the reflected ray.\nQUESTIONS:\n1. Describe the reflected ray off the aluminium foil and how this compares to\nthe reflected ray off the mirror.\n.\nVISIT\nWatch a video about the\ncreative way that\nscientists have tried to\nanswer the question:\n\"What is light?\"\nbit.ly/GAMvAL\n2. Why do you think you observed these differences?\n.\n..\n106\n.\nEnergy and Change\n\nCan you now see why reflections off rippled water are not clear, but rather\nblurred? This is because the light rays have not reflected parallel to each other\nas they do from a smooth surface, but have scattered in different directions.\nThe following table shows the difference between a smooth surface and a rough\nsurface. Straight parallel rays are approaching the surface. You need to draw in\nthe reflected rays to show specular (clear) reflection from a smooth surface and\ndiffuse (unclear) reflection from a rough surface.\n.\nTAKE NOTE\n'Diffuse' can mean\nunclear as well as\nspread out. In this\nexample, the reflection\nis unclear because the\nrays are spread out or\ndiffuse.\nSpecular diffusion from a smooth\nsurface\nDiffuse reflection from a rough\nsurface.\nVisible light is the range of frequencies of light that are visible to the human eye,\nand is responsible for the sense of sight. Are you curious to find out how we\nactually see light? Let's discover more in the next section.\n.\n4.6 How do we see light?\n.\nNEW WORDS\n• retina\n• stimulate\nHow is it that we are able to see light? Light that is absorbed by objects does\nnot enter the eye. Only reflected light or direct light from luminous objects can\nenter the eye and be interpreted. Have a look at the following image which\nshows the outer structure of the eye.\nWe can see the iris, the pupil and the sclera. The sclera is a the tough white,\nouter part of the eye, which acts as protection. The iris is the coloured part of\nthe eye which differs from person to person. It is circular and surrounds the\npupil. Light enters the eye through the pupil.\n.\nVISIT\n2012 Nobel Prize: How do\nwe see light?\nbit.ly/1a4zs2D\n.\n.\n107\n.\nChapter 4.\nVisible light\n\nThe size of your pupil changes in different light conditions. In bright light, the pupil\ncontracts (gets smaller) to let less light through (as on the left), and in low light your\npupil dilates (gets bigger) to let more light through (as on the right).\nLet's take a look at the internal structure of the human eye. The following\ndiagram shows a cross section through the eye. The eye is actually a large ball,\nand only a small part is visible on the outside. Covering the iris is a tough,\ntransparent layer called the cornea. Behind the iris is the lens. Both the cornea\nand the lens help you to focus the light entering your eyes, as we will learn\nabout in the next section.\n.\nTAKE NOTE\nThe fovea is the part of\nthe eye located in the\ncentre of the retina\nwhere the clearest\nimage is formed.\nA diagram of the eye.\nThe light travels through the eye and hits the retina at the back of the eyeball.\nThe retina is a layer of tissue lining the back of the eyeball, as indicated in the\ndiagram, it is the yellow layer. The retina consists of cells which are sensitive to\nlight. Light enters the eye and forms an image on the back of the eyeball. The\nway in which light hits the back of the eye, is similar to what happens in a\npinhole camera. The receptor cells convert the light energy into electrical nerve\nimpulses. These impulses travel out of the eye through the optic nerve and to\nthe brain where they are interpreted as sight.\n.\nTAKE NOTE\nThe cell is the basic\nstructural and\nfunctional unit of all\nliving things. We will be\nlearning more about the\ncell next year in Gr 9\nLife and Living.\n.\nVISIT\nFind your blind spot with\nthis optical illusion.\nbit.ly/19jumEr\nSo how do we see colour? Do you remember when we spoke about why the\nladybird appears red and black? Look at the following diagram again.\n..\n108\n.\nEnergy and Change\n\nThe white light hits the ladybird's surface. The white light has all the colours of\nlight, but when it hits the red surface, only the red light is reflected. The other\ncolours are absorbed by the red surface. This means that when we look at the\nred parts of the ladybird, we only get red light reflected into our eyes.\nTherefore, when this reflected light hits our retina and the electrical impulse is\nsent to our brains, we see the red colour.\n.\nDID YOU KNOW?\nEach of your eyes has a\nsmall blind spot at the\nback of the retina where\nthe optic nerve\nattaches. You do not\nnormally notice the hole\nin your vision because\nyour eyes work together\nto fill in each other's\nblind spot.\n.\nACTIVITY: Seeing colours\n.\nMATERIALS:\n• coloured pens or pencils\nINSTRUCTIONS:\n.\nDID YOU KNOW?\nThe cells in your eye\ncome in different\nshapes. Rod-shaped\ncells allow you to see\nshapes, and\ncone-shaped cells allow\nyou to see colour.\n1. Answer the following questions about how we see objects.\n2. Draw a ray diagram to accompany your written answer.\n3. An example has been done for you.\nLook at the picture of a sunflower.\nA black and yellow sunflower.\n.\n.\n109\n.\nChapter 4.\nVisible light\n\n.\nWe can draw a ray diagram to show why we see the green leaves as green, as\nshown below. The green surface of the leaves absorb all the colours of white\nlight except green light which is reflected into our eyes.\nNow explain why the petals appear yellow and the centre appears black. Use\nthe concepts of absorption and reflection in your explanation. Draw diagrams\nto support your answer.\n.\nHeath has bought himself a blue car.\nExplain why we see the car as blue by\nusing the absorption and reflection of\nlight. Draw a diagram to support your\nanswer.\nHeath's blue car.\n..\n110\n.\nEnergy and Change\n\n.\n.\n.\n.\nVISIT\nA simulation on colour\nvision.\nbit.ly/18TbpEA\nWe have looked at opaque and transparent substances, absorption of light,\nreflection of light and how we see light. We are now going to go back to\ntransparent substances and see how light can interact with these materials.\n.\n4.7 Refraction of light\nDo you remember the last time you drank a cold drink with a straw? Did you\nnotice that the straw did not look straight anymore once it was in the water or\ncool drink?\n.\nNEW WORDS\n• refraction\n• medium\n• optical density\nWhy does the pencil in this glass of water look bent?\nLet's investigate this by examining what happens to light when it passes\nthrough a glass block.\n.\n.\n111\n.\nChapter 4.\nVisible light\n\n.\n.\nINVESTIGATION:\nWhat happens to light when it\npasses through a glass block\n.\nWe are going to investigate what happens to a ray of light when it passes from\nair and into a glass block and then from the glass block back into air. We are\ngoing to use a glass block with parallel sides.\nBefore we start the investigation, we need to think about how we are going to\ndetermine if light changes direction or not. Do you remember in the\ninvestigation on reflection where we measured the angle of incidence and the\nangle of reflection? What did we find in this investigation?\nWhen light passes through a transparent substance, we can also measure the\nangles. Look at the following diagram. The angle of incidence (i) is measured\nbetween the incident light ray and the normal line. As the light passes through\nthe transparent substance, the angle of refraction (r) is the angle between the\nrefracted light ray and the normal.\nA light ray passing from one medium to another.\nIn the diagram above, you can see that the angle of refraction is smaller than\nthe angle of incidence. Therefore, the refracted light ray changed direction\nwhen it entered the transparent medium. We can also say something about\nwhich direction it bent towards. Did the light ray bend towards or away from\nthe normal line?\nThe next diagram shows another outcome.\n..\n112\n.\nEnergy and Change\n\n.\nA light ray passing from one medium to another.\nIn the diagram above, does the refracted ray change direction when it enters\nthe transparent medium? Give a reason for your answer.\nIn which direction did the refracted ray change?\nWe are now ready to start our investigation.\nAIM: To determine whether light changes direction when it passes through a\nparallel-sided glass block.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS:\n• glass block\n• ray box, laser pointer or other light source\n• protractor\nMETHOD:\n.\nTAKE NOTE\nThe emergent ray from\na parallel sided block is\nparallel to the incident\nray.\n1. Put the glass block in the centre of a piece of white paper and trace around\nit.\n2. Shine a ray of light into the glass block. The ray should be at an angle to\nthe surface of the block.\n.\n.\n113\n.\nChapter 4.\nVisible light\n\n.\n3. Trace the light ray with pencil and mark the point at which it enters the\nglass block.\n4. The light ray emerges on the other side of the glass block. Mark the point\nat which it emerges with a pencil and trace the emergent ray.\n5. Remove the glass block. Your diagram should look similar to the one\nabove.\n6. Draw a line joining the incident ray and emergent ray. You have traced the\nrefracted ray through the glass block.\n7. Draw the normal lines where the incident ray meets the block and where\nthe emergent ray leaves the block.\n8. Measure the angles labelled 1, 2, 3 and 4 as shown on the diagram with a\nprotractor.\n9. Fill in the measurements in the table.\n10. Repeat the steps above three times using different angles of incidence\n(angle 1).\n..\n114\n.\nEnergy and Change\n\n.\nRESULTS AND OBSERVATIONS:\nFill your results into the following table.\nExperimental\nrepeat\nAngle 1\nAngle 2\nAngle 3\nAngle 4\n1\n2\n3\n4\n1. Which pairs of angles are equal in the measurements you have taken?\n2. Which of the angles you measured are the angles of incidence and which\nare the angles of refraction? Write this down below and mark them on the\ndiagram above.\n3. What do you notice about the angle of incidence and angle of refraction\nfor each of your sets of measurements?\n4. Did the light entering the glass block bend towards or away from the\nnormal line?\n5. Make the angle of incidence zero (make the light ray enter the block\nperpendicular to the surface). What is the angle of refraction?\nCONCLUSION:\nWhat can you conclude from your results?\n.\n.\nVISIT\nLearn more about\nrefraction with this\nsimulation.\nbit.ly/GAxLmc\nThe angle of incidence is not equal to the angle of refraction because the light\nhas changed direction as it enters the glass. Therefore, when light travels from\none medium to another, it bends, or changes direction. This is called refraction.\n.\n.\n115\n.\nChapter 4.\nVisible light\n\nWhen light enters a different medium at right angles then it does not change\ndirection.\nSo why does the light refract? Light behaves as a wave does and waves travel\nat different speeds in different media. For example, light travels faster in air\nthan it does in water. When light enters a different medium, it changes speed,\nand if it entered at an angle other than 90o, then it also changes direction. The\nmore dense the medium, the slower the light moves.\nDo you remember learning about density last term in Matter and Materials?\nWrite down your own definition for density in the space below.\n.\nTAKE NOTE\nRemember that\nalthough we learn\nabout Natural Sciences\nin 4 strands throughout\nthe year, there are many\nconnections and links\nbetween the strands.\nIf light moves from a less dense medium, like air, into a denser medium, like\nglass, then the light slows down. The light will bend towards the normal line.\n.\nVISIT\nThe speed of light in glass.\nbit.ly/1fcfJVZ\nIf light moves from a more dense medium to a less dense medium then the light\nspeeds up and moves away from the normal.\nWhen light refracts and changes direction as it passes through different\nmediums, it can distort what we see. Think back to the pencil or straw in a glass\nof water at the start of the section. We can now explain why a drinking straw or\npencil in a glass of water looks bent. The light bends when it moves from one\nmedium to another. Light moves from the air to glass to water, and therefore\nchanges direction.\nIf you have stood in a pool of water before and looked down, have you noticed\nhow short your legs appear to be? Let's have a look at this a bit more in the\nnext activity.\n..\n116\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magic coin trick\n.\nMATERIALS:\n• coin\n• prestik\n• opaque bowl or cup\n• water\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Put a small amount of prestik onto the bottom of the bowl.\n3. Stick the coin to the bottom of the bowl.\n4. Take small steps back from the desk/table until you cannot see the coin\nover the lip of the bowl.\n5. Ask your partner to slowly pour water into the bowl and observe.\nQUESTIONS:\n.\nVISIT\nWatch a video that shows\nand explains the coin\nactivity.\nbit.ly/15NmXXO\n1. What happened when your partner poured the water into the bowl?\n2. Where does the coin appear to be?\n3. Explain why the coin can be seen when the water is added, but not before.\nThe diagrams below will help you explain what is happening in words.\n.\nTAKE NOTE\nThe diagrams used here\nshow the container as\ntransparent so that you\ncan see the coin inside,\nwhereas you will\nactually be using an\nopaque container.\nEmpty container.\nContainer with water.\n.\n.\n.\n117\n.\nChapter 4.\nVisible light\n\nRefraction can be used to explain why images appear to be distorted when we\nview them through transparent mediums. For example, if you are looking at\nyour legs or hands through some water, they will appear closer than they\nactually are as the light is refracted. Look at the photograph of the glass with\nwater in it in front of diagonal lines. Can you see how the lines are distorted\nwhen the light travels through the water and glass compared to when it does\nnot?\nLight refraction through glass and water.\nCan you remember how we split white light into the separate colours of the\nvisible spectrum in the beginning of this chapter? What did we use to do this in\nthe activity?\nWe can do this because the different\ncolours of light bend by different\namounts when the light enters a\ndifferent medium. Different colours of\nlight will slow down to different\nspeeds, causing them to bend by\ndifferent amounts.\nRefraction through a triangular prism.\nWhen the white light entered the prism it refracted. The different colours of\nlight travel at different speeds in the prism so they refracted at different angles\nand split up. Red light refracts the least and the violet light refracts the most as\nyou can see in the following diagram.\n..\n118\n.\nEnergy and Change\n\nPrisms are not the only objects that can split white light into separate colours.\nIn fact, a rainbow is a good example of white light splitting up.\nA rainbow.\nLight from the Sun enters the raindrops and refracts. The light is then reflected\noff the back of the raindrop. When the light passes out of the raindrop it is\nrefracted again and the colours split up even more as shown in the diagram.\nA raindrop refracts and reflects light, dispersing white light into the colours of the visible\nspectrum.\n.\n.\n119\n.\nChapter 4.\nVisible light\n\nWhat colour is at the top of a rainbow and which colour is at the bottom?\nDoes this match the order which we see in the diagram showing how light is\nrefracted and reflected in a raindrop?\nHow does this happen? When we see a rainbow, we see a combination of\nmillions of raindrops. Although each raindrop refracts and reflects all 7 colours,\nwe only see only colour of light reflected from each particular raindrop. This\ndepends on the angle of the raindrop from our position. Therefore, the\nraindrops higher up in the sky reflect red light to us and the rain drops lower\ndown reflect violet light to us. This is shown in the following diagram.\nWe see rainbows with red at the top and violet at the bottom due to the combination of\nmillions of raindrops. We only see one colour reflected from a particular raindrop,\ndepending on its position in the sky.\nWe are now going to look at an application of the refraction of light.\nLenses\n.\nNEW WORDS\n• diverge\n• converge\n• focus\nDo you remember when we spoke about how we see light and the structure of\nthe eye, we mentioned that there is a lens just behind the iris? Another place\nwhere you may have seen lenses before are in reading glasses which some\npeople wear to correct their vision. Or, have you seen how a magnifying glass\nmakes things appear bigger. What are lenses and how do they work?\nA magnifying glass makes things look bigger.\n..\n120\n.\nEnergy and Change\n\nA lens is a transparent object which focuses or refracts light. When light is\nspread out, we say it has diverged. Some lenses will diverge light while others\nwill converge light, bringing the light rays together. When light rays are all\nbrought to the same point, we say they have been focused. Let's have a look at\nthis more closely.\n.\nACTIVITY: Diverging and converging light with\nlenses\n.\nMATERIALS:\n• ray box or light source\n• concave lens\n• convex lens\n• piece of paper\n• pencil\nBefore we start, it is important that you know the difference between a convex\nand a concave lens.\nConvex lens\nConcave lens\nA convex lens has one\nside which curves or\nbulges outwards. A\nconvex lens converges\nlight.\nA concave lens has one\nside which curves or is\nhollowed inwards. A\nconcave lens diverges\nlight.\n.\nTAKE NOTE\nA lens can have two\nsides which are concave\nand it is then called a\nbiconcave lens or two\nsides which are convex\nand it is then called a\nbiconvex lens.\n.\n.\n121\n.\nChapter 4.\nVisible light\n\n.\nINSTRUCTIONS:\n1. Place a ray box or light source on one side of a piece of paper and turn it\non. Observe the light rays. You might see something as shown in the\nphotograph here.\nThree rays coming out of a ray box.\n2. Turn the ray box off.\n3. Place the convex lens (with the rounded surface) on the piece of paper\nwhere the light rays will pass through it. Trace around it.\n4. Turn on the ray box or light source and observe what happens to the rays\nwhen they pass through the lens.\nLight rays passing through a convex lens.\n5. Trace the path of the light rays on your piece of paper.\n6. Describe what has happened to the light rays.\n7. Mark the point where the light rays cross. This is called the focal point of a\nconvex lens.\n8. Turn off the ray box or light source and place a new piece of paper in front\nof it.\n9. Now place the concave lens in the path of the light rays and trace around\nthe lens.\n10. Turn on the light source and observe what happens to the rays.\n..\n122\n.\nEnergy and Change\n\n.\n11. Trace the path of the rays on the piece of paper.\nA concave lens in front of the rays of light.\n12. Describe what has happened to the light rays.\n13. Turn off the light rays and extend the rays you have drawn until they meet\nat a point in front of the lens. This is the focal point of a concave lens.\n14. If you still have your pin hole cameras, place a convex and concave lens in\nfront of the camera and observe the image that forms.\nViewing a light source through a pinhole camera with different lenses.\n15. Is the image larger or smaller when you observe through a concave lens?\n16. Is the image larger or smaller when you observe through a convex lens?\n.\n.\n.\n123\n.\nChapter 4.\nVisible light\n\nWe have now seen how lenses can disperse or focus light. Have a look at the\nfollowing diagrams which show how a biconvex lens converges light and a\nbiconcave lens diverges light.\n..\n124\n.\nEnergy and Change\n\nConverging lens\nDiverging lens\nA converging lens refracts the light\nentering it and bends the light rays\nto a focal point on the other side of\nthe lens.\nA diverging lens refracts the light\nentering it and bends the light rays\naway from each other. The light\nrays can be traced back to a focal\npoint in front of the lens.\nWhat do we use lenses for? Think of a magnifying glass. If you hold a\nmagnifying glass over a picture or words then it enlarges the image. Is a\nmagnifying glass an example of a diverging or converging lens?\nLet's think about how this works. Imagine you are looking at the ladybird from\nthe beginning of the chapter through a magnifying glass. The ladybird looks\nbigger than what it actually is. When the object you are viewing is closer to the\nlens than the focal point, you see a virtual image of the ladybird that is larger\nthan the object.\nHave a look at the first diagram below. Can you see that the ladybird is between\nthe focal point and the lens? The rays reflected from the ladybird are refracted\nby the magnifying glass and enter the person's eye.\n.\n.\n125\n.\nChapter 4.\nVisible light\n\nIn the next diagram you can see how your eyes see a virtual image of the\nladybird which is bigger than the object. The more curved the convex lens is in\na magnifying glass, the greater its ability to magnify objects.\n.\nTAKE NOTE\nWhen you hold a\nmagnifying glass up\nand view a distant\nobject, the object\nappears smaller and\nupside down. Unlike\nwhen viewing the\nladybird close up, the\ndistant object is beyond\nthe focal point of the\nlens, which results in\nthis effect.\n.\nVISIT\nHow do lenses work?\nbit.ly/GABjoO\nDo you remember what the human eye looks like? We have lenses in our eyes\nto allow us to see. The light enters the eye and passes through the lens. The\nlens focuses the light onto the back of our retina so that a clear image is formed.\nWhat type of lens do we have in our eyes? Give a reason for your answer.\nIn order for a clear image to form, the lens in our eye needs to focus the light\nrays coming into our eyes so that the focal point falls on the retina. This\ndepends on the shape of the lens in our eyes. Sometimes, people have lenses in\ntheir eyes that cannot focus properly. Have a look at the following diagram\nwhich shows a normal eye and then an eye which focuses before the retina\n(near-sighted) and behind the retina (far-sighted).\n..\n126\n.\nEnergy and Change\n\nOptical glasses, or spectacles, are used to correct near or far-sightedness.\nIf you are near-sighted you need a diverging lens. Would this be a biconcave or\nbiconvex lens?\n.\nDID YOU KNOW?\nA contact lens is\ndesigned to rest on the\ncornea of the eye and\ncorrect vision. Leonardo\nda Vinci was the first to\ncome up with the idea\nin the 16th century to\nhelp prevent eye\ninfection.\n.\nDID YOU KNOW?\nA microscope makes a\ntiny, nearby object look\nmuch bigger. A\ntelescope makes a\nlarge, distant object\nlook much closer and\nbrighter. In both, light\nfrom the object passes\nthrough two or more\nlenses to form an\nimage. The lens shapes\nand distances between\nthem determine how\nthe image is produced.\nIf you are far-sighted you need a converging lens. Would this be a biconcave or\nbiconvex lens?\nAn optometrist holds a lens in front of a patient's eye to correct her vision.\nThe following image shows how lenses can be used to correct far and\nnear-sightedness.\n.\n.\n127\n.\nChapter 4.\nVisible light\n\n.\nTAKE NOTE\nNext term in Planet\nEarth and Beyond we\nwill look at how lenses\nare used in optical\ntelescopes to view\nobjects in space.\n.\nACTIVITY: Research careers in optics\n.\n.\nVISIT\nAn interview conducted\nwith an optometrist.\nbit.ly/19WxYYa\nThere are many different careers in the field of geometric optics.\nINSTRUCTIONS:\n1. Work in groups of 3.\n2. Interview someone in the field of geometric optics and find out how they\nchose their career and what and where they studied.\n3. Write a paragraph explaining the career and the study options available in\norder to qualify for that career.\n4. Here are some examples of careers in geometric optics.\na) Optometry\nb) Ophthalmology\nc) Optoelectronics\nd) Illumination engineering\n.\n..\n128\n.\nEnergy and Change\n\n.\nVISIT\nWant to take part in some\nreal science research?\nCheck out these citizen\nscience projects to get\ninvolved easily.\nbit.ly/15KjnmD\nRemember to discover more online by visiting http://www.curious.org.za and\nby typing the links in the Visit margin boxes into your internet browser to watch\nany videos, play with simulations or read an interesting article.\nType the bit.ly link for the video or site that you want to visit into the address bar of your\nbrowser on your computer, tablet or mobile phone.\n. .\nSUMMARY:\n.\nKey Concepts\n• Light travels in straight lines.\n• White light consists of all the colours of the visible spectrum.\n• The colour spectrum can be seen when white light is dispersed by a\nprism or a raindrop (rainbow).\n• Light cannot pass through opaque objects.\n• Light can pass through transparent objects.\n• Light is absorbed by some materials.\n• A material appears to be a certain colour because it reflects that part of\nthe colour spectrum. Other wavelengths of light are absorbed.\n• In reflection, the angle of incidence is equal to the angle of reflection.\n• On a smooth surface, parallel rays of light are all reflected at the same\nangle.\n• On rough surfaces, the light is scattered and the image produced is not\nclear.\n• The human eye has specialised cells in the retina which convert light\ninto electrical nerve impulses. The nerve impulses are transmitted to\nthe brain via the optic nerve, where they are interpreted.\n• Light travels at different speeds in different media.\n• When light enters a different medium at an angle, the light is refracted.\n• If the light slows down, the light bends towards the normal line.\n• If the light speeds up, the light bends away from the normal line.\n• Converging lenses refract and focus light.\n• Diverging lenses and triangular prisms refract and disperse light.\n• Lenses have many applications, for example, in glasses to correct vision,\nmicroscopes, telescopes and magnifying glasses.\n.\nConcept Map\nThe concept map on the next page shows how all the concepts relating to\nvisible light link together.\nComplete the map to reinforce what you have\nlearned in this chapter.\n.\n.\n129\n.\nChapter 4.\nVisible light\n\n.\n\n.\n.\nREVISION:\n.\n1. Match the correct definitions to the terms in the following table. Write the\nletter of the definition next to the correct number below. [12 marks]\nTerm\nDefinition\n1. Radiation\nA. Light cannot pass\nthrough.\n2. Visible light\nB. The angle of incidence\nequals the angle of\nreflection when a ray is\nreflected off a smooth\nsurface.\n3. Opaque\nC. One of the ways in\nwhich energy is\ntransferred, specifically\nthrough a vacuum\n4. Transparent\nD. When light enters a\ntransparent medium it\ncan change direction.\n5. Absorption\nE. Curved inwards.\n6. Reflection\nF. The spectrum of light\nwhich we are able to see.\n7. Retina\nG. Bulging outwards.\n8. Refraction\nH. A transparent object\nable to refract and focus\nlight.\n.\n.\n131\n.\nChapter 4.\nVisible light\n\n.\nTerm\nDefinition\n9. Diverging\nI. Light can pass through.\n10. Lens\nJ. When light rays are\nspread out from a point.\n11. Concave\nK. A layer of tissue at the\nback of the eye which is\nsensitive to light.\n12. Convex\nL. When the surface of a\nsubstance absorbs\ncertain colours of light.\nAnswers:\n1:\n2:\n3:\n4:\n5:\n6:\n7:\n8:\n9:\n10:\n11:\n12:\n..\n132\n.\nEnergy and Change\n\n.\n2. A beam of white light is shone through a glass prism. It splits up into seven\ncolours which are shone on a screen. A learner took a photograph which is\nshown below and drew a ray diagram to show the prism. The colours are\nmarked 1 to 7 in the diagram.\nA photograph of the prism.\nA diagram drawn by the learner.\na) What does this tell us about white light? [1 mark]\nb) Why does the light do this when it passes through the prism? [3\nmarks]\nc) What colour is at label 1 and what colour is at label 7? Explain your\nanswer. [3 marks]\nd) What label corresponds to the colour of grass? [1 mark]\ne) Can you see there are two other lighter, white rays emerging from the\nprism? What do you think this is the result of? [2 marks]\n3. Why does an opaque object cast a shadow? [2 marks]\n.\n.\n133\n.\nChapter 4.\nVisible light\n\n.\n4. Look at the following photograph of water in a pond and answer the\nquestions.\nWater in a pond.\na) How are we able to see the image of the wooden poles sticking up on\nthe edge of the pond? [2 marks]\nb) Why is the image not clear, but blurred? [2 marks]\n5. Two learners are discussing the colours of light. They decide that white\nand black are not really colours of light. If they are not colours, then how\ncan we see them? [5 marks]\n6. Explain how we are able to see the different colours on the South African\nflag. [6 marks]\n..\n134\n.\nEnergy and Change\n\n.\n7. Draw a ray diagram in the space provided to show how we see the green\npart of the flag. [5 marks]\n.\n8. Which diagram shown below correctly shows the path of a ray of light\nthrough a triangular piece of glass? [2 marks]\n.\n.\n135\n.\nChapter 4.\nVisible light\n\n.\n9. Complete the following sentence and write it out in full on the lines\nprovided: When light travels from a less dense into a more dense\ntransparent medium, it refracts and bends\nthe normal line.\nWhen light travels from more dense to a less dense medium, it refracts and\nbends\nfrom the normal line. [2 marks]\n10. Draw a diagram to show what is meant by 'when the refracted ray bends\ntowards the normal'. Mark the angle of incidence and angle of refraction.\nIndicate which medium is denser [4 marks]\n.\n11. Study the following diagram and answer the questions that follow.