Season

A season is a division of the year marked by changes in weather , ecology and hours of daylight . Seasons result from the yearly orbit of the Earth around the Sun and the tilt of the Earth 's rotational axis relative to the plane of the orbit . In temperate and polar regions , the seasons are marked by changes in the intensity of sunlight that reaches the Earth 's surface , variations of which may cause animals to go into hibernation or to migrate , and plants to be dormant .   During May , June , and July , the northern hemisphere is exposed to more direct sunlight because the hemisphere faces the sun . The same is true of the southern hemisphere in November , December , and January . It is the tilt of the Earth that causes the Sun to be higher in the sky during the summer months which increases the solar flux . However , due to seasonal lag , June , July , and August are the hottest months in the northern hemisphere and December , January , and February are the hottest months in the southern hemisphere .   In temperate and subpolar regions , four calendar-based seasons are generally recognized : spring , autumn or fall , and winter . Ecologists often use a six-season model for temperate climate regions : prevernal , vernal , estival , serotinal , autumnal , and hibernal . Many tropical regions have two seasons : the rainy , wet , or monsoon season and the dry season . Some have a third cool , mild , or harmattan season . Seasons often held special significance for agrarian societies , whose lives revolved around planting and harvest times , and the change of seasons was often attended by ritual .   In some parts of the world , some other `` seasons '' capture the timing of important ecological events such as hurricane season , tornado season , and wildfire season . The most historically important of these are the three seasons -- flood , growth , and low water -- which were previously defined by the former annual flooding of the Nile in Egypt .


Season creep

In phenology , season creep is observed changes in the timing of the seasons , such as earlier indications of spring widely observed in temperate areas across the Northern Hemisphere .  Phenological records analyzed by climate scientists have shown significant temporal trends in the observed time of seasonal events ,  from the end of the 20th century and continuing into the 21st century . In Europe , season creep has been associated with the arrival of spring moving up by approximately one week in a recent 30-year period .  Other studies have put the rate of season creep measured by plant phenology in the range of 2 -- 3 days per decade advancement in spring , and 0.3 -- 1.6 days per decade delay in autumn , over the past 30 -- 80 years .   Observable changes in nature related to season creep include birds laying their eggs earlier and buds appearing on some trees in late winter . In addition to advanced budding , flowering trees have been blooming earlier , for example the culturally important cherry blossoms in Japan ,  and Washington , D.C.  Northern hardwood forests have been trending toward leafing out sooner , and retaining their green canopies longer .  The agricultural growing season has also expanded by 10 -- 20 days over the last few decades .   The effects of season creep have been noted by non-scientists as well , including gardeners who have advanced their spring planting times ,  and experimented with plantings of less hardy warmer climate varieties of non-native plants . While summer growing seasons are expanding , winters are getting warmer and shorter , resulting in reduced winter ice cover on bodies of water ,  earlier ice-out ,  earlier melt water flows ,  and earlier spring lake level peaks .  Some spring events , or `` phenophases '' , have become intermittent or unobservable ; for example , bodies of water that once froze regularly most winters now freeze less frequently ,  and formerly migratory birds are now seen year-round in some areas .


Seattle

Seattle ( -LSB- siˈætəl -RSB- ) is a seaport city on the west coast of the United States and the seat of King County , Washington . With an estimated 704,352 residents , Seattle is the largest city in both the state of Washington and the Pacific Northwest region of North America . In July 2013 , it was the fastest-growing major city in the United States and remained in the Top 5 in May 2015 with an annual growth rate of 2.1 % . In July 2016 , Seattle was again the fastest-growing major U.S. city , with a 3.1 % annual growth rate . The city is situated on an isthmus between Puget Sound ( an inlet of the Pacific Ocean ) and Lake Washington , about 100 mi south of the Canada -- United States border . A major gateway for trade with Asia , Seattle is the fourth-largest port in North America in terms of container handling .   The Seattle area was previously inhabited by Native Americans for at least 4,000 years before the first permanent European settlers . Arthur A. Denny and his group of travelers , subsequently known as the Denny Party , arrived from Illinois via Portland , Oregon , on the schooner Exact at Alki Point on November 13 , 1851 . The settlement was moved to the eastern shore of Elliott Bay and named `` Seattle '' in 1852 , after Chief Si'ahl of the local Duwamish and Suquamish tribes .   Logging was Seattle 's first major industry , but by the late-19th century , the city had become a commercial and shipbuilding center as a gateway to Alaska during the Klondike Gold Rush . Growth after World War II was partially due to the local Boeing company , which established Seattle as a center for aircraft manufacturing . The Seattle area developed as a technology center beginning in the 1980s , with companies like Microsoft becoming established in the region . In 1994 , Internet retailer Amazon was founded in Seattle . The stream of new software , biotechnology , and Internet companies led to an economic revival , which increased the city 's population by almost 50,000 between 1990 and 2000 .   Seattle has a noteworthy musical history . From 1918 to 1951 , nearly two dozen jazz nightclubs existed along Jackson Street , from the current Chinatown / International District , to the Central District . The jazz scene developed the early careers of Ray Charles , Quincy Jones , Ernestine Anderson , and others . Seattle is also the birthplace of hip-hop sensation Neema , rock musician Jimi Hendrix , origin of the bands Nirvana , Pearl Jam , Soundgarden , Alice in Chains and the alternative rock subgenre grunge .


Seawall

A seawall ( or sea wall ) is a form of coastal defense constructed where the sea , and associated coastal processes , impact directly upon the landforms of the coast . The purpose of a sea wall is to protect areas of human habitation , conservation and leisure activities from the action of tides , waves , or tsunamis . As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea .   The coast is generally a high-energy , dynamic environment with spatial variations over a wide range of timescales . The coast is exposed to erosion by rivers and winds as well as the sea , so that a combination of denudational processes will work against a sea wall .  Because of these persistent natural forces , sea walls need to be maintained ( and eventually replaced ) to maintain their effectiveness .   The many types of sea wall in use today reflect both the varying physical forces they are designed to withstand , and location specific aspects , such as local climate , coastal position , wave regime , and value of landform . Sea walls are hard engineering shore-based structures which protect the coast from erosion . But various environmental problems and issues may arise from the construction of a sea wall , including disrupting sediment movement and transport patterns . Combined with a high construction cost , this has led to an increasing use of other soft engineering coastal management options such as beach replenishment .   Sea walls may be constructed from various materials , most commonly reinforced concrete , boulders , steel , or gabions . Other possible construction materials are : vinyl , wood , aluminium , fibreglass composite , and large biodegrable sandbags made of jute and coir . In the UK , sea wall also refers to an earthen bank used to create a polder , or a dike construction .


Seawater

Seawater , or salt water , is water from a sea or ocean . On average , seawater in the world 's oceans has a salinity of about 3.5 % ( 35 g/L , or 0.600 M ) This means that every kilogram ( roughly one litre by volume ) of seawater has approximately 35 g of dissolved salts ( predominantly sodium and chloride ions ) . Average density at the surface is 1.025 kg/L . Seawater is denser than both fresh water and pure water ( density 1.0 kg/L at 4 C ) because the dissolved salts increase the mass by a larger proportion than the volume . The freezing point of seawater decreases as salt concentration increases . At typical salinity , it freezes at about -2 C . The coldest seawater ever recorded ( in a liquid state ) was in 2010 , in a stream under an Antarctic glacier , and measured -2.6 C. Seawater pH is typically limited to a range between 7.5 and 8.4 . However , there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units .


Second Grinnell expedition

The Second Grinnell expedition of 1853–1855 was an American effort, financed by Henry Grinnell, to determine the fate of the Franklin's lost expedition. Led by Elisha Kent Kane, the team explored areas northwest of Greenland, now called Grinnell Land. While failing to determine the fate of Sir John Franklin, the expedition set a new record for northward penetration, delineated 960 miles (1,540 km) of unexplored coastline north of 82° latitude, and discovered the long-sought open Polar Sea. Kane collected valuable geographical, climate and magnetic observations before abandoning the brig Advance to the pack ice in 1855. While three members of the crew were lost, the epic journey of the survivors inspired the public as a vivid tale of Arctic survival.


Second law of thermodynamics

The second law of thermodynamics states that the total entropy of an isolated system can only increase over time . It can remain constant in ideal cases where the system is in a steady state ( equilibrium ) or undergoing a reversible process . The increase in entropy accounts for the irreversibility of natural processes , and the asymmetry between future and past .   Historically , the second law was an empirical finding that was accepted as an axiom of thermodynamic theory . Statistical thermodynamics , classical or quantum , explains the microscopic origin of the law .   The second law has been expressed in many ways . Its first formulation is credited to the French scientist Sadi Carnot in 1824 , who showed that there is an upper limit to the efficiency of conversion of heat to work in a heat engine .


Self-publishing

Self-publishing is the publication of any book or other media by its author without the involvement of an established publisher . A self-published physical book is said to have been privately printed . The author is in control of the entire process including , for a book , the design of the cover and interior , formats , price , distribution , marketing , and public relations . The authors can do it all themselves or may outsource some or all the work to companies which offer these services .   Self-publishing is not limited to physical books . E-books , pamphlets , brochures , websites , and other media are commonly self-published .


