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The rediscovery of the Nepōhualtzintzin was due to the Mexican engineer David Esparza Hidalgo, who in his travels throughout Mexico found diverse engravings and paintings of this instrument and reconstructed several of them in gold, jade, encrustations of shell, etc. Very old Nepōhualtzintzin are attributed to the Olme...
Russia. The Russian abacus, the "schoty" (, plural from , counting), usually has a single slanted deck, with ten beads on each wire (except one wire with four beads for quarter-ruble fractions). 4-bead wire was introduced for quarter-kopeks, which were minted until 1916. The Russian abacus is used vertically, with each...
The Russian abacus was brought to France around 1820 by mathematician Jean-Victor Poncelet, who had served in Napoleon's army and had been a prisoner of war in Russia. To Poncelet's French contemporaries, it was something new. Poncelet used it, not for any applied purpose, but as a teaching and demonstration aid. The T...
The red-and-white abacus is used in contemporary primary schools for a wide range of number-related lessons. The twenty bead version, referred to by its Dutch name "rekenrek" ("calculating frame"), is often used, either on a string of beads or on a rigid framework. Neurological analysis. Learning how to calculate with ...
Binary abacus. The binary abacus is used to explain how computers manipulate numbers. The abacus shows how numbers, letters, and signs can be stored in a binary system on a computer, or via ASCII. The device consists of beads on parallel wires arranged in three rows; each bead represents a switch which can be either "o...
Acid An acid is a molecule or ion capable of either donating a proton (i.e. hydrogen ion, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, pr...
Common aqueous acids include hydrochloric acid (a solution of hydrogen chloride that is found in gastric acid in the stomach and activates digestive enzymes), acetic acid (vinegar is a dilute aqueous solution of this liquid), sulfuric acid (used in car batteries), and citric acid (found in citrus fruits). As these exam...
Definitions and concepts. Modern definitions are concerned with the fundamental chemical reactions common to all acids. Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and Brønsted–Lowry definitions are the most relevant. The Brønsted–Lowry definition is the...
An Arrhenius base, on the other hand, is a substance that increases the concentration of hydroxide (OH−) ions when dissolved in water. This decreases the concentration of hydronium because the ions react to form H2O molecules: Due to this equilibrium, any increase in the concentration of hydronium is accompanied by a d...
Both theories easily describe the first reaction: CH3COOH acts as an Arrhenius acid because it acts as a source of H3O+ when dissolved in water, and it acts as a Brønsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia (NH3),...
Lewis acids. A third, only marginally related concept was proposed in 1923 by Gilbert N. Lewis, which includes reactions with acid–base characteristics that do not involve a proton transfer. A Lewis acid is a species that accepts a pair of electrons from another species; in other words, it is an electron pair acceptor....
The second reaction can be described using either theory. A proton is transferred from an unspecified Brønsted acid to ammonia, a Brønsted base; alternatively, ammonia acts as a Lewis base and transfers a lone pair of electrons to form a bond with a hydrogen ion. The species that gains the electron pair is the Lewis ac...
Acid–base conjugate pairs differ by one proton, and can be interconverted by the addition or removal of a proton (protonation and deprotonation, respectively). The acid can be the charged species and the conjugate base can be neutral in which case the generalized reaction scheme could be written as . In solution there ...
Nomenclature. Arrhenius acids are named according to their anions. In the classical naming system, the ionic suffix is dropped and replaced with a new suffix, according to the table following. The prefix "hydro-" is used when the acid is made up of just hydrogen and one other element. For example, HCl has chloride as i...
Stronger acids have a larger acid dissociation constant, "K"a and a lower p"K"a than weaker acids. Sulfonic acids, which are organic oxyacids, are a class of strong acids. A common example is toluenesulfonic acid (tosylic acid). Unlike sulfuric acid itself, sulfonic acids can be solids. In fact, polystyrene functionali...
Lewis acid strength in non-aqueous solutions. Lewis acids have been classified in the ECW model and it has been shown that there is no one order of acid strengths. The relative acceptor strength of Lewis acids toward a series of bases, versus other Lewis acids, can be illustrated by C-B plots. It has been shown that to...
Polyprotic acids. Polyprotic acids, also known as polybasic acids, are able to donate more than one proton per acid molecule, in contrast to monoprotic acids that only donate one proton per molecule. Specific types of polyprotic acids have more specific names, such as diprotic (or dibasic) acid (two potential protons t...