\na) This diagram is a drawing that a learner made during an investigation\ninto the refraction of light. What does the red line represent in this\ndiagram? [1 mark]\n..\n136\n.\nEnergy and Change\n\n.\nb) What do the blue lines represent? Label this on the diagram. [1 mark]\nc) The light passes from the air and into a block of another medium. Is\nthis medium more or less dense than air? Give a reason for your\nanswer. [2 marks]\nd) What type of medium could the block be made from? [1 mark]\ne) Label the incident ray and the emergent ray on the diagram. [2 marks]\nf) Label the angles of incidence (i) and angles of refraction (r) on the\ndiagram. [2 marks]\n12. Which diagram shown below shows the path of a light beam passing\nthrough a rectangular glass prism correctly? [2 marks]\n13. Why does it look like the tree trunk in the photograph is skew? [2 marks]\n.\n.\n137\n.\nChapter 4.\nVisible light\n\n.\n14. What shape does a lens have to have in order to focus the light? [1 mark]\n15. Draw a ray diagram to show how a converging lens focuses light to a point.\n[4 marks]\n.\n16. Which eyesight defect can be fixed by using a converging lens? Explain\nwhat this defect is and why it can be corrected. [4 mark]\nTotal [74 marks]\n.\n..\n138\n.\nEnergy and Change\n\n.\n.\n.\nGLOSSARY\nammeter:\ndevice that measures the strength of an electric\ncurrent\nampere:\nthe standard unit for measuring electric current\nangle of incidence:\nthe angle between the incident ray and the normal\nline\nangle of reflection:\nthe angle between the reflected ray and the normal\nline\nattract:\nto pull something closer\ncell:\na source of energy for an electric circuit\ncomponent:\na part of a larger system\ncomposition:\nthe parts of a mixture\nconductor:\na substance which easily transmits electricity, heat,\nsound or light\nconverge:\nlight rays that come together and focus on a point\ndelocalised:\nnot limited to a particular place, free to move\ndischarge:\nthe sudden flow of charged particles between two\nelectrically charged objects\ndispersion:\nspreading of something over an area\ndiverge:\nlight rays that spread apart as they move further\nand further away from a point\nearth:\n(or ground) to connect with a conductor to the\nground, or the earth\nearthing:\na way to prevent electrical charge from building up\non an object, or to neutralise an electric charge, by\nallowing the excess charge to flow into the Earth\nelectric circuit:\na complete path through which electrons can move\nelectric current:\nthe movement of charge in an electric circuit\nelectrodes:\na conductor which allows electricity to enter a\nsubstance\nelectrolysis:\nthe use of electricity to separate chemicals in a\nsolution\nelectromagnet:\na device which becomes a magnet when electric\ncurrent passes through it\nelectroplating:\ncovering an object with a thin layer of metal using\nelectrolysis\nelectrostatic charge:\nthe electric charge resulting from static electricity\ncaused by an excess or deficiency of electrons on\nthe surface of an object\nflammable:\nsomething is easily set on fire\nfocus:\nbring together to the same point\nfriction:\nthe resistance that results when two surfaces are\nrubbed or moved against each other\nfuse:\na safety device designed to melt and break the\ncircuit if an electric current reaches too high a level\n.\n.\n139\n.\nChapter 4.\nVisible light\n\n.\nignite:\nto light something\nincident ray:\nthe ray of light which hits a surface\nluminous:\nbright or shining\nmedium:\nsubstance through which waves (such as light) can\ntravel\nneutral:\nwhen the number of positive charges (from the\nprotons) is equal to the number of negative\ncharges (from the electrons); the (positive and\nnegative) charges balance each other so that the\nobject is neither positively nor negatively charged\nnormal line:\nthis is an imaginary line which is drawn at 90o to\nthe surface\nopaque:\nsomething that you cannot see through; no light\npasses through the object\noptical density:\na measure of how well a medium allows light to\ntravel through it\noptics:\nthe scientific study of sight and the behaviour of\nlight\nparallel circuit:\na circuit that provides more than one pathway for\nthe current to pass through it\nperpendicular:\nat right angles\npropagation:\nspreading into new areas\nqualitative:\ndescribing something in terms of its properties or\ncharacteristics rather than by a number or\nmeasurement\nradiation:\nthe emission of energy as electromagnetic waves\nrectilinear:\nstraight lines\nreflect:\nthrow back without absorbing\nreflected ray:\nthe ray of light which leaves a surface\nrefraction:\nthe change in direction of a wave passing from one\nmedium to another caused by its change in speed\nrepel:\nto push something away\nresistance:\nthe opposition to the movement of charge in a\nconductor\nresistor:\na component in an electrical circuit which slows the\nmovement of charge\nretina:\na layer at the back of the eyeball which is made up\nof light sensitive cells\nseries:\ncomponents connected in series provide only one\npathway for electrical current; they are connected\none after another\nstatic electricity:\nthe build-up of a stationary electric charge (either\npositive or negative) on the surface of an object\nstimulate:\nto cause activity\nswitch:\na control component in an electrical circuit which\nopens or closes the circuit\ntranslucent:\nsemi-transparent; some light is able to pass through\nbut not enough for details to be seen clearly\ntransmit:\nto cause light to pass through space or medium\n..\n140\n.\nEnergy and Change\n\n.\ntransparent:\nsomething that you can see through; light passes\nthrough the object\nvariable:\nsomething that can vary or change\nvisible spectrum:\nthe portion of the wave spectrum that is visible to\nthe human eye\n.\n.\n141\n.\nChapter 4.\nVisible light\n\n\n\n. .\n1\n.\nThe solar system\n..\n144\n..\nKEY QUESTIONS:\n• How does the Sun produce its energy?\n• How can we observe the Sun without damaging our eyes?\n• What objects are in orbit around the Sun in our solar system?\n• Why are there two types of planets?\n• How do the planets in our solar system differ?\n• What are asteroids and comets?\n• What is the difference between a planet and a dwarf planet?\n• Why is life possible on Earth?\nOur solar system includes the Sun and all the objects that orbit around the Sun.\nAs you will find out, a variety of objects are in orbit around the Sun: eight\nplanets, many dwarf planets, asteroids, Kuiper Belt objects and comets.\n.\n1.1 The Sun\n.\nNEW WORDS\n• solar system\n• star\n• nuclear fusion\n• convection\n• sunspot\n• solar wind\nBefore we look at the Sun close up, let's summarise what you learned about the\nSun in Grades 6 and 7:\n1. The Sun is our closest star and is very important for life on Earth as it\nprovides us with light and heat.\n2. The Sun is located at the very centre of our solar system.\n3. The Earth and other planets all orbit around the Sun, held in orbit by the\nforce of gravity.\n.\nVISIT\nSecrets of a dynamic Sun\n(video)\nbit.ly/1h0io4b\nWhat do you think the Sun would look like if it was further away, like the other\nstars we see at night?\nLet's look at the Sun in more detail.\n\nAn image of the Sun taken with the SOHO space satellite.\n.\nTAKE NOTE\nIt is very important that\nyou do not look at the\nSun directly! The Sun\ncan damage your eyes\npermanently!\n.\nVISIT\nThe birth of the solar\nsystem (video)\nbit.ly/1i8Bfrx\n.\nVISIT\nHow the Sun works.\nbit.ly/1gy769C\nDo you know what the Sun is made of? The Sun is mostly made up of hydrogen\ngas (about 71%), and also helium gas (about 27%) with a tiny amount of other\ngases. The temperature at the Sun's surface is very high, around 5500 oC.\nHowever, that is nothing compared to deep inside the Sun. At the Sun's centre,\nor core, it is about 15 million oC. It is so hot at the Sun's centre that nuclear\nreactions can occur, which change atoms from one element to another. In the\nSun's case, four hydrogen nuclei are squeezed or fused together to form a new\nhelium nucleus. This process is called nuclear fusion.\nThis nuclear fusion reaction releases energy because the new helium nuclei\nproduced have very slightly less mass than the four hydrogen nuclei used to\nmake them. How can this be? Well, according to the famous scientist Albert\nEinstein, energy and mass are equivalent. Some of the mass in the hydrogen\nnuclei is converted and released as energy when the nuclei fuse to make helium.\nA very large amount of energy is released. This energy travels outwards from\nthe Sun's core towards its surface. The energy eventually reaches the Sun's\nsurface somewhere between 17,000 and 100,000 years later! The Sun's energy\nthen spreads out into the solar system in the form of heat and light.\nYou are now going to observe the Sun to look at its surface features.\nRemember, you should never look directly at the Sun as it can permanently\ndamage your eyes. You can use either a telescope with a filter on it or a pinhole\nto project an image of the Sun onto a screen to safely view the Sun's image.\n.\n.\n145\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing the Sun using a telescope\n.\nMATERIALS:\n• telescope\n• white card\n• chair to rest the card on\n• cardboard to make a shade collar\n• pair of scissors\n• pencil\n.\nVISIT\nInteract with this\nsimulation to visualize the\neffects of gravity on\norbital paths of the Sun,\nEarth and Moon.\nbit.ly/1a2mJCL\n.\nTAKE NOTE\nNEVER look directly at\nthe Sun, even with\nsunglasses on as you\ncan permanently\ndamage your eyes.\nINSTRUCTIONS:\n1. Take a piece of cardboard and place it up against the narrowest end of the\ntelescope.\n2. Draw an outline around the edge of the telescope on the card to use as a\nguide for cutting to make the collar.\n3. Cut out inside the circle you just drew so that the cardboard can fit over\nthe telescope as shown in the figure above. You can cut a single slit into\nthe circle from the edge of the card as shown in the diagram\n4. Place the collar on the telescope. Adjust the size of the cut out circle if\nnecessary (for example if your telescope is slightly wider in the middle\nthan at the end, you may want to make your circle slightly larger). This\ncollar shades the area, where the image will fall, from stray light.\n5. Select the lowest magnification eyepiece lens you have and insert it into\nthe telescope's eyepiece.\n6. Focus the telescope by looking at a distant object (NOT the Sun).\n7. Point the telescope at the Sun (do NOT look through the telescope to do\nthis).\n8. Place a chair behind the telescope and rest a white piece of card on it. The\ncard should be tilted towards the telescope.\n9. Adjust the direction in which the telescope is pointing until the image of\nthe Sun appears on the white paper card. This may take some time.\n10. Keeping the telescope still, move the white card toward or away from the\neyepiece until the image of the Sun fits neatly in the middle of the card.\n..\n146\n.\nPlanet Earth and Beyond\n\n.\nAdjust the chair's position as needed.\n11. Adjust the tilt of the white card until the Sun's image is circular.\nQUESTIONS:\n1. Looking carefully you should see that the Sun's image moves slowly across\nthe white card. What causes this motion?\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n.\n.\nTAKE NOTE\nRevise the model of the\natom that you learned\nabout in Matter and\nMaterials if you are\nunsure of some of the\nterms used here, such\nas nucleus, which is at\nthe centre of an atom,\nand consists of protons\nand neutrons.\nAlternatively, if you do not have access to a telescope or binoculars, you can\nperform the following activity to view the Sun.\n.\nACTIVITY: Observing the Sun with a pinhole\ncamera\n.\nIn this activity you will reflect an image of the Sun onto a white card or screen\nfor your learners to observe. This method has the advantage of not needing a\ntelescope or binoculars, however, the solar image produced will be a bit fuzzy.\nHowever, it should be good enough to show large sunspots. This activity is\ndesigned as a teacher-led demonstration. If you have a sunlit window or door to\nyour class you can do this activity in the classroom. If you do not have a\nclassroom with a sunlit window, or if your class is very small, you can do the\nactivity outdoors, reflecting the Sun's image onto a shaded wall or back into a\ndarkened classroom.\n.\n.\n147\n.\nChapter 1.\nThe solar system\n\n.\n.\nVISIT\nThree years of the Sun in\nthree minutes.\nbit.ly/19nCfGu\nAs a rough guide, begin with a distance of around 8 m between the white card\nand the mirror. The further away you place the mirror from the white screen the\nfainter and larger the image will appear. At closer distances the image will be\nbrighter but it may not be in very good focus.\n.\nVISIT\nWhere does the Sun get\nits energy?\nbit.ly/1azFmsM\nAs mentioned in the previous activity, sunspots are sometimes (not always)\nvisible on the Sun's surface. Therefore, you could repeat this activity over the\ncourse of several days to see if any sunspots or sunspot groups change shape,\nsize, or position over time.\nMATERIALS:\n• small pocket mirror or hand mirror\n• piece of plain cardboard (or paper) to fit over the mirror (or alternatively\ntape)\n• white cardboard screen\n• bin bags or curtains for darkening the classroom\n.\nVISIT\nE = mc2 explained (video).\nbit.ly/16mVFNI\nMETHOD:\n1. Cut the plain cardboard or paper so it fits over the mirror.\n2. Cut or punch a very small hole, about 5 mm, in the middle of the plain\ncardboard.\n3. If you do not have cardboard, you can use tape to cover all but a small\nportion of the surface of the mirror.\n4. Place the mirror on a window sill in the Sun and tilt it so that it catches the\nsunlight and reflects it into the classroom. If your classroom is very small,\nplacing the mirror outside on a chair may be a better option in order to get\na larger image.\n5. Darken the classroom using curtains or bin bags, excluding where the\nmirror is.\n6. Reflect the sunlight from the mirror onto a wall of the darkened room.\n7. Put the white cardboard or paper on the wall where the reflected light\nshowing the Sun's image falls.\n8. Observe the image of the Sun.\n..\n148\n.\nPlanet Earth and Beyond\n\n.\n9. Remove the white cardboard from the wall and take three steps towards\nthe mirror with the cardboard still facing the mirror. Note what happens to\nthe image of the Sun on the cardboard.\nQUESTIONS:\n1. As you moved the white cardboard screen closer towards the mirror, what\ndid you notice happened to the image of the Sun?\n.\nDID YOU KNOW?\nAlbert Einstein\nexplained the\nmass-energy\nequivalence with the\nfamous equation\nE = mc2.\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n3. When the Sun reflects off the surface of the mirror, what can you say about\nthe angle of incidence and the angle of reflection of the ray?\n.\nDid you notice any features on the Sun's surface when you viewed it in class?\nLet's find out what some of these surface features could have been in the next\nactivity.\n.\nVISIT\nFiery looping rain on the\nSun (video)\nbit.ly/16qmriQ\n.\n.\n149\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing sunspots on the Sun's\nsurface\n.\nINSTRUCTIONS:\n1. Look at the images of the Sun which were taken in June 2013.\n2. Answer the questions that follow.\nA: DATE: 02.06.2013\n.\nVISIT\nLearn more about the\nresearch that NASA is\ndoing about our Sun with\nthe Solar and Heliospheric\nObservatory (SOHO).\nbit.ly/1fQhd8u\nB: DATE: 03.06.2013\n..\n150\n.\nPlanet Earth and Beyond\n\n.\nC: DATE: 04.06.2013\nQUESTIONS:\n.\nTAKE NOTE\nThis information about\nthe Sun's surface and\nsunspots is additional\ninformation for your\ninterest. Be curious and\ndiscover more!\n1. How many groups of dark spots do you see in each image?\n2. What do you notice about the positions of the spots in each image?\n3. Why do you think the spots have moved?\n4. What do you think these spots are?\n.\nSunspots and the Sun's surface\nThe Sun's surface often has little blemishes on it. These dark spots on the Sun\nare called sunspots. They are areas that are slightly cooler than the rest of the\nSun's surface. The Sun's surface is typically about 5500 oC and a typical\nsunspot has a temperature about 3900 oC.\n.\n.\n151\n.\nChapter 1.\nThe solar system\n\nImage of a sunspot. For perspective, take note of the size of the Earth in the lower left.\n.\nVISIT\nView real time images of\nthe Sun and track\nsunspots.\nbit.ly/19ZoU6c\nAs the Sun is made up of gas, there is no solid surface like on Earth. So when\none says that you are looking at the Sun's surface what are you actually looking\nat? Imagine that you are standing in thick fog (mist) with a friend. You can see\nthings close to you, like your hand in front of you and your friend standing next\nto you. However, because the fog is so thick you cannot see far into the\ndistance. Similarly, when we look at the Sun, we cannot see right into the centre\nof the Sun. As you go deeper and deeper in towards the centre of the Sun the\ngas begins to get thicker and thicker so that we cannot see through it. The\ndeepest depth that we can see into the Sun's gas is what we call the Sun's\nsurface.\nSunspots are areas that are slightly cooler, and therefore darker, than the rest of\nthe Sun's surface. A typical sunspot only lasts a few days. When a sunspot lasts\nfor several days you can observe it move across the Sun's disc. The sunspot\nappears to move across the Sun because the Sun is spinning slowly on its own\naxis.\n.\nDID YOU KNOW?\nThe number of sunspots\non the Sun increases\nand decreases in a\nregular pattern which\nrepeats every 11 years.\nWhen there are more\nsunspots the Sun is\nmore active and there\nare more solar storms\nand more of the Sun's\nenergy reaches the\nEarth.\nThe outer atmosphere of the Sun is called the corona. Gas particles from the\ncorona are constantly escaping into space, forming the solar wind. When the\nSun is very active, violent eruptions called solar flares occur on its surface.\n..\n152\n.\nPlanet Earth and Beyond\n\nA large loop of gas extending over 35 Earth diameters out from the Sun's surface.\n.\n1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.\n1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.\nChapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "12" }, { "title": "Radiation of light", "content": "", "chapter_id": "4.1" }, { "title": "Spectrum of visible light", "content": "4.2 Spectrum of visible light\n.\nNEW WORDS\n• composition\n• visible spectrum\n• dispersion\nThe visible light spectrum is the light that we are able to see with our naked\neyes. Have you ever wondered why everything is colourful and not just black\nand white? Have you ever seen a rainbow and wondered where the colours\nhave come from? The colours that we see everyday are part of the visible light\nspectrum. Let's investigate the visible light spectrum.\n.\nACTIVITY: Splitting white light\n.\nMATERIALS:\n• triangular perspex prism\n• ray box and power source\nINSTRUCTIONS:\n1. Connect the ray box to the power source. If you do not have a ray box,\nyour teacher will show you how to use a piece of cardboard with a slit cut\ninto it.\n2. Place the triangular prism on a white background.\n3. Shine a beam of white light through the side of the prism.\nQUESTIONS:\n1. Draw a picture showing what you observe.\n.\n.\n89\n.\nChapter 4.\nVisible light\n\n.\n.\n2. Write a description of what you observed.\n3. Write down the order in which the colours appear.\n4. If you repeat the experiment, does the order of the colours change?\n5. What do the different colours we see tell us about the composition of\nwhite light?\n.\n..\n90\n.\nEnergy and Change\n\nSo, what have we learned so far? Light radiates from luminous objects and\nalways travels in straight lines. The white light that we see is made up of the 7\ndifferent colours of the spectrum. When the 7 colours are travelling together we\nsee them as white light.\nThe 7 colours of the visible spectrum are Red, Orange, Yellow, Green, Blue,\nIndigo and Violet. Each colour has a different wavelength and frequency. Have\na look at the following image which shows the spectrum of visible light.\n.\nTAKE NOTE\nYou can use the\nabbreviation ROYGBIV\nto remember the order\nof the colours.\nThe colours combine to form white light.\n.\nTAKE NOTE\nThe primary colours of\nlight are red, green and\nblue.\n.\nACTIVITY: Colour spinning wheels\n.\nMATERIALS:\n• white cardboard\n• coloured pens or pencils (red, orange, yellow, green, blue, indigo, violet)\n• string\n• scissors\n• round object\nINSTRUCTIONS:\n1. Draw a circle on the cardboard. You can trace around a round object such\nas a cup or saucer to do this. Cut out the circle.\n.\n.\n91\n.\nChapter 4.\nVisible light\n\n.\n2. Now divide the circle into 7 equal segments. If you do not have indigo and\nviolet colours, but just one purple pen or crayon, then you can divide the\ncircle into 6 equal segments rather.\n3. Shade in each segment a different colour, in the order red, orange, yellow,\ngreen, blue, indigo, violet (or just purple if you do not have indigo and\nviolet).\n.\nDID YOU KNOW?\nAn artist might tell you\nthat the primary colours\nof paint are red, yellow\nand blue. This is\ndifferent to the primary\ncolours of light. This is\nbecause the pigments\nyellow, blue and red\ncannot be mixed from\nother pigments. In\nprinting, the primary\ncolours are magenta,\nyellow and cyan.\n4. Next, make two holes, one on either side of the centre as shown below.\n5. Thread the string through the holes and tie it in a loop.\n6. You are now ready to spin the wheel. Holding the ends of the loop in each\nhand, twirl the string over, like you would a skipping rope, so that the\nstring twists. Once the string is tightly twisted, pull your hands apart, then\nbring them back together. Continue bringing your hands in and out and\nwatch the circle spin.\n.\nVISIT\nThere is no pink light.\nbit.ly/1b2gFXU\n7. What do you observe about the colour of the wheel as it spins faster?\n.\n..\n92\n.\nEnergy and Change\n\nSo far we have been talking about the visible light spectrum. As we mentioned\nin the beginning, this is the light that we can see. We also spoke about how light\ntravels in electromagnetic waves. We can only see light with a certain range of\nwavelengths. What does this mean?\n.\nDID YOU KNOW?\nWavelengths can be as\nsmall as one billionth of\na meter, as with gamma\nrays. Wavelengths can\neven be as long as\nmeters, for example in\nradio waves.\nThe size of a wave is measured in wavelengths. A wavelength is the distance\nbetween two corresponding points on two consecutive waves. Normally this is\ndone by measuring from peak to peak or from trough to trough. Have a look at\nthe following diagram which illustrates a wavelength.\n.\nDID YOU KNOW?\nIn police forensics,\nultraviolet light can be\nused along with a\nspecial powder to\ndetect finger and shoe\nprints that can help\nsolve crimes.\nThe wavelengths of the different colours of visible light are different lengths, as\nshown in the following diagram.\nWe can also talk about the frequency of a wave. If a wave has a long\nwavelength, then it has a low frequency; if it has a short wavelength, then it has\na high frequency.\nOf visible light, orange and red light have the longest wavelengths (and lowest frequency)\nand violet, indigo and blue have the shorter wavelengths (and highest frequency).\n.\n.\n93\n.\nChapter 4.\nVisible light\n\nWhen it comes to visible light, we only see wavelengths of 400 to 700 billionths\nof a meter. This is called the visible spectrum. But, light waves are just part of\nthe wave spectrum. There is invisible light with shorter wavelengths, such as\nultraviolet light, and there are longer wavelengths, such as infrared light.\nHave you ever looked through a window and wondered why it is made of glass?\nLet's find out how light behaves when it strikes the surface of different types of\nmaterials in the next section.\n.", "chapter_id": "4.2" }, { "title": "Opaque and transparent substances", "content": "4.3 Opaque and transparent substances\n.\nNEW WORDS\n• opaque\n• transparent\n• translucent\n• transmit\nThree different things happen when light hits a surface, it can be reflected\n(bounce off), absorbed or transmitted (pass through). Glass reflects some light\nbut most of the light is transmitted straight through. That's why we can see\nobjects on the other side of a closed window.\nWe say that glass is transparent. Let's find out more about what this means. If a\nsubstance is not transparent, it is opaque.\n.\nACTIVITY: Shadow Play\n.\nMATERIALS:\n• cardboard\n• clear plastic\n• plastic shopping bag\n• scissors\n• light source (ray box or light bulb)\nINSTRUCTIONS:\n1. Cut out three shapes from your cardboard. All of the shapes should be\nsimilar but three different sizes: small, medium and large.\n2. Switch on the light source.\n3. Hold your first shape a short distance in front of the light source.\n4. Look at the shadow that forms. Write down what you observe.\n5. Hold your second shape the same distance in front of the light source.\n6. Look at the shadow that forms. Write down what you observe.\n7. Hold your third shape the same distance in front of the light source.\n8. Look at the shadow that forms. Write down what you observe.\n9. The shadow is formed on the side furthest from the light source. It is dark\n..\n94\n.\nEnergy and Change\n\n.\nin colour and larger than the first and second shadows.\n10. Use your first cardboard shape as a template and cut the shape from the\nclear plastic and the plastic shopping bag.\n11. Hold the clear plastic shape the same distance from the light source. Write\ndown what you observe.\n12. Hold the plastic shopping bag shape the same distance from the light\nsource. Write down what you observe.\nQUESTIONS\n1. When you held the cardboard up to the light, did it allow light to pass\nthrough it? How do you know this?\n2. Is the cardboard shape opaque or transparent?\n3. What did you notice about the shadows formed by the different size\ncardboard shapes?\n4. Draw a diagram to show how the shadow is formed behind the opaque\nshape. Use straight lines with arrowheads to represent the rays of light.\n.\n.\n.\n95\n.\nChapter 4.\nVisible light\n\n.\n5. The distance between the shape and the light source was kept the same.\nWhat do you think would have happened to the shadow if the distance\nwas increased?\n6. Test your idea from question 5 by moving your cardboard shapes closer to\nand further away from the light source. What do you see? Were you\ncorrect in your prediction?\n7. Is the clear plastic shape opaque or transparent?\n8. Did the clear plastic cast a shadow?\n9. Explain why the cardboard casts a shadow but the clear plastic does not.\n10. Is the plastic shopping bag shape opaque or transparent?\n11. Explain why the shopping bag casts a lighter shadow.\n.\n..\n96\n.\nEnergy and Change\n\nWhat have we learned? Shadows are formed because light travels in straight\nlines and cannot pass through opaque objects.\nSubstances which transmit most of the light and only absorb or reflect a little bit\nare called transparent. Can you list some everyday objects which are\ntransparent?\nSubstances which completely reflect or absorb light without transmitting any\nare called opaque. Can you list some everyday objects which are opaque?\nSome substances, such as the plastic shopping bag, allow some light to pass\nthrough, but not all of it. This substance is translucent, or semi-transparent.\nShadows can be useful. Sundials have\nbeen used since ancient times as a\ntime-keeping device, like a watch or a\nclock. As the position of the Sun\nchanges in the sky, the shadow cast by\nthe style moves across the surface of\nthe sundial. The surface is marked with\nnumbers, allowing the shadow to\nindicate time of day.\nWe can use transparent objects to make filters. If we want red light we use a\nred glass bulb or a red plastic film placed in front of the light. Only red light is\nable to transmit through the red glass or plastic. The other colours are absorbed\nby the filter.\nThese are different colour filters for a camera. The red filter will only allow red light\nthrough and so the photograph will have a red effect applied to it. The other colours of\nlight are absorbed by the filter.\nNow that we have seen some examples of transparent and opaque substances,\nlet's take a closer look at what it means to absorb or reflect light.\n.\n.\n97\n.\nChapter 4.\nVisible light\n\n.", "chapter_id": "4.3" }, { "title": "Absorption of light", "content": "4.4 Absorption of light\nLook at this picture of a ladybird. Why\nis it red and black? And why is the leaf\nso green? How do we see the different\ncolours? It all has to do with what\nhappens when light hits a surface.\nWhen light hits a surface, some of the\nlight is absorbed and the rest is\nreflected. It is the reflected light that\nreaches our eyes and allows us to see\nthe object.\nA ladybird.\nPreviously, we learned that white light is a mixture of different colours. When\nwhite light from the Sun hits the red shell of the ladybird all of the colours are\nabsorbed, except red. Red light is reflected back to our eyes and so we see a\nred ladybird.\nWe see the red shell of the ladybird as red light is reflected and the other colours are\nabsorbed.\nThe green leaf absorbs all the colours except green which it reflects back into\nour eyes.\n..\n98\n.\nEnergy and Change\n\nWe see a green leaf as green light is reflected and the other colours are absorbed by the\nleaf's surface.