Sensitivity analysis

Sensitivity analysis is the study of how the uncertainty in the output of a mathematical model or system ( numerical or otherwise ) can be apportioned to different sources of uncertainty in its inputs . A related practice is uncertainty analysis , which has a greater focus on uncertainty quantification and propagation of uncertainty ; ideally , uncertainty and sensitivity analysis should be run in tandem .   The process of recalculating outcomes under alternative assumptions to determine the impact of a variable under sensitivity analysis can be useful for a range of purposes , including :  Testing the robustness of the results of a model or system in the presence of uncertainty .  Increased understanding of the relationships between input and output variables in a system or model .  Uncertainty reduction , through the identification of model inputs that cause significant uncertainty in the output and should therefore be the focus of attention in order to increase robustness ( perhaps by further research ) .  Searching for errors in the model ( by encountering unexpected relationships between inputs and outputs ) .  Model simplification -- fixing model inputs that have no effect on the output , or identifying and removing redundant parts of the model structure .  Enhancing communication from modelers to decision makers ( e.g. by making recommendations more credible , understandable , compelling or persuasive ) .  Finding regions in the space of input factors for which the model output is either maximum or minimum or meets some optimum criterion ( see optimization and Monte Carlo filtering ) .  In case of calibrating models with large number of parameters , a primary sensitivity test can ease the calibration stage by focusing on the sensitive parameters . Not knowing the sensitivity of parameters can result in time being uselessly spent on non-sensitive ones .  To seek to identify important connections between observations , model inputs , and predictions or forecasts , leading to the development of better models .


Sensor-based sorting

Sensor-based sorting , is an umbrella term for all applications where particles are singularly detected by a sensor technique and rejected by an amplified mechanical , hydraulic or pneumatic process . The technique is generally applied in the three industries mining , recycling and food processing and used in the particle size range between 0.5 and . Since sensor-based sorting is a single particle separation technology , the throughput is proportional to the average particle size and weight fed onto the machine .


September 11 attacks

The September 11 attacks ( also referred to as 9/11 ) The expression `` 9/11 '' is pronounced `` nine eleven '' . The slash is not part of the pronunciation . The name is frequently used in British English as well as in American English , even though the dating conventions differ . were a series of four coordinated terrorist attacks by the Islamic terrorist group al-Qaeda on the United States on the morning of Tuesday , September 11 , 2001 . The attacks killed 2,996 people , injured over 6,000 others , and caused at least $ 10 billion in property and infrastructure damage .   Four passenger airliners operated by two major U.S. passenger air carriers ( United Airlines and American Airlines ) -- all of which departed from airports in the northeastern United States bound for California -- were hijacked by 19 al-Qaeda terrorists . Two of the planes , American Airlines Flight 11 and United Airlines Flight 175 , were crashed into the North and South towers , respectively , of the World Trade Center complex in New York City . Within an hour and 42 minutes , both 110-story towers collapsed , with debris and the resulting fires causing partial or complete collapse of all other buildings in the World Trade Center complex , including the 47-story 7 World Trade Center tower , as well as significant damage to ten other large surrounding structures . A third plane , American Airlines Flight 77 , was crashed into the Pentagon ( the headquarters of the United States Department of Defense ) in Arlington County , Virginia , leading to a partial collapse of the building 's western side . The fourth plane , United Airlines Flight 93 , initially was steered toward Washington , D.C. , but crashed into a field in Stonycreek Township near Shanksville , Pennsylvania , after its passengers tried to overcome the hijackers . It was the deadliest incident for firefighters and law enforcement officers in the history of the United States , with 343 and 72 killed respectively .   Suspicion for the attack quickly fell on al-Qaeda . The United States responded to the attacks by launching the War on Terror and invading Afghanistan to depose the Taliban , which had harbored al-Qaeda . Many countries strengthened their anti-terrorism legislation and expanded the powers of law enforcement and intelligence agencies to prevent terrorist attacks . Although al-Qaeda 's leader , Osama bin Laden , initially denied any involvement , in 2004 he claimed responsibility for the attacks . Al-Qaeda and bin Laden cited U.S. support of Israel , the presence of U.S. troops in Saudi Arabia , and sanctions against Iraq as motives . Having evaded capture for almost a decade , bin Laden was located and killed by SEAL Team Six of the U.S. Navy in May 2011 .   The destruction of the World Trade Center and nearby infrastructure caused serious damage to the economy of Lower Manhattan and had a significant effect on global markets , closing Wall Street until September 17 and the civilian airspace in the U.S. and Canada until September 13 . Many closings , evacuations , and cancellations followed , out of respect or fear of further attacks . Cleanup of the World Trade Center site was completed in May 2002 , and the Pentagon was repaired within a year . On November 18 , 2006 , construction of One World Trade Center began at the World Trade Center site . The building was officially opened on November 3 , 2014 . Numerous memorials have been constructed , including the National September 11 Memorial & Museum in New York City , the Pentagon Memorial in Arlington County , Virginia , and the Flight 93 National Memorial in a field in Stonycreek Township near Shanksville , Pennsylvania .


Series and parallel circuits

Components of an electrical circuit or electronic circuit can be connected in many different ways . The two simplest of these are called series and parallel and occur frequently . Components connected in series are connected along a single path , so the same current flows through all of the components . Components connected in parallel are connected , so the same voltage is applied to each component .   A circuit composed solely of components connected in series is known as a series circuit ; likewise , one connected completely in parallel is known as a parallel circuit .   In a series circuit , the current through each of the components is the same , and the voltage across the circuit is the sum of the voltages across each component . In a parallel circuit , the voltage across each of the components is the same , and the total current is the sum of the currents through each component .   Consider a very simple circuit consisting of four light bulbs and one 6 V battery . If a wire joins the battery to one bulb , to the next bulb , to the next bulb , to the next bulb , then back to the battery , in one continuous loop , the bulbs are said to be in series . If each bulb is wired to the battery in a separate loop , the bulbs are said to be in parallel . If the four light bulbs are connected in series , there is same current through all of them , and the voltage drop is 1.5 V across each bulb , which may not be sufficient to make them glow . If the light bulbs are connected in parallel , the currents through the light bulbs combine to form the current in the battery , while the voltage drop is across each bulb and they all glow .   In a series circuit , every device must function for the circuit to be complete . One bulb burning out in a series circuit breaks the circuit . In parallel circuits , each light has its own circuit , so all but one light could be burned out , and the last one will still function .


Settlement of the Americas

Available scientific evidence indicates that modern humans emerged from Africa over 100,000 years ago , yet did not arrive in the Americas until less than 20,000 years ago . Current understanding of the settlement of the Americas derives from advances in four interrelated disciplines : archaeology , Pleistocene geology , physical anthropology , and DNA analysis . While there is general agreement that the Americas were first settled from Asia , the pattern of migration , its timing , and the place ( s ) of origin in Asia of the peoples who migrated to the Americas remain unclear . In the 2000s , researchers sought to use familiar tools to validate or reject established theories , such as Clovis first . The archeological evidence suggests that the Paleo-Indians ' first dispersal into the Americas occurred near the end of the last glacial period or , more specifically , what is known as the Last Glacial Maximum ( LGM ) , around 16,500 -- 13,000 years ago .   The settlement of the Americas is of intense interest to archaeologists and anthropologists . Modern biochemical techniques , as well as the accumulation of archaeological and geological evidence , have shed progressively more light on the subject ; however , significant questions remain unresolved .


Severe weather

Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage , serious social disruption , or loss of human life . Types of severe weather phenomena vary , depending on the latitude , altitude , topography , and atmospheric conditions . High winds , hail , excessive precipitation , and wildfires are forms and effects of severe weather , as are thunderstorms , downbursts , lightning , tornadoes , waterspouts , tropical cyclones , and extratropical cyclones . Regional and seasonal severe weather phenomena include blizzards , snowstorms , ice storms , and duststorms .


Seville

Seville ( -LSB- səˈvɪl -RSB- Sevilla -LSB- seˈβiʎa -RSB- , -LSB- seˈβi ʝa -RSB- ) is the capital and largest city of the autonomous community of Andalusia and the province of Seville , Spain . It is situated on the plain of the river Guadalquivir . The inhabitants of the city are known as sevillanos ( feminine form : sevillanas ) or hispalenses , after the Roman name of the city , Hispalis . Seville has a municipal population of about 703,000 , and a metropolitan population of about 1.5 million , making it the fourth-largest city in Spain and the 30th most populous municipality in the European Union . Its Old Town , with an area of 4 km ² , contains three UNESCO World Heritage Sites : the Alcázar palace complex , the Cathedral and the General Archive of the Indies . The Seville harbour , located about 80 km from the Atlantic Ocean , is the only river port in Spain . Seville is also the hottest major metropolitan area in the geographical Western Europe , with summer average high temperatures of above 35 ° C.   Seville was founded as the Roman city of Hispalis . It later became known as Ishbiliya after the Muslim conquest in 712 . During the Muslim rule in Spain , Seville came under the jurisdiction of the Caliphate of Córdoba before becoming the independent Taifa of Seville ; later it was ruled by the Muslim Almoravids and the Almohads until finally being incorporated into the Christian Kingdom of Castile under Ferdinand III in 1248 . After the discovery of the Americas , Seville became one of the economic centres of the Spanish Empire as its port monopolised the trans-oceanic trade and the Casa de Contratación ( House of Trade ) wielded its power , opening a Golden Age of arts and literature . In 1519 , Ferdinand Magellan departed from Seville for the first circumnavigation of the Earth . Coinciding with the Baroque period of European history , the 17th century in Seville represented the most brilliant flowering of the city 's culture ; then began a gradual economic and demographic decline as silting in the Guadalquivir forced the trade monopoly to relocate to the nearby port of Cádiz .   The 20th century in Seville saw the tribulations of the Spanish Civil War , decisive cultural milestones such as the Ibero-American Exposition of 1929 and Expo ' 92 , and the city 's election as the capital of the Autonomous Community of Andalusia .