A triprotic acid (H3A) can undergo one, two, or three dissociations and has three dissociation constants, where "K"a1 > "K"a2 > "K"a3. An inorganic example of a triprotic acid is orthophosphoric acid (H3PO4), usually just called phosphoric acid. All three protons can be successively lost to yield H2PO, then HPO, ...
A plot of these fractional concentrations against pH, for given "K"1 and "K"2, is known as a Bjerrum plot. A pattern is observed in the above equations and can be expanded to the general "n" -protic acid that has been deprotonated "i" -times: where "K"0 = 1 and the other K-terms are the dissociation constants for the a...
Weak acid–weak base equilibrium. In order for a protonated acid to lose a proton, the pH of the system must rise above the p"K"a of the acid. The decreased concentration of H+ in that basic solution shifts the equilibrium towards the conjugate base form (the deprotonated form of the acid). In lower-pH (more acidic) sol...
Example: Diprotic acid. For each diprotic acid titration curve, from left to right, there are two midpoints, two equivalence points, and two buffer regions. Equivalence points. Due to the successive dissociation processes, there are two equivalence points in the titration curve of a diprotic acid. The first equivalence...
Applications of acids. In industry. Acids are fundamental reagents in treating almost all processes in modern industry. Sulfuric acid, a diprotic acid, is the most widely used acid in industry, and is also the most-produced industrial chemical in the world. It is mainly used in producing fertilizer, detergent, batterie...
Acids are often used to remove rust and other corrosion from metals in a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuric acid in a car battery. In food. Tartaric acid is an important component of some commonly used foods like unripened mangoes and tamarind. Natural ...
Carbonic acid is one of the most common acid additives that are widely added in soft drinks. During the manufacturing process, CO2 is usually pressurized to dissolve in these drinks to generate carbonic acid. Carbonic acid is very unstable and tends to decompose into water and CO2 at room temperature and pressure. Ther...
Human bodies contain a variety of organic and inorganic compounds, among those dicarboxylic acids play an essential role in many biological behaviors. Many of those acids are amino acids, which mainly serve as materials for the synthesis of proteins. Other weak acids serve as buffers with their conjugate bases to keep ...
An α-amino acid has a central carbon (the α or "alpha" carbon) that is covalently bonded to a carboxyl group (thus they are carboxylic acids), an amino group, a hydrogen atom and a variable group. The variable group, also called the R group or side chain, determines the identity and many of the properties of a specific...
Fatty acids and fatty acid derivatives are another group of carboxylic acids that play a significant role in biology. These contain long hydrocarbon chains and a carboxylic acid group on one end. The cell membrane of nearly all organisms is primarily made up of a phospholipid bilayer, a micelle of hydrophobic fatty aci...
It is the decrease in pH that signals the brain to breathe faster and deeper, expelling the excess CO2 and resupplying the cells with O2. Cell membranes are generally impermeable to charged or large, polar molecules because of the lipophilic fatty acyl chains comprising their interior. Many biologically important molec...
Common acids. Sulfonic acids. A sulfonic acid has the general formula RS(=O)2–OH, where R is an organic radical. Carboxylic acids. A carboxylic acid has the general formula R-C(O)OH, where R is an organic radical. The carboxyl group -C(O)OH contains a carbonyl group, C=O, and a hydroxyl group, O-H. Halogenated carboxyl...
Bitumen Bitumen ( , ) is an immensely viscous constituent of petroleum. Depending on its exact composition, it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the material is commonly referred to as asphalt or tar. Whether found in nat...
In material sciences and engineering, the terms "asphalt" and "bitumen" are often used interchangeably and refer both to natural and manufactured forms of the substance, although there is regional variation as to which term is most common. Worldwide, geologists tend to favor the term "bitumen" for the naturally occurri...
Terminology. Etymology. The Latin word traces to the Proto-Indo-European root "*gʷet-" "pitch". The word "asphalt" is derived from the late Middle English, in turn from French "asphalte", based on Late Latin "asphaltum", which is the latinisation of the Greek ("ásphaltos"), a word meaning "asphalt/bitumen/pitch", which...
Modern terminology. Bitumen mixed with clay was usually called "asphaltum", but the term is less commonly used today. In American English, "asphalt" is equivalent to the British "bitumen". However, "asphalt" is also commonly used as a shortened form of "asphalt concrete" (therefore equivalent to the British "asphalt" o...