\nWhat about the black spots of the ladybird? Is black a colour? The black spots\non the ladybird absorb all the colours and no light is reflected. That is why they\nappear black.\n.\nTAKE NOTE\nAlthough we can get\nblack paint as a\npigment, black is not a\ncolour of light. Black is\nthe result of the\ncomplete absorption of\nlight.\nDo you remember learning about heat as energy transfer in Gr 7? We looked at\nthe absorption of heat. We saw that black, matt objects absorbed all of the light\nenergy, while white objects reflected all of it. Black, matt (not shiny) objects\nabsorb all of the colours of light and reflect none and so appear black to our\neyes.\nWhat about a white object? Why do you think white objects look white? Have a\nlook at the following diagram for a clue.\n.\n.\n99\n.\nChapter 4.\nVisible light\n\n.\n.\nACTIVITY: Why do objects look red under red\nlight?\n.\nMATERIALS:\n• piece of red plastic to act as a filter\n• light source (light bulb or torch)\n• white object\nINSTRUCTIONS:\n1. Place a white object on the desk.\n2. Switch on your light source and place the red plastic in front of the light.\n3. Shine the light (with the red plastic in front) onto the piece of white paper.\nQUESTIONS:\n1. What colour was the page under normal light?\n2. Why does the page appear white in normal light?\n3. What did you see when the red plastic filter shone on the white page?\n4. Explain why the paper changed colour.\n.\nLet's now look more at what we mean by reflection of light.\n..\n100\n.\nEnergy and Change\n\n.", "chapter_id": "4.4" }, { "title": "Reflection of light", "content": "4.5 Reflection of light\n.\nNEW WORDS\n• reflect\n• incident ray\n• reflected ray\n• normal line\n• angle of\nincidence\n• angle of\nreflection\n• perpendicular\nWhen light hits a surface it is\noften reflected off the surface.\nThis photograph shows how\nlight is reflected off a still lake,\ncreating a mirror image of the\ntree. The still, flat surface of the\nlake has acted as a mirror.\nA tree reflection.\nHave some fun with these photos of reflections in water. One photograph is the\nright way up and the other one is upside down! Which one is which?\nReflections on the Negro River in the\nAmazon.\nReflections in the Arno River in Italy.\nMost surfaces reflect light. When light strikes a reflective surface, it can change\ndirection. Let's look at how this happens.\nWhen light reflects off a surface the ray which hits the surface, it is called the\nincident ray. The ray of light which is reflected from the surface is called the\nreflected ray. When we draw diagrams of reflection we also draw in an\nimaginary line to help us measure different angles. This line is called the normal.\nThe normal line is always drawn perpendicular to the surface.\nBetween the normal line and the incident and reflected rays, there are two\nangles. These are:\n• angle of incidence - the angle between the incident ray and normal line\n• angle of reflection - the angle between the reflected ray and normal line\nThe following diagram explains these concepts.\n.\n.\n101\n.\nChapter 4.\nVisible light\n\nLet's investigate the relationship between the angle of incidence and the angle\nof reflection.\n.\nINVESTIGATION:\nIs there a relationship between the\nangles of incidence and reflections?\n.\nAIM: To investigate the reflection of light from a surface.\nINVESTIGATIVE QUESTION:\nLook at the diagram above and try to formulate an investigative question for\nthis investigation.\nHYPOTHESIS: The angle of incidence is equal to the angle of reflection\nMATERIALS AND APPARATUS:\n• mirror\n• white paper\n• pencil\n• protractor\n• ruler\n• ray box\nMETHOD:\n1. Put a white piece of paper on the desk.\n2. Use your ruler to draw a straight line near the top of the white paper.\n..\n102\n.\nEnergy and Change\n\n.\n3. Use your protractor to make a right\nangle in the middle of your pencil\nline. This is the normal line.\nMarking a right angle with a protractor.\n4. Place your mirror upright along the\nfirst line.\n5. Shine a light from the ray box along\nthe paper so that it \"hits\" the mirror\nwhere your normal line and your\nmirror meet.\nA mirror is placed on the line and a ray\nshone to strike the mirror at the normal\nline.\n6. Use a pencil to mark the incident\nlight ray.\nMarking the incident light ray.\n7. Use a pencil to mark the reflected\nlight ray.\nMarking the reflected ray.\n8. Remove the mirror and switch off\nthe ray box.\n9. Use a ruler and pencil to draw a line\nfrom the points you have marked on\neach ray to the normal line.\nDrawing in the rays.\n.\n.\n103\n.\nChapter 4.\nVisible light\n\n.\n10. Mark the angle of incidence (i) and\nangle of reflection (r).\nYour ray diagram should look similar to\nthis.\n11. Turn the ray box on again to confirm\nthat your pencil lines follow the rays.\nThe ray diagram overlaps the actual rays.\n12. Use a protractor and measure the\nangle of incidence and the angle of\nreflection and record your results in\nthe table.\n13. Repeat this method 3 more times,\neach time using a different angle of\nincidence.\nA different angle of incidence.\n.\nTAKE NOTE\nKeep one of the sheets\nwith your drawn ray\ndiagram for the next\nactivity.\nRESULTS:\nFill your results into the following table.\nRepeat\nAngle of Incidence\nAngle of Reflection\n1\n2\n3\n4\nANALYSIS:\n1. Has your investigation provided everything you need to answer your\ninvestigative question?\n..\n104\n.\nEnergy and Change\n\n.\n2. How could you improve this investigation to get more accurate results?\nCONCLUSION:\nWhat can you conclude based on your results?\n.\nWhenever light is reflected from a surface, the angle of incidence to equal to\nthe angle of reflection. On a smooth surface all the light rays are reflected in the\nsame way and so the image is clear and focused.\nA mirror is an example of a smooth surface. The image you see is focused and\nclear. As you can see in the photograph, the scientists and engineers are clear\nand focused in the mirror image.\nA mirror segment from one of NASA's telescopes provides a clear and focused reflection.\n.\nTAKE NOTE\nIn reflection, not only is\nthe angle of incidence\nequal to the angle of\nreflection, but the\nincident ray and\nreflection ray are also in\nthe same plane.\n.\nVISIT\nWhat colour is a mirror?\n(video)\nbit.ly/GABdNZ\nWhat happens when we do not have a smooth surface? Have a look at the\nphoto.\n.\n.\n105\n.\nChapter 4.\nVisible light\n\nWhy is the reflection of the grass and reeds not clear, but rather blurred?\n.\nACTIVITY: Light reflection off aluminium foil\n.\nMATERIALS:\n• aluminium foil\n• white paper\n• ray box\nINSTRUCTIONS:\n1. If possible, use the white sheets of paper from the last investigation where\nyou drew your ray diagrams.\n2. Similar to what you did in the last investigation, set up a ray box and direct\nthe ray along the line of incidence which you drew.\n3. Crumple a piece of aluminium foil and place this in the spot instead of the\nmirror.\n4. Observe the reflected ray.\nQUESTIONS:\n1. Describe the reflected ray off the aluminium foil and how this compares to\nthe reflected ray off the mirror.\n.\nVISIT\nWatch a video about the\ncreative way that\nscientists have tried to\nanswer the question:\n\"What is light?\"\nbit.ly/GAMvAL\n2. Why do you think you observed these differences?\n.\n..\n106\n.\nEnergy and Change\n\nCan you now see why reflections off rippled water are not clear, but rather\nblurred? This is because the light rays have not reflected parallel to each other\nas they do from a smooth surface, but have scattered in different directions.\nThe following table shows the difference between a smooth surface and a rough\nsurface. Straight parallel rays are approaching the surface. You need to draw in\nthe reflected rays to show specular (clear) reflection from a smooth surface and\ndiffuse (unclear) reflection from a rough surface.\n.\nTAKE NOTE\n'Diffuse' can mean\nunclear as well as\nspread out. In this\nexample, the reflection\nis unclear because the\nrays are spread out or\ndiffuse.\nSpecular diffusion from a smooth\nsurface\nDiffuse reflection from a rough\nsurface.\nVisible light is the range of frequencies of light that are visible to the human eye,\nand is responsible for the sense of sight. Are you curious to find out how we\nactually see light? Let's discover more in the next section.\n.", "chapter_id": "4.5" }, { "title": "How do we see light?", "content": "4.6 How do we see light?\n.\nNEW WORDS\n• retina\n• stimulate\nHow is it that we are able to see light? Light that is absorbed by objects does\nnot enter the eye. Only reflected light or direct light from luminous objects can\nenter the eye and be interpreted. Have a look at the following image which\nshows the outer structure of the eye.\nWe can see the iris, the pupil and the sclera. The sclera is a the tough white,\nouter part of the eye, which acts as protection. The iris is the coloured part of\nthe eye which differs from person to person. It is circular and surrounds the\npupil. Light enters the eye through the pupil.\n.\nVISIT\n2012 Nobel Prize: How do\nwe see light?\nbit.ly/1a4zs2D\n.\n.\n107\n.\nChapter 4.\nVisible light\n\nThe size of your pupil changes in different light conditions. In bright light, the pupil\ncontracts (gets smaller) to let less light through (as on the left), and in low light your\npupil dilates (gets bigger) to let more light through (as on the right).\nLet's take a look at the internal structure of the human eye. The following\ndiagram shows a cross section through the eye. The eye is actually a large ball,\nand only a small part is visible on the outside. Covering the iris is a tough,\ntransparent layer called the cornea. Behind the iris is the lens. Both the cornea\nand the lens help you to focus the light entering your eyes, as we will learn\nabout in the next section.\n.\nTAKE NOTE\nThe fovea is the part of\nthe eye located in the\ncentre of the retina\nwhere the clearest\nimage is formed.\nA diagram of the eye.\nThe light travels through the eye and hits the retina at the back of the eyeball.\nThe retina is a layer of tissue lining the back of the eyeball, as indicated in the\ndiagram, it is the yellow layer. The retina consists of cells which are sensitive to\nlight. Light enters the eye and forms an image on the back of the eyeball. The\nway in which light hits the back of the eye, is similar to what happens in a\npinhole camera. The receptor cells convert the light energy into electrical nerve\nimpulses. These impulses travel out of the eye through the optic nerve and to\nthe brain where they are interpreted as sight.\n.\nTAKE NOTE\nThe cell is the basic\nstructural and\nfunctional unit of all\nliving things. We will be\nlearning more about the\ncell next year in Gr 9\nLife and Living.\n.\nVISIT\nFind your blind spot with\nthis optical illusion.\nbit.ly/19jumEr\nSo how do we see colour? Do you remember when we spoke about why the\nladybird appears red and black? Look at the following diagram again.\n..\n108\n.\nEnergy and Change\n\nThe white light hits the ladybird's surface. The white light has all the colours of\nlight, but when it hits the red surface, only the red light is reflected. The other\ncolours are absorbed by the red surface. This means that when we look at the\nred parts of the ladybird, we only get red light reflected into our eyes.\nTherefore, when this reflected light hits our retina and the electrical impulse is\nsent to our brains, we see the red colour.\n.\nDID YOU KNOW?\nEach of your eyes has a\nsmall blind spot at the\nback of the retina where\nthe optic nerve\nattaches. You do not\nnormally notice the hole\nin your vision because\nyour eyes work together\nto fill in each other's\nblind spot.\n.\nACTIVITY: Seeing colours\n.\nMATERIALS:\n• coloured pens or pencils\nINSTRUCTIONS:\n.\nDID YOU KNOW?\nThe cells in your eye\ncome in different\nshapes. Rod-shaped\ncells allow you to see\nshapes, and\ncone-shaped cells allow\nyou to see colour.\n1. Answer the following questions about how we see objects.\n2. Draw a ray diagram to accompany your written answer.\n3. An example has been done for you.\nLook at the picture of a sunflower.\nA black and yellow sunflower.\n.\n.\n109\n.\nChapter 4.\nVisible light\n\n.\nWe can draw a ray diagram to show why we see the green leaves as green, as\nshown below. The green surface of the leaves absorb all the colours of white\nlight except green light which is reflected into our eyes.\nNow explain why the petals appear yellow and the centre appears black. Use\nthe concepts of absorption and reflection in your explanation. Draw diagrams\nto support your answer.\n.\nHeath has bought himself a blue car.\nExplain why we see the car as blue by\nusing the absorption and reflection of\nlight. Draw a diagram to support your\nanswer.\nHeath's blue car.\n..\n110\n.\nEnergy and Change\n\n.\n.\n.\n.\nVISIT\nA simulation on colour\nvision.\nbit.ly/18TbpEA\nWe have looked at opaque and transparent substances, absorption of light,\nreflection of light and how we see light. We are now going to go back to\ntransparent substances and see how light can interact with these materials.\n.", "chapter_id": "4.6" }, { "title": "Refraction of light", "content": "4.7 Refraction of light\nDo you remember the last time you drank a cold drink with a straw? Did you\nnotice that the straw did not look straight anymore once it was in the water or\ncool drink?\n.\nNEW WORDS\n• refraction\n• medium\n• optical density\nWhy does the pencil in this glass of water look bent?\nLet's investigate this by examining what happens to light when it passes\nthrough a glass block.\n.\n.\n111\n.\nChapter 4.\nVisible light\n\n.\n.\nINVESTIGATION:\nWhat happens to light when it\npasses through a glass block\n.\nWe are going to investigate what happens to a ray of light when it passes from\nair and into a glass block and then from the glass block back into air. We are\ngoing to use a glass block with parallel sides.\nBefore we start the investigation, we need to think about how we are going to\ndetermine if light changes direction or not. Do you remember in the\ninvestigation on reflection where we measured the angle of incidence and the\nangle of reflection? What did we find in this investigation?\nWhen light passes through a transparent substance, we can also measure the\nangles. Look at the following diagram. The angle of incidence (i) is measured\nbetween the incident light ray and the normal line. As the light passes through\nthe transparent substance, the angle of refraction (r) is the angle between the\nrefracted light ray and the normal.\nA light ray passing from one medium to another.\nIn the diagram above, you can see that the angle of refraction is smaller than\nthe angle of incidence. Therefore, the refracted light ray changed direction\nwhen it entered the transparent medium. We can also say something about\nwhich direction it bent towards. Did the light ray bend towards or away from\nthe normal line?\nThe next diagram shows another outcome.\n..\n112\n.\nEnergy and Change\n\n.\nA light ray passing from one medium to another.\nIn the diagram above, does the refracted ray change direction when it enters\nthe transparent medium? Give a reason for your answer.\nIn which direction did the refracted ray change?\nWe are now ready to start our investigation.\nAIM: To determine whether light changes direction when it passes through a\nparallel-sided glass block.\nHYPOTHESIS: Write a hypothesis for this investigation.\nMATERIALS AND APPARATUS:\n• glass block\n• ray box, laser pointer or other light source\n• protractor\nMETHOD:\n.\nTAKE NOTE\nThe emergent ray from\na parallel sided block is\nparallel to the incident\nray.\n1. Put the glass block in the centre of a piece of white paper and trace around\nit.\n2. Shine a ray of light into the glass block. The ray should be at an angle to\nthe surface of the block.\n.\n.\n113\n.\nChapter 4.\nVisible light\n\n.\n3. Trace the light ray with pencil and mark the point at which it enters the\nglass block.\n4. The light ray emerges on the other side of the glass block. Mark the point\nat which it emerges with a pencil and trace the emergent ray.\n5. Remove the glass block. Your diagram should look similar to the one\nabove.\n6. Draw a line joining the incident ray and emergent ray. You have traced the\nrefracted ray through the glass block.\n7. Draw the normal lines where the incident ray meets the block and where\nthe emergent ray leaves the block.\n8. Measure the angles labelled 1, 2, 3 and 4 as shown on the diagram with a\nprotractor.\n9. Fill in the measurements in the table.\n10. Repeat the steps above three times using different angles of incidence\n(angle 1).\n..\n114\n.\nEnergy and Change\n\n.\nRESULTS AND OBSERVATIONS:\nFill your results into the following table.\nExperimental\nrepeat\nAngle 1\nAngle 2\nAngle 3\nAngle 4\n1\n2\n3\n4\n1. Which pairs of angles are equal in the measurements you have taken?\n2. Which of the angles you measured are the angles of incidence and which\nare the angles of refraction? Write this down below and mark them on the\ndiagram above.\n3. What do you notice about the angle of incidence and angle of refraction\nfor each of your sets of measurements?\n4. Did the light entering the glass block bend towards or away from the\nnormal line?\n5. Make the angle of incidence zero (make the light ray enter the block\nperpendicular to the surface). What is the angle of refraction?\nCONCLUSION:\nWhat can you conclude from your results?\n.\n.\nVISIT\nLearn more about\nrefraction with this\nsimulation.\nbit.ly/GAxLmc\nThe angle of incidence is not equal to the angle of refraction because the light\nhas changed direction as it enters the glass. Therefore, when light travels from\none medium to another, it bends, or changes direction. This is called refraction.\n.\n.\n115\n.\nChapter 4.\nVisible light\n\nWhen light enters a different medium at right angles then it does not change\ndirection.\nSo why does the light refract? Light behaves as a wave does and waves travel\nat different speeds in different media. For example, light travels faster in air\nthan it does in water. When light enters a different medium, it changes speed,\nand if it entered at an angle other than 90o, then it also changes direction. The\nmore dense the medium, the slower the light moves.\nDo you remember learning about density last term in Matter and Materials?\nWrite down your own definition for density in the space below.\n.\nTAKE NOTE\nRemember that\nalthough we learn\nabout Natural Sciences\nin 4 strands throughout\nthe year, there are many\nconnections and links\nbetween the strands.\nIf light moves from a less dense medium, like air, into a denser medium, like\nglass, then the light slows down. The light will bend towards the normal line.\n.\nVISIT\nThe speed of light in glass.\nbit.ly/1fcfJVZ\nIf light moves from a more dense medium to a less dense medium then the light\nspeeds up and moves away from the normal.\nWhen light refracts and changes direction as it passes through different\nmediums, it can distort what we see. Think back to the pencil or straw in a glass\nof water at the start of the section. We can now explain why a drinking straw or\npencil in a glass of water looks bent. The light bends when it moves from one\nmedium to another. Light moves from the air to glass to water, and therefore\nchanges direction.\nIf you have stood in a pool of water before and looked down, have you noticed\nhow short your legs appear to be? Let's have a look at this a bit more in the\nnext activity.\n..\n116\n.\nEnergy and Change\n\n.\n.\nACTIVITY: Magic coin trick\n.\nMATERIALS:\n• coin\n• prestik\n• opaque bowl or cup\n• water\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Put a small amount of prestik onto the bottom of the bowl.\n3. Stick the coin to the bottom of the bowl.\n4. Take small steps back from the desk/table until you cannot see the coin\nover the lip of the bowl.\n5. Ask your partner to slowly pour water into the bowl and observe.\nQUESTIONS:\n.\nVISIT\nWatch a video that shows\nand explains the coin\nactivity.\nbit.ly/15NmXXO\n1. What happened when your partner poured the water into the bowl?\n2. Where does the coin appear to be?\n3. Explain why the coin can be seen when the water is added, but not before.\nThe diagrams below will help you explain what is happening in words.\n.\nTAKE NOTE\nThe diagrams used here\nshow the container as\ntransparent so that you\ncan see the coin inside,\nwhereas you will\nactually be using an\nopaque container.\nEmpty container.\nContainer with water.\n.\n.\n.\n117\n.\nChapter 4.\nVisible light\n\nRefraction can be used to explain why images appear to be distorted when we\nview them through transparent mediums. For example, if you are looking at\nyour legs or hands through some water, they will appear closer than they\nactually are as the light is refracted. Look at the photograph of the glass with\nwater in it in front of diagonal lines. Can you see how the lines are distorted\nwhen the light travels through the water and glass compared to when it does\nnot?\nLight refraction through glass and water.\nCan you remember how we split white light into the separate colours of the\nvisible spectrum in the beginning of this chapter? What did we use to do this in\nthe activity?\nWe can do this because the different\ncolours of light bend by different\namounts when the light enters a\ndifferent medium. Different colours of\nlight will slow down to different\nspeeds, causing them to bend by\ndifferent amounts.\nRefraction through a triangular prism.\nWhen the white light entered the prism it refracted. The different colours of\nlight travel at different speeds in the prism so they refracted at different angles\nand split up. Red light refracts the least and the violet light refracts the most as\nyou can see in the following diagram.\n..\n118\n.\nEnergy and Change\n\nPrisms are not the only objects that can split white light into separate colours.\nIn fact, a rainbow is a good example of white light splitting up.\nA rainbow.\nLight from the Sun enters the raindrops and refracts. The light is then reflected\noff the back of the raindrop. When the light passes out of the raindrop it is\nrefracted again and the colours split up even more as shown in the diagram.\nA raindrop refracts and reflects light, dispersing white light into the colours of the visible\nspectrum.\n.\n.\n119\n.\nChapter 4.\nVisible light\n\nWhat colour is at the top of a rainbow and which colour is at the bottom?\nDoes this match the order which we see in the diagram showing how light is\nrefracted and reflected in a raindrop?\nHow does this happen? When we see a rainbow, we see a combination of\nmillions of raindrops. Although each raindrop refracts and reflects all 7 colours,\nwe only see only colour of light reflected from each particular raindrop. This\ndepends on the angle of the raindrop from our position. Therefore, the\nraindrops higher up in the sky reflect red light to us and the rain drops lower\ndown reflect violet light to us. This is shown in the following diagram.\nWe see rainbows with red at the top and violet at the bottom due to the combination of\nmillions of raindrops. We only see one colour reflected from a particular raindrop,\ndepending on its position in the sky.\nWe are now going to look at an application of the refraction of light.\nLenses\n.\nNEW WORDS\n• diverge\n• converge\n• focus\nDo you remember when we spoke about how we see light and the structure of\nthe eye, we mentioned that there is a lens just behind the iris? Another place\nwhere you may have seen lenses before are in reading glasses which some\npeople wear to correct their vision. Or, have you seen how a magnifying glass\nmakes things appear bigger. What are lenses and how do they work?\nA magnifying glass makes things look bigger.\n..\n120\n.\nEnergy and Change\n\nA lens is a transparent object which focuses or refracts light. When light is\nspread out, we say it has diverged. Some lenses will diverge light while others\nwill converge light, bringing the light rays together. When light rays are all\nbrought to the same point, we say they have been focused. Let's have a look at\nthis more closely.\n.\nACTIVITY: Diverging and converging light with\nlenses\n.\nMATERIALS:\n• ray box or light source\n• concave lens\n• convex lens\n• piece of paper\n• pencil\nBefore we start, it is important that you know the difference between a convex\nand a concave lens.\nConvex lens\nConcave lens\nA convex lens has one\nside which curves or\nbulges outwards. A\nconvex lens converges\nlight.\nA concave lens has one\nside which curves or is\nhollowed inwards. A\nconcave lens diverges\nlight.\n.\nTAKE NOTE\nA lens can have two\nsides which are concave\nand it is then called a\nbiconcave lens or two\nsides which are convex\nand it is then called a\nbiconvex lens.\n.\n.\n121\n.\nChapter 4.\nVisible light\n\n.\nINSTRUCTIONS:\n1. Place a ray box or light source on one side of a piece of paper and turn it\non. Observe the light rays. You might see something as shown in the\nphotograph here.\nThree rays coming out of a ray box.\n2. Turn the ray box off.\n3. Place the convex lens (with the rounded surface) on the piece of paper\nwhere the light rays will pass through it. Trace around it.\n4. Turn on the ray box or light source and observe what happens to the rays\nwhen they pass through the lens.\nLight rays passing through a convex lens.\n5. Trace the path of the light rays on your piece of paper.\n6. Describe what has happened to the light rays.\n7. Mark the point where the light rays cross. This is called the focal point of a\nconvex lens.\n8. Turn off the ray box or light source and place a new piece of paper in front\nof it.\n9. Now place the concave lens in the path of the light rays and trace around\nthe lens.\n10. Turn on the light source and observe what happens to the rays.\n..\n122\n.\nEnergy and Change\n\n.\n11. Trace the path of the rays on the piece of paper.\nA concave lens in front of the rays of light.\n12. Describe what has happened to the light rays.\n13. Turn off the light rays and extend the rays you have drawn until they meet\nat a point in front of the lens. This is the focal point of a concave lens.\n14. If you still have your pin hole cameras, place a convex and concave lens in\nfront of the camera and observe the image that forms.\nViewing a light source through a pinhole camera with different lenses.\n15. Is the image larger or smaller when you observe through a concave lens?\n16. Is the image larger or smaller when you observe through a convex lens?\n.\n.\n.\n123\n.\nChapter 4.\nVisible light\n\nWe have now seen how lenses can disperse or focus light. Have a look at the\nfollowing diagrams which show how a biconvex lens converges light and a\nbiconcave lens diverges light.\n..\n124\n.\nEnergy and Change\n\nConverging lens\nDiverging lens\nA converging lens refracts the light\nentering it and bends the light rays\nto a focal point on the other side of\nthe lens.\nA diverging lens refracts the light\nentering it and bends the light rays\naway from each other. The light\nrays can be traced back to a focal\npoint in front of the lens.\nWhat do we use lenses for? Think of a magnifying glass. If you hold a\nmagnifying glass over a picture or words then it enlarges the image. Is a\nmagnifying glass an example of a diverging or converging lens?\nLet's think about how this works. Imagine you are looking at the ladybird from\nthe beginning of the chapter through a magnifying glass. The ladybird looks\nbigger than what it actually is. When the object you are viewing is closer to the\nlens than the focal point, you see a virtual image of the ladybird that is larger\nthan the object.\nHave a look at the first diagram below. Can you see that the ladybird is between\nthe focal point and the lens? The rays reflected from the ladybird are refracted\nby the magnifying glass and enter the person's eye.\n.\n.\n125\n.\nChapter 4.\nVisible light\n\nIn the next diagram you can see how your eyes see a virtual image of the\nladybird which is bigger than the object. The more curved the convex lens is in\na magnifying glass, the greater its ability to magnify objects.\n.\nTAKE NOTE\nWhen you hold a\nmagnifying glass up\nand view a distant\nobject, the object\nappears smaller and\nupside down. Unlike\nwhen viewing the\nladybird close up, the\ndistant object is beyond\nthe focal point of the\nlens, which results in\nthis effect.\n.\nVISIT\nHow do lenses work?\nbit.ly/GABjoO\nDo you remember what the human eye looks like? We have lenses in our eyes\nto allow us to see. The light enters the eye and passes through the lens. The\nlens focuses the light onto the back of our retina so that a clear image is formed.\nWhat type of lens do we have in our eyes? Give a reason for your answer.\nIn order for a clear image to form, the lens in our eye needs to focus the light\nrays coming into our eyes so that the focal point falls on the retina. This\ndepends on the shape of the lens in our eyes. Sometimes, people have lenses in\ntheir eyes that cannot focus properly. Have a look at the following diagram\nwhich shows a normal eye and then an eye which focuses before the retina\n(near-sighted) and behind the retina (far-sighted).\n..\n126\n.\nEnergy and Change\n\nOptical glasses, or spectacles, are used to correct near or far-sightedness.\nIf you are near-sighted you need a diverging lens. Would this be a biconcave or\nbiconvex lens?\n.\nDID YOU KNOW?\nA contact lens is\ndesigned to rest on the\ncornea of the eye and\ncorrect vision. Leonardo\nda Vinci was the first to\ncome up with the idea\nin the 16th century to\nhelp prevent eye\ninfection.