Sewage sludge

Sewage sludge refers to the residual , semi-solid material that is produced as a by-product during sewage treatment of industrial or municipal wastewater . The term septage is also referring to sludge from simple wastewater treatment but is connected to simple on-site sanitation systems , such as septic tanks .   When fresh sewage or wastewater enters a primary settling tank , approximately 50 % of the suspended solid matter will settle out in an hour and a half . This collection of solids is known as raw sludge or primary solids and is said to be `` fresh '' before anaerobic processes become active . The sludge will become putrescent in a short time once anaerobic bacteria take over , and must be removed from the sedimentation tank before this happens .   This is accomplished in one of two ways . In an Imhoff tank , fresh sludge is passed through a slot to the lower story or digestion chamber where it is decomposed by anaerobic bacteria , resulting in liquefaction and reduced volume of the sludge . After digesting for an extended period , the result is called `` digested '' sludge and may be disposed of by drying and then landfilling . More commonly with domestic sewage , the fresh sludge is continuously extracted from the tank mechanically and passed to separate sludge digestion tanks that operate at higher temperatures than the lower story of the Imhoff tank and , as a result , digest much more rapidly and efficiently .   Biosolids is a term often used in conjunction with reuse of sewage sludge after sewage sludge treatment . Biosolids can be defined as organic wastewater solids that can be reused after stabilization processes such as anaerobic digestion and composting . Opponents of sewage sludge reuse reject this term as a public relations term .


Sewage sludge treatment

Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment . Sludge is mostly water with lesser amounts of solid material removed from liquid sewage . Primary sludge includes settleable solids removed during primary treatment in primary clarifiers . Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors .   Sludge treatment is focused on reducing sludge weight and volume to reduce disposal costs , and on reducing potential health risks of disposal options . Water removal is the primary means of weight and volume reduction , while pathogen destruction is frequently accomplished through heating during thermophilic digestion , composting , or incineration . The choice of a sludge treatment method depends on the volume of sludge generated , and comparison of treatment costs required for available disposal options . Air-drying and composting may be attractive to rural communities , while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities , and economies of scale may encourage energy recovery alternatives in metropolitan areas .   Energy may be recovered from sludge through methane gas production during anaerobic digestion or through incineration of dried sludge , but energy yield is often insufficient to evaporate sludge water content or to power blowers , pumps , or centrifuges required for dewatering . Coarse primary solids and secondary sewage sludge may include toxic chemicals removed from liquid sewage by sorption onto solid particles in clarifier sludge . Reducing sludge volume may increase the concentration of some of these toxic chemicals in the sludge .


Shale gas

Shale gas is natural gas that is found trapped within shale formations . Shale gas has become an increasingly important source of natural gas in the United States since the start of this century , and interest has spread to potential gas shales in the rest of the world . In 2000 shale gas provided only 1 % of U.S. natural gas production ; by 2010 it was over 20 % and the U.S. government 's Energy Information Administration predicts that by 2035 , 46 % of the United States ' natural gas supply will come from shale gas .   Some analysts expect that shale gas will greatly expand worldwide energy supply . China is estimated to have the world 's largest shale gas reserves .   The Obama administration believed that increased shale gas development would help reduce greenhouse gas emissions . In 2012 , US carbon dioxide emissions dropped to a 20-year low .   A 2013 review by the United Kingdom Department of Energy and Climate Change noted that most studies of the subject have estimated that life-cycle greenhouse gas ( GHG ) emissions from shale gas are similar to those of conventional natural gas , and are much less than those from coal , usually about half the greenhouse gas emissions of coal ; the noted exception was a 2011 study by Howarth and others of Cornell University , which concluded that shale GHG emissions were as high as those of coal . More recent studies have also concluded that life-cycle shale gas GHG emissions are much less than those of coal , among them , studies by Natural Resources Canada ( 2012 ) , and a consortium formed by the US National Renewable Energy Laboratory with a number of universities ( 2012 ) .   Some 2011 studies pointed to high rates of decline of some shale gas wells as an indication that shale gas production may ultimately be much lower than is currently projected . But shale-gas discoveries are also opening up substantial new resources of tight oil / `` shale oil '' .


Shock (circulatory)

Circulatory shock , commonly known as shock , is a life-threatening medical condition of low blood perfusion to tissues resulting in cellular injury and inadequate tissue function . The typical signs of shock are low blood pressure , rapid heart rate , signs of poor end-organ perfusion ( i.e. : low urine output , confusion , or loss of consciousness ) , and weak pulses .   The shock index ( SI ) , defined as heart rate divided by systolic blood pressure , is an accurate diagnostic measure that is more useful than hypotension and tachycardia in isolation . Under normal conditions , a number between 0.5 and 0.8 is typically seen . Should that number increase , so does suspicion of an underlying state of shock . Blood pressure alone may not be a reliable sign for shock , as there are times when a person is in circulatory shock but has a stable blood pressure .   Circulatory shock is not related to the emotional state of shock . Circulatory shock is a life-threatening medical emergency and one of the most common causes of death for critically ill people . Shock can have a variety of effects , all with similar outcomes , but all relate to a problem with the body 's circulatory system . For example , shock may lead to hypoxemia ( a lack of oxygen in arterial blood ) or cardiac and/or respiratory arrest .   One of the key dangers of shock is that it progresses by a positive feedback mechanism . Poor blood supply leads to cellular damage , which results in an inflammatory response to increase blood flow to the affected area . This is normally very useful to match up supply with tissue demand for nutrients . However , if enough tissue causes this , it will deprive vital nutrients from other parts of the body . Additionally , the ability of the circulatory system to meet this increase in demand causes saturation , a major result of which is that other parts of the body begin to respond in a similar way , thus exacerbating the problem . Due to this chain of events , immediate treatment of shock is critical to survival .


Shutdown of thermohaline circulation

A shutdown or slowdown of the thermohaline circulation is an effect of global warming on a major ocean circulation .   Data from 2010 NASA suggested that the Atlantic Meridional Overturning Circulation has not slowed down , but may have actually sped up slightly in the recent past . However , this has been superseded by a 2015 study that suggests ` that the Gulf Stream has weakened by 15-20 % '


Sierra Madre Occidental

The Sierra Madre Occidental is a major mountain range system of the North American Cordillera , that runs northwest -- southeast through Northwestern and Western Mexico , and along the Gulf of California . The Sierra Madre is part of the American Cordillera , a chain of mountain ranges ( cordillera ) that consists of an almost continuous sequence of mountain ranges that form the western `` backbone '' of North America , Central America , South America and Antarctica .


Silurian

The Silurian is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period , at million years ago ( Mya ) , to the beginning of the Devonian Period , Mya . As with other geologic periods , the rock beds that define the period 's start and end are well identified , but the exact dates are uncertain by several million years . The base of the Silurian is set at a major Ordovician-Silurian extinction event when 60 % of marine species were wiped out .   A significant evolutionary milestone during the Silurian was the diversification of jawed and bony fish . Multi-cellular life also began to appear on land in the form of small , bryophyte-like and vascular plants that grew beside lakes , streams , and coastlines , and terrestrial arthropods are also first found on land during the Silurian . However , terrestrial life would not greatly diversify and affect the landscape until the Devonian .


Sinking of MV Sewol

The sinking of Sewol , also referred to as the Sewol Ferry Disaster , occurred on the morning of 16 April 2014 , en route from Incheon to Jeju in South Korea . The ferry capsized while carrying 476 people , mostly secondary school students from Danwon High School ( Ansan City ) . The 6,825-ton vessel sent a distress signal from about 2.7 km north off Byeongpungdo at 08:58 Korea Standard Time ( 23:58 UTC , 15 April 2014 ) . In total , 304 passengers and crew members died in the disaster . Of the approximately 172 survivors , more than half were rescued by fishing boats and other commercial vessels that arrived at the scene approximately 40 minutes after the South Korean coast guard .   The sinking of Sewol resulted in widespread social and political reaction within South Korea . Many criticized the actions of the captain and most of the crew . More criticized the ferry operator and the regulators who oversaw its operations . Additional criticism was directed at the South Korean government and media for its disaster response ( including the poor showing of the then Korean coastguard ) and attempts to downplay government culpability .   On 15 May 2014 , the captain and three crew members were charged with murder , while the other 11 members of the crew were indicted for abandoning the ship . An arrest warrant was also issued for Yoo Byung-eun , the owner of Chonghaejin Marine , which operated Sewol , but he could not be found despite a nationwide manhunt . On 22 July 2014 , police revealed that they had established that a dead man found in a field 415 kilometres south of Seoul was Yoo . Foul play was ruled out , but police say they have yet to establish the cause of Yoo 's death .   On the first anniversary of the disaster , as part of commemorations for the victims of the sinking of Sewol , 4,475 people held electronic candles to form the shape of the ferry in an attempt to set a Guinness World Record for the largest torchlight image .