Composition. Normal composition. The components of bitumen include four main classes of compounds: Bitumen typically contains, elementally 80% by weight of carbon; 10% hydrogen; up to 6% sulfur; and molecularly, between 5 and 25% by weight of asphaltenes dispersed in 90% to 65% maltenes. Most natural bitumens also cont...
Additives, mixtures and contaminants. For economic and other reasons, bitumen is sometimes sold combined with other materials, often without being labeled as anything other than simply "bitumen". Of particular note is the use of re-refined engine oil bottoms – "REOB" or "REOBs"the residue of recycled automotive engine ...
Natural deposits of bitumen include lakes such as the Pitch Lake in Trinidad and Tobago and Lake Bermudez in Venezuela. Natural seeps occur in the La Brea Tar Pits and the McKittrick Tar Pits in California, as well as in the Dead Sea. Bitumen also occurs in unconsolidated sandstones known as "oil sands" in Alberta, Can...
Much smaller heavy oil or bitumen deposits also occur in the Uinta Basin in Utah, US. The Tar Sand Triangle deposit, for example, is roughly 6% bitumen. Bitumen may occur in hydrothermal veins. An example of this is within the Uinta Basin of Utah, in the US, where there is a swarm of laterally and vertically extensive ...
History. Paleolithic times. Bitumen use goes back to the Middle Paleolithic, where it was shaped into tool handles or used as an adhesive for attaching stone tools to hafts. The earliest evidence of bitumen use was discovered when archeologists identified bitumen material on Levallois flint artefacts that date to about...
Ancient times. The use of natural bitumen for waterproofing and as an adhesive dates at least to the fifth millennium BC, with a crop storage basket discovered in Mehrgarh, of the Indus Valley civilization, lined with it. By the 3rd millennium BC refined rock asphalt was in use in the region, and was used to waterproof...
In approximately 40 AD, Dioscorides described the Dead Sea material as "Judaicum bitumen", and noted other places in the region where it could be found. The Sidon bitumen is thought to refer to material found at Hasbeya in Lebanon. Pliny also refers to bitumen being found in Epirus. Bitumen was a valuable strategic res...
Continental Europe. In 1553, Pierre Belon described in his work "Observations" that "pissasphalto", a mixture of pitch and bitumen, was used in the Republic of Ragusa (now Dubrovnik, Croatia) for tarring of ships. An 1838 edition of "Mechanics Magazine" cites an early use of asphalt in France. A pamphlet dated 1621, by...
United Kingdom. Among the earlier uses of bitumen in the United Kingdom was for etching. William Salmon's "Polygraphice" (1673) provides a recipe for varnish used in etching, consisting of three ounces of virgin wax, two ounces of mastic, and one ounce of asphaltum. By the fifth edition in 1685, he had included more as...
In 1838, there was a flurry of entrepreneurial activity involving bitumen, which had uses beyond paving. For example, bitumen could also be used for flooring, damp proofing in buildings, and for waterproofing of various types of pools and baths, both of which were also proliferating in the 19th century. One of the earl...
Bitumen was thought in 19th century Britain to contain chemicals with medicinal properties. Extracts from bitumen were used to treat catarrh and some forms of asthma and as a remedy against worms, especially the tapeworm. United States. The first use of bitumen in the New World was by aboriginal peoples. On the west co...
In the horse-drawn era, US streets were mostly unpaved and covered with dirt or gravel. Especially where mud or trenching often made streets difficult to pass, pavements were sometimes made of diverse materials including wooden planks, cobble stones or other stone blocks, or bricks. Unpaved roads produced uneven wear a...
Canada. Canada has the world's largest deposit of natural bitumen in the Athabasca oil sands, and Canadian First Nations along the Athabasca River had long used it to waterproof their canoes. In 1719, a Cree named Wa-Pa-Su brought a sample for trade to Henry Kelsey of the Hudson's Bay Company, who was the first recorde...
Photography and art. Bitumen was used in early photographic technology. In 1826, or 1827, it was used by French scientist Joseph Nicéphore Niépce to make the oldest surviving photograph from nature. The bitumen was thinly coated onto a pewter plate which was then exposed in a camera. Exposure to light hardened the bitu...