\n.\nDID YOU KNOW?\nA microscope makes a\ntiny, nearby object look\nmuch bigger. A\ntelescope makes a\nlarge, distant object\nlook much closer and\nbrighter. In both, light\nfrom the object passes\nthrough two or more\nlenses to form an\nimage. The lens shapes\nand distances between\nthem determine how\nthe image is produced.\nIf you are far-sighted you need a converging lens. Would this be a biconcave or\nbiconvex lens?\nAn optometrist holds a lens in front of a patient's eye to correct her vision.\nThe following image shows how lenses can be used to correct far and\nnear-sightedness.\n.\n.\n127\n.\nChapter 4.\nVisible light\n\n.\nTAKE NOTE\nNext term in Planet\nEarth and Beyond we\nwill look at how lenses\nare used in optical\ntelescopes to view\nobjects in space.\n.\nACTIVITY: Research careers in optics\n.\n.\nVISIT\nAn interview conducted\nwith an optometrist.\nbit.ly/19WxYYa\nThere are many different careers in the field of geometric optics.\nINSTRUCTIONS:\n1. Work in groups of 3.\n2. Interview someone in the field of geometric optics and find out how they\nchose their career and what and where they studied.\n3. Write a paragraph explaining the career and the study options available in\norder to qualify for that career.\n4. Here are some examples of careers in geometric optics.\na) Optometry\nb) Ophthalmology\nc) Optoelectronics\nd) Illumination engineering\n.\n..\n128\n.\nEnergy and Change\n\n.\nVISIT\nWant to take part in some\nreal science research?\nCheck out these citizen\nscience projects to get\ninvolved easily.\nbit.ly/15KjnmD\nRemember to discover more online by visiting http://www.curious.org.za and\nby typing the links in the Visit margin boxes into your internet browser to watch\nany videos, play with simulations or read an interesting article.\nType the bit.ly link for the video or site that you want to visit into the address bar of your\nbrowser on your computer, tablet or mobile phone.\n. .\nSUMMARY:\n.\nKey Concepts\n• Light travels in straight lines.\n• White light consists of all the colours of the visible spectrum.\n• The colour spectrum can be seen when white light is dispersed by a\nprism or a raindrop (rainbow).\n• Light cannot pass through opaque objects.\n• Light can pass through transparent objects.\n• Light is absorbed by some materials.\n• A material appears to be a certain colour because it reflects that part of\nthe colour spectrum. Other wavelengths of light are absorbed.\n• In reflection, the angle of incidence is equal to the angle of reflection.\n• On a smooth surface, parallel rays of light are all reflected at the same\nangle.\n• On rough surfaces, the light is scattered and the image produced is not\nclear.\n• The human eye has specialised cells in the retina which convert light\ninto electrical nerve impulses. The nerve impulses are transmitted to\nthe brain via the optic nerve, where they are interpreted.\n• Light travels at different speeds in different media.\n• When light enters a different medium at an angle, the light is refracted.\n• If the light slows down, the light bends towards the normal line.\n• If the light speeds up, the light bends away from the normal line.\n• Converging lenses refract and focus light.\n• Diverging lenses and triangular prisms refract and disperse light.\n• Lenses have many applications, for example, in glasses to correct vision,\nmicroscopes, telescopes and magnifying glasses.\n.\nConcept Map\nThe concept map on the next page shows how all the concepts relating to\nvisible light link together.\nComplete the map to reinforce what you have\nlearned in this chapter.\n.\n.\n129\n.\nChapter 4.\nVisible light\n\n.\n\n.\n.\nREVISION:\n.\n1. Match the correct definitions to the terms in the following table. Write the\nletter of the definition next to the correct number below. [12 marks]\nTerm\nDefinition\n1. Radiation\nA. Light cannot pass\nthrough.\n2. Visible light\nB. The angle of incidence\nequals the angle of\nreflection when a ray is\nreflected off a smooth\nsurface.\n3. Opaque\nC. One of the ways in\nwhich energy is\ntransferred, specifically\nthrough a vacuum\n4. Transparent\nD. When light enters a\ntransparent medium it\ncan change direction.\n5. Absorption\nE. Curved inwards.\n6. Reflection\nF. The spectrum of light\nwhich we are able to see.\n7. Retina\nG. Bulging outwards.\n8. Refraction\nH. A transparent object\nable to refract and focus\nlight.\n.\n.\n131\n.\nChapter 4.\nVisible light\n\n.\nTerm\nDefinition\n9. Diverging\nI. Light can pass through.\n10. Lens\nJ. When light rays are\nspread out from a point.\n11. Concave\nK. A layer of tissue at the\nback of the eye which is\nsensitive to light.\n12. Convex\nL. When the surface of a\nsubstance absorbs\ncertain colours of light.\nAnswers:\n1:\n2:\n3:\n4:\n5:\n6:\n7:\n8:\n9:\n10:\n11:\n12:\n..\n132\n.\nEnergy and Change\n\n.\n2. A beam of white light is shone through a glass prism. It splits up into seven\ncolours which are shone on a screen. A learner took a photograph which is\nshown below and drew a ray diagram to show the prism. The colours are\nmarked 1 to 7 in the diagram.\nA photograph of the prism.\nA diagram drawn by the learner.\na) What does this tell us about white light? [1 mark]\nb) Why does the light do this when it passes through the prism? [3\nmarks]\nc) What colour is at label 1 and what colour is at label 7? Explain your\nanswer. [3 marks]\nd) What label corresponds to the colour of grass? [1 mark]\ne) Can you see there are two other lighter, white rays emerging from the\nprism? What do you think this is the result of? [2 marks]\n3. Why does an opaque object cast a shadow? [2 marks]\n.\n.\n133\n.\nChapter 4.\nVisible light\n\n.\n4. Look at the following photograph of water in a pond and answer the\nquestions.\nWater in a pond.\na) How are we able to see the image of the wooden poles sticking up on\nthe edge of the pond? [2 marks]\nb) Why is the image not clear, but blurred? [2 marks]\n5. Two learners are discussing the colours of light. They decide that white\nand black are not really colours of light. If they are not colours, then how\ncan we see them? [5 marks]\n6. Explain how we are able to see the different colours on the South African\nflag. [6 marks]\n..\n134\n.\nEnergy and Change\n\n.\n7. Draw a ray diagram in the space provided to show how we see the green\npart of the flag. [5 marks]\n.\n8. Which diagram shown below correctly shows the path of a ray of light\nthrough a triangular piece of glass? [2 marks]\n.\n.\n135\n.\nChapter 4.\nVisible light\n\n.\n9. Complete the following sentence and write it out in full on the lines\nprovided: When light travels from a less dense into a more dense\ntransparent medium, it refracts and bends\nthe normal line.\nWhen light travels from more dense to a less dense medium, it refracts and\nbends\nfrom the normal line. [2 marks]\n10. Draw a diagram to show what is meant by 'when the refracted ray bends\ntowards the normal'. Mark the angle of incidence and angle of refraction.\nIndicate which medium is denser [4 marks]\n.\n11. Study the following diagram and answer the questions that follow.\na) This diagram is a drawing that a learner made during an investigation\ninto the refraction of light. What does the red line represent in this\ndiagram? [1 mark]\n..\n136\n.\nEnergy and Change\n\n.\nb) What do the blue lines represent? Label this on the diagram. [1 mark]\nc) The light passes from the air and into a block of another medium. Is\nthis medium more or less dense than air? Give a reason for your\nanswer. [2 marks]\nd) What type of medium could the block be made from? [1 mark]\ne) Label the incident ray and the emergent ray on the diagram. [2 marks]\nf) Label the angles of incidence (i) and angles of refraction (r) on the\ndiagram. [2 marks]\n12. Which diagram shown below shows the path of a light beam passing\nthrough a rectangular glass prism correctly? [2 marks]\n13. Why does it look like the tree trunk in the photograph is skew? [2 marks]\n.\n.\n137\n.\nChapter 4.\nVisible light\n\n.\n14. What shape does a lens have to have in order to focus the light? [1 mark]\n15. Draw a ray diagram to show how a converging lens focuses light to a point.\n[4 marks]\n.\n16. Which eyesight defect can be fixed by using a converging lens? Explain\nwhat this defect is and why it can be corrected. [4 mark]\nTotal [74 marks]\n.\n..\n138\n.\nEnergy and Change\n\n.\n.\n.\nGLOSSARY\nammeter:\ndevice that measures the strength of an electric\ncurrent\nampere:\nthe standard unit for measuring electric current\nangle of incidence:\nthe angle between the incident ray and the normal\nline\nangle of reflection:\nthe angle between the reflected ray and the normal\nline\nattract:\nto pull something closer\ncell:\na source of energy for an electric circuit\ncomponent:\na part of a larger system\ncomposition:\nthe parts of a mixture\nconductor:\na substance which easily transmits electricity, heat,\nsound or light\nconverge:\nlight rays that come together and focus on a point\ndelocalised:\nnot limited to a particular place, free to move\ndischarge:\nthe sudden flow of charged particles between two\nelectrically charged objects\ndispersion:\nspreading of something over an area\ndiverge:\nlight rays that spread apart as they move further\nand further away from a point\nearth:\n(or ground) to connect with a conductor to the\nground, or the earth\nearthing:\na way to prevent electrical charge from building up\non an object, or to neutralise an electric charge, by\nallowing the excess charge to flow into the Earth\nelectric circuit:\na complete path through which electrons can move\nelectric current:\nthe movement of charge in an electric circuit\nelectrodes:\na conductor which allows electricity to enter a\nsubstance\nelectrolysis:\nthe use of electricity to separate chemicals in a\nsolution\nelectromagnet:\na device which becomes a magnet when electric\ncurrent passes through it\nelectroplating:\ncovering an object with a thin layer of metal using\nelectrolysis\nelectrostatic charge:\nthe electric charge resulting from static electricity\ncaused by an excess or deficiency of electrons on\nthe surface of an object\nflammable:\nsomething is easily set on fire\nfocus:\nbring together to the same point\nfriction:\nthe resistance that results when two surfaces are\nrubbed or moved against each other\nfuse:\na safety device designed to melt and break the\ncircuit if an electric current reaches too high a level\n.\n.\n139\n.\nChapter 4.\nVisible light\n\n.\nignite:\nto light something\nincident ray:\nthe ray of light which hits a surface\nluminous:\nbright or shining\nmedium:\nsubstance through which waves (such as light) can\ntravel\nneutral:\nwhen the number of positive charges (from the\nprotons) is equal to the number of negative\ncharges (from the electrons); the (positive and\nnegative) charges balance each other so that the\nobject is neither positively nor negatively charged\nnormal line:\nthis is an imaginary line which is drawn at 90o to\nthe surface\nopaque:\nsomething that you cannot see through; no light\npasses through the object\noptical density:\na measure of how well a medium allows light to\ntravel through it\noptics:\nthe scientific study of sight and the behaviour of\nlight\nparallel circuit:\na circuit that provides more than one pathway for\nthe current to pass through it\nperpendicular:\nat right angles\npropagation:\nspreading into new areas\nqualitative:\ndescribing something in terms of its properties or\ncharacteristics rather than by a number or\nmeasurement\nradiation:\nthe emission of energy as electromagnetic waves\nrectilinear:\nstraight lines\nreflect:\nthrow back without absorbing\nreflected ray:\nthe ray of light which leaves a surface\nrefraction:\nthe change in direction of a wave passing from one\nmedium to another caused by its change in speed\nrepel:\nto push something away\nresistance:\nthe opposition to the movement of charge in a\nconductor\nresistor:\na component in an electrical circuit which slows the\nmovement of charge\nretina:\na layer at the back of the eyeball which is made up\nof light sensitive cells\nseries:\ncomponents connected in series provide only one\npathway for electrical current; they are connected\none after another\nstatic electricity:\nthe build-up of a stationary electric charge (either\npositive or negative) on the surface of an object\nstimulate:\nto cause activity\nswitch:\na control component in an electrical circuit which\nopens or closes the circuit\ntranslucent:\nsemi-transparent; some light is able to pass through\nbut not enough for details to be seen clearly\ntransmit:\nto cause light to pass through space or medium\n..\n140\n.\nEnergy and Change\n\n.\ntransparent:\nsomething that you can see through; light passes\nthrough the object\nvariable:\nsomething that can vary or change\nvisible spectrum:\nthe portion of the wave spectrum that is visible to\nthe human eye\n.\n.\n141\n.\nChapter 4.\nVisible light\n\n\n\n. .\n1\n.\nThe solar system\n..\n144\n..\nKEY QUESTIONS:\n• How does the Sun produce its energy?\n• How can we observe the Sun without damaging our eyes?\n• What objects are in orbit around the Sun in our solar system?\n• Why are there two types of planets?\n• How do the planets in our solar system differ?\n• What are asteroids and comets?\n• What is the difference between a planet and a dwarf planet?\n• Why is life possible on Earth?\nOur solar system includes the Sun and all the objects that orbit around the Sun.\nAs you will find out, a variety of objects are in orbit around the Sun: eight\nplanets, many dwarf planets, asteroids, Kuiper Belt objects and comets.\n.\n1.1 The Sun\n.\nNEW WORDS\n• solar system\n• star\n• nuclear fusion\n• convection\n• sunspot\n• solar wind\nBefore we look at the Sun close up, let's summarise what you learned about the\nSun in Grades 6 and 7:\n1. The Sun is our closest star and is very important for life on Earth as it\nprovides us with light and heat.\n2. The Sun is located at the very centre of our solar system.\n3. The Earth and other planets all orbit around the Sun, held in orbit by the\nforce of gravity.\n.\nVISIT\nSecrets of a dynamic Sun\n(video)\nbit.ly/1h0io4b\nWhat do you think the Sun would look like if it was further away, like the other\nstars we see at night?\nLet's look at the Sun in more detail.\n\nAn image of the Sun taken with the SOHO space satellite.\n.\nTAKE NOTE\nIt is very important that\nyou do not look at the\nSun directly! The Sun\ncan damage your eyes\npermanently!\n.\nVISIT\nThe birth of the solar\nsystem (video)\nbit.ly/1i8Bfrx\n.\nVISIT\nHow the Sun works.\nbit.ly/1gy769C\nDo you know what the Sun is made of? The Sun is mostly made up of hydrogen\ngas (about 71%), and also helium gas (about 27%) with a tiny amount of other\ngases. The temperature at the Sun's surface is very high, around 5500 oC.\nHowever, that is nothing compared to deep inside the Sun. At the Sun's centre,\nor core, it is about 15 million oC. It is so hot at the Sun's centre that nuclear\nreactions can occur, which change atoms from one element to another. In the\nSun's case, four hydrogen nuclei are squeezed or fused together to form a new\nhelium nucleus. This process is called nuclear fusion.\nThis nuclear fusion reaction releases energy because the new helium nuclei\nproduced have very slightly less mass than the four hydrogen nuclei used to\nmake them. How can this be? Well, according to the famous scientist Albert\nEinstein, energy and mass are equivalent. Some of the mass in the hydrogen\nnuclei is converted and released as energy when the nuclei fuse to make helium.\nA very large amount of energy is released. This energy travels outwards from\nthe Sun's core towards its surface. The energy eventually reaches the Sun's\nsurface somewhere between 17,000 and 100,000 years later! The Sun's energy\nthen spreads out into the solar system in the form of heat and light.\nYou are now going to observe the Sun to look at its surface features.\nRemember, you should never look directly at the Sun as it can permanently\ndamage your eyes. You can use either a telescope with a filter on it or a pinhole\nto project an image of the Sun onto a screen to safely view the Sun's image.\n.\n.\n145\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing the Sun using a telescope\n.\nMATERIALS:\n• telescope\n• white card\n• chair to rest the card on\n• cardboard to make a shade collar\n• pair of scissors\n• pencil\n.\nVISIT\nInteract with this\nsimulation to visualize the\neffects of gravity on\norbital paths of the Sun,\nEarth and Moon.\nbit.ly/1a2mJCL\n.\nTAKE NOTE\nNEVER look directly at\nthe Sun, even with\nsunglasses on as you\ncan permanently\ndamage your eyes.\nINSTRUCTIONS:\n1. Take a piece of cardboard and place it up against the narrowest end of the\ntelescope.\n2. Draw an outline around the edge of the telescope on the card to use as a\nguide for cutting to make the collar.\n3. Cut out inside the circle you just drew so that the cardboard can fit over\nthe telescope as shown in the figure above. You can cut a single slit into\nthe circle from the edge of the card as shown in the diagram\n4. Place the collar on the telescope. Adjust the size of the cut out circle if\nnecessary (for example if your telescope is slightly wider in the middle\nthan at the end, you may want to make your circle slightly larger). This\ncollar shades the area, where the image will fall, from stray light.\n5. Select the lowest magnification eyepiece lens you have and insert it into\nthe telescope's eyepiece.\n6. Focus the telescope by looking at a distant object (NOT the Sun).\n7. Point the telescope at the Sun (do NOT look through the telescope to do\nthis).\n8. Place a chair behind the telescope and rest a white piece of card on it. The\ncard should be tilted towards the telescope.\n9. Adjust the direction in which the telescope is pointing until the image of\nthe Sun appears on the white paper card. This may take some time.\n10. Keeping the telescope still, move the white card toward or away from the\neyepiece until the image of the Sun fits neatly in the middle of the card.\n..\n146\n.", "chapter_id": "4.7" }, { "title": "Planet Earth and Beyond", "content": "Planet Earth and Beyond\n\n.\nAdjust the chair's position as needed.\n11. Adjust the tilt of the white card until the Sun's image is circular.\nQUESTIONS:\n1. Looking carefully you should see that the Sun's image moves slowly across\nthe white card. What causes this motion?\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n.\n.\nTAKE NOTE\nRevise the model of the\natom that you learned\nabout in Matter and\nMaterials if you are\nunsure of some of the\nterms used here, such\nas nucleus, which is at\nthe centre of an atom,\nand consists of protons\nand neutrons.\nAlternatively, if you do not have access to a telescope or binoculars, you can\nperform the following activity to view the Sun.\n.\nACTIVITY: Observing the Sun with a pinhole\ncamera\n.\nIn this activity you will reflect an image of the Sun onto a white card or screen\nfor your learners to observe. This method has the advantage of not needing a\ntelescope or binoculars, however, the solar image produced will be a bit fuzzy.\nHowever, it should be good enough to show large sunspots. This activity is\ndesigned as a teacher-led demonstration. If you have a sunlit window or door to\nyour class you can do this activity in the classroom. If you do not have a\nclassroom with a sunlit window, or if your class is very small, you can do the\nactivity outdoors, reflecting the Sun's image onto a shaded wall or back into a\ndarkened classroom.\n.\n.\n147\n.", "chapter_id": "20" }, { "title": "The solar system", "content": "Chapter 1.\nThe solar system\n\n.\n.\nVISIT\nThree years of the Sun in\nthree minutes.\nbit.ly/19nCfGu\nAs a rough guide, begin with a distance of around 8 m between the white card\nand the mirror. The further away you place the mirror from the white screen the\nfainter and larger the image will appear. At closer distances the image will be\nbrighter but it may not be in very good focus.\n.\nVISIT\nWhere does the Sun get\nits energy?\nbit.ly/1azFmsM\nAs mentioned in the previous activity, sunspots are sometimes (not always)\nvisible on the Sun's surface. Therefore, you could repeat this activity over the\ncourse of several days to see if any sunspots or sunspot groups change shape,\nsize, or position over time.\nMATERIALS:\n• small pocket mirror or hand mirror\n• piece of plain cardboard (or paper) to fit over the mirror (or alternatively\ntape)\n• white cardboard screen\n• bin bags or curtains for darkening the classroom\n.\nVISIT\nE = mc2 explained (video).\nbit.ly/16mVFNI\nMETHOD:\n1. Cut the plain cardboard or paper so it fits over the mirror.\n2. Cut or punch a very small hole, about 5 mm, in the middle of the plain\ncardboard.\n3. If you do not have cardboard, you can use tape to cover all but a small\nportion of the surface of the mirror.\n4. Place the mirror on a window sill in the Sun and tilt it so that it catches the\nsunlight and reflects it into the classroom. If your classroom is very small,\nplacing the mirror outside on a chair may be a better option in order to get\na larger image.\n5. Darken the classroom using curtains or bin bags, excluding where the\nmirror is.\n6. Reflect the sunlight from the mirror onto a wall of the darkened room.\n7. Put the white cardboard or paper on the wall where the reflected light\nshowing the Sun's image falls.\n8. Observe the image of the Sun.\n..\n148\n.\nPlanet Earth and Beyond\n\n.\n9. Remove the white cardboard from the wall and take three steps towards\nthe mirror with the cardboard still facing the mirror. Note what happens to\nthe image of the Sun on the cardboard.\nQUESTIONS:\n1. As you moved the white cardboard screen closer towards the mirror, what\ndid you notice happened to the image of the Sun?\n.\nDID YOU KNOW?\nAlbert Einstein\nexplained the\nmass-energy\nequivalence with the\nfamous equation\nE = mc2.\n2. Draw a picture of what the surface of the Sun looks like on the white card\nin the circle below.\n3. When the Sun reflects off the surface of the mirror, what can you say about\nthe angle of incidence and the angle of reflection of the ray?\n.\nDid you notice any features on the Sun's surface when you viewed it in class?\nLet's find out what some of these surface features could have been in the next\nactivity.\n.\nVISIT\nFiery looping rain on the\nSun (video)\nbit.ly/16qmriQ\n.\n.\n149\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Observing sunspots on the Sun's\nsurface\n.\nINSTRUCTIONS:\n1. Look at the images of the Sun which were taken in June 2013.\n2. Answer the questions that follow.\nA: DATE: 02.06.2013\n.\nVISIT\nLearn more about the\nresearch that NASA is\ndoing about our Sun with\nthe Solar and Heliospheric\nObservatory (SOHO).\nbit.ly/1fQhd8u\nB: DATE: 03.06.2013\n..\n150\n.\nPlanet Earth and Beyond\n\n.\nC: DATE: 04.06.2013\nQUESTIONS:\n.\nTAKE NOTE\nThis information about\nthe Sun's surface and\nsunspots is additional\ninformation for your\ninterest. Be curious and\ndiscover more!\n1. How many groups of dark spots do you see in each image?\n2. What do you notice about the positions of the spots in each image?\n3. Why do you think the spots have moved?\n4. What do you think these spots are?\n.\nSunspots and the Sun's surface\nThe Sun's surface often has little blemishes on it. These dark spots on the Sun\nare called sunspots. They are areas that are slightly cooler than the rest of the\nSun's surface. The Sun's surface is typically about 5500 oC and a typical\nsunspot has a temperature about 3900 oC.\n.\n.\n151\n.\nChapter 1.\nThe solar system\n\nImage of a sunspot. For perspective, take note of the size of the Earth in the lower left.\n.\nVISIT\nView real time images of\nthe Sun and track\nsunspots.\nbit.ly/19ZoU6c\nAs the Sun is made up of gas, there is no solid surface like on Earth. So when\none says that you are looking at the Sun's surface what are you actually looking\nat? Imagine that you are standing in thick fog (mist) with a friend. You can see\nthings close to you, like your hand in front of you and your friend standing next\nto you. However, because the fog is so thick you cannot see far into the\ndistance. Similarly, when we look at the Sun, we cannot see right into the centre\nof the Sun. As you go deeper and deeper in towards the centre of the Sun the\ngas begins to get thicker and thicker so that we cannot see through it. The\ndeepest depth that we can see into the Sun's gas is what we call the Sun's\nsurface.\nSunspots are areas that are slightly cooler, and therefore darker, than the rest of\nthe Sun's surface. A typical sunspot only lasts a few days. When a sunspot lasts\nfor several days you can observe it move across the Sun's disc. The sunspot\nappears to move across the Sun because the Sun is spinning slowly on its own\naxis.\n.\nDID YOU KNOW?\nThe number of sunspots\non the Sun increases\nand decreases in a\nregular pattern which\nrepeats every 11 years.\nWhen there are more\nsunspots the Sun is\nmore active and there\nare more solar storms\nand more of the Sun's\nenergy reaches the\nEarth.\nThe outer atmosphere of the Sun is called the corona. Gas particles from the\ncorona are constantly escaping into space, forming the solar wind. When the\nSun is very active, violent eruptions called solar flares occur on its surface.\n..\n152\n.\nPlanet Earth and Beyond\n\nA large loop of gas extending over 35 Earth diameters out from the Sun's surface.\n.\n1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.\n1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.\nChapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "21" }, { "title": "The Sun", "content": "", "chapter_id": "1.1" }, { "title": "Objects around the Sun", "content": "1.2 Objects around the Sun\n.\nVISIT\nExplore the solar system\nfrom your computer with\nthis 3D environment\nbit.ly/1c9rpbM and\nview any objects in the\nsolar system with this\ninteractive simulator\nbit.ly/1gyasJR\n.\nNEW WORDS\n• terrestrialplanet\n• gas giant\n• dwarf planet\nThe Sun is by far the largest and most massive object in our solar system\nmaking up 98% of the total mass of the solar system. Due to the Sun's massive\nsize, its large gravitational pull causes the planets and other objects in the solar\nsystem to orbit around it.\nIn orbit around the Sun are the eight planets along with their moons, dwarf\nplanets and many much smaller objects like asteroids, Kuiper belt objects and\ncomets. You will learn all about these objects later on in this chapter.\n.\nTAKE NOTE\n'terra' is the Latin word\nfor land or earth.\nThe four planets closest to the Sun are Mercury, Venus, Earth and Mars. These\nare called terrestrial planets because they have solid rocky surfaces. Further\nout, lie the gas giants Jupiter, Saturn, Uranus, and Neptune. These are much\nlarger than the terrestrial planets and are mainly made of gas with small cores of\nrocky materials. In between the terrestrial planets and the gas giants lies the\nasteroid belt and out beyond the orbit of Neptune lies the Kuiper belt.\nAs you can see, there are lots of different types of objects orbiting the Sun, and\nnot all of them are planets! To be classed as a planet, an object must:\n1. orbit around the Sun\n2. be large enough that its own gravity pulls it into a spherical shape\n3. clear out smaller objects in its orbit, by either flinging them into another\norbit or by attracting and then sticking them to itself (this means that there\nare no other similar sized objects orbiting in their vicinity)\nYou will learn about planets and the other objects orbiting the Sun in more\ndetail later on in this chapter. Let's begin by learning more about the size and\nscale of the solar system.\n.\n.\n153\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: The scale of the solar system\n.\n.\nVISIT\nIs there gravity in space?\nbit.ly/180O2Xl\nThe orbits and planets in the solar system which we are going to model.\nMATERIALS:\n• grapefruit\n• peppercorns\n• salt grains\n• poppy seeds\n• pea\n• grape\n• measuring tape\nINSTRUCTIONS:\n1. Go outside to a large field for this activity. Start at one end of the field.\n2. Put the grapefruit on the ground, this represents the Sun.\n3. Measure 4.2 m away from the grapefruit and put a grain of salt on the\nground. This represents Mercury. If you do not have a measuring tape then\ncount four big strides away from the Sun instead.\n4. Repeat this for each of the planets in the solar system. Your teacher will\ntell you the distance each planet lies from the Sun and will give you the\nappropriate object to represent your planet.\n5. Guess how far away you think the next closest star after the Sun is.\n.\n..\n154\n.\nPlanet Earth and Beyond\n\nLet's now make a smaller model of the solar system.\n.\nACTIVITY: Make a hanging solar system\n.\nMATERIALS:\n.\nVISIT\nCompare the planets\nusing this tool from NASA.\nbit.ly/16qofIJ\n• cardboard about 30 cm across\n• paper\n• string or thread\n• pair of scissors\n• tape\n• string\n• pencil, crayons, or markers\n• compass (for drawing circles)\n• nail (for making a hole in the cardboard)\nINFORMATION TABLE:\nObject\nOrbit radius (cm)\nObject radius (cm)\nSun\n-\n5.0* - this is NOT to\nscale\nMercury\n0.4\n0.2\nVenus\n0.7\n0.8\nEarth\n1.0\n0.8\nMars\n1.5\n0.4\nJupiter\n5.0\n5.1\nSaturn\n9.2\n4.1\nUranus\n18.6\n1.6\nNeptune\n29.1\n1.6\n* Note that if the Sun were drawn at the same scale as the rest of the planets, its\nradius should be 50 cm rather than 5 cm!\n.\nTAKE NOTE\nThe scale of the orbits\ndiffers from the scale of\nthe object sizes in the\ntable here. If they were\non the same scale then\nthe Sun and planets\nwould be much much\nsmaller.