Sinking of the RMS Lusitania

The sinking of the Cunard ocean liner RMS Lusitania occurred on Friday , 7 May 1915 during the First World War , as Germany waged submarine warfare against the United Kingdom who had implemented a naval blockade of Germany . The ship was identified and torpedoed by the German U-boat and sank in 18 minutes . The vessel went down 11 mi off the Old Head of Kinsale , Ireland , killing 1,198 and leaving 761 survivors . The sinking turned public opinion in many countries against Germany , contributed to the American entry into World War I and became an iconic symbol in military recruiting campaigns of why the war was being fought .   Lusitania had the misfortune to fall victim to torpedo attack relatively early in the First World War , before tactics for evading submarines were properly implemented or understood . The contemporary investigations in both the UK and the United States into the precise causes of the ship 's loss were obstructed by the needs of wartime secrecy and a propaganda campaign to ensure all blame fell upon Germany . Argument over whether the ship was a legitimate military target raged back and forth throughout the war as both sides made misleading claims about the ship . Before Lusitania sailed , the German embassy had placed warnings in American newspapers that the ship would be targeted as it was carrying war munitions . At the time she was sunk , she was carrying over 4 million rounds of small-arms ammunition ( .303 caliber ) , almost 5,000 shrapnel shell casings ( for a total of some fifty tons ) , and 3,240 brass percussion fuses , in addition to 1,266 passengers and a crew of 696 . Several attempts have been made over the years since the sinking to dive to the wreck seeking information about precisely how the ship sank , and argument continues to the present day .


Sinking of the RMS Titanic

The sinking of the RMS Titanic occurred on the night of 14 April through to the morning of 15 April 1912 in the North Atlantic Ocean , four days into the ship 's maiden voyage from Southampton to New York City . The largest passenger liner in service at the time , Titanic had an estimated 2,224 people on board when she struck an iceberg at around 23:40 ( ship 's time ) on Sunday , 14 April 1912 . Her sinking two hours and forty minutes later at 02:20 ( 05:18 GMT ) on Monday , 15 April resulted in the deaths of more than 1,500 people , which made it one of the deadliest peacetime maritime disasters in history .   Titanic received six warnings of sea ice on 14 April but was travelling near her maximum speed when her lookouts sighted the iceberg . Unable to turn quickly enough , the ship suffered a glancing blow that buckled her starboard ( right ) side and opened five of her sixteen compartments to the sea . Titanic had been designed to stay afloat with four of her forward compartments flooded but no more , and the crew soon realised that the ship would sink . They used distress flares and radio ( wireless ) messages to attract help as the passengers were put into lifeboats . In accordance with existing practice , Titanic 's lifeboat system was designed to ferry passengers to nearby rescue vessels , not to hold everyone on board simultaneously ; therefore with the ship sinking rapidly and help still hours away , there was no safe refuge for many of the passengers and crew . Compounding this , poor management of the evacuation meant many boats were launched before they were completely full .   Thus , when Titanic sank , over a thousand passengers and crew were still on board . Almost all those who jumped or fell into the water drowned within minutes due to the effects of hypothermia . arrived on the scene about an hour and a half after the sinking and rescued the last of the survivors by 09:15 on 15 April , some nine and a half hours after the collision . The disaster caused widespread outrage over the lack of lifeboats , lax regulations , and the unequal treatment of the three passenger classes during the evacuation . Subsequent inquiries recommended sweeping changes to maritime regulations , leading to the establishment in 1914 of the International Convention for the Safety of Life at Sea ( SOLAS ) , which still governs maritime safety today .


Situation awareness

Situational awareness or situation awareness ( SA ) is the perception of environmental elements and events with respect to time or space , the comprehension of their meaning , and the projection of their status after some variable has changed , such as time , or some other variable , such as a predetermined event . It is also a field of study concerned with understanding of the environment critical to decision-makers in complex , dynamic areas from aviation , air traffic control , ship navigation , power plant operations , military command and control , and emergency services such as fire fighting and policing ; to more ordinary but nevertheless complex tasks such as driving an automobile or riding a bicycle .   Situation awareness involves being aware of what is happening in the vicinity to understand how information , events , and one 's own actions will impact goals and objectives , both immediately and in the near future . One with an adept sense of situation awareness generally has a high degree of knowledge with respect to inputs and outputs of a system , an innate `` feel '' for situations , people , and events that play out because of variables the subject can control . Lacking or inadequate situation awareness has been identified as one of the primary factors in accidents attributed to human error . Thus , situation awareness is especially important in work evironments where the information flow can be quite high and poor decisions may lead to serious consequences ( such as piloting an airplane , functioning as a soldier , or treating critically ill or injured patients ) .   As outlined below , three facets of SA have been in focus in research , namely SA States , SA Systems , and SA processes . SA States refers to the actual awareness of the situation . SA Systems refers to the distribution of SA in teams and between objects in the environment , and to the exchange of SA between system parts . SA Processes refers to the updating of SA States , and what guides the moment-to-moment change of SA .   Having complete , accurate , and up-to-the-minute SA is essential where technological and situational complexity on the human decision-maker are a concern . Situation awareness has been recognized as a critical , yet often elusive , foundation for successful decision-making across a broad range of complex and dynamic systems , including aviation , air traffic control , ship navigation , health care , emergency response , military command and control operations , and offshore oil and nuclear power plant management .


Six degrees of separation

Six degrees of separation is the idea that all living things and everything else in the world are six or fewer steps away from each other so that a chain of `` a friend of a friend '' statements can be made to connect any two people in a maximum of six steps . It was originally set out by Frigyes Karinthy in 1929 and popularized in an eponymous 1990 play written by John Guare .


Skepticism

Skepticism ( American English ) or scepticism ( British English ; see spelling differences ) is generally any questioning attitude or doubt towards one or more items of putative knowledge or belief . It is often directed at domains , such as morality ( moral skepticism ) , religion ( skepticism about the existence of God ) , or knowledge ( skepticism about the possibility of knowledge , or of certainty ) . Formally , skepticism as a topic occurs in the context of philosophy , particularly epistemology , although it can be applied to any topic such as politics , religion , and pseudoscience .   Philosophical skepticism comes in various forms . Radical forms of skepticism deny that knowledge or rational belief is possible and urge us to suspend judgment on many or all controversial matters . More moderate forms of skepticism claim only that nothing can be known with certainty , or that we can know little or nothing about the `` big questions '' in life , such as whether God exists or whether there is an afterlife . Religious skepticism is `` doubt concerning basic religious principles ( such as immortality , providence , and revelation ) '' . Scientific skepticism concerns testing beliefs for reliability , by subjecting them to systematic investigation using the scientific method , to discover empirical evidence for them .


Smart grid

A smart grid is an electrical grid which includes a variety of operational and energy measures including smart meters , smart appliances , renewable energy resources , and energy efficient resources . Electronic power conditioning and control of the production and distribution of electricity are important aspects of the smart grid .   Smart grid policy is organized in Europe as Smart Grid European Technology Platform . Policy in the United States is described in § 17381 .   Roll-out of smart grid technology also implies a fundamental re-engineering of the electricity services industry , although typical usage of the term is focused on the technical infrastructure .


Smog

Smog is a type of air pollutant . The word `` smog '' was coined in the early 20th century as a portmanteau of the words smoke and fog to refer to smoky fog , its opacity , and odour . The word was then intended to refer to what was sometimes known as pea soup fog , a familiar and serious problem in London from the 19th century to the mid 20th century . This kind of visible air pollution is composed of nitrogen oxides , sulfur oxides , ozone , smoke or particulates among others ( less visible pollutants include carbon monoxide , CFCs and radioactive sources ) . Human-made smog is derived from coal emissions , vehicular emissions , industrial emissions , forest and agricultural fires and photochemical reactions of these emissions .   Modern smog , as found for example in Los Angeles , is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog . In certain other cities , such as Delhi , smog severity is often aggravated by stubble burning in neighboring agricultural areas . The atmospheric pollution levels of Los Angeles , Beijing , Delhi , Mexico City , Tehran and other cities are increased by inversion that traps pollution close to the ground . It is usually highly toxic to humans and can cause severe sickness , shortened life or death .


Snow

Snow pertains to frozen crystalline water throughout its life cycle , starting when it precipitates from clouds and accumulates on surfaces , then metamorphoses in place , and ultimately melts , slides or sublimates away . Snowstorms organize and develop by feeding on sources of atmospheric moisture and cold air . Snowflakes nucleate around particles in the atmosphere by attracting supercooled water droplets , which freeze in hexagonal-shaped crystals . Snowflakes take on a variety of shapes , basic among these are platelets , needles , columns and rime . As snow accumulates into a snowpack , it may blow into drifts . Over time , accumulated snow metamorphoses , by sintering , sublimation and freeze-thaw . Where the climate is cold enough for year-to-year accumulation , a glacier may form . Otherwise , snow typically melts seasonally , causing runoff into streams and rivers and recharging groundwater .   Major snow-prone areas include the polar regions , the upper half of the Northern Hemisphere and mountainous regions worldwide with sufficient moisture and cold temperatures . In the Southern Hemisphere , snow is confined primarily to mountainous areas , apart from Antarctica .   Snow affects such human activities as transportation : creating the need for keeping roadways , wings , and windows clear ; agriculture : providing water to crops and safeguarding livestock ; such sports as skiing , snowboarding , snowmachine travel ; and warfare : impairing target acquisition , degrading the performance of combatants and materiel , and impeding mobility . Snow affects ecosystems , as well , by providing an insulating layer during winter under which plants and animals are able to survive the cold .