Modern use. Global use. The vast majority of refined bitumen is used in construction: primarily as a constituent of products used in paving and roofing applications. According to the requirements of the end use, bitumen is produced to specification. This is achieved either by refining or blending. It is estimated that ...
The remaining 5% of bitumen is used mainly for sealing and insulating purposes in a variety of building materials, such as pipe coatings, carpet tile backing and paint. Bitumen is applied in the construction and maintenance of many structures, systems, and components, such as: Rolled asphalt concrete. The largest use o...
When maintenance is performed on asphalt pavements, such as milling to remove a worn or damaged surface, the removed material can be returned to a facility for processing into new pavement mixtures. The bitumen in the removed material can be reactivated and put back to use in new pavement mixes. With some 95% of paved ...
Bitumen emulsion. Bitumen emulsions are colloidal mixtures of bitumen and water. Due to the different surface tensions of the two liquids, stable emulsions cannot be created simply by mixing. Therefore, various emulsifiers and stabilizers are added. Emulsifiers are amphiphilic molecules that differ in the charge of the...
During the storage of bitumen emulsions, bitumen particles sediment, agglomerate (flocculation), or fuse (coagulation), which leads to a certain instability of the bitumen emulsion. How fast this process occurs depends on the formulation of the bitumen emulsion but also storage conditions such as temperature and humidi...
Adhesion problems are reported for anionic emulsions in contact with quartz-rich aggregates. They are substituted by cationic emulsions achieving better adhesion. The extensive range of bitumen emulsions is covered insufficiently by standardization. DIN EN 13808 for cationic asphalt emulsions has been existing since Ju...
T The "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill...
Synthetic crude oil. Synthetic crude oil, also known as syncrude, is the output from a bitumen upgrader facility used in connection with oil sand production in Canada. Bituminous sands are mined using enormous (100-ton capacity) power shovels and loaded into even larger (400-ton capacity) dump trucks for movement to an...
Non-upgraded crude bitumen. Canadian bitumen does not differ substantially from oils such as Venezuelan extra-heavy and Mexican heavy oil in chemical composition, and the real difficulty is moving the extremely viscous bitumen through oil pipelines to the refinery. Many modern oil refineries are extremely sophisticated...
Because of the difficulty of moving crude bitumen through pipelines, non-upgraded bitumen is usually diluted with natural-gas condensate in a form called dilbit or with synthetic crude oil, called synbit. However, to meet international competition, much non-upgraded bitumen is now sold as a blend of multiple grades of ...
Bitumen was used starting in the 1960s as a hydrophobic matrix aiming to encapsulate radioactive waste such as medium-activity salts (mainly soluble sodium nitrate and sodium sulfate) produced by the reprocessing of spent nuclear fuels or radioactive sludges from sedimentation ponds. One of the main problems is the swe...
This also causes the matrix to swell. The swelling pressure due to osmotic effect under constant volume can be as high as 200 bar. If not properly managed, this high pressure can cause fractures in the near field of a disposal gallery of bituminised medium-level waste. When the bituminised matrix has been altered by sw...
Different types of bitumen have been used: blown bitumen (partly oxidized with air oxygen at high temperature after distillation, and harder) and direct distillation bitumen (softer). Blown bitumens like Mexphalte, with a high content of saturated hydrocarbons, are more easily biodegraded by microorganisms than direct ...
Production. About 164,000,000 tons were produced in 2019. It is obtained as the "heavy" (i.e., difficult to distill) fraction. Material with a boiling point greater than around 500°C is considered asphalt. Vacuum distillation separates it from the other components in crude oil (such as naphtha, gasoline and diesel). Th...
Oil sands. Naturally occurring crude bitumen impregnated in sedimentary rock is the prime feed stock for petroleum production from "oil sands", currently under development in Alberta, Canada. Canada has most of the world's supply of natural bitumen, covering 140,000 square kilometres (an area larger than England), givi...
Alternatives and bioasphalt. Although uncompetitive economically, bitumen can be made from nonpetroleum-based renewable resources such as sugar, molasses and rice, corn and potato starches. Bitumen can also be made from waste material by fractional distillation of used motor oil, which is sometimes otherwise disposed o...
Albanian bitumen extraction has a long history and was practiced in an organized way by the Romans. After centuries of silence, the first mentions of Albanian bitumen appeared only in 1868, when the Frenchman Coquand published the first geological description of the deposits of Albanian bitumen. In 1875, the exploitati...
A life-cycle assessment study of the