\nINSTRUCTIONS:\n1. Cut out the cardboard into a circle of radius 15 cm. Use a compass and\npencil to mark out the circle for cutting.\n2. Mark the centre of the circle. This will be the position of the Sun.\n3. Using a compass, draw the orbits of the 8 planets on the card. The first four\nplanets orbit relatively close to the Sun, then there is a gap (the asteroid\nbelt), then the last five planets orbit very far from the Sun. The radius of\neach circle, representing each planet's orbit, is shown in the table above.\n4. Using the sharp point of the scissors' blade, or a large nail, punch a hole in\nthe centre of the card (this is where the Sun will hang).\n5. Punch one hole on each circle (orbit); a planet will hang from each hole.\n6. Cut out one circle from the paper to represent the Sun.\n.\n.\n155\n.\nChapter 1.\nThe solar system\n\n.\n7. Repeat this for each of the planets. The range in size of the Sun and the\nplanets is far too large to represent accurately, so as a rough\nrepresentation use the radii listed in the table to make your circles. The\nsizes of Mercury and Mars are very small in relation to the other planets. If\nyou are battling to cut circles this size, then make them slightly bigger.\n8. Colour in each planet and the Sun according to the pictures later in this\nchapter.\n9. Tape a length of string or thread to the Sun and each planet.\n10. Lace the other end of each string or thread through the correct hole in the\nlarge cardboard circle.\n11. Tape the end of the string to the top side of the cardboard.\n12. After all the planets and the Sun are attached, adjust the length of the\nstrings so that the planets and Sun all fall to the same depth when the\ncircle is held up in the air.\n13. To hang your model, tie three pieces of string to the top of the cardboard\naround the edge. Then tie these three together and tie them to a longer\nstring (from which you'll hang your model).\nQUESTION:\nWhy did you adjust the string lengths so that the Sun and all the planets hang at\nthe same height?\n.\nVISIT\nBuild your own solar\nsystem with this orbit\nsimulator.\nbit.ly/H6mWsc\n.\n.\nVISIT\nRead more about the\ncurrent research taking\nplace at NASA's Mars\nScience Laboratory.\nbit.ly/18Cv79E\nNow that you have an idea of the size and scale of the planets in our solar\nsystem, let's compare the two groups of planets, the inner worlds, Mercury,\nVenus, Earth and Mars with outer worlds, Jupiter, Saturn, Uranus and Neptune,\nin more detail. Look at the following pictures which compare the features of the\ntwo groups of planets.\nThe relative sizes of the terrestrial planets and gas giants, from left to right: Mercury,\nVenus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Note that the planets are not\nspaced at equal separations from each other, but are shown in this way to fit on the page.\nHow do the sizes of the terrestrial planets and gas giants compare with each\nother?\n..\n156\n.\nPlanet Earth and Beyond\n\nLet's now look at the compositions of the two types of planets.\nThe above image shows the internal structure of the terrestrial planets. They all\nhave a metal core, a rocky mantle and a thin outer crust. They also have a thin\natmosphere (Mercury has an extremely thin atmosphere). The Earth's\natmosphere is unique in the solar system in that it contains abundant oxygen,\nwhich is necessary to sustain life on Earth.\n.\nDID YOU KNOW?\nWhen it is winter on\nMars you can see polar\nice caps forming on the\nplanet, like on Earth.\nHowever, unlike the\nEarth's polar ice caps\nwhich are made of\nfrozen water, the ice\ncaps on Mars are made\nof frozen carbon\ndioxide. This frozen\ncarbon dioxide comes\nfrom Mars' atmosphere.\nThe image below shows the structure of the gas giants. They are mostly made\nof hydrogen and helium gases and are much less dense than the rocky\nterrestrial planets.\n.\nDID YOU KNOW?\nPluto was reclassified\nfrom planet to dwarf\nplanet in 2006.\nAlthough Pluto orbits\nthe Sun and is almost\nround, it has not cleared\nout other objects in its\norbit, and so it cannot\nbe classified as a planet.\nThere are many more\ndwarf planets at similar\ndistances from the Sun\nas Pluto.\nAs you go deeper into the atmospheres of Saturn and Jupiter their atmospheres\nget denser and denser until they gradually become a liquid. This liquid\nhydrogen is called metallic hydrogen. Deeper down they have a solid core\nmade of rocky materials.\nUranus and Neptune have thick atmospheres which have methane in addition to\nhydrogen and helium. The methane gives them their blue colour. Scientists\nthink that below their atmospheres they have a slushy mantle made of water,\nammonia and methane ices. At their centres they have a rocky-icy core.\nLook at the pictures below. They show images of the gas giants. What features\ndo you see that the gas giants all have in common?\n.\n.\n157\n.\nChapter 1.\nThe solar system\n\nThis image of Jupiter in shadow was taken\nby the space probe Galileo as it studied\nJupiter in 1998.\nThis image of Saturn was taken with the\nHubble Space Telescope. Can you see\nsome of its moons?\n.\nDID YOU KNOW?\nHydrogen is a liquid\ndeep inside Jupiter and\nSaturn because the\nhydrogen molecules\nhave been squeezed\ntogether due to the\nenormous pressure at\nthose depths caused by\nthe weight of the\nplanet's atmosphere\nabove.\nUranus, taken with the Hubble Space Telescope. What do you notice that is strange\nabout Uranus?\nNeptune is to the bottom right of this picture, just out of view. This image was taken by\nthe space probe Voyager 2 as it flew past Neptune in 1989.\n.\nVISIT\nDiscover more online at\nNASA's Solar System\nExploration site.\nbit.ly/1azHL6M\nYou can see that all the gas giants have rings. None of the terrestrial planets\nhave rings.\n..\n158\n.\nPlanet Earth and Beyond\n\nAnother difference between the inner rocky and outer gas giant planets, are the\nnumber of moons orbiting each planet. Look at the table below which shows\nthe number of moons each planet in our solar system has.\nPlanet\nNumber of Moons\nMercury\n0\nVenus\n0\nEarth\n1\nMars\n2\nJupiter\n67\nSaturn\n62\nUranus\n27\nNeptune\n13\n.\nTAKE NOTE\nSome older textbooks\nor websites that you\nvisit may still refer to\nPluto as a planet as they\nhave not been updated.\nWhat can you say in general about the number of moons that the two types of\nplanet have?\n.\nTAKE NOTE\nNew moons are\ndiscovered all the time,\nso these numbers may\nchange over time.\nThe terrestrial planets are much closer to the Sun than the gas giants. Because\nof this, the terrestrial planets orbit the Sun in less time than the gas giants,\nbecause they have a shorter distance to cover.\nLets see how the distance from the Sun affects the planets' temperatures.\n.\n.\n159\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary Temperatures\n.\n.\nTAKE NOTE\nIce does not just refer to\nwater ice, but other\nfrozen elements and\ncompounds too. Also,\nthe rocky-ice materials\ndo not resemble any\nrock or ice you would\nsee on Earth, since the\ntemperatures and\npressures on these\nplanets and gas giants\nare much, much higher.\nINSTRUCTIONS:\n1. Look at the table, it shows the surface temperatures of each of the planets.\n2. Correctly label each of the planets on the thermometer using the\ntemperature information provided in the table.\nPlanet\nTemperature (oC)\nMercury\n167\nVenus\n464\nEarth\n15\nMars\n-65\nJupiter\n-110\nSaturn\n-140\nUranus\n-195\nNeptune\n-200\n..\n160\n.\nPlanet Earth and Beyond\n\n.\nQUESTIONS:\n1. Which planet has the lowest average temperature?\n2. Why do you think this is?\n3. What do you notice about the average temperatures of the terrestrial\nplanets compared with the gas giants?\n4. If you exclude Venus, how does the ordering of the planets from the Sun\ncompare with their average temperature?\n.\nClearly the terrestrial planets and gas giants have very different properties.\nLet's compare them.\n.\nACTIVITY: Comparing terrestrial planets and gas\ngiants\n.\nINSTRUCTIONS:\n1. The table below compares the two types of planet. Fill in the missing gaps.\nTerrestrial Planets\nGas Giants\nclose to the Sun\nfrom the Sun\nclosely spaced orbits\nwidely spaced orbits\nsmall masses\nlarge masses\nsmall radii\nradii\n.\n.\n161\n.\nChapter 1.\nThe solar system\n\n.\nTerrestrial Planets\nGas Giants\nmainly rocky\nmainly\nsolid surface\nsurface\nhigh density\ndensity\nslower rotation\nfaster rotation\nmoons\nmany moons\nrings\nmany rings\nthin atmosphere\natmosphere\nwarm\nWhy do you think the two types of planets are so different?\n.\nWhen the solar system was forming, the difference in temperature across the\nearly solar system caused the inner planets to be rocky and the outer ones to be\ngaseous. Close to the Sun it was hot and only materials with very high melting\npoints, such as metals, could remain solid and form planets. Further away from\nthe Sun, where it was cold, compounds like water and methane were frozen.\nAstronomers call these frozen compounds ices. Therefore the cores of the gas\ngiants contain rocky and icy compounds. As the abundance of metals in the\nuniverse is very small, the inner planets are much smaller than the gas giants.\nThe gas giants could also attract large amounts of hydrogen and helium to their\natmospheres due to their size.\nLet's continue to compare the rocky planets and the gas giants.\n..\n162\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing the inner and outer planets\n.\nINSTRUCTIONS:\nUse the information in the table below to answer the questions that follow.\nPlanet\nDensity\n(kg/m3)\nDiameter\n(km)\nDistance\nfrom the\nSun\n(million\nkm)\nDay length\n(hours)\nYear length\n(Earth\ndays)\nMercury\n5427\n4879\n57.9\n4222.6\n88\nVenus\n5243\n12104\n108.2\n2802.0\n224.7\nEarth\n5514\n12756\n149.6\n24.0\n365.25\nMars\n3933\n6792\n206.6\n24.7\n687.0\nJupiter\n1326\n142984\n740.5\n9.9\n4331\nSaturn\n687\n120536\n1352.6\n10.7\n10747\nUranus\n1271\n51118\n2741.3\n17.2\n30589\nNeptune\n1638\n49528\n4444.5\n16.1\n59800\nQUESTIONS:\n1. Given that the density of water is 1000 kg/m3, which of the planets would\nfloat on water? Explain your answer.\n2. Compare the densities of the rocky planets and the gas giants. Which type\nof planet tends to be more dense? Explain why.\n3. Which planet has the shortest day?\n4. Compare the day length for the rocky planets and the gas giants. Which\ntype of planet tends to have the shortest day? What does this tell you\nabout how fast the two types of planet rotate on their axis?\n.\n.\n163\n.\nChapter 1.\nThe solar system\n\n.\n5. Which planet orbits around the Sun the fastest? Why is this?\n6. Which planet's year is shorter than its day?\n7. Plot a bar graph to show the distance each planet is from the Sun. Use the\nfollowing space for your graph.\n.\n.\nVISIT\nSolar System 101: NASA's\n'Homework helper' can\nshow you where to look to\nfind out more.\nbit.ly/H6nbDD\n.\n..\n164\n.\nPlanet Earth and Beyond\n\nMercury\n.\nTAKE NOTE\nThe following pages\nprovide some\ninteresting, extra\ninformation about the\nplanets in our solar\nsystem.\nMercury, imaged by the Messenger\nspacecraft, is covered with craters like our\nMoon.\n• Mercury's atmosphere is very thin\nand constantly being lost into\nspace because the planet's\ngravity is too small to hold onto it.\n• Mercury has the most extreme\ntemperatures in the solar system,\nreaching 426 oC during the day\nand -173 oC during the night.\nVenus\nThe surface of Venus in false colour\n(bottom left) and the top of the\natmosphere (top left) as seen with the\nMagellan spacecraft.\n• Venus is the hottest planet in the\nsolar system, the temperature is\nhot enough to melt lead!\n• Venus has clouds of sulphuric\nacid.\n• Venus rotates in the opposite\ndirection to all the other planets.\n.\nTAKE NOTE\nVenus has a thick dense\natmosphere mostly\nmade up of carbon\ndioxide which is an\neffective greenhouse\ngas. This is why Venus\nhas the highest surface\ntemperature, as you\nsaw in the activity of\nPlanetary\nTemperatures.\n.\n.\n165\n.\nChapter 1.\nThe solar system\n\nEarth\nThis famous image is a photograph taken of\nEarth in 1990 by Voyager 1 from 6 billion\nkilometers away. Earth appears as a tiny\ndot (the blueish-white speck approximately\nhalfway down the brown band to the right).\nThe coloured bands are scattered light rays\nfrom the Sun.\n• To date, Earth is the only planet in\nthe universe known to harbour\nlife.\n• The average distance between\nthe Sun and Earth is called an\nastronomical unit (AU) and is\nequivalent to 150 million\nkilometres.\n.\nDID YOU KNOW?\nAs Voyager 1 was\nleaving the solar\nsystem, Carl Sagan, a\nfamous astronomer,\nrequested that they\nturn the camera around\nto take a photograph of\nEarth across a great\nexpanse of space.\n.\nVISIT\nCarl Sagan - Pale Blue Dot\n(video)\nbit.ly/1h0msBx\n.\nDID YOU KNOW?\nThe largest volcano in\nthe solar system,\nOlympus Mons, is on\nMars and is three times\ntaller than Mount\nEverest.\nMars\nMars is nicknamed the Red Planet because\nof its red surface, as the rocks on are rich in\niron. The white smudges in the middle are\nwater-ice clouds.\n• Mars' surface is like a dry red\ndesert. Mars has mountains,\nvolcanoes and valleys just like\nEarth.\n• Mars is home to the deepest and\nlongest valley in the solar system,\nValles Marineris, which is almost\nas wide as Australia!\n..\n166\n.\nPlanet Earth and Beyond\n\nMars and the Search for Life\nScientists are interested in Mars because they think that Mars might have\nonce had liquid water on its surface, and perhaps life.\nChannels, valleys,\nand gullies are found all over Mars, suggesting that liquid water might have\nonce flowed through them. Although there is no liquid water on the planet's\nsurface now, scientists think that there may still be some water in cracks and\ntiny holes in underground rock. Mars has been visited many times by robotic\nlanders.\nThe first lander, NASA's Viking 1, landed on Mars in 1976, a long time before\nyou were born! It took the first close-up pictures of the Martian surface but\nfound no evidence of life. Water ice has been discovered below the planet's\nsurface, and minerals indicating that liquid water was once present have also\nbeen found by Mars landers. The latest lander currently exploring Mars is\nNASA's Mars Science Laboratory mission, with its rover named Curiosity.\nCuriosity landed on Mars in August 2012 and is busy investigating the planet's\nrocks near a giant crater called the Gale crater.\nOne of the main aims\nof the Mars Science Laboratory is to determine whether Mars ever had an\nenvironment capable of supporting life.\nThe Curiosity rover.\nOne of the first colour images of Mars' surface taken by the Curiosity rover. You can\nsee part of the rover at the bottom of the photograph.\n.\nVISIT\nWatch the first 12 month's\nof Curiosity's explorations\nin 2 minutes.\nbit.ly/1b7mAKH\n.\nVISIT\nNASA's curiosity finds\nwater in Martian soil in\n2013.\nbit.ly/HasUIX\n.\n.\n167\n.\nChapter 1.\nThe solar system\n\nJupiter\nMagnetic storms cause the aurorae seen on\nJupiter near its poles.\n• Jupiter's diameter is over ten\ntimes the Earth's diameter.\n• Jupiter rotates slightly faster at\nthe equator (remember it is not a\nsolid object, but a large ball of\ngas).\n• Jupiter's famous great red spot, is\na giant hurricane that has been\nraging for at least 300 years. This\nstorm's area is larger than the\nEarth.\nSaturn\n.\nVISIT\nSaturn close-up (video).\nbit.ly/15XvvyG\nSaturn's beautiful rings, imaged with the\nCassini spacecraft.\n• Saturn would float on water if you\nhad an ocean large enough.\n• Saturn is famous for its rings. The\nrings are over 200 000 km wide\nand only a few tens of metres\nthick.\n..\n168\n.\nPlanet Earth and Beyond\n\nUranus\nUranus spins on its side. Scientists think\nUranus may have been knocked on its side\nby a collision with a large object early in its\nhistory.\n• Uranus is believed to have an\nocean of liquid water, ammonia,\nand methane above a rocky core.\n• Uranus was the first planet\ndiscovered using a telescope.\n.\nVISIT\nTake a virtual ride with\nVoyager 1 and 2 past\nJupiter, Saturn, Uranus,\nand Neptune.\nbit.ly/1azPLVm\nNeptune\nNeptune and its \"Great Dark Spot\" (middle\nleft). This is a giant storm that was raging\non the planet until very recently. The winds\nreached nearly 1931 km/hour.\n• Neptune has the strongest winds\nin the solar system. With storm\nwinds recorded at over 10 times\nthat of hurricanes on Earth.\n• Neptune has the most methane in\nits atmosphere out of all the gas\ngiants, which gives it its blue\ncolour.\n.\n.\n169\n.\nChapter 1.\nThe solar system\n\n.\n.\nACTIVITY: Planetary holidays\n.\nIn this activity you will write a travel brochure for a trip to your favourite planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\n• example travel brochures\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a travel brochure for a trip to your chosen planet. Include real facts\nabout the planet and think about what unusual things you could see and\ndo on the planet.\n.\n.\nACTIVITY: Planet fact sheet\n.\nIn this activity you will make a one page fact sheet about your chosen planet.\nMATERIALS:\n• information about the planets\n• pictures of the planets\nINSTRUCTIONS:\n1. Research information about your chosen planet.\n2. Write a one page fact sheet about your chosen planet.\n.\nLet's now look at some of the other objects that we find in our solar system.\n..\n170\n.\nPlanet Earth and Beyond\n\nAsteroids\n.\nNEW WORDS\n• asteroid\n• asteroid belt\nAsteroids are small rocky objects that are believed to be left over from the\nformation of our solar system 4.6 billion years ago. They range in size from tens\nof metres across to several hundred kilometres across and come in a variety of\nshapes. Most asteroids are found in the asteroid belt, which lies between the\norbits of Mars and Jupiter. More than 100,000 asteroids lie in the asteroid belt\nand several thousand of the largest ones have been named.\n.\nDID YOU KNOW?\nIn the region of the\nasteroid belt closest to\nthe Sun, the asteroids\nare mainly metallic\nobjects. Those further\naway are rocky objects.\nRocky asteroids appear\ndarker than metallic\nasteroids.\nAn image of asteroid 951 Gaspra taken with the Galileo spacecraft 5300 kilometres away.\nGaspra is 19 x 12 x 11 km. Notice how the asteroid's surface has many craters.\nAlthough science fiction movies give the impression that the asteroid belt is a\ntightly packed region of dangerous rocks, in reality the asteroids are separated\nfrom each other by millions of kilometres. However, very rarely, collisions\nbetween asteroids do occur which is why asteroids are covered with impact\ncraters. We will look at impact craters more closely in the following activity.\n.\nVISIT\nA record close asteroid\nfly-by past Earth.\nbit.ly/180Pmte\n.\n.\n171\n.\nChapter 1.\nThe solar system\n\n.\n.\nINVESTIGATION:\nImpact craters\n.\nINVESTIGATIVE QUESTIONS: How does the mass of an object affect the size of\nthe crater it leaves? How does the height at which an object is dropped affect\nthe size of the crater it leaves?\nHYPOTHESIS:\nWhat do you think will happen?\n.\nVISIT\nJoin NASA on an\nunderwater mission,\ncalled NEEMO, which is\nactually about practicing\nexploration to an asteroid.\nHelp the crew prepare by\nclassifying the underwater\nimages.\nbit.ly/15XvI4P\nIDENTIFY VARIABLES:\n1. What are you keeping constant in this experiment?\n2. What are you changing in this experiment?\nMATERIALS:\n• deep tray or large plastic container\n• measuring scales\n• ruler\n• sand\n• a marble\n• a ball bearing\n• chair or step ladder\n• measuring tape (at least 2 m long)\nMETHOD:\n1. Fill the tray or plastic container with sand to a depth of 10 cm.\n2. Smooth the surface of the sand using the long edge of a ruler.\n3. Measure the mass of the marble and record it in the table below.\n4. Drop the marble from a height of 1 m into the tray of sand and observe the\ncrater that forms.\n5. Carefully remove the marble, without disturbing the shape of the crater\nand measure the diameter of the crater using the ruler.\n6. Record the diameter of the crater in the table below.\n7. Smooth the sand.\n8. Repeat steps 3-7\n..\n172\n.\nPlanet Earth and Beyond\n\n.\n9. Measure the mass of the ball bearing and record it in the table below.\n10. Drop the ball bearing from a height of 1 m into the tray of sand and\nobserve the crater that forms.\n11. Carefully remove the ball bearing and measure the diameter of the crater\nusing the ruler.\n12. Record the diameter of the crater in the table below.\n13. Smooth the sand.\n14. Repeat steps 9 -13.\n15. Drop the ball bearing into the sand from a height of 2 m. You may need to\nstand on a chair or step ladder to do this.\n16. Record the size of the crater formed in the table below.\n17. Smooth the sand.\n18. Repeat steps 15-17, dropping the ball bearing from heights of 1.5m, 0.5m\nand 0.25m. Record all your measurements in the table below.\n19. If you have time you can make repeated measurements.\nRESULTS AND OBSERVATIONS:\nRecord your results and observations in the following table.\nObject\nMass (kg)\nDrop\nHeight (m)\nCrater\ndiameter -\nreading 1\n(cm)\nCrater\ndiameter -\nreading 2\n(cm)\nAverage\ncrater\ndiameter\n(cm)\nmarble\n1\nball bearing\n1\nball bearing\n2\nball bearing\n1.5\nball bearing\n0.5\nball bearing\n0.25\nEVALUATION:\nHow reliable was your experiment? How could it be improved?\nCONCLUSIONS:\nWrite a conclusion for this investigation based on your results.\n.\n.\n173\n.\nChapter 1.\nThe solar system\n\n.\nQUESTIONS:\n1. How did the mass of the object affect the size of the crater?\n2. How did the height at which the object was dropped affect the size of the\ncrater?\n3. Why do you think the drop height affected the size of the crater?\n.\nDID YOU KNOW?\nAs Jupiter is more\nmassive than all the\nother planets in the\nsolar system, its large\ngravity attracts many\nasteroids and comets\ntravelling in towards the\ninner solar system that\nwould otherwise\npotentially crash into\nthe Earth.\n4. What does this investigation tell us about craters on the surfaces of\nplanets?\n.\nKuiper Belt objects\n.\nNEW WORDS\n• Kuiper Belt\n• Kuiper Belt\nobject\n• dwarf planet\n• comet\n• Oort Cloud\nThe Kuiper belt is a region of space filled with trillions of small objects that lies\nin the outer reaches of the solar system, past the orbit of Neptune. The Kuiper\nbelt is a region between 30 and 50 times the Earth's distance from the Sun. This\nbelt is similar to the closer asteroid belt, except that the objects are not made of\nrock, but rather of frozen ices. These icy objects can range in size from a\nfraction of a kilometre to more than a 1000 km across and are called Kuiper belt\nobjects. The two largest known members of the Kuiper Belt are Eris and Pluto,\nboth dwarf planets.\n..\n174\n.\nPlanet Earth and Beyond\n\nThe Kuiper belt (the pale blue dot dots) is shown beyond the orbit of Neptune. Its\nmembers include the dwarf planets Pluto and Eris.\nWhat keeps the objects in the Kuiper Belt in orbit around the Sun?\n.\nVISIT\nGerard Kuiper (1905 -\n1973) is regarded by many\nas the father of modern\nplanetary science. He is\nwell known for his many\ndiscoveries. Read more\nabout them here.\nbit.ly/16mZX7C\n.\nDID YOU KNOW?\nNASA launched a space\nprobe called New\nHorizons to study Pluto\nand other Kuiper Belt\nobjects in more detail in\n2006. It will arrive at\nPluto in 2015.\nDwarf planets\nDwarf planets are objects that orbit the Sun, just like the planets. However, they\nare smaller than planets. Due to their small size, they are unable to meet the\nofficial definition of a planet. Can you remember what the three criteria are to\nbe classed as a planet? List them below.\nTo be classed as a planet an object must:\n.\nVISIT\nWhy Pluto is not a planet\nanymore (video).\nbit.ly/1fQiWLd\nAsteroids are clearly not planets as they have irregular shapes and they are not\nspherical. Some dwarf planets are spherical, but they do not meet the third\ncriterion. With their weak gravities they are unable to clear out other objects\nfrom their orbits. Which famous ex-planet is now considered a dwarf planet\nbecause it failed to meet the third criterion?\nFor many years the object Pluto was considered to be a planet. However, since\nthe 1990s many more objects very similar to Pluto have been discovered\norbiting the Sun out past Neptune's orbit. This resulted in new criteria to be\ndrawn up to be considered a planet and Pluto was demoted to dwarf planet\nstatus\n.\n.\n175\n.\nChapter 1.\nThe solar system\n\nThis image shows the five dwarf planets that have been discovered to date, Pluto,\nHaumea, Makemake, Eris and Ceres in relation to the size of the Earth. Some even have\ntheir own moons, which are shown. Ceres is in the asteroid belt and the other four are in\nthe Kuiper Belt.\n.\nVISIT\nRead more about dwarf\nplanets.\nbit.ly/H6nJtd\n.\nDID YOU KNOW?\nScientists estimate that\nthere might be 200 or\nmore dwarf planets in\nthe Kuiper Belt, and\nthousands more beyond\nthe Kuiper Belt.\nComets and the Oort Cloud\nComets are icy, dusty objects, orbiting around the Sun at great distances.\nComets are found in the Kuiper Belt and in the predicted Oort Cloud. The Oort\nCloud is thought to be a huge cloud of icy objects surrounding the Sun at the\nvery edge of our solar system at a distance between 5,000 and 100,000 times\nthe Earth's distance from the Sun!\n.\nDID YOU KNOW?\nPluto was named by\nVenetia Burney, an 11\nyear old from Oxford,\nEngland, in 1930. She\nsuggested that the\nplanet be named after\nthe Roman god of the\nunderworld, Pluto.\nA comet will remain in the Kuiper Belt or Oort Cloud unless it is disturbed by\nanother comet. If this happens, then the comet's orbit changes and occasionally\nthe comet will come into the inner solar system for us to see.\nThe hypothetical Oort Cloud is a huge cloud of icy objects or comets surrounding the\nouter reaches of our solar system.\n..\n176\n.\nPlanet Earth and Beyond\n\nWe can only see comets directly when they come into the inner solar system\nbecause they are small and only visible by reflected sunlight. As a comet\napproaches the Sun, the Sun's heat evaporates the dust and ices it consists of,\nforming a bright dust tail which is visible from Earth. Some comet dust tails can\nbe millions of kilometres long. The dust tail usually points back along the path\nof the comet.\nComets often have a second tail called an ion tail. The ion tail is made of ions\nthat are pushed away from the comet's head by particles emitted from the Sun's\natmosphere, called the solar wind. Let's find out more about this type of tail.\n.\nACTIVITY: A comet's ion tail\n.\nIn this activity you will make your own comet and explore how a comet's ion tail\nmoves.\nMATERIALS:\n.\nTAKE NOTE\nAn ion is an atom with\nan electrical charge due\nto the gain or loss of\nelectrons.\n• table tennis ball\n• sellotape\n• tissue paper or crepe paper\n• scissors\nINSTRUCTIONS:\n1. Cut the tissue paper or crepe papers into several strips (at least 4) about 1\ncm wide by about 15 cm long.\n2. Attach the paper strips to the ping pong ball, evenly spread around the\nequator of the ball using the sellotape. Wrap the sellotape around the ball\na few times if needed to secure the paper in place. You have now made\nyour comet and ion tail.\n3. Hold out your comet in front of you and blow on the ball hard so that the\nion tail is blown away from you. You are representing the Sun and your\nbreath represents the solar wind, blowing on the comet's ion tail.\n4. Continuing to blow fairly hard on the ball, move the ball from left to right\nand observe which way the paper moves.\nQUESTIONS:\n1. Which direction did the ion tail move when you held up the comet in front\nof you and blew on the comet?\n2. Which direction did the ion tail move when you moved the ball left and\nright while still blowing?\nIn a similar way, a comet's ion tail always points away from the Sun.\n.\n.\n.\n177\n.\nChapter 1.\nThe solar system\n\n.\nVISIT\nLearn more about comets\nwith this interactive\nwebsite.\nbit.ly/GXWfFL\nComet West, photographed in 1995. Here you can see that the comet actually has two\ntails. The white tail is the dust tail and the blue tail is the ion tail made of charged\nparticles evaporated from the comet's surface.\n.\nVISIT\nHalley's comet is visible\nfrom Earth every 75 to 76\nyears.\nbit.ly/16n0y9k\nComets that come into the inner solar system do not live forever. The Sun's\nheat melts comets, just like a snowman melts out in the Sun. After several\nthousand years the remains are so small that they no longer form a tail. Some\ncomets completely melt away.\n.", "chapter_id": "1.2" }, { "title": "Earth's position in the solar system", "content": "1.3 Earth's position in the solar system\n.\nNEW WORDS\n• astronomical\nunit (AU)\n• habitable zone\n• photosynthesis\nAs you discovered in the last section, the Earth, along with the other planets,\norbits around the Sun. The Earth is the third most distant planet from the Sun,\nlying in between Venus and Mars. Let's compare the Earth and its two\nneighbours in more detail.\n.\nACTIVITY: The Sun's Habitable Zone\n.\nProperty\nVenus\nEarth\nMars\nDistance from Sun (AU)\n0.7\n1.0\n1.5\nAverage Temperature (oC)\n464\n15\n-63\nMATERIALS:\n• pencil\n• ruler\nINSTRUCTIONS:\n1. Look at the data provided in the table. It shows the distance from the Sun\nfor three planets (in units of one Earth-Sun distance or Astronomical Unit).\nIt also shows the average temperature on each planet in degrees Celsius.\n2. Plot a graph to show the data in the table. Mark each point with an X.