Snowball Earth

The Snowball Earth hypothesis proposes that Earth 's surface became entirely or nearly entirely frozen at least once , sometime earlier than 650 Mya ( million years ago ) . Proponents of the hypothesis argue that it best explains sedimentary deposits generally regarded as of glacial origin at tropical palaeolatitudes , and other enigmatic features in the geological record . Opponents of the hypothesis contest the implications of the geological evidence for global glaciation and the geophysical feasibility of an ice - or slush-covered ocean , and emphasize the difficulty of escaping an all-frozen condition . A number of unanswered questions remain , including whether the Earth was a full snowball , or a `` slushball '' with a thin equatorial band of open ( or seasonally open ) water .   The snowball Earth episodes occurred before the sudden radiation of multicellular bioforms , known as the Cambrian explosion . The most recent snowball episode may have triggered the evolution of multicellularity . Another , much earlier and longer snowball episode , the Huronian glaciation , which occurred 2400 to 2100 Mya , may have been triggered by the first appearance of oxygen in the atmosphere , the `` Great Oxygenation Event . ''


Sociology

Sociology is the study of social behavior or society , including its origins , development , organization , networks , and institutions . It is a social science that uses various methods of empirical investigation and critical analysis to develop a body of knowledge about social order , disorder , and change . Many sociologists aim to conduct research that may be applied directly to social policy and welfare , while others focus primarily on refining the theoretical understanding of social processes . Subject matter ranges from the micro-sociology level of individual agency and interaction to the macro level of systems and the social structure .   The traditional focuses of sociology include social stratification , social class , social mobility , religion , secularization , law , sexuality and deviance . As all spheres of human activity are affected by the interplay between social structure and individual agency , sociology has gradually expanded its focus to further subjects , such as health , medical , military and penal institutions , the Internet , education , social capital and the role of social activity in the development of scientific knowledge .   The range of social scientific methods has also expanded . Social researchers draw upon a variety of qualitative and quantitative techniques . The linguistic and cultural turns of the mid-twentieth century led to increasingly interpretative , hermeneutic , and philosophic approaches towards the analysis of society . Conversely , the end of the 1990s and the beginning of 2000s have seen the rise of new analytically , mathematically and computationally rigorous techniques , such as agent-based modelling and social network analysis .   Social research informs politicians and policy makers , educators , planners , legislators , administrators , developers , business magnates , managers , social workers , non-governmental organizations , non-profit organizations , and people interested in resolving social issues in general . There is often a great deal of crossover between social research , market research , and other statistical fields .


Socompa

Socompa is a large complex stratovolcano at the border of Argentina and Chile . It is best known for its large debris avalanche deposit , which is widely accepted as the best-preserved example of this type of deposit in the world , and also notable as the home of the world 's most elevated known microbial ecosystems .   The western rim of the volcano borders the Monturaqui Basin , which is draped with the aforementioned deposit . Escondida Mining currently has a network of roads throughout this area , from beneath which they pump ground water for use at the nearby copper mine . The southern margin of the deposit is bordered by the Antofagasta to Salta trans-Andean railway , although this is rarely used .   The volcano is difficult to reach - either from the north along dirt tracks south of the Miscanti Pass , or from the west via the Escondida copper mine . Both routes require a full-day 's driving and for any reasonable amount of time to be spent at Socompa would need significant planning .


Soil

Soil is a mixture of minerals , organic matter , gases , liquids , and countless organisms that together support life on Earth . Soil is a natural body called the pedosphere which has four important functions : it is a medium for plant growth ; it is a means of water storage , supply and purification ; it is a modifier of Earth 's atmosphere ; it is a habitat for organisms ; all of which , in turn , modify the soil .   Soil is called the Skin of the Earth and interfaces with the lithosphere , the hydrosphere , the atmosphere , and the biosphere . The term pedolith , used commonly to refer to the soil , literally translates ground stone . Soil consists of a solid phase of minerals ( the soil matrix ) and organic matter , as well as a porous phase that holds gases ( the soil atmosphere ) and water ( the soil solution ) . Accordingly , soils are often treated as a three-state system of solids , liquids , and gases .   Soil is a product of the influence of climate , relief ( elevation , orientation , and slope of terrain ) , organisms , and its parent materials ( original minerals ) interacting over time . Soil continually undergoes development by way of numerous physical , chemical and biological processes , which include weathering with associated erosion . Given its complexity and strong internal connectedness soil has been considered as an ecosystem by soil ecologists .   Most soils have a dry bulk density ( density of soil taking into account voids when dry ) between 1.1 and 1.6 g/cm3 , while the soil particle density is much higher , in the range of 2.6 to 2.7 g/cm3 . Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic , although fossilized soils are preserved from as far back as the Archean .   Soil science has two basic branches of study : edaphology and pedology . Edaphology is concerned with the influence of soils on living things . Pedology is focused on the formation , description ( morphology ) , and classification of soils in their natural environment . In engineering terms , soil is referred to as regolith , or loose rock material that lies above the solid geology . Soil is commonly referred to as earth or dirt ; technically , the term dirt should be restricted to displaced soil .   As soil resources serve as a basis for food security , the international community advocates its sustainable and responsible use through different types of soil governance .


Soil respiration

Soil respiration refers to the production of carbon dioxide when soil organisms respire . This includes respiration of plant roots , the rhizosphere , microbes and fauna .   Soil respiration is a key ecosystem process that releases carbon from the soil in the form of CO2 . CO2 is acquired from the atmosphere and converted into organic compounds in the process of photosynthesis . Plants use these organic compounds to build structural components or respire them to release energy . When plant respiration occurs below-ground in the roots , it adds to soil respiration . Over time , plant structural components are consumed by heterotrophs . This heterotrophic consumption releases CO2 and when this CO2 is released by below-ground organisms , it is considered soil respiration .   The amount of soil respiration that occurs in an ecosystem is controlled by several factors . The temperature , moisture , nutrient content and level of oxygen in the soil can produce extremely disparate rates of respiration . These rates of respiration can be measured in a variety of methods . Other methods can be used to separate the source components , in this case the type of photosynthetic pathway ( C3/C4 ) , of the respired plant structures .   Soil respiration rates can be largely affected by human activity . This is because humans have the ability to and have been changing the various controlling factors of soil respiration for numerous years . Global climate change is composed of numerous changing factors including rising atmospheric CO2 , increasing temperature and shifting precipitation patterns . All of these factors can affect the rate of global soil respiration . Increased nitrogen fertilization by humans also has the potential to effect rates over the entire Earth .   Soil respiration and its rate across ecosystems is extremely important to understand . This is because soil respiration plays a large role in global carbon cycling as well as other nutrient cycles . The respiration of plant structures releases not only CO2 but also other nutrients in those structures , such as nitrogen . Soil respiration is also associated with positive feedbacks with global climate change . Positive feedbacks are when a change in a system produces response in the same direction of the change . Therefore , soil respiration rates can be effected by climate change and then respond by enhancing climate change .


Solar System

The Solar SystemCapitalization of the name varies . The International Astronomical Union , the authoritative body regarding astronomical nomenclature , specifies capitalizing the names of all individual astronomical objects , but uses mixed `` Solar System '' and `` solar system '' in their naming guidelines document . The name is commonly rendered in lower case ( `` solar system '' ) , as , for example , in the Oxford English Dictionary and Merriam-Webster 's 11th Collegiate Dictionary . is the gravitationally bound system comprising the Sun and the objects that orbit it , either directly or indirectly.The natural satellites ( moons ) orbiting the Solar System 's planets are an example of the latter . Of those objects that orbit the Sun directly , the largest eight are the planets , Historically , several other bodies were once considered planets , including , from its discovery in 1930 until 2006 , Pluto . See Former planets . with the remainder being significantly smaller objects , such as dwarf planets and small Solar System bodies . Of the objects that orbit the Sun indirectly , the moons , two are larger than the smallest planet , Mercury.The two moons larger than Mercury are Ganymede , which orbits Jupiter , and Titan , which orbits Saturn . Although bigger than Mercury , both moons have less than half the mass of Mercury .   The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud . The vast majority of the system 's mass is in the Sun , with the majority of the remaining mass contained in Jupiter . The four smaller inner planets , Mercury , Venus , Earth and Mars , are terrestrial planets , being primarily composed of rock and metal . The four outer planets are giant planets , being substantially more massive than the terrestrials . The two largest , Jupiter and Saturn , are gas giants , being composed mainly of hydrogen and helium ; the two outermost planets , Uranus and Neptune , are ice giants , being composed mostly of substances with relatively high melting points compared with hydrogen and helium , called volatiles , such as water , ammonia and methane . All planets have almost circular orbits that lie within a nearly flat disc called the ecliptic .   The Solar System also contains smaller objects . The asteroid belt , which lies between the orbits of Mars and Jupiter , mostly contains objects composed , like the terrestrial planets , of rock and metal . Beyond Neptune 's orbit lie the Kuiper belt and scattered disc , which are populations of trans-Neptunian objects composed mostly of ices , and beyond them a newly discovered population of sednoids . Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity . Such objects are categorized as dwarf planets . Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris . In addition to these two regions , various other small-body populations , including comets , centaurs and interplanetary dust clouds , freely travel between regions . Six of the planets , at least four of the dwarf planets , and many of the smaller bodies are orbited by natural satellites , See List of natural satellites of the Solar System for the full list of natural satellites of the eight planets and first five dwarf planets usually termed `` moons '' after the Moon . Each of the outer planets is encircled by planetary rings of dust and other small objects .   The solar wind , a stream of charged particles flowing outwards from the Sun , creates a bubble-like region in the interstellar medium known as the heliosphere . The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium ; it extends out to the edge of the scattered disc . The Oort cloud , which is thought to be the source for long-period comets , may also exist at a distance roughly a thousand times further than the heliosphere . The Solar System is located in the Orion Arm , 26,000 light-years from the center of the Milky Way .


Solar activity and climate

Solar irradiance variation has been a main driver of climate change over geologic time , but its role in the recent warming has been found to be insignificant .