\n..\n178\n.\nPlanet Earth and Beyond\n\n.\n3. The Sun's habitable zone extends from 0.8 to 1.4 AU and is shaded in red in\nthe graph paper. This is the region where scientists think a planet has to lie\nin order for there to be life on the planet.\nGraph showing the average temperature and the distance from the Sun of Venus, Earth and Mars.\n.\nDID YOU KNOW?\nIt is completely safe to\nfly through a comet's\ntail. The only thing that\nwould hit your space\nship would be\nmicroscopic pieces of\ndust.\nQUESTIONS:\n1. What is the average temperature on Venus?\n2. Can liquid water exist on Venus? Why?\n3. What is the average temperature on Mars?\n4. Is liquid water likely to be found on Mars? Why?\n.\nVISIT\nOur solar system's\nhabitable zone (video)\nbit.ly/15XwDT1\n5. What is the average temperature on Earth?\n.\n.\n179\n.\nChapter 1.\nThe solar system\n\n.\n6. Can liquid water exist on Earth? Why?\n7. Which planet/s lie within the Sun's habitable zone (the red shaded region\nin the graph)?\n.\nThe average temperature on Earth is a moderate 15 oC. Because of this, water\ncan exist in liquid form on Earth. This is important because scientists think that\nliquid water is one of the key things needed for life. Venus has an average\ntemperature of 464 oC and no liquid water exists on Venus because it is too hot.\nOn Mars, the opposite is true. The average temperature on Mars is -63 oC and\nany water on Mars would be frozen. Earth is unique in our solar system as it is\nthe only planet known to have liquid water on its surface and to harbour life.\nIf the Earth were too close to the Sun it would be too hot and all the water\nwould evaporate from the oceans, like it has on Venus. If the Earth were too far\nfrom the Sun it would be too cold, and all the water would be frozen, like on\nMars. Earth is at just the right distance from the Sun to have liquid water on its\nsurface. The other planets in the solar system are either too close or too far\nfrom the Sun. The range of distances that a planet can lie from the Sun and still\nhave liquid water on the planet's surface is called the habitable zone. Estimates\nfor the habitable zone in our solar system range from 0.8 - 1.4 astronomical\nunits (AU).\n.\nTAKE NOTE\nAn astronomical unit\ncorresponds to the\naverage distance\nbetween the Earth and\nthe Sun.\n.\nDID YOU KNOW?\nThe habitable zone is\nsometimes called the\nGoldilocks zone after\nthe famous children's\nstory where Goldilocks\neats the porridge that is\nneither too hot nor too\ncold.\nOur Sun's habitable zone (light green). The Earth is the only planet in our solar system\nwhich lies within our Sun's habitable zone. It is just the right distance from the Sun for\nliquid water to remain on the planet, something which scientists think is essential for life.\n..\n180\n.\nPlanet Earth and Beyond\n\nWhat other conditions do you think are necessary for life on Earth or other\nplanets? List your answers in the space below.\n.\nTAKE NOTE\nOther stars also have\nhabitable zones.\nScientists believe that\nplanets orbiting other\nstars within the\nhabitable zone could\nsupport life forms.\n.\nVISIT\nKepler Mission: A search\nfor habitable planets.\nbit.ly/HdBXYI\n.\nTAKE NOTE\nYou may have heard a\nlot about global\nwarming and the\ngreenhouse effect in the\nnews and in our studies\nin Energy and Change.\nScientists think that in order for life to arise and survive on a planet:\n• there must be sunlight for plants to grow.\n• the planet must be located in the habitable zone of a star so that there are\nmoderate temperatures and liquid water.\n• there must be oxygen for respiration.\nWhich of the planets in the solar system receive light from the Sun?\nWhich of the planets in the solar system have moderate temperatures and liquid\nwater on their surface?\nWhich of the planets in the solar system have significant amounts of oxygen in\ntheir atmosphere or oceans?\nAs you can see the Earth is very fortunate, because it lies at just the right\ndistance from the Sun to have moderate temperatures and abundant liquid\nwater. The Sun provides the energy for plants to grow. There is plenty of\noxygen in Earth's present day atmosphere and oceans, which means that life\ncan survive on land and in the Earth's oceans. The Earth is unique in that it is the\nonly planet we know of that has life.\nThe greenhouse effect\nDuring the day, the Sun shines through the atmosphere heating the Earth's\nsurface. At night, the Earth's surface cools, releasing the heat back into space.\nSome of the heat is trapped by greenhouse gases in the air like carbon dioxide,\nwhich causes the Earth to remain warmer than it would have otherwise. This is\ncalled the greenhouse effect.\nScientists think that due to human activities, like cutting down forests and\nburning fossil fuels, the greenhouse effect is now too strong. Scientists are more\nthan 90 % certain that the increase in greenhouse gases has caused the average\ntemperature on Earth to rise. This is known as global warming.\nVenus provides us with a clue as to what might happen to the Earth if global\nwarming continues. Venus' thick atmosphere has led to a runaway greenhouse\neffect on the planet, heating it to 462 oC. Venus's oceans have boiled away\nleaving behind a hot, inhospitable planet. We should therefore try our best to\nlook after our precious planet!\n.\n.\n181\n.\nChapter 1.\nThe solar system\n\nThe beginnings of life\nScientists do not know how life began on Earth, but they estimate that the early\nancestor of modern bacteria was alive on Earth 3.5 billion years ago. The early\nEarth's atmosphere had almost no oxygen. Instead, it was composed mainly of\ncarbon dioxide, nitrogen and water vapour with some methane and ammonia.\nCarbon dioxide and water vapour were pumped into the atmosphere during\nvolcanic eruptions, which caused the atmosphere to change over time.\nEventually the water vapour in the atmosphere condensed to form rain, forming\nthe first oceans. Eventually living organisms (bacteria) appeared in the oceans.\nThese simple organisms used sunlight, water and carbon dioxide in the oceans\nto produce sugars and oxygen. What is this process called?\nThis is where the first oxygen in the ocean and atmosphere came from. That\noxygen made it possible for other organisms to develop and flourish and is the\nreason that you are here today.\nScientists are busy exploring the possible locations for the origin of life, including hot\nsprings and tidal pools. Recently, some scientists have started to support the hypothesis\nthat life originated in deep sea hydrothermal vents, as shown in the image. These vents\nare like underwater volcanoes. The investigation continues to try to understand how life\noriginated on Earth.\n.\nDID YOU KNOW?\nThe moons Europa\n(orbiting Jupiter) and\nTitan (orbiting Saturn)\nare considered to be\nplaces where life may\nexist. Europa's surface\nis covered in smooth\nwater ice and scientists\nthink that there might\nbe a water ocean\nbeneath the icy surface.\nTitan has liquid lakes\nand seas on its surface,\nalthough they are not\nmade of water, but\nrather liquid methane\nand ethane. Some\nscientists think that life\nmay be able to survive\nin these lakes.\n.\nVISIT\nDo you enjoy English and\nScience? Read more\nabout a career as a\nscience writer.\nbit.ly/18CxYiZ\n..\n182\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• The Sun produces its energy at its centre via nuclear fusion reactions,\nwhere hydrogen nuclei are squeezed together to form helium nuclei.\n• The Sun's energy is transported to the surface and radiates equally in\nall directions.\n• Our solar system consists of the Sun and all the objects that are held in\norbit around the Sun by gravity.\n• Objects such as planets, dwarf planets, asteroids, comets and Kuiper\nBelt objects orbit around the Sun.\n• The 8 planets in our solar system have their own properties and\ncharacteristics.\n• The planets can be split into two groups, the inner small rocky terrestrial\nplanets and the outer large gas giants.\n• The asteroid belt is the area where most asteroids are found in our solar\nsystem, lying between the orbits of Mars and Jupiter\n• The Oort Cloud is a hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar system.\n• Sometimes, comets from the Oort Cloud come close to the sun. We can\nonly see them when they come into the inner solar system because they\nare small and only visible by reflected sunlight.\n• Scientists think that some of the conditions necessary for sustained\nlife include moderate temperatures, liquid water, sunlight (energy) and\noxygen.\n• The Earth is the third planet from the Sun and the only planet in the solar\nsystem known to harbour life.\n• The Earth lies within the Sun's habitable zone; the range of distances\nthat a planet can lie from a star and still have liquid water on the planet's\nsurface.\n.\nConcept Map\nComplete the concept map which summarises the key concepts from this\nchapter about our solar system.\n.\nVISIT\nGlobal warming: How\nhumans are affecting our\nplanet.\nbit.ly/1c9toNa\n.\nDID YOU KNOW?\nAverage temperatures\non Earth have increased\nby 0.8oC around the\nworld since 1880, with\nthe biggest increase in\nthe last few decades.\nThe rate of warming is\nalso increasing.\n.\n.\n183\n.\nChapter 1.\nThe solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. How does the Sun produce its energy? [2 marks]\n2. Why do sunspots look darker than the rest of the surface of the sun? [2\nmarks]\n3. What keeps the planets and other bodies in our solar system in orbit? [1\nmark]\n4. Name the terrestrial planets. [4 marks]\n5. Name the gas giants. [4 marks]\n6. Where is the asteroid belt located? [1 mark]\n7. Where is the Kuiper belt located? [1 mark]\n8. Why are the gas giants so much larger than the terrestrial planets? [2\nmarks]\n9. List the planets in increasing distance from the Sun. [4 marks]\n.\n.\n185\n.\nChapter 1.\nThe solar system\n\n.\n10. Which planets have rings? [4 marks]\n11. Why is Venus so hot? [2 marks]\n12. On which planet have landers found frozen water in the rocks under the\nplanet's surface? [1 mark]\n13. The following diagram shows the solar system at the centre.\na) What does the blue space represent? [1 mark]\nb) What is mostly found in this space? [1 mark]\n14. Why can we only see comets as they come close to the Sun? [3 marks]\n15. What is the official definition of a planet and why was Pluto downgraded\nto a dwarf planet? [4 marks]\n..\n186\n.\nPlanet Earth and Beyond\n\n.\n16. Why can the Earth support life? [4 marks]\n17. What would happen to the Earth if it warmed significantly, like Venus has\nin the past? [2 marks]\n18. The following diagram shows the system of planets around the star Gliese\n667C.\nThe planets around another star.\na) Which of these planets are possible candidates for life? [1 mark]\nb) Explain your answer above. [2 marks]\nTotal [46 marks]\n.\n.\n.\n187\n.\nChapter 1.\nThe solar system\n\n. .\n2\n.\nBeyond the solar system\n..\n188\n..\nKEY QUESTIONS:\n• How far is our second closest star, Proxima Centauri?\n• What is a galaxy and how many different types of galaxy are there?\n• Where is our Sun located within our own Milky Way Galaxy?\n• How do galaxies arrange themselves on the largest scales in the\nUniverse?\n• How large is the observable Universe and how many galaxies does it\ncontain?\n.\n2.1 The Milky Way Galaxy\nAt the darkest places on Earth, far away from city lights, you can see thousands\nof stars at night using nothing but your eyes. In fact there are many more stars\nin the sky which are too faint for us to see.\nAll of the individual stars that you can see are members of our Milky Way\nGalaxy. A galaxy is a massive collection of stars, gas and dust all held together\nby gravity. The Milky Way has about 200 billion stars and our Sun is just one of\nthose stars in the Milky Way Galaxy.\nFrom the Earth, the Milky Way looks like a bright hazy band of light across the\nsky, mixed in with dark dusty patches. This was called Galaxies Kuklos by the\nGreeks which means the Milky Circle because they thought it looked like milk\nspilled across the sky. The Romans changed the name to Via Lactea which\nmeans the Milky Road or the Milky Way.\nThe Milky Way stretching across the sky viewed from Sutherland. The dark shape of the\nSALT telescope can be seen in the foreground with the night sky in the background\n(SAAO)\n.\nNEW WORDS\n• galaxy\n• galaxy disk\n• galaxy bulge\n• spiral arm\nIf you could travel outside the Milky Way and look down on it from above, the\ngalaxy would look like a giant spiral in space as shown in the following image.\n.\nVISIT\nTime lapse video of the\nMilky Way.\nbit.ly/19Ylkal\n\nThis is what the Milky Way would look like if you could see it from far away in space.\nScientists only know this from many observations made from Earth. No one has actually\nbeen that far away from our galaxy to look at it. The structure is what we have inferred\nfrom other observations.\n.\nVISIT\nDiscover more online and\nread about missions\nbeyond our solar system.\nbit.ly/1iaQrog\nThe image shows what scientists think our galaxy looks like. You can see the\nspiral arms of our Milky Way. These are bluish in colour and are filled with dust\nand gas and hot young stars. The thin dark wisps in the image are dust lanes,\nregions where the gas is very dusty. The central part of the galaxy is more\norangey in colour than the spiral arms. This is because the stars found at the\ncentre of the galaxy tend to be older and cooler than the young hot blue stars.\nScientists think that there are five major spiral arms in our galaxy. These are the\nNorma Arm, the Scutum-Crux Arm, the Sagittarius Arm, the Perseus Arm and\nthe Cygnus Arm.\nOur Sun is located in a small spiral arm called the Orion (or Local) Arm which\nlies between the Sagittarius Arm and the Perseus Arm. Our Sun is about halfway\nout from the centre of the galaxy.\n.\nDID YOU KNOW?\nOur Solar System is\norbiting around the\ncentre of the Milky Way\nat thousands of\nkilometres per hour. But\neven at that speed, it\nstill takes over 200\nmillion years for us to\nmake one complete\norbit around the Milky\nWay Galaxy.\nAll the stars in this galaxy are revolving around the centre of the galaxy. Just as\nthe Earth travels around the Sun, the Sun and our entire solar system is\ntravelling around the centre of the Milky Way Galaxy at a speed of 250 km/s.\nEven though we are travelling incredibly fast, it takes the Sun about 225 million\nyears to complete one orbit around the galaxy centre. The Milky Way is truly\nmassive, measuring a staggering 950 000 000 000 000 000 km across!\n.\n.\n189\n.", "chapter_id": "1.3" }, { "title": "Beyond the solar system", "content": "Chapter 2.\nBeyond the solar system\n\nThe Sun's position in the Milky Way.\nIf, instead of looking down on the Milky Way Galaxy, you looked at it from one\nside you would see that the Galaxy looks like this:\n.\nDID YOU KNOW?\nIf you could shrink the\nsolar system so that the\ndistance from the Sun\nto Pluto is 2.5 cm, the\nMilky Way would have a\ndiameter of 2000 km\n(about the distance\nfrom Durban to\nWindhoek!)\nLooking at the Milky Way from the side.\n.\nTAKE NOTE\nTo us the Earth seems\nbig, but the Earth is\nonly a very small part of\nthe Solar System. And\nour Solar System is a\nvery small part of the\nMilky Way Galaxy. And\nour galaxy is only a very\nsmall part of the whole\nUniverse.\nThe Milky Way is shaped like a giant fried egg. It is about a hundred times wider\nthan it is thick, and it bulges in the middle. The central lump is called the bulge\nand the rest of the galaxy outside the bulge is called the disk.\nAs you know, we are inside the Milky Way Galaxy. So when you look at the thin\nmilky-looking band stretching across the sky at night, what do you think you are\nactually looking at?\n..\n190\n.\nPlanet Earth and Beyond\n\nThe thin band of light that you see is actually the stars in the Sagittarius arm as\nyou look inwards towards the centre of the galaxy. There are so many stars\ndensely packed together that you cannot make out individual stars with your\neyes. Therefore you just see a haze of light. Above and below the plane of the\ndisk there are very few stars.\n.\nVISIT\nWhy is it dark at night?\nbit.ly/HcrKgf\nIf you look closely at the image of\nthe Milky Way above, you can\nsee several round fuzzy blobs\ndotted about above and below\nthe disk. These are called\nglobular clusters and are vast\ncollections of hundreds of\nthousands of ancient stars tightly\npacked together by gravity. The\nMilky Way has an estimated 160\nglobular clusters. The oldest\nstars in the galaxy are found in\nthese globular clusters, some are\nalmost as old as the Universe\nitself.\nA globular cluster called M80. The stars in this\nglobular cluster are around 12.5 billion years old.\nOur Sun is a mere 4.5 billion years old.\n.\nACTIVITY: Draw the Milky Way\n.\nMATERIALS:\n• black paper\n• white crayon, pencil or paint\n• glue - optional\n• glitter or sand - optional\n• newspaper for working on\n• white or silver pencil/pen for labelling\n• sticker - optional\nINSTRUCTIONS:\n.\nVISIT\nVideo showing us\nzooming out from the\nEarth to outside our\ngalaxy.\nbit.ly/1iaQDnt\n1. Draw or paint a picture of the Milky Way. You can use the picture in the\ntext above as a guide. The galaxy has five major spiral arms, and some\nsmaller ones including our Orion Arm. The galaxy also has a bulge in the\nmiddle.\n2. If you are going to use glitter or sand, glue along your spiral arms and in\nthe central bulge.\n3. Scatter glitter or sand over the picture, each grain represents a star in our\nMilky Way.\n4. Tilt the picture onto the newspaper to remove any excess glitter.\n5. Label each of the major arms of the Milky Way Galaxy.\n6. On the Orion Arm place a sticker or mark a point halfway out from the\ngalaxy centre. This marks the position of the Sun.\n.\n.\n.\n191\n.\nChapter 2.\nBeyond the solar system\n\nHow do you think astronomers know what the Milky Way looks like from the\noutside when they have never been outside the Milky Way? The task is similar\nto trying to figure out the shape of a forest from outside when you are in the\nmiddle of the forest. How would you go about this?\n.\nVISIT\nThe sound of interstellar\nspace.\nbit.ly/1cbfjil\nAstronomers look at the sky in all directions and count the number of stars that\nthey see, they also measure the distance to each of the stars so that they can\nbuild up a three dimensional map of the galaxy. One of the difficulties that\nastronomers have in doing this is seeing through all the dust in the galaxy which\ndims the optical light coming from the stars.\n.\nACTIVITY: Make the Milky Way\n.\nMATERIALS:\n• thick piece of black cardboard at least 30 cm across\n• other materials for your model, either collected by you or supplied by your\nteacher\n.\nTAKE NOTE\nWe will learn more\nabout the life cycle of\nstars in Gr 9. Younger\nstars are hotter and\nbright white or blue in\ncolour, while older stars\nare cooler and more\nyellow and red in colour.\nINSTRUCTIONS:\n1. You need to build a 3 dimensional model of the Milky Way Galaxy. You will\neither need to collect the most appropriate materials for your model\nbeforehand, or else your teacher will supply you with a selection of\nmaterials to use in class.\n2. Cut out a circle of radius 15 cm from the black card and use this to build\nyour 3D model.\n3. You must show the central bulge, the spiral arms and the different\ncoloured stars.\n4. Mark the position of our Sun on your model.\n5. Using your model, view it from different angles and compare the view you\nhave with the images of the Milky Way in this chapter.\nQUESTIONS:\n1. What are the two main parts that make up our Milky Way Galaxy?\n2. Where are the spiral arms located; in the disk or the bulge of our galaxy?\n3. Is our Sun found in the central bulge or in a spiral arm in the disk?\n..\n192\n.\nPlanet Earth and Beyond\n\n.\n4. How far from the centre of the galaxy is our Sun located?\n.\n.\n2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.\n2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.\n2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.\nChapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "25" }, { "title": "The Milky Way Galaxy", "content": "", "chapter_id": "2.1" }, { "title": "Our nearest star", "content": "2.2 Our nearest star\nThe Sun is our closest star, and is only 150 million kilometres from Earth. When\nyou look up at the sky at night, if you are lucky enough to be far from the glare\nof city lights, you can see thousands of stars. For those of you in a city, perhaps\nyou can see hundreds of stars, depending on the amount of light pollution from\nstreet lights and other light sources. As you know, there are actually billions of\nstars in our galaxy but most of them are too faint to see from Earth.\nA constellation is a group of stars that, when viewed from Earth, form a pattern\nin the sky. One famous constellation that is visible, even from big cities in South\nAfrica, is the Southern Cross or Crux. The two bright stars at the bottom left\npointing towards the cross are called the pointers.\n.\nNEW WORDS\n• Proxima\nCentauri\n• Alpha Centauri\n• constellation\n.\nDID YOU KNOW?\nYou can find south\nusing the Southern\nCross Constellation.\nJust extend the long\naxis of the cross 4 times\nand then go straight\ndown to the horizon to\nfind south.\nThe Pointers (circled) and the Southern Cross.\nThe brightest of the Pointers looks slightly orange if you look closely. This star is\ncalled Alpha Centauri and is our closest easily visible star after the Sun. Alpha\nCentauri is actually part of a triple star system which is where three stars are in\norbit around each other. The two main stars of the system are called Alpha\nCentauri A and Alpha Centauri B. They orbit close together, on average about\neleven times the Earth-Sun distance from each other.\n.\nVISIT\nScale of the Universe.\nbit.ly/185Yjlc\nA smaller, fainter star, called Proxima Centauri, orbits much farther out. If you\nwere to look at Alpha Centauri through a small telescope, instead of one star\nyou would be able to make out the two separate stars Alpha Centauri A and B\nnext to each other. Proxima Centauri is much fainter and further away from the\nother two so you would not see this one with the other two.\n.\n.\n193\n.\nChapter 2.\nBeyond the solar system\n\nA comparison of the sizes of the Alpha Centauri star system and the Sun.\n.\nDID YOU KNOW?\nProxima Centauri was\ndiscovered in 1915 by\nthe Scottish astronomer\nRobert Innes. He was\nthe director of what was\nthen the Union\nObservatory in South\nAfrica.\nProxima Centauri, the closest star to our own Sun, is about 40 trillion km away\nfrom the Earth. Alpha Centauri A and B are slightly farther away, at 42 trillion\nkm away from us. Our closest star is 694 times farther away than Pluto is. These\nnumbers are astronomically large! As the numbers are so large, astronomers do\nnot use kilometres to measure the distances to stars, but use larger units based\non the speed of light, which you will discover in the next section of this chapter.\nDo you know how much a trillion or a billion is? Have a look at the following\ntable:\nIn words\nIn number format\none thousand\n1 000\none million\n1 000 000\none billion\n1 000 000 000\none trillion\n1 000 000 000\n.\nDID YOU KNOW?\nAstronomers have\nrecently discovered a\nplanet similar in size to\nthe Earth orbiting\naround Alpha Centauri\nB, but we think it is too\nclose to the star to have\nlife on it.\n.", "chapter_id": "2.2" }, { "title": "Light years, light hours and light minutes", "content": "2.3 Light years, light hours and light minutes\n.\nNEW WORDS\n• light minute\n• light hour\n• light year\nOur solar system is a pretty big place. Our nearest neighbour, the Moon, is on\naverage 384 400 kilometres away, and the closest to us that our nearest planet\nVenus gets is about 42 million kilometres. The Sun is about 150 million\nkilometres away and the closest that Pluto can ever get to us is 4.3 billion\nkilometres. These large numbers are impractical to use and so we rather use\nmuch larger distance units based on the speed of light. This makes the numbers\nsmaller and easier to deal with.\nThis is just like using metres instead of centimetres to make the numbers smaller\nwhen you measure a distance. For example, if you are telling a friend how far it\nis from your house to school, you would say it is 7.5 km, and not 7 500 000 cm.\nLet's begin by comparing the speed of light with the speed of some other things\nthat move very fast.\n..\n194\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Travelling fast\n.\nA cheetah, the fastest land mammal, can\nreach speeds of 120 km/h, as fast as cars on\nthe highway.\nA Peregrine Falcon, the fastest animal, can\nfly as fast as 389 km/h.\n.\nVISIT\nHow to break the speed of\nlight.\nbit.ly/H7MoO0\nJapan's high speed train the JR-Maglev\nMLX01 has reached 581 km/h.\nNASA's scramjet the X-43 flies at 7000\nkm/h.\nThe international space station (ISS) orbits the Earth at a speed of 27 744 km/h.\nWhat about light? Light travels at about 1080 million km/h, or 299 792 458 m/s.\n.\n.\n195\n.\nChapter 2.\nBeyond the solar system\n\n.\nINSTRUCTIONS:\n1. Imagine you are going on a trip from Cape Town to Durban, which is a\ndistance of 1753 km.\n2. Calculate how long it would take you to complete the trip travelling at the\nspeeds of the animals and modes of transport in the examples above.\n3. Fill in your answers in the table below.\nRemember the formula: time = distance\nspeed\nMode of\ntransport\nSpeed (km/h)\nDistance between\nCape Town and\nDurban (km)\nTime taken for\nthe journey\ncheetah\n120\n1753\n14.6 hours\nperegrine falcon\n1753\nhours\nhigh speed train\n1753\nhours\nNASA's scramjet\n1753\nminutes\nInternational\nspace station\n1753\nseconds\nlight\n1753\nseconds\n.\nLight is amazingly fast. Look at the examples below.\nIn one second light can travel…\nLight takes…\nbetween Cape Town and\nJohannesburg 214 times.\n0.0000003 seconds to travel 100 m.\nbetween Cape Town and London,\nEngland, 31 times.\n1.3 seconds to travel from the Earth to\nthe Moon.\naround the Earth 7.5 times.\n8 minutes to travel from the Sun to\nthe Earth.\n.\nVISIT\nHow far is a light second?\nbit.ly/1h4IYcE\n..\n196\n.\nPlanet Earth and Beyond\n\nFor distances within the solar system, astronomers use units called light hours\nand light minutes.\nA light hour is the distance that light travels in one hour. Despite its name, a\nlight hour is not a unit of time, it is a unit of distance.\nWhat do you think a light minute corresponds to?\nWhich do you think is a smaller distance, a light hour or a light minute, and why?\n.\nVISIT\nHow far is a light year?\nbit.ly/GZCzBy\nAstronomers use units called light years to measure the distances between\nstars and galaxies. One light year is almost 10 trillion kilometres. As you can see,\na light year is very, very far.\nLight years, light hours and light minutes measure distances. They also tell us\nsomething else very interesting. If you measure the distance to a light source in\nlight travel time, you can work out how long light emitted from the distant\nsource takes to reach you. Light that is emitted from an object one light year\naway from you, takes one year to reach your eyes. Similarly, light that is emitted\nfrom an object one light hour away, takes one hour to reach your eyes.\nHow long do you think light emitted from one light minute away takes to reach\nyour eyes?\n.\nVISIT\nScale of the Universe\ninteractive animation.\nbit.ly/1bavNSv\nThis may sound very strange to you because when you switch on a lamp in your\nhome you see the light straight away. You do not have to wait for the light from\nthe lamp to reach you. You do not notice that it actually takes some time for the\nlight from the lamp to reach your eyes because light travels extremely fast.\n.\nVISIT\nHow big is the Universe?\nbit.ly/AddYnaj\nLight travels so fast, that if you were standing a metre away from the lamp it\nwould only take only three billionths of a second for the light from the lamp to\nreach your eyes. It is therefore no surprise that you don't notice the delay.\n.\n.\n197\n.\nChapter 2.\nBeyond the solar system\n\n.\n.\nACTIVITY: Scale of the solar system\n.\nINSTRUCTIONS:\n1. The table below shows the distance that each planet lies from the Sun in\nkilometres (km) and then in light hours or light minutes.\n2. Study the table and answer the questions that follow.\nDistances of each planet from the Sun.\nPlanet\nDistance from the Sun\n(million km)\nDistance from the Sun\nin light hours or\nminutes\nMercury\n57.9\n3.2 light minutes\nVenus\n108.2\n6.0 light minutes\nEarth\n149.6\n8.3 light minutes\nMars\n227.9\n12.7 light minutes\nJupiter\n778.6\n43.3 light minutes\nSaturn\n1433.5\n1.3 light hours\nUranus\n2872.5\n2.7 light hours\nNeptune\n4495.1\n4.2 light hours\nQUESTIONS:\n.\nDID YOU KNOW?\nThe speed of light is\nspecial, nothing can\nmove faster than the\nspeed of light, it is like a\ncosmic speed limit.\n1. How far away from the Sun is Earth?\n2. How long does light take to travel from the Sun to the Earth?\n3. What does the answer to (2) imply about our view of the Sun?\n4. How many times further away from the Sun than the Earth is Neptune?\n5. How far away from the Sun is Neptune in light hours?\n..\n198\n.\nPlanet Earth and Beyond\n\n.\n6. How long does light from the Sun take to reach Neptune?\n.\nVISIT\nThe size of the Universe.