Solar cycle

The solar cycle or solar magnetic activity cycle is the nearly periodic 11-year change in the Sun 's activity ( including changes in the levels of solar radiation and ejection of solar material ) and appearance ( changes in the number and size of sunspots , flares , and other manifestations ) .   They have been observed ( by changes in the sun 's appearance and by changes seen on Earth , such as auroras ) for centuries .   The changes on the sun cause effects in space , in the atmosphere , and on Earth 's surface . While it is the dominant variable in solar activity , aperiodic fluctuations also occur .


Solar eclipse of August 21, 2017

A total solar eclipse will take place on Monday , August 21 , 2017 . A solar eclipse occurs when the Moon passes between Earth and the Sun , thereby totally or partly obscuring the image of the Sun for a viewer on Earth . A total solar eclipse occurs when the Moon 's apparent diameter is larger than the Sun 's , blocking all direct sunlight , turning day into darkness . Totality occurs in a narrow path across Earth 's surface , with the partial solar eclipse visible over a surrounding region thousands of kilometers wide .   This eclipse is the 22nd of the 77 members of Saros series 145 , the one that also produced the solar eclipse of August 11 , 1999 . Members of this series are increasing in duration . The longest eclipse in this series will occur on June 25 , 2522 and last for 7 minutes and 12 seconds .


Solar energy

Solar energy is radiant light and heat from the Sun that is harnessed using a range of ever-evolving technologies such as solar heating , photovoltaics , solar thermal energy , solar architecture , molten salt power plants and artificial photosynthesis .   It is an important source of renewable energy and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power . Active solar techniques include the use of photovoltaic systems , concentrated solar power and solar water heating to harness the energy . Passive solar techniques include orienting a building to the Sun , selecting materials with favorable thermal mass or light-dispersing properties , and designing spaces that naturally circulate air .   The large magnitude of solar energy available makes it a highly appealing source of electricity . The United Nations Development Programme in its 2000 World Energy Assessment found that the annual potential of solar energy was 1,575 -- 49,837 exajoules ( EJ ) . This is several times larger than the total world energy consumption , which was 559.8 EJ in 2012 .   In 2011 , the International Energy Agency said that `` the development of affordable , inexhaustible and clean solar energy technologies will have huge longer-term benefits . It will increase countries ' energy security through reliance on an indigenous , inexhaustible and mostly import-independent resource , enhance sustainability , reduce pollution , lower the costs of mitigating global warming , and keep fossil fuel prices lower than otherwise . These advantages are global . Hence the additional costs of the incentives for early deployment should be considered learning investments ; they must be wisely spent and need to be widely shared '' .


Solar irradiance

Solar irradiance is the power per unit area received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument . Irradiance may be measured in space or at the Earth 's surface after atmospheric absorption and scattering . It is measured perpendicular to the incoming sunlight . Total solar irradiance ( TSI ) , is a measure of the solar power over all wavelengths per unit area incident on the Earth 's upper atmosphere . The solar constant is a conventional measure of mean TSI at a distance of one astronomical Unit ( AU ) . Irradiance is a function of distance from the Sun , the solar cycle , and cross-cycle changes . Irradiance on Earth is also measured perpendicular to the incoming sunlight . Insolation is the power received on Earth per unit area on a horizontal surface . It depends on the height of the Sun above the horizon .


Solar minimum

Solar minimum is the period of least solar activity in the 11 year solar cycle of the sun . During this time , sunspot and solar flare activity diminishes , and often does not occur for days at a time . The date of the minimum is described by a smoothed average over 12 months of sunspot activity , so identifying the date of the solar minimum usually can only happen 6 months after the minimum takes place . Solar minima are not generally correlated with changes in climate but recent studies have shown a correlation with regional weather patterns .   Solar minimum is contrasted with the solar maximum , where there may be hundreds of sunspots .


Solar panel

Solar panels absorb the sunlight as a source of energy to generate electricity or heat .   A photovoltaic ( PV ) module is a packaged , connect assembly of typically 6x10 photovoltaic solar cells . Photovoltaic modules constitute the photovoltaic array of a photovoltaic system that generates and supplies solar electricity in commercial and residential applications . Each module is rated by its DC output power under standard test conditions ( STC ) , and typically ranges from 100 to 365 Watts ( W ) . The efficiency of a module determines the area of a module given the same rated output an 8 % efficient 230 W module will have twice the area of a 16 % efficient 230 W module . There are a few commercially available solar modules that exceed efficiency of 22 % and reportedly also exceeding 24 % . A single solar module can produce only a limited amount of power ; most installations contain multiple modules . A photovoltaic system typically includes an array of photovoltaic modules , an inverter , a battery pack for storage , interconnection wiring , and optionally a solar tracking mechanism .   The most common application of solar panels is solar water heating systems .   The price of solar power has continued to fall so that in many countries it is cheaper than ordinary fossil fuel electricity from the grid ( there is `` grid parity '' ) .


Solar particle event

A solar proton event ( SPE ) , or `` proton storm '' , occurs when particles ( mostly protons ) emitted by the Sun become accelerated either close to the Sun during a flare or in interplanetary space by CME shocks . The events can include other nuclei such as helium ions and HZE ions . These particles cause multiple effects . They can penetrate the Earth 's magnetic field and cause ionization in the ionosphere . The effect is similar to auroral events , except that protons rather than electrons are involved . Energetic protons are a significant radiation hazard to spacecraft and astronauts .


Solar phenomena

Solar phenomena are the natural phenomena occurring within the magnetically heated outer atmospheres in the Sun . These phenomena take many forms , including solar wind , radio wave flux , energy bursts such as solar flares , coronal mass ejection or solar eruptions , coronal heating and sunspots .   These phenomena are generated by a helical dynamo near the center of the Sun 's mass that generates strong magnetic fields and a chaotic dynamo near the surface that generates smaller magnetic field fluctuations .   The total sum of all solar fluctuations is referred to as solar variation . The collective effect of all solar variations within the Sun 's gravitational field is referred to as space weather . A major weather component is the solar wind , a stream of plasma released from the Sun 's upper atmosphere . It is responsible for the aurora , natural light displays in the sky in the Arctic and Antarctic . Space weather disturbances can cause solar storms on Earth , disrupting communications , as well as geomagnetic storms in Earth 's magnetosphere and sudden ionospheric disturbances in the ionosphere . Variations in solar intensity also affect Earth 's climate . These variations can explain events such as ice ages and the Great Oxygenation Event , while the Sun 's future expansion into a red giant will likely end life on Earth .   Solar activity and related events have been recorded since the 8th century BCE . Babylonians inscribed and possibly predicted solar eclipses , while the earliest extant report of sunspots dates back to the Chinese Book of Changes , . The first extant description of the solar corona was in 968 , while the earliest sunspot drawing was in 1128 and a solar prominence was described in 1185 in the Russian Chronicle of Novgorod . The invention of the telescope allowed major advances in understanding , allowing the first detailed observations in the 1600s . Solar spectroscopy began in the 1800s , from which properties of the solar atmosphere could be determined , while the creation of daguerreotypy led to the first solar photographs on 2 April 1845 . Photography assisted in the study of solar prominences , granulation and spectroscopy . Early in the 20th century , interest in astrophysics surged in America . A number of new observatories were built with solar telescopes around the world . The 1931 invention of the coronagraph allowed the corona to be studied in full daylight .


Solar power

Solar power is the conversion of energy from sunlight into electricity , either directly using photovoltaics ( PV ) , or indirectly using concentrated solar power . Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam . Photovoltaic cells convert light into an electric current using the photovoltaic effect .   Photovoltaics were initially solely used as a source of electricity for small and medium-sized applications , from the calculator powered by a single solar cell to remote homes powered by an off-grid rooftop PV system . Commercial concentrated solar power plants were first developed in the 1980s . The 392 MW Ivanpah installation is the largest concentrating solar power plant in the world , located in the Mojave Desert of California .   As the cost of solar electricity has fallen , the number of grid-connected solar PV systems has grown into the millions and utility-scale solar power stations with hundreds of megawatts are being built . Solar PV is rapidly becoming an inexpensive , low-carbon technology to harness renewable energy from the Sun . The current largest photovoltaic power station in the world is the 850 MW Longyangxia Dam Solar Park , in Qinghai , China .   The International Energy Agency projected in 2014 that under its `` high renewables '' scenario , by 2050 , solar photovoltaics and concentrated solar power would contribute about 16 and 11 percent , respectively , of the worldwide electricity consumption , and solar would be the world 's largest source of electricity . Most solar installations would be in China and India . Currently , as of 2016 , solar power provides just 1 % of total worldwide electricity production but growing 33 % per annum .


Solar power in Florida

Solar power in Florida has been increasing , as the cost of solar power systems using photovoltaics ( PV ) has decreased in recent years . In 2008 , Florida adopted a net metering rule that allows any electric utility customer generating up to 2 MW ( 2,000 kW ) of power to use net metering , which provides a retail rate credit for kilowatt-hours of electricity delivered to the utility , rolled over from month to month , and paid out in cash by the utility once a year at the avoided cost rate .   In 2006 , the State of Florida enacted the Florida Renewable Energy Technologies and Energy Efficiency Act , which provided consumers with rebates and tax credits for solar photovoltaic systems . The program was closed in 2010 . Later , the Florida Public Service Commission mandated that the state 's large utilities offer individual solar rebates . The program opened in 2011 and was closed in 2015 after the Commission deemed it to not be cost-effective for non-solar customers .   The federal Residential Energy Efficient Property Credit ( income tax credit on IRS Form 5695 ) for residential PV and solar thermal was extended in December 2015 to remain at 30 % of system cost ( parts and installation ) for systems put into service by the end of 2019 , then 26 % until the end of 2020 , and then 22 % until the end of 2021 . It applies to a taxpayer 's principal and/or second residences , but not to a property that is rented out . There is no maximum cap on the credit , and the credit can be applied toward the Alternative Minimum Tax , and any excess credit ( greater than that year 's tax liability ) can be rolled into the following year .   In 2009 , Florida Power & Light built the state 's first solar power plant , the FPL DeSoto Next Generation Solar Energy Center . At the time , the 25-MW plant was the largest of its kind . In 2010 , FPL built the world 's first hybrid solar-natural gas energy center .   Florida has low electricity costs compared with other states , which makes individual solar investment less attractive . Florida ranks ninth nationally in solar resource strength according to the National Renewable Energy Laboratory and tenth in solar generation by the Solar Energy Industries Association .


Solar power in the United States

Solar power in the United States includes utility-scale solar power plants as well as local distributed generation , mostly from rooftop photovoltaics . As of the end of 2016 , the U.S. had 40 gigawatts ( GW ) of installed photovoltaic capacity , having almost doubled in capacity from the previous year . In the twelve months through March 2017 , utility scale solar power generated 38.3 terawatt-hours ( TWh ) , 0.94 % of total U.S. electricity . During the same time period total solar generation , including estimated distributed solar photovoltaic generation , was 59.8 TWh , 1.47 % of total U.S. electricity . In terms of total installed capacity , by year end 2015 the USA ranked 4th in the world behind China , Germany , and Japan . In 2016 , 39 % of all new electricity generation capacity in the country came from solar , more than any other source and ahead of natural gas ( 29 % ) . By 2015 , solar employment had overtaken oil and gas as well as coal employment in the U.S.   The United States conducted much early research in photovoltaics and concentrated solar power . The U.S. is among the top countries in the world in electricity generated by the Sun and several of the world 's largest utility-scale installations are located in the desert Southwest . The oldest solar power plant in the world is the 354-megawatt ( MW ) SEGS thermal power plant , in California . The Ivanpah Solar Electric Generating System is a solar thermal power project in the California Mojave Desert , 40 miles ( 64 km ) southwest of Las Vegas , with a gross capacity of 392 MW . The 280 MW Solana Generating Station is a solar power plant near Gila Bend , Arizona , about 70 mi southwest of Phoenix , completed in 2013 . When commissioned it was the largest parabolic trough plant in the world and the first U.S. solar plant with molten salt thermal energy storage .   There are plans to build many other large solar plants in the United States . Many states have set individual renewable energy goals with solar power being included in various proportions . Governor Jerry Brown has signed legislation requiring California 's utilities to obtain 50 percent of their electricity from renewable energy sources by the end of 2030 .


Solar water heating

Solar water heating ( SWH ) is the conversion of sunlight into heat for water heating using a solar thermal collector . A variety of configurations are available at varying cost to provide solutions in different climates and latitudes . SWHs are widely used for residential and some industrial applications .   A sun-facing collector heats a working fluid that passes into a storage system for later use . SWH are active ( pumped ) and passive ( convection-driven ) . They use water only , or both water and a working fluid . They are heated directly or via light-concentrating mirrors . They operate independently or as hybrids with electric or gas heaters . In large-scale installations , mirrors may concentrate sunlight onto a smaller collector .   The global solar thermal market is dominated by China , Europe , Japan and India , although Israel was one of the first countries to mandate installation of SWH in 1980 , leading to a flourishing industry .


Soldering

Soldering ( AmE : -LSB- ˈsɒdərɪŋ -RSB- , BrE : -LSB- ˈsɒldərɪŋ -RSB- ) , is a process in which two or more items ( usually metal ) are joined together by melting and putting a filler metal ( solder ) into the joint , the filler metal having a lower melting point than the adjoining metal . Soldering differs from welding in that soldering does not involve melting the work pieces . In brazing , the filler metal melts at a higher temperature , but the work piece metal does not melt . In the past , nearly all solders contained lead , but environmental and health concerns have increasingly dictated use of lead-free alloys for electronics and plumbing purposes .


Solubility

Solubility is the property of a solid , liquid , or gaseous chemical substance called solute to dissolve in a solid , liquid , or gaseous solvent . The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature , pressure and the pH of the solution . The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration , where adding more solute does not increase the concentration of the solution and begins to precipitate the excess amount of solute . The solubility of a substance is an entirely different property from the rate of solution , which is how fast it dissolves .   Most often , the solvent is a liquid , which can be a pure substance or a mixture . One may also speak of solid solution , but rarely of solution in a gas ( see vapor -- liquid equilibrium instead ) .   The extent of solubility ranges widely , from infinitely soluble ( without limit ) ( fully miscible ) such as ethanol in water , to poorly soluble , such as silver chloride in water . The term insoluble is often applied to poorly or very poorly soluble compounds . A common threshold to describe something as insoluble is less than 0.1 g per 100 mL of solvent .   Under certain conditions , the equilibrium solubility can be exceeded to give a so-called supersaturated solution , which is metastable . Metastability of crystals can also lead to apparent differences in the amount of a chemical that dissolves depending on its crystalline form or particle size . A supersaturated solution generally crystallises when ` seed ' crystals are introduced and rapid equilibration occurs . Phenylsalicylate is one such simple observable substance when fully melted and then cooled below its fusion point .   Solubility is not to be confused with the ability to ` dissolve ' a substance , because the solution might also occur because of a chemical reaction . For example , zinc ` dissolves ' ( with effervescence ) in hydrochloric acid as a result of a chemical reaction releasing hydrogen gas in a displacement reaction . The zinc ions are soluble in the acid .   The smaller a particle is , the faster it dissolves although there are many factors to add to this generalization .   Crucially solubility applies to all areas of chemistry , geochemistry , inorganic , physical , organic and biochemistry . In all cases it will depend on the physical conditions ( temperature , pressure and concentration ) and the enthalpy and entropy directly relating to the solvents and solutes concerned .  By far the most common solvent in chemistry is water which is a solvent for most ionic compounds as well as a wide range of organic substances . This is a crucial factor in acidity/alkalinity and much environmental and geochemical work .


Soon and Baliunas controversy

The Soon and Baliunas controversy involved the publication in 2003 of a review study written by aerospace engineer Willie Soon and astronomer Sallie Baliunas in the journal Climate Research , which was quickly taken up by the G.W. Bush administration as a basis for amending the first Environmental Protection Agency Report on the Environment .   The paper was strongly criticized by numerous scientists for its methodology and for its misuse of data from previously published studies , prompting concerns about the peer review process of the paper . The controversy resulted in the resignation of half of the editors of the journal and in the admission by its publisher Otto Kinne that the paper should not have been published as it was .


Soot

Soot -LSB- ˈsʊt -RSB- is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons . It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolysed fuel particles such as coal , cenospheres , charred wood , and petroleum coke that may become airborne during pyrolysis and that are more properly identified as cokes or chars .   Soot causes cancer and lung disease , and is the second-biggest human cause of global warming .


Sound reinforcement system

A sound reinforcement system is the combination of microphones , signal processors , amplifiers , and loudspeakers in speaker cabinets all controlled by an audio mixing board that makes live or pre-recorded sounds louder and may also distribute those sounds to a larger or more distant audience . In many situations , a sound reinforcement system is also used to enhance or alter the sound of the sources on the stage , typically by using electronic effects , such as reverb , as opposed to simply amplifying the sources unaltered .   A sound reinforcement system for a rock concert in a stadium may be very complex , including hundreds of microphones , complex live sound mixing and signal processing systems , tens of thousands of watts of amplifier power , and multiple loudspeaker arrays , all overseen by a team of audio engineers and technicians . On the other hand , a sound reinforcement system can be as simple as a small public address ( PA ) system , consisting of , for example , a single microphone connected to a 100 watt amplified loudspeaker for a singer-guitarist playing in a small coffeehouse . In both cases , these systems reinforce sound to make it louder or distribute it to a wider audience .   Some audio engineers and others in the professional audio industry disagree over whether these audio systems should be called sound reinforcement ( SR ) systems or PA systems . Distinguishing between the two terms by technology and capability is common , while others distinguish by intended use ( e.g. , SR systems are for live event support and PA systems are for reproduction of speech and recorded music in buildings and institutions ) . In some regions or markets , the distinction between the two terms is important , though the terms are considered interchangeable in many professional circles .


South Australia

South Australia ( abbreviated as SA ) is a state in the southern central part of Australia . It covers some of the most arid parts of the country . With a total land area of 983482 km2 , it is the fourth-largest of Australia 's states and territories . It has a total of 1.7 million people , and its population is the most highly centralised of any state in Australia , with more than 75 percent of South Australians living in the capital , Adelaide , or its environs . Other population centres in the state are relatively small .   South Australia shares borders with all of the other mainland states , and with the Northern Territory ; it is bordered to the west by Western Australia , to the north by the Northern Territory , to the north-east by Queensland , to the east by New South Wales , to the south-east by Victoria , and to the south by the Great Australian Bight . The state comprises less than 8 percent of the Australian population and ranks fifth in population among the six states and two territories . The majority of its people reside in Adelaide . Most of the remainder are settled in fertile areas along the south-eastern coast and River Murray . The state 's colonial origins are unique in Australia as a freely settled , planned British province , rather than as a convict settlement . Official settlement began on 28 December 1836 , when the colony was proclaimed at the Old Gum Tree by Governor John Hindmarsh .   As with the rest of the continent , the region had been long occupied by Aboriginal peoples , who were organised into numerous tribes and languages . The first British settlement to be established was Kingscote , Kangaroo Island , on 26 July 1836 , five months before Adelaide was founded . The guiding principle behind settlement was that of systematic colonisation , a theory espoused by Edward Gibbon Wakefield that was later employed by the New Zealand Company . The goal was to establish the province as a centre of civilisation for free immigrants , promising civil liberties and religious tolerance . Although its history is marked by economic hardship , South Australia has remained politically innovative and culturally vibrant . Today , it is known for its fine wine and numerous cultural festivals . The state 's economy is dominated by the agricultural , manufacturing and mining industries . The state has an increasingly significant finance sector as well .