\nbit.ly/1h4JJlM\n7. Imagine you have a cousin living on Neptune. You and your cousin both\ndecide to look at the Sun, each of you using a telescope with a special\nsolar filter so as not to damage your eyes. As you are watching the Sun\nyou suddenly notice a big blob of gas thrown off in a massive solar flare.\nYou cousin says she cannot see it. Why is that?\n.\nAs you can see, the solar system is very large. The orbit of Neptune is over 4\nlight hours from the Sun and the Kuiper Belt and Oort Cloud extend out even\nfurther than this.\nThe distance to the next closest star, Proxima Centauri, is 40 trillion km. This\ncorresponds to 4.24 light years. This means that light from the star takes just\nover four years to reach Earth. Let's investigate the distances to some of our\nclosest stars.\n.\nACTIVITY: Our closest stars\n.\nINSTRUCTIONS:\n1. Look at the table showing our closest stars and the star map.\n2. Answer the questions below.\nStar\nDistance (light years)\nProxima Centauri\n4.24\nAlpha Centauri\n4.37\nBarnard's Star\n5.96\nWISE 1049-5319\n6.52\nWolf 359\n7.78\nLalande 21185\n8.29\nSirius\n8.58\n.\n.\n199\n.\nChapter 2.\nBeyond the solar system\n\n.\nThe following map shows the Sun in the centre with the locations of our closest\nstars. Each solid ring represents a distance of 2, 4, 6 and 8 light years from the\nSun respectively. The dotted circle represents the Oort Cloud.\n.\nTAKE NOTE\nThe star map is shown\nin two dimensions, on a\nflat plane. Remember\nthat the stars are\nlocated in 3 dimensions\nin space.\nQUESTIONS:\n.\nDID YOU KNOW?\nThe Milky Way is so\nlarge that light takes\n100 000 years to cross\nfrom one side to the\nother side.\n1. Which star is our closest neighbour, excluding the Sun?\n2. How far is Sirius?\n3. How long does light from Barnard's Star take to reach us?\n4. Explain in your own words what the statement \"Sirius is 8.58 light years\naway from Earth\" means.\n.\n..\n200\n.\nPlanet Earth and Beyond\n\nOur closest stars are less than ten light years away, however most stars in our\ngalaxy are much farther away. The distances to stars are generally measured in\ntens, hundreds or even thousands of light years and the distances between\ngalaxies are truly enormous as you will discover in the next section.\n.", "chapter_id": "2.3" }, { "title": "What is beyond the Milky Way Galaxy?", "content": "2.4 What is beyond the Milky Way Galaxy?\n.\nNEW WORDS\n• galaxy\n• galaxy group\n• galaxy cluster\n• filament\n• void\n• Universe\nOur galaxy, the Milky Way, is only one out of a total of about 100 to 200 billion\ngalaxies that astronomers estimate to be in the Universe. That's more than 10\ntimes the total number of people on Earth.\nAs well as stars, galaxies contain vast amounts of gas and dust. Galaxies come\nin a variety of shapes and sizes. The Milky Way is an average-sized spiral galaxy:\nit is 100 000 light years across and contains around 200 billion stars.\n.\nTAKE NOTE\nThe distances between\ngalaxies are even larger\nthan the sizes of\ngalaxies and are\nmeasured in millions or\neven billions of light\nyears.\nSmall galaxies may contain\nonly a few million stars, while\nlarge galaxies can have several\ntrillion stars.\nOur closest galaxy neighbour\nis called the Andromeda\nGalaxy. Andromeda is 2.5\nmillion light years away from\nthe Milky Way. If you wanted\nto travel to Andromeda and\ncould travel as fast as light, it\nwould still take you 2.5 million\nyears to get there.\nOur closest neighbouring galaxy, Andromeda. Light\nfrom the galaxy takes 2.5 million years to reach\nEarth and so the light that hits your eyes now from\nthat galaxy was emitted before there were humans\non Earth.\n.\nDID YOU KNOW?\nThe Milky Way and\nAndromeda galaxies\nare on a collision course.\nAstronomers estimate\nthat the two galaxies\nwill collide in around 4\nbillion years time. No\nneed to worry just yet!\nThis illustration shows a stage in the predicted collision between our Milky Way Galaxy\nand the neighboring Andromeda Galaxy, as it will unfold over the next several billion\nyears. This image shows how we think Earth's night sky will look like in 3.75 billion years\ntime.\n.\n.\n201\n.\nChapter 2.\nBeyond the solar system\n\nThere are five main types of galaxies. You do not need to know these names.\nThis is included for your interest.\n• spiral\n• barred spiral\n• elliptical\n• lenticular\n• irregular\n.\nVISIT\nThe largest known galaxy\nin the Universe.\nbit.ly/AddXJcR\nSpiral galaxy named NGC 4414.\nBarred spiral galaxy named NGC 1300.\n.\nVISIT\nWhat is the Universe?\nbit.ly/1eFW3XI\nHow big is the Universe?\nbit.ly/16sqdIB\nElliptical galaxy NGC 1132.\nA lenticular galaxy, called NGC 5866.\nIrregular galaxy named NGC 1427A.\nLet's do an activity to explore the different types of galaxies we see.\n.\nVISIT\nSomething fun - have a\nlook at this picture of a\ncheetah created using\nthousands of images of\ngalaxies from Galaxy Zoo.\nbit.ly/177itzq\n..\n202\n.\nPlanet Earth and Beyond\n\n.\n.\nACTIVITY: Comparing galaxies\n.\nMATERIALS:\n• images of the galaxies to be compared\nINSTRUCTIONS:\n1. Look at the images of the of six galaxies used in this activity.\n2. Using the information in this chapter, write down in the table what type of\ngalaxy our Milky Way Galaxy is.\n3. Write down in the table below what type of galaxy (spiral, barred spiral,\nelliptical or irregular) you think each galaxy is.\n.\nVISIT\nGalaxy Zoo - take part in\nsome real astronomical\nresearch by classifying the\nshapes of different\ngalaxies in this citizen\nscience project.\nbit.ly/AddXQVQ\nGalaxy Name\nGalaxy type\nThe Milky Way Galaxy.\nGalaxy M 89. The galaxy is 60\nmillion light years away.\nGalaxy NGC 4622. The galaxy is 111\nmillion light years away.\n.\n.\n203\n.\nChapter 2.\nBeyond the solar system\n\n.\nGalaxy Name\nGalaxy type\nThe Large Magellanic Cloud galaxy.\nThis satellite galaxy of our own\nMilky Way is only 163 000 light\nyears away.\nThe Spindle Galaxy, 44 million light\nyears away.\nQUESTION:\nList the galaxies in the table above in increasing order of distance from our\nMilky Way Galaxy.\n.\n.\nVISIT\nWhat is dark matter?\nbit.ly/1ab5oFO\nHave a look at the following diagram which shows the location of Earth in the\nUniverse. You do not need to know this classification; this is included for your\ninterest.\n..\n204\n.\nPlanet Earth and Beyond\n\n• Most galaxies are found gathered together in gigantic galaxy\nneighbourhoods, called galaxy groups. Our Milky Way is found in a group\nof galaxies called The Local Group.\n• Galaxy clusters are even larger, spanning tens of millions of light years,\nand can contain hundreds or even thousands of galaxies.\n• Many clusters of galaxies come together to form superclusters of galaxies.\nOur own local group is part of the Virgo supercluster.\n• Gravity holds the galaxies in groups, clusters and superclusters together.\n.\nVISIT\nHow do we know how\nmany galaxies there are in\nthe Universe?\nbit.ly/HfeA0O\nGalaxies in the Hubble Extreme Deep Field. Every smudge in the image is a distant galaxy.\n.\nDID YOU KNOW?\nThe Hubble Extreme\nDeep Field is the most\ndistant picture of the\nUniverse ever taken.\nAstronomers used the\nHubble Telescope to\ntake an image of a small\npatch of sky. Around\n5500 galaxies of all\nshapes, sizes and\ncolours were discovered\nin the image.\n.\n.\n205\n.\nChapter 2.\nBeyond the solar system\n\nThe Observable Universe\n.\nDID YOU KNOW?\nOn the largest scales\nthe Universe resembles\na giant bath sponge.\nThe galaxy clusters are\narranged in thin walls\ncalled filaments.\nBetween the filaments\nare huge gaps which\ncontain very few\ngalaxies and so are\ncalled voids.\nThis computer generated graphic represents a slice of the sponge-like structure of the\nUniverse. All the galaxies lie along thin walls called filaments. The darker areas show the\nvoids where there are no galaxies.\nAstronomers estimate that the age of the Universe is 13.7 billion years old. This\nmight make you imagine that you can see objects from as far as 13.7 billion light\nyears away in all directions. If you were to draw a sphere around the Earth, with\na radius of 13.7 billion light years, with the Earth placed at the centre, the surface\nof the sphere would represent the limit of how far light could travel to Earth in\n13.7 billion years. The surface would represent the edge of the observable\nUniverse as seen from Earth. You might therefore assume that the diameter of\nthe observable Universe is 27.4 billion light years (2 times 13.7).\n.\nVISIT\nDo we expand with the\nUniverse?\nbit.ly/AddYyTd\nHowever, you would actually be wrong. Astronomers estimate the size of the\nobservable Universe to be 93 billion light years in diameter, which is much,\nmuch larger. The reason that the size is much larger than expected is because\nthe Universe is expanding and galaxies are moving further and further away\nfrom the Earth as the space between them expands. So we are able to see\ngalaxies that are now very far away because when they emitted their light they\nwere closer to Earth. The size of the whole Universe, which includes regions too\nfar from Earth for us to see at this time, is unknown.\n.\nVISIT\nRead interesting articles\non the latest\ndevelopments in\nastronomical research on\nSpace Scoop, an\nastronomy news service.\nbit.ly/1fSxJ84\n..\n206\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• A galaxy is a collection of millions or billions of stars, together with gas\nand dust, held together by gravity.\n• Galaxies come in all shapes and sizes.\n• Our home galaxy, the Milky Way Galaxy, is a spiral galaxy containing\naround 200 billion stars. Our Sun is just one of those stars.\n• After the Sun, our nearest star is Alpha Centauri, the brighter of the two\npointer stars in the Southern Cross Constellation\n• Light minutes, light hours and light years are used to measure distances\nin space because the distances are so immense.\n– A light minute is the distance that light can travel in one minute.\n– A light hour is the distance that light can travel in one hour.\n– A light year is the distance that light can travel in one year.\n• Beyond the Milky Way Galaxy, are many more galaxies.\n• Astronomers estimate the size of the observable Universe to be 93\nbillion light years in diameter.\n.\nConcept Map\nRemember that you can also add your own notes to the concept maps to\nexpand and personalise them.\n.\n.\n207\n.\nChapter 2.\nBeyond the solar system\n\n.\n\n.\n.\nREVISION:\n.\n1. What is the name of our second closest star? How far away is it? [2 marks]\n2. What is the name of our second closest easily visible star? Is it really a\nsingle star? [2 marks]\n3. What is the definition of a light year? [2 marks]\n4. What is a galaxy? [3 marks]\n5. Where is the Sun located within the Milky Way? [2 marks]\n6. How many stars are in our Milky Way Galaxy? [1 mark]\n7. Name the 4 main types of galaxies. [4 marks]\n8. What kind of galaxy is the Milky Way? [2 marks]\n.\n.\n209\n.\nChapter 2.\nBeyond the solar system\n\n.\n9. Draw an image of the Milky Way Galaxy as viewed from the top and as\nviewed from the side. Note the position of the Sun in both images. Include\nthe labels: spiral arm, bulge, disk. [8 marks]\n.\n10. Why does it look as though the Milky Way is a splash of milk or a starry\nroad across the sky? [2 marks]\n11. What is a group of galaxies? [2 marks]\n12. What is the name of the group of galaxies that the Milky Way is a member\nof? [1 mark]\n13. What are clusters of galaxies and superclusters of galaxies? [2 marks]\n..\n210\n.\nPlanet Earth and Beyond\n\n.\n14. What is the size of the observable Universe? [1 mark]\n15. Bonus question: On the largest scales what does the Universe look like?\nName the two types of structure which make up the Universe on the\nlargest scales? [2 marks]\nTotal [34 marks]\nTotal with extension [36 marks]\n.\n.\n.\n211\n.\nChapter 2.\nBeyond the solar system\n\n. .\n3\n.\nLooking into space\n..\n212\n..\nKEY QUESTIONS:\n• How did early cultures observe and interpret the night sky?\n• How does a telescope help us to see more objects in the sky and in\ngreater detail?\n• What kind of telescopes are there?\n• Why is South Africa a good place for locating telescopes?\n.\n3.1 Early viewing of space\n.\nNEW WORDS\n• constellation\n• starlore\nIn dark conditions away from city lights, thousands of stars are visible in the\nnight sky. Early cultures around the world gazed at the stars in wonder. They\nnoted the movement of the stars and planets across the sky and used this to\nmark the passage of time. People often grouped the stars they saw into\npatterns called constellations. Early cultures tended to associate the stars and\nplanets they saw in the night sky with animals or gods and told stories, which\nwere passed on from generation to generation, about the patterns in the sky\nwhich were passed down from generation to generation.\nThe stars that are visible depend upon your location on Earth and also the time\nof year. The southern sky, which we see from South Africa, is full of beautiful\nstars and several prominent constellations are visible in the sky including the\nSouthern Cross or Crux, Orion and Pavo the Peacock.\nIn the following activities you will have the opportunity to observe the night sky\nand familiarise yourself with some of the most famous southern constellations.\n.\nACTIVITY: Using star maps to observe the night\nsky\n.\nMATERIALS:\n• star map\n• clear skies\n• pencil\n• paper or this workbook\n• torch - optional\n\n.\nBelow is an example star map of the Southern Hemisphere. Ignore the positions\nof the Moon and the planets. You can generate your own, customised star map\nfor your exact location using the link in the Visit margin box.\n.\nVISIT\nCreate your own star map\nfor your area.\nbit.ly/1a4N1nU\n.\nDID YOU KNOW?\nEarly telescopes were\nwere used by\nmerchants to spot\napproaching trade ships\nor pirates. Telescopes\nalso gave rise to the\nfirst high-speed\ntelecommunications\nnetworks, as spyglasses\nwere used to observe\nsignals from kilometres\naway.\nINSTRUCTIONS:\n1. Go outside at night with your star map.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the following constellations in the sky: Pavo, Phoenix and\nCrux (indicated with green arrows on the star map).\n4. Draw a picture of each of the constellations as you see them.\n5. See if you can spot any of the planets, these will not twinkle like the stars\ndo.\n.\n.\n213\n.", "chapter_id": "2.4" }, { "title": "Looking into space", "content": "Chapter 3.\nLooking into space\n\n.\n.\nTAKE NOTE\nToday professional\nastronomers formally\nrecognise 88\nconstellations, 23 of\nwhich are in the\nsouthern hemisphere.\nDRAWINGS:\nDraw your pictures in the space below. If you have used separate paper you can\nstick your pictures in here.\n.\nVISIT\nLearn how to view the\nnight sky with Google\nEarth.\nbit.ly/16pYL3u\n.\n.\n.\nACTIVITY: Observing the Southern Cross (Crux)\n.\nMATERIALS:\n• picture of the Southern Cross constellation and star map\n• clear skies\n• pencil\n• paper or this workbook\n..\n214\n.\nPlanet Earth and Beyond\n\n.\nThe Southern Cross or Crux (top right) and the Pointers (bottom left).\n.\nDID YOU KNOW?\nThese workbooks were\ncreated by Siyavula\nwith the help of\ncontributors and\nvolunteers. Read more\nabout Siyavula here.\nwww.siyavula.com\nINSTRUCTIONS:\n1. Go outside around 8 pm with your star map (if in the Western half of the\ncountry, closer to Cape Town), or if you live in the Eastern half of the\ncountry, (closer to Johannesburg or Durban) go out an hour earlier around\n7pm.\n2. Wait a few minutes to let your eyes adjust to the dark.\n3. Try to identify the Southern Cross constellation using the star map.\n4. Draw a picture of the Southern Cross and the Pointers as you see them.\nMake a note of the date and time of your picture and in roughly which\ndirection you are facing (north, south, east or west).\n5. Draw or paste your image (if you have used separate paper) into the space\nbelow.\n6. Repeat the observations at least twice so that you have a minimum of three\nobservations on different nights, over the course of a few weeks, and try as\nbest as possible to make your observations at the same time each night.\nDRAWINGS:\n.\n.\n.\n215\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nDID YOU KNOW?\nSome people believe\nthat the builders of the\nancient pyramids of\nGiza in Egypt placed\nthem specifically to look\nthe same from above as\nthe three \"belt stars\" of\nthe constellation Orion\nlook from Earth.\nQUESTION:\nWhat did you notice about the orientation of the Southern Cross as you made\nyour observations?\n.\nAlthough the stars appear to lie in patterns when viewed from the surface of the\nEarth, in reality the stars within a constellation are unrelated, and they can lie at\nvastly different distances from Earth. When we look at the stars at night, we\nonly see a two dimensional projection on the sky of three dimensional space, as\nyou can see in this photograph showing the constellation, Orion.\n.\nVISIT\nStellarium - a free, open\nsource programme for\nyour computer to to\ngenerate a realistic,\nreal-time 3D simulation of\nthe night sky.\nbit.ly/1aE2lmj\n..\n216\n.\nPlanet Earth and Beyond\n\nThe Orion Constellation, seen here as the three bright stars in the middle\nmaking up Orion's belt and the 4 stars in each corner.\nYou might imagine that all the stars lie at the same distance from Earth. This\nisn't true, the stars lie at different distances. The closest star in Orion is called\nBellatrix and is around 250 light years away. The furthest star Meissa is around\n1100 light years away, roughly the same distance as the Orion nebula (1300 light\nyears). But, when viewed from Earth, we see them making up a pattern in\nrelation to each other.\nNow that you are familiar with some of the constellations in the Southern sky,\nincluding the Southern Cross you can learn what some of the early cultures in\nSouthern Africa thought about them.\n.\nVISIT\nRead more about\ntraditional African\nstarlore.\nbit.ly/H022dZ\nAs you can imagine there are many stories associated with the constellations in\nthe sky. In the following activity you will carry out research to find an example\nstory to tell to your class.\n.\nACTIVITY: Constellation starlore\n.\nThe /Xam Bushman imaged that the two pointer stars of the Southern Cross\nwere two male lions who had once been men before they were thrown up into\nthe sky to be stars by a magical girl. The three brightest stars in the Southern\nCross were seen as female lions, perhaps women also changed into stars by the\nmagical girl.\nThe Khoikhoi thought that the Pointers were the eyes of some great beast and\nthey were called Mura which means the eyes.\nIn Sotho, Tswana and Venda cultures, these stars are called Dithutlwa which\nmeans the Giraffes. The bright stars of the Southern Cross are male giraffes, and\nthe two Pointer stars are female giraffes. The Venda named the fainter stars of\nthe Southern Cross Thudana, which means the Little Giraffe. The Sotho used\nthese stars to indicate the beginning of the cultivating season which began\nwhen the giraffe stars were seen close to the south-western horizon just after\nsunset.\n.\n.\n217\n.\nChapter 3.\nLooking into space\n\n.\nINSTRUCTIONS:\n1. Search for a story about a constellation found in the South African sky.\n2. Use a South African starmap as a guide to the constellations found in\nSouth Africa.\n3. Research information on the origin of the story and any beliefs associated\nwith it.\n4. Tell your classmates about the constellation and story you have found out\nabout.\n5. Your teacher will decide on the format of this presentation which might be\na poster or oral presentation.\n.\n.\nVISIT\nRead more about some\nSouth African starlore:\nbit.ly/1cbF7uu and\nbit.ly/1abUL5z\nIn their quest to find out more about planets, stars and galaxies, people\ninvented instruments to observe them in more detail. In the next section we will\nlearn about the telescope: an invention used to study the stars.\n.\n3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "30" }, { "title": "Early viewing of space", "content": "", "chapter_id": "3.1" }, { "title": "Telescopes", "content": "3.2 Telescopes\n.\nNEW WORDS\n• celestial\n• telescope\n• chromatic\naberration\n• primary mirror\n.\nVISIT\nHistory of the telescope.\nbit.ly/1ibkZ9o\nUnfortunately, we cannot visit distant stars or galaxies to study them directly as\nthey are so far away. Instead astronomers study stars and galaxies by analysing\nthe visible light, radio waves and electromagnetic radiation that they receive\nfrom them.\nThe Andromeda galaxy, viewed with the Hubble Space\nTelescope. Humans can only see it as a tiny faint smudge in\nthe sky with the naked eye.\nHuman eyes can see\nvery far. Andromeda\nGalaxy which is 2.5\nmillion light-years\naway is visible to the\nnaked eye. However,\nwe cannot make out\nany detail as it\nappears as only a tiny\nsmudge on the sky to\nour eyes even though\nin reality it is 220 000\nlight years across.\nLight is emitted from stars and galaxies and travels in a straight line in all\ndirections. When you look at a star, you only see the light rays that hit your eye.\nIn Energy and Change, we learnt about visible light. How is the energy of light\ntransferred through space?\nThe further away a star is, the more the starlight is spread out and so less of the\ntotal light from the star reaches your eye. This makes distant objects faint and\ndifficult to see clearly. If we had huge eyes we would be able to see distant\nobjects more clearly because our eyes would gather more of their light.\n..\n218\n.\nPlanet Earth and Beyond\n\nDo you remember making a pinhole camera in Energy and Change? Have a look\nat the following diagram which illustrates this again.\nWhich way is the image projected onto the screen?\n.\nTAKE NOTE\nLuminous objects, such\nas the Sun and other\nstars, emit light. The\ntree is NOT a luminous\nobject as it does not\nemit its own light light.\nIt reflects the light from\nthe Sun.\nThis is the same way in which images are formed on your retina when you view\nan object, as shown in the following image.\nImages formed on the light-detecting retina at the back of your eye are upside down.\nAn object that is far away projects a small image of the object onto the retina at\nthe back of your eye making it difficult to see fine details in the image.\n.\nVISIT\nThe beauty of the night\nsky.\nbit.ly/1h5dy5M\nMore distant objects appear smaller on our retina.\n.\n.\n219\n.\nChapter 3.\nLooking into space\n\nTelescopes help us see faint, distant objects more clearly because they collect\nmore light from the objects than our eyes do. They also magnify the image.\nAs revision of what we learned in Energy and Change last term, answer the\nfollowing questions.\nWhat type of lens is shown in the above image?\nWhat happens to the light when it passes through the lens?\n.\nDID YOU KNOW?\nImages formed on your\nretina are actually\nupside down. Your brain\n\"corrects\" the image, so\nthat you do not notice.\nLet's take a closer look at how a telescope works.\n.\nACTIVITY: Telescopes as light buckets\n.\nThere is only so much light emitted from an object each second. Little packets\nof light are called photons. Our eye needs at least 500 photons, or packets of\nlight, coming into it every second for our brains to sense that something is\nthere. In this activity you are going to represent photons from a distant galaxy\nusing pepper grains or hundreds and thousands.\n..\n220\n.\nPlanet Earth and Beyond\n\n.\nMATERIALS:\n• paper plate\n• piece of paper 3cm by 3cm\n• pencil or pen\n• torch\n• pepper grains or hundreds and thousands\n• wooden skewers\n• foam (bath sponge will do, ideally as wide as the paper plate in one\ndirection)\n• tape - optional\n• scissors\nINSTRUCTIONS:\n.\nVISIT\nHow telescopes work.\nbit.ly/1abV9B9\n1. On the piece of paper draw an image of your eye including the pupil and\niris.\n2. Tape or place the image of your eye onto the middle of a paper plate. The\npaper plate represents a telescope mirror or lens.\n3. Take the foam and cut it into a thin strip about 3 cm wide and as long as\nthe paper plate across.\n4. Stick six skewers into the foam equally spaced along the strip. Trim the\npointed edges off that are sticking out for safety. You will use this foam\nstrip later in this activity.\n5. Shine a torch light just above the picture of the\neye on the plate.\nWhen an object is closer,\nmore light reaches your\neye.\n6. Slowly move the torch further away from the\nplate and watch how the light spreads out and\ndims.\n7. Note how much of the torch light the eye's pupil\nreceives compared to the paper plate.\n8. Now remove the torch and get ready to use the\npepper grains or hundreds and thousands.\nThese will represent photons or packets of light.\nThe further away an object,\nthe less light that reaches\nyour eye.\n.\n.\n221\n.\nChapter 3.\nLooking into space\n\n.\n9. Sprinkle these photons for one second over the\nplate.\n10. Note roughly how many photons get into the\neye compared with how many hit the paper\nplate representing the telescope mirror or lens.\nSprinkle the pepper grains\nor hundreds of thousands.\n11. Now place the foam across the centre of the\npaper plate. The skewers should be pointing\nstraight up. This represents a strip of the\ntelescope mirror with the skewers representing\nlight rays from distant objects.\n12. The telescope mirror is actually curved. Bend\nthe foam upwards at either end so that the\nskewers begin to come together in the middle.\nThe skewers represent the\nlight rays hitting the mirror\nof the telescope.\n.\nVISIT\nHow to make a small, easy\ntelescope.\nbit.ly/19YIAVH\n13. Turn the foam over and direct the skewers into\nthe picture of the eye. The light rays from a\nlarge strip of the mirror are now entering the\nsmall pupil of the eye.\nNow you can see how a\ntelescope's mirror can\ncollect lots of light and\ndirect it into a small\ndetector, like your eye.\nQUESTIONS:\n1. Which collects more of the torch light as the torch moves further away:\nthe eye's pupil or the paper plate?\n2. Did the eye collect enough photons in one second to detect the light?\n..\n222\n.\nPlanet Earth and Beyond\n\n.\n3. Did the telescope mirror (paper plate) collect enough photons for the eye\nto detect the light?\n4. How do you think all the light that hits the telescope mirror is concentrated\nso that it can enter our eyes or a small telescope detector?\n.\nTelescopes have big lenses or mirrors to collect as much light as possible. This\nis how they are able to see faint objects. Telescopes also concentrate or focus\nthe light and redirect it into our small eye so that we can see the dim object.\nAlternatively, telescopes can redirect the light into special detectors that record\nimages, similar to a cell phone camera.\n.\nACTIVITY: Compare your eye with SALT\n.\nThe Southern African Large Telescope (SALT) takes pictures of some of the\nmost distant and faintest objects in the Universe. SALT's camera takes images\nwith exposure times typically of twenty minutes, after which the camera shutter\ncloses and the resulting image is displayed on a computer. The longer the\nexposure, the more light that the telescope can gather to make the image. The\nhuman eye does not have a shutter. We seem to see continuously, rather than\nas a succession of still images. However, the eye does have a kind of exposure\ntime. In this activity you will estimate the exposure time of your eye by\nestimating your reaction time and then compare it with SALT's typical exposure\ntime.\nMATERIALS:\n• ruler\n• calculator\n• pencil or pen\nINSTRUCTIONS:\n1. Work in pairs for this activity.\n2. Look at your partner's eyes. Estimate the diameter of their pupils using a\nruler held close to their eye. Be careful not to actually touch your partner's\neyes.\n3. Write down the diameter of pupil in the table below.\n4. Compare the diameter of the pupil with that of the Southern African Large\nTelescope (SALT) which is roughly 10 m in diameter.\n5. Calculate how many times larger than an eye SALT is. (Remember to\ncompare the areas rather than the diameters).\n6. One of the pair: hold a pen or pencil directly in front of you, while the other\nperson stands opposite you and prepares to catch it.\n.\n.\n223\n.\nChapter 3.\nLooking into space\n\n.\n7. Drop the pen or pencil and see if you partner can catch it.\n8. Estimate the reaction time of your partner. Is it a second? Is it a tenth of a\nsecond? Is it a thousandth of a second?\n9. Repeat steps 6 - 8 swapping places.\n10. Fill in your reaction times in the table below, these represent the exposure\ntime of your eye.\n11. Complete the questions.\nTable to record your results:\nEye\nSALT\nSALT / Eye\nDiameter of\ncollecting lens /\nmirror\ncm\ncm\nArea of\ncollecting lens /\nmirror\ncm2\ncm2\nExposure time\nseconds\nseconds\nHint: Convert the diameter of SALT to cm. Convert the exposure time of SALT\nto seconds. To simplify the calculation of the area of the SALT mirror assume it\nis a circle with a radius of 5 m. The area of a circle is given by the formula A =\nπr2.\nQUESTIONS:\n1. Why should you compare the area of the telescope and eye's pupil rather\nthan their diameters?\n2. How many times more light does the SALT telescope collect compared\nwith your eye?\n3. What would happen to your reaction time if your eye had to accumulate\nlight over a longer interval before sending an image to the brain?\n4. How many times longer can SALT expose for than your eye?\n.\n..\n224\n.