South Pacific convergence zone

The South Pacific Convergence Zone ( SPCZ ) , a reverse-oriented monsoon trough , is a band of low-level convergence , cloudiness and precipitation extending from the Western Pacific Warm Pool at the maritime continent south-eastwards towards French Polynesia and as far as the Cook Islands ( 160W , 20S ) . The SPCZ is a portion of the Intertropical Convergence Zone ( ITCZ ) which lies in a band extending east-west near the Equator but can be more extratropical in nature , especially east of the International Date Line . It is considered the largest and most important piece of the ITCZ , and has the least dependence upon heating from a nearby landmass during the summer than any other portion of the monsoon trough . The SPCZ can affect the precipitation on Polynesian islands in the southwest Pacific Ocean , so it is important to understand how the SPCZ behaves with large-scale , global climate phenomenon , such as the ITCZ , El Niño -- Southern Oscillation , and the Interdecadal Pacific oscillation ( IPO ) , a portion of the Pacific decadal oscillation .


South Pole

The South Pole , also known as the Geographic South Pole or Terrestrial South Pole , is one of the two points where the Earth 's axis of rotation intersects its surface . It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole .   Situated on the continent of Antarctica , it is the site of the United States Amundsen -- Scott South Pole Station , which was established in 1956 and has been permanently staffed since that year . The Geographic South Pole should not be confused with the South Magnetic Pole , which is defined based on the Earth 's magnetic field . The South Pole is at the center of the Southern Hemisphere .


Southern Ocean

The Southern Ocean , also known as the Antarctic Ocean or the Austral Ocean , comprises the southernmost waters of the World Ocean , generally taken to be south of 60 ° S latitude and encircling Antarctica . As such , it is regarded as the fourth-largest of the five principal oceanic divisions : smaller than the Pacific , Atlantic , and Indian Oceans but larger than the Arctic Ocean . This ocean zone is where cold , northward flowing waters from the Antarctic mix with warmer subantarctic waters .   By way of his voyages in the 1770s , Captain James Cook proved that waters encompassed the southern latitudes of the globe . Since then , geographers have disagreed on the Southern Ocean 's northern boundary or even existence , considering the waters part of the Pacific , Atlantic , and Indian Oceans , instead . This remains the current official policy of the International Hydrographic Organization ( IHO ) , since a 2000 revision of its definitions including the Southern Ocean as the waters south of the 60th parallel has not yet been adopted . Others regard the seasonally-fluctuating Antarctic Convergence as the natural boundary .


Space Shuttle Challenger disaster

On January 28 , 1986 , the NASA shuttle orbiter mission STS-51-L and the tenth flight of Space Shuttle Challenger ( OV-99 ) broke apart 73 seconds into its flight , killing all seven crew members , which consisted of five NASA astronauts and two payload specialists . The spacecraft disintegrated over the Atlantic Ocean , off the coast of Cape Canaveral , Florida , at 11:39 EST ( 16:39 UTC ) . Disintegration of the vehicle began after an O-ring seal in its right solid rocket booster ( SRB ) failed at liftoff . The O-ring was not designed to fly under unusually cold conditions as in this launch . Its failure caused a breach in the SRB joint it sealed , allowing pressurized burning gas from within the solid rocket motor to reach the outside and impinge upon the adjacent SRB aft field joint attachment hardware and external fuel tank . This led to the separation of the right-hand SRB 's aft field joint attachment and the structural failure of the external tank . Aerodynamic forces broke up the orbiter .   The crew compartment and many other vehicle fragments were eventually recovered from the ocean floor after a lengthy search and recovery operation . The exact timing of the death of the crew is unknown ; several crew members are known to have survived the initial breakup of the spacecraft . The shuttle had no escape system , and the impact of the crew compartment with the ocean surface was too violent to be survivable .   The disaster resulted in a 32-month hiatus in the shuttle program and the formation of the Rogers Commission , a special commission appointed by United States President Ronald Reagan to investigate the accident . The Rogers Commission found NASA 's organizational culture and decision-making processes had been key contributing factors to the accident , with the agency violating its own safety rules . NASA managers had known since 1977 that contractor Morton Thiokol 's design of the SRBs contained a potentially catastrophic flaw in the O-rings , but they had failed to address this problem properly . NASA managers also disregarded warnings ( an example of `` go fever '' ) from engineers about the dangers of launching posed by the low temperatures of that morning , and failed to adequately report these technical concerns to their superiors .   As a result of the disaster , the Air Force decided to cancel its plans to use the Shuttle for classified military satellite launches from Vandenberg Air Force Base in California , deciding to use the Titan IV instead .   Approximately 17 percent of Americans witnessed the launch live because of the presence of Payload Specialist Christa McAuliffe , who would have been the first teacher in space . Media coverage of the accident was extensive : one study reported that 85 percent of Americans surveyed had heard the news within an hour of the accident . The Challenger '' disaster has been used as a case study in many discussions of engineering safety and workplace ethics .


Space and survival

Space and survival refers to the idea that the long-term survival of the human species and civilization requires proper use of the resources of outer space and the need for space colonization and space science . The concept posits that inaction could lead to human extinction . A related observation is that limited time and resources may be available for the colonization of space . Various scenarios for human survival have been discussed in science and popular culture , particularly humanity 's prospects after catastrophic events in the solar system and factors that could help or hinder survival .   The earliest appearance of a connection between space exploration and human survival appears in Louis J. Halle 's 1980 article in Foreign Affairs , in which he stated colonization of space will keep humanity safe should global nuclear warfare occur . This idea has received more attention in recent years as advancing technology makes cheap space travel more feasible .


Spain

Spain ( España -LSB- esˈpaɲa -RSB- ) , officially the Kingdom of Spain ( -LSB- Reino de España , links = no -RSB- ) , is a sovereign state located on the Iberian Peninsula in southwestern Europe , with two large archipelagoes , the Balearic Islands in the Mediterranean Sea and the Canary Islands off the North African Atlantic coast , two cities Ceuta and Melilla in the North African mainland and several small islands in the Alboran Sea near the Moroccan coast . Its mainland is bordered to the south and east by the Mediterranean Sea except for a small land boundary with Gibraltar ; to the north and northeast by France , Andorra , and the Bay of Biscay ; and to the west and northwest by Portugal and the Atlantic Ocean . It is the only European country to have a border with an African country ( Morocco ) and its African territory accounts for nearly 5 % of its population , mostly in the Canary Islands but also in Ceuta and Melilla .   With an area of 505990 km2 , Spain is the largest country in Southern Europe , the second largest country in Western Europe and the European Union , and the fourth largest country in the European continent . By population , Spain is the sixth largest in Europe and the fifth in the European Union . Spain 's capital and largest city is Madrid ; other major urban areas include Barcelona , Valencia , Seville , Bilbao and Málaga .   Modern humans first arrived in the Iberian Peninsula around 35,000 years ago . Iberian cultures along with ancient Phoenician , Greek and Carthaginian settlements developed on the peninsula until it came under Roman rule around 200 BCE , after which the region was named Hispania , based on the earlier Phoenician name Span or Spania . In the Middle Ages , the area was conquered by Germanic tribes and later by the Moors . Spain emerged as a unified country in the 15th century , following the marriage of the Catholic Monarchs and the completion of the eight centuries-long reconquest , or Reconquista from the Moors in 1492 . In the early modern period , Spain became one of history 's first global colonial empires , leaving a vast cultural and linguistic legacy that includes over 500 million Spanish speakers , making Spanish the world 's second most spoken first language , after Mandarin Chinese .   Spain is a democracy organised in the form of a parliamentary government under a constitutional monarchy . It is a middle power and a major developed country with the world 's fourteenth largest economy by nominal GDP and sixteenth largest by purchasing power parity . It is a member of the United Nations ( UN ) , the European Union ( EU ) , the Eurozone , the Council of Europe ( CoE ) , the Organization of Ibero-American States ( OEI ) , the North Atlantic Treaty Organization ( NATO ) , the Organisation for Economic Co-operation and Development ( OECD ) , the World Trade Organization ( WTO ) and many other international organisations .


Spanish flu

The Spanish flu, also known as the 1918 flu pandemic, was an unusually deadly influenza pandemic caused by the H1N1 influenza A virus. Lasting from February 1918 to April 1920, it infected 500 million people – about a third of the world's population at the time – in four successive waves. The death toll is typically estimated to have been somewhere between 17 million and 50 million, and possibly as high as 100 million, making it one of the deadliest pandemics in human history. The first observations of illness and mortality were documented in the United States (in Kansas and New York City, and months before, in December 1917, at Camp Greene, North Carolina), France, Germany, and the United Kingdom. To maintain morale, World War I censors minimized these early reports. Newspapers were free to report the epidemic's effects in neutral Spain, such as the grave illness of King Alfonso XIII, and these stories created a false impression of Spain as especially hard hit. This gave rise to the name "Spanish" flu. Historical and epidemiological data are inadequate to identify with certainty the pandemic's geographic origin, with varying views as to its location.