\nPlanet Earth and Beyond\n\nTelescopes can collect more light from faint and distant objects because they\nhave larger collecting areas and because they can accumulate light over longer\nperiods of time to make an image. This means that you can see fainter objects\nwith telescopes that you would be able to see using just your eye.\nTelescopes also magnify (enlarge) the image that you see, so it takes up more\nroom on your retina allowing you to see the object more clearly.\nA convex (converging) lens used as a magnifying glass. The resulting image is larger than\nthe object. Telescopes magnify images from distant stars and galaxies.\nMagnification comes at a price however. A fixed amount of light is received\nfrom any object, so if you make the image larger, its gets fainter as the light is\nspread out within the image. This is why it is so important to collect as much\nlight as possible.\n.\nVISIT\nThe atmosphere and\noptical telescopes.\nbit.ly/1bSTS1d\nThe larger a telescope's mirror or lens, the better it is at seeing narrowly\nseparated objects as individual objects and the sharper the images look.\nThe most important feature of a telescope is how much light it can collect,\nwhich depends upon the area of the lens or mirror. The larger the light\ncollecting area, the more light a telescope gathers and the higher resolution\n(ability to see fine detail) it has. So the size of a telescope is far more important\nthan its magnification.\nNow that we have briefly looked at how telescopes work, we are going to look\nat the different types of telescopes, namely:\n• optical telescopes\n• radio telescopes\n• space telescopes\nOptical telescopes\nOptical telescopes collect visible light from celestial objects. There are two\ntypes of optical telescopes.\n1. Refracting telescopes use lenses to collect and focus the light from distant\nobjects.\n2. Reflecting telescopes use mirrors to collect and focus the light from\ndistant objects.\n.\n.\n225\n.\nChapter 3.\nLooking into space\n\n1. Refracting telescopes\nRefracting telescopes use a converging (convex) lens to collect and bend the\nlight rays inwards to the focal point (also called the focus) of the telescope. The\nlight collecting lens is called the objective lens.\n.\nTAKE NOTE\nAs astronomical objects\nare so far away, their\nlight rays are\nconsidered to be\nparallel to each other.\nOnce light is brought to a focus, it is then magnified by another lens called the\neyepiece lens. Look at the optical ray diagram below showing a simple\nrefracting telescope.\nThe telescope objective lens collects and focuses the light from a distant tree\nforming a real inverted image of the tree. The eyepiece lens, like a magnifying\nglass, then enlarges the image collected by the objective lens, producing a\nlarger, virtual image. This images is what we see when we look through the\ntelescope.\nWhat kind of lenses are the objective lens and the eyepiece lens?\n.\nTAKE NOTE\nA real image is called\nreal because light rays\nactually pass through\nthe point where the\nimage is formed. A\nvirtual image is called a\nvirtual image because\nthe light rays do not\nactually come from the\nimage, they just appear\nto have come from the\nimage.\nLook at the following picture which shows how white light is refracted (bent) as\nit travels through a prism. As we learnt in Energy and Change, when light travels\nthrough glass it slows down and so it bends or refracts.\n..\n226\n.\nPlanet Earth and Beyond\n\nDo all the colours undergo the same amount of refraction? Which colour is bent\nthe most?\nWhite light is a mixture of all the colours of the rainbow. Different colours are\nrefracted by different amounts as they travel through the prism so the white\nlight is split into its different colours. How do you think this affects the images\nproduced by refracting telescopes?\nLenses are shaped to bend light by a certain desired amount. However, the\ndifferent colours that make up white light bend by slightly different amounts.\nThis means that different colours come to a focus at slightly different distances\nfrom the objective lens. Each colour will produce its own image and they will be\nslightly misaligned with each other resulting in a slightly blurry image. This\neffect is called chromatic aberration and all lenses suffer from this effect.\nBlue light is bent more than red light and so different colours are focused at different\ndistances from the lens. The different coloured images are overlaid upon each other and,\nbecause they are misaligned, the resulting image is blurry.\n.\n.\n227\n.\nChapter 3.\nLooking into space\n\nThe main disadvantages of refracting telescopes are:\n1. Light travels through the lenses in the telescope and so the lenses have to\nbe perfect. There must be no bubbles of air in the glass which would distort\nthe image. It is difficult to and expensive to make large perfect lenses.\n2. The light travels through the lenses and so they can only be supported\naround their edges, where they are thinnest and weakest. This limits the\nsize of refracting telescopes because if a lens is too large it will sag under\nits own weight and distort the image.\n3. Lenses suffer from chromatic aberration which blurs the image.\n2. Reflecting telescopes\nIn the 1680s, Isaac Newton invented the reflecting telescope. Reflecting\ntelescopes use a curved primary mirror to collect light from distant objects and\nreflect it to a focus.\n.\nDID YOU KNOW?\nThe first successful\nreflecting telescope\nbuilt was the Newtonian\nTelescope, by Isaac\nNewton, which is where\nthe design gets its\nname.\n.\nTAKE NOTE\nRemember that for\neach ray, the angle of\nincidence is equal to the\nangle of reflection, as\nyou learned in Energy\nand Change.\nThere are many different types of reflecting telescopes. A prime focus reflector\nis the simplest type of reflector telescope. In this design, a recording structure is\nplaced at the focal point to obtain the focused image. In the old days, in very\nlarge telescopes, a person would actually sit in an \"observing cage\" to view the\nimage directly or operate a camera. However, now a detector is used and is\noperated from outside of the telescope. The position of the detector is shown in\nthe following diagram with a red cross.\nA prime focus reflector with a detector at the focal point, marked with an X.\n..\n228\n.\nPlanet Earth and Beyond\n\nMore complex designs of reflecting telescopes use a secondary small mirror to\nreflect the light towards the eyepiece lens.\n• A Newtonian reflector reflects the light to an eyepiece on the side of the\ntelescope tube. This design is often used for amateur telescopes because\nhaving the eyepiece on the side of the tube makes the telescope easy to\nuse.\n• A Cassegrain reflector reflects light through a small hole in the primary\nmirror. This kind of telescope is often used for large professional\ntelescopes as it allows heavy detectors to be placed at the bottom of the\ntelescope. This makes them easy to reach for repairs and also means that\nthe weight of the detectors does not affect the telescope tube.\n.\nDID YOU KNOW?\nThe Cassegrain reflector\nis named after a\nreflecting telescope\ndesign that was\npublished in 1672 and\nhas been attributed to\nLaurent Cassegrain.\nA group of Newtonian telescopes.\nThe following ray diagrams show the difference between a Newtonian and\nCassegrain reflector.\nRay diagrams for some example reflecting telescopes. The Newtonian reflector is often\nused in amateur telescopes. The Cassegrain telescope is often used at large\nobservatories.\n.\n.\n229\n.\nChapter 3.\nLooking into space\n\nThe SAAO 1.9 m reflecting\ntelescope. Detectors are\nbolted onto the\nCassegrain focus at the\nbottom of the telescope\n(metal boxes under the\norange tubing). (Credit:\nSAAO).\nThe secondary mirror in a reflecting telescope must be very small. Why do you\nthink this is so?\nDo you think that reflecting telescopes suffer from chromatic aberration? Why?\n.\nVISIT\nCurious about the\nUniverse, but don't know\nwhere to start? Have a\nlook at this step-by-step\nguide to becoming an\nawesome amateur\nastronomer.\nbit.ly/1gBwrQ8\n.\nDID YOU KNOW?\nNASA is currently\nplanning the successor\nfor the Hubble Space\nTelescope, called the\nJames Webb Space\nTelescope (JWST). It will\nbe launched into space\nin 2018.\nThe advantages of a reflecting telescope include:\n1. The glass of the mirror does not have to be perfect throughout, only the\nsurface has to be perfect.\n2. The mirror can be supported across the whole of its back so it won't sag.\n3. Making large mirrors is easier and cheaper than making big lenses.\n4. They do not suffer from chromatic aberration.\nOptical telescopes on the ground do however have some disadvantages:\n1. They can only be used at night.\n2. They cannot be used in bad weather (rain, cloud, snow etc).\nOptical telescopes are best placed on the tops of remote mountains. Discuss\nwithin your class why you think this is. Take some notes in the space below.\n..\n230\n.\nPlanet Earth and Beyond\n\nThe largest telescopes in the world today are reflecting telescopes. In the next\nsection you will learn about one of the largest reflecting telescopes in the world\nwhich is located right here in South Africa.\nSALT\n.\nNEW WORDS\n• SALT\nThe Southern African Large Telescope (SALT) is the\nlargest optical telescope in the southern hemisphere\nand among the largest in the world. SALT was\ncompleted in 2005 and is located in the Karoo in the\nNorthern Cape, near the town, Sutherland.\nAstronomers use telescopes like SALT to study\nplanets, stars and galaxies. SALT can detect the light\nfrom faint or distant objects in the Universe a billion\ntimes too faint to be seen with the naked eye.\nThe SALT telescope has a large mirror which collects\nlight. SALT's primary mirror is a hexagonal shape\nmeasuring 11.1 m by 9.8 m across and is made up of 91\nindividual 1.2 m hexagonal mirrors. SALT is a prime\nfocus reflector. What does this mean?\nThe SALT telescope just\noutside Sutherland.\n.\nVISIT\nThe SALT website.\nbit.ly/1fSW6CH\nSALT does not\nhave a\ntelescope tube.\nInstead there is\na network of\nmetal struts\nwhich support\nthe tracker and\npayload at the\ntop of the\ntelescope.\nThe whole\ntelescope\nstructure\nweighs 85 tons.\nThe payload\ncontains\ndetectors\nwhich take\npictures of the\nnight sky.\nSALT's giant mirror, made up of 91 individual mirrors.\n.\nVISIT\nThe Southern African\nLarge Telescope (video).\nbit.ly/17e0xFy\n.\n.\n231\n.\nChapter 3.\nLooking into space\n\nStars move during the night just as the Sun\nmoves across the sky in the day. The telescope\nmust follow the stars as they move. The\ntracker at the top of SALT is used to follow the\ndrifting stars carrying the detectors along with\nit as it tracks the stars.\nSALT is currently being used to study stars, in\nparticular binary star systems where two stars\norbit around each other. Astronomers also use\nthe telescope to study galaxies and some of\nthe most violent explosions in the Universe\ncalled supernovae and Gamma Ray Bursts\nwhich occur when massive stars explode at the\nend of their lives. SALT is also looking at the\nUniverse on the largest of scales, in order to\nanswer the questions how did the Universe\nbegin, and what will happen to it in the future?\nThe SALT telescope structure.\n(Credit: SALT)\n.\nVISIT\nWhat is a radio telescope?\nbit.ly/1a4LbTW\nThe Karoo is an ideal place to host SALT because it is far away from towns and\ncities so there is very little light pollution. The area is also at a high elevation,\ndry and there are no extreme weather conditions, such as flooding or storms.\nDespite it being so remote at the observatory site there is good infrastructure,\nincluding roads and electricity, in the surrounding area of Sutherland.\nRadio telescopes\n.\nNEW WORDS\n• antenna\n• receiver\n• amplifier\n• SKA\nRadio waves are a type of electromagnetic radiation (or light) that humans\ncannot see with their eyes. They have very long wavelengths compared to\noptical light. Purple light, for example, has a wavelength of 400 nm whereas red\nlight has a wavelength of 700 nm. Radio wavelengths are much longer; radio\nwaves have wavelengths from approximately one millimeter to hundreds of\nmetres.\n.\nTAKE NOTE\nDo you remember\nlearning about\nwavelength in Energy\nand Change? A\nwavelength is the\ndistance between two\ncorresponding points on\ntwo consecutive waves.\nRadio telescopes detect radio\nwaves coming from distant\nobjects. Radio telescopes have\nseveral advantages over optical\ntelescopes. They can be used in\nbad weather, as radio waves\nare not blocked by clouds.\nThey can also be used during\nthe day and at night.\nMany objects in space emit\nradio waves, for example some\ngalaxies, stars and nebulae\nwhich are giant clouds of dust\nand gas where stars are born.\nSome objects emit radio waves\nbut do not emit optical light,\ntherefore looking at the sky at\nradio wavelengths reveals a\ncompletely different picture of\nour Universe.\nAn optical (white) and radio (orange) image of the\ngalaxy NGC 1316. The radio emission spans over\none million light years and engulfs the optical light\nat the centre.\n..\n232\n.\nPlanet Earth and Beyond\n\nIf your eyes could see radio waves at night, rather than white light, instead of\nseeing pointlike stars, you would see distant star-forming regions, bright\ngalaxies and beautiful giant clouds around old exploded stars.\n.\nVISIT\nAtacama Large\nMillimeter/sub-millimeter\nArray (ALMA) is a new\nradio telescope in Chile's\nAtacama desert. It will\nopen an entirely new\n'window' into the\nUniverse, allowing\nscientists to search for our\ncosmic origins.\nWatch a video on some of\nthe latest research and\nimages released from\nALMA.\nbit.ly/17GzMnB\n.\nDID YOU KNOW?\nRapidly rotating star\nremnants, called\npulsars, were first\ndiscovered using a radio\ntelescope in 1967.\nAstronomers initially\nconsidered the\npossibility that the\nregular pulses of radio\nwaves were signals\nfrom an alien civilisation\nbut quickly realised that\nthis was not the case.\nRadio telescopes typically look like large dishes. The dish or antenna, acts like\nthe primary mirror in a reflecting telescope, collecting the radio waves and\nreflecting them up to a smaller mirror which then reflects the radio waves to a\nradio wave detector. Radio wave detectors are called receivers. An amplifier\namplifies the signal and sends it to a computer which processes the information\nfrom the receiver to create colour images which we can see.\nRadio telescopes need to be placed far away from cities and towns as\nman-made radio interference can interfere with the telescope's observations.\nPart of the KAT-7 radio telescope array in the Northern Cape.\n.\n.\n233\n.\nChapter 3.\nLooking into space\n\nMeerKAT and the SKA\n.\nDID YOU KNOW?\nThe SKA central\ncomputer will have the\nprocessing power of\nabout one hundred\nmillion computers. The\ndishes of the SKA will\nproduce 10 times the\nglobal internet traffic.\nThe MeerKAT radio\ntelescope array is currently\nunder construction in the\nNorthern Cape. MeerKAT is\nscheduled to be complete in\n2016 and when it is finished\nit will have 64 radio dishes\neach 13.5 m in diameter. The\nMeerKAT array will be the\nlargest and most sensitive\nradio telescope in the\nsouthern hemisphere until\nthe Square Kilometre Array\n(SKA) is completed around\n2024.\nThe KAT-7 test array in the Northern Cape is a test\narray for the larger MeerKAT array.\n.\nVISIT\nA video on the SKA.\nbit.ly/1aE3b2A\nRead more about the SKA\nonline.\nbit.ly/H02OHY\nThe Square Kilometre Array (SKA) will be the most powerful telescope ever. It\nwill have a total collecting area of one square kilometer. It will have 3000 radio\ndishes each about 15 m wide which will act together as one large telescope. As\nwell as the 3000 radio dishes there will be two other types of radio wave\ndetectors.\n.\nDID YOU KNOW?\nThe data collected by\nthe SKA in a single day\nwould take nearly two\nmillion years to\nplayback on an ipod.\nThe location of SKA in South Africa, and other African countries.\n..\n234\n.\nPlanet Earth and Beyond\n\nMany different countries are working together to build, and pay for, the SKA. At\nleast 13 countries and close to 100 organisations are already involved, and more\nare joining the project. Most of the SKA will be located in South Africa. There\nwill also be locations in Australia and some stations in eight African partner\ncountries namely, Botswana, Ghana, Kenya, Madagascar, Mauritius,\nMozambique, Namibia, and Zambia.\n.\nDID YOU KNOW?\nRadio astronomy\nobservatories use diesel\ncars around the\ntelescopes because the\nignition of the spark\nplugs in petrol cars can\ninterfere with radio\nobservations.\nOne of the SKA dishes.\n.\nTAKE NOTE\nJobs are not just limited\nto astronomers:\nengineers, computer\nscientists and\nadministrative staffare\nneeded to run the\ntelescopes.\nMeerKAT and the SKA will be used to investigate how galaxies change over\ntime, our understanding of gravity, the origin of cosmic magnetism, how the\nvery first stars formed, other planets around other stars, and whether we are\nalone in the Universe.\n.\nACTIVITY: Careers in Astronomy\n.\nINSTRUCTIONS:\nDiscuss in class with your teacher and classmates what sorts of careers you\nthink are now available in astronomy in South Africa because of the\nconstruction of SALT and MeerKAT / SKA. Think about and discuss the skills\nneeded in each of the roles you discuss.\n.\n.\n.\n235\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Draw a telescope\n.\nMATERIALS:\n• paper\n• pencils or crayons\n.\nDID YOU KNOW?\nThe SKA will be so\nsensitive it could detect\nTV signals from planets\norbiting other stars.\nINSTRUCTIONS:\n1. Pick either an optical telescope or radio telescope and draw a picture of\nthe telescope.\n2. Label the different parts of the telescope and describe what they do.\n.\nTAKE NOTE\nThe sensitivity of a radio\ntelescope depends\nupon the area of the\ncollecting dish and the\nsensitivity of the radio\nreceiver. In order to\nproduce sharp radio\nimages comparable to\nimages from optical\ntelescopes a radio\ntelescope must be\nmuch larger than an\noptical telescope.\n.\n.\n..\n236\n.\nPlanet Earth and Beyond\n\nSpace telescopes\n.\nVISIT\nThe Hubble Space\nTelescope (videos)\nbit.ly/1873WQd and\nbit.ly/1abWIiG and\nsome of the best images\nfrom Hubble\nbit.ly/1deIJLS\nRadio waves and visible light form part of what is called the electromagnetic\nspectrum of light. There are other types of light at different wavelengths that\nwe cannot see with our eyes including X-rays, ultraviolet and infrared light.\n.\nDID YOU KNOW?\nThe Hubble Space\nTelescope is named\nafter Edward Hubble,\nconsidered to be one of\nthe most important\ncosmologists of the\n20th century. Hubble\ndiscovered there were\ngalaxies beyond our\nown and helped confirm\nthat the universe is\nexpanding.\nThe Earth's atmosphere blocks X-rays, ultraviolet and infrared light and stops\nthem from reaching the ground. So if we want to observe this kind of light from\nstars and galaxies, we need to put telescopes in space. This is why X-ray\ntelescopes and infrared telescopes are placed in space.\nA picture of an X-ray telescope called XMM-Newton.\nThe advantages of space telescopes are that they can observe the whole sky\nand operate during both night and day. Images taken with space telescopes are\nfar sharper than images taken with telescopes on the ground, because images\nare not smeared or blurred by turbulence in the Earth's atmosphere, as with\nimages take from ground telescopes. This is why the Hubble Space Telescope\nimages are so detailed even though it is a relatively small reflective telescope.\nThe major disadvantages of space telescopes are their costs and the fact that if\nsomething goes wrong they are extremely difficult to fix.\nThe Hubble Space Telescope has a 2.4m diameter collecting mirror.\n.\n.\n237\n.\nChapter 3.\nLooking into space\n\n.\n.\nACTIVITY: Telescope information poster\n.\nMATERIALS:\n• paper\n• pencils or crayons\n• pictures downloaded from the internet or copied from books - optional\nINSTRUCTIONS:\n1. Pick a telescope that you want to make a poster about. It can be a\nground-based or space-based telescope.\n2. Describe the telescope and explain how it works. Include a diagram or\npicture of the telescope and label its main parts in your poster.\n3. List some of the science that the telescope is used for in your poster.\n4. List some of the advantages and disadvantages of the type of telescope\nyou have chosen in your poster.\n.\n.\nVISIT\nHow many people are in\nspace right now? Find out\nhere.\nbit.ly/18Gzr83\n.\nVISIT\nLearn more about the\nJames Webb Space\nTelescope (video).\nbit.ly/1h5hUd9\nDid you know that these workbooks were created at Siyavula with the\ninput from many contributors and volunteers? Just turn to the front of\nyour workbook to see the long list!\nRead more about Siyavula at our website: www.siyavula.com and like our\nFacebook page.\nSiyavula has also created a range of textbooks for other grades and\nsubjects, and we are going to be producing more. These textbooks and\nworkbooks are openly-licensed and freely available for you to use and\ndownload.\n..\n238\n.\nPlanet Earth and Beyond\n\n. .\nSUMMARY:\n.\nKey Concepts\n• Early cultures observed the stars and grouped them together in patterns\nor constellations.\n• Telescopes allow astronomers to see distant, faint objects in more detail.\n• The performance of a telescope is measured by how much light it can\ncollect. Larger telescopes can collect more light and see finer details\nthan smaller telescopes.\n• Optical telescopes detect optical light from distant objects.\n• Most modern day optical telescopes use mirrors to collect and focus the\nlight from distant objects.\n• Radio telescopes collect and focus radio waves, emitted from distant\nobjects in space.\n• South Africa is host to one of the the most advanced optical telescopes\nin the world, the Southern African Large Telescope (SALT).\n• South Africa will also host a large part of the soon to be constructed SKA\nradio telescope which will be the largest radio telescope in the world\nonce complete.\n.\nConcept Map\nThe concept maps in this workbook we made using an open source, free\nprogramme. If you would like to make your own concept maps for your other\nsubjects, you can download the programme from the link in the visit box.\n.\nVISIT\nThe concept maps in your\nworkbooks were created\nat Siyavula using an open\nsource programme. You\ncan download it from this\nlink if you want to use it to\ncreate your own concept\nmaps for your other\nsubjects.\nbit.ly/1fSWS2s\n.\nVISIT\nScience is about curiosity,\ndiscovery and innovation!\nbit.ly/18GzSyZ\n.\n.\n239\n.\nChapter 3.\nLooking into space\n\n.\n\n.\n.\nREVISION:\n.\n1. What do astronomers call patterns of stars in the sky? [1 mark]\n2. Name three famous southern constellations. [3 marks]\n3. What do optical refracting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n4. What do optical reflecting telescopes use to collect and focus light from\ndistant objects? [1 mark]\n5. List two advantages that reflecting telescopes have over refracting\ntelescopes. [2 marks]\n6. What sort of light do radio telescopes detect? [1 mark]\n7. List two advantages that radio telescopes have over optical telescopes. [2\nmarks]\n8. Why are X-ray telescopes located in space? [1 mark]\n.\n.\n241\n.\nChapter 3.\nLooking into space\n\n.\n9. Why does the Hubble Space Telescope produce such sharp images even\nthough it is much smaller than most professional ground based\ntelescopes? [1 mark]\n10. Why should astronomers look at objects at different wavelengths? [1 mark]\n11. What is the name of the largest optical telescope located in the Northern\nCape? [1 mark]\n12. List three reasons why the SALT telescope is located near Sutherland in\nthe Northern Cape. [3 marks]\n13. How many dishes will the MeerKAT array have? [1 mark]\n14. How many dishes will the SKA array have? [1 mark]\n15. List two areas of astronomy that will be studied using the SKA telescope.\n[2 marks]\nTotal [22 marks]\n.\n..\n242\n.\nPlanet Earth and Beyond\n\nWhat can you transform our Earth into? Be curious!\n.\n.\n243\n.\nChapter 3.\nLooking into space\n\n.\n.\n.\nGLOSSARY\nAlpha Centauri:\nour second closest easily visible star after the Sun;\nit is actually two stars orbiting very close together\namplifier:\na device which amplifies (to make something\nbigger) the radio wave signals\nantenna:\nthe dish or other device used to collect radio waves\nin a radio telescope\nasteroid belt:\nthe area where most asteroids are found in our\nsolar system, lying between the orbits of Mars and\nJupiter\nasteroid:\na small rocky object orbiting the Sun\nastronomical unit\n(AU):\nthe average distance between the Earth and the\nSun, equal to around 150 million kilometres\ncelestial:\npositioned in or relating to the sky, or outer space\nas observed in astronomy\nchromatic aberration:\nan optical effect where different colours are\nrefracted by different amounts in a lens leading to\na distorted image\ncomet:\na small object made of ice and dust which\nsometimes enters the inner solar system; when a\ncomet enters the inner solar system, part of it\nevaporates to form a long tail of ice and dust\npointing away from the Sun\nconstellation:\na group of stars that form a pattern in the sky when\nviewed from Earth\nconvection:\none of the three ways to transport heat energy (the\nother two are conduction and radiation); as a liquid\nor gas is heated, it becomes less dense and rises;\nwhile denser colder material sinks, creating a flow\nof moving liquid or gas which transports heat\nenergy along with it\ndwarf planet:\na large, roughly spherical object orbiting a star\nwhich cannot be classed as a planet because it is\nnot large enough to sweep out other objects from\nits orbit\nfilament:\na threadlike structure in space containing galaxies\nand galaxy groups and clusters\ngalaxy bulge:\na spheroidal (rugby ball shaped) distribution of old\nstars at the centre of a galaxy\ngalaxy cluster:\na collection of over 50 or more galaxies, held\ntogether by gravity\ngalaxy disk:\nthe flat distribution of stars, gas and dust in a\ngalaxy\ngalaxy group:\na collection of about 50 or less galaxies, held\ntogether by gravity\ngalaxy:\na collection of millions or billions of stars, gas and\ndust all held together by gravity\n..\n244\n.\nPlanet Earth and Beyond\n\n.\ngas giant:\na large planet made mostly of gas with no solid\nsurface; the four outermost planets in the solar\nsystem are gas giants\nhabitable zone:\nthe region surrounding a star in which water can\nremain in its liquid state\nKuiper Belt:\nregion of space filled with trillions of small objects\nthat lie in the outer reaches of the solar system,\npast the orbit of Neptune\nKuiper Belt object:\na small icy object orbiting the Sun out beyond the\norbit of Neptune\nlight hour:\nthe distance that light travels in one hour\nlight minute:\nthe distance that light travels in one minute\nlight year:\nthe distance that light travels in one year\nnuclear fusion:\nthe process by which stars produce their energy;\nlight atomic nuclei come together and merge to\nform heavier atomic nuclei, releasing energy as\nthey do so; in the Sun, hydrogen nuclei fuse with\nother hydrogen nuclei to form heavier helium nuclei\nOort Cloud:\na hypothetical huge cloud of icy objects (comets)\nsurrounding the Sun at the very edge of our solar\nsystem at a distance between 5,000 and 100,000\ntimes the Earth's distance from the Sun\nphotosynthesis:\nthe process by which green plants and some other\norganisms use sunlight to synthesise foods from\ncarbon dioxide and water producing oxygen as a\nbyproduct\nprimary mirror:\nthe light-collecting mirror in an optical telescope\nProxima Centauri:\nour second closest star after the Sun\nreceiver:\na device that detects radio wave signals\nSALT:\nthe Southern African Large Telescope, the largest\noptical telescope in the southern hemisphere\nSKA:\nthe Square Kilometre Array, the largest planned\nradio telescope array in the world\nsolar system:\nthe Sun, and the collection of planets and smaller\nobjects that orbit around the Sun\nsolar wind:\nthe continuous flow of charged particles from the\nSun that extends out to the far reaches of the solar\nsystem\nspiral arm:\na region of stars, gas and dust forming a curved\nshape spiralling out from the centre of a spiral\ngalaxy\nstar:\na huge ball of burning gas which emits energy in\nthe form of light and heat\nstarlore:\nmythical stories about the stars, planets and\nconstellations\nsunspot:\na dark region or spot which appears on the surface\nof the Sun from time to time; sunspots are cooler\nthan the rest of the Sun's surface\ntelescope:\nan instrument used to look at distant objects, which\nmakes distant objects appear brighter, larger and\nclearer; optical telescopes collect visible light and\nradio telescopes collect radio waves\n.\n.\n245\n.\nChapter 3.\nLooking into space\n\n.\nterrestrial planet:\na planet with a rocky surface like the Earth's\nsurface; the four innermost planets in the solar\nsystem are terrestrial planets\nUniverse:\nall of existence, including all planets, stars, galaxies,\nthe space between objects, and all matter and\nenergy\nvoid:\na vast empty bubble in space found between\nfilaments\n..\n246\n.\nPlanet Earth and Beyond\n\n.\n.\n247\n.\nChapter 3.\nLooking into space\n\nImage Attribution\n1\nhttp://www.flickr.com/photos/chefranden/3507963245/\n. . . . . . . . . . . . . . . . . . . . . . . . . .\n106\n2\nhttp://en.wikipedia.org/wiki/File:Prime_focus_telescope.svg\n. . . . . . . . . . . . . . . . . . . . . . . .\n228", "chapter_id": "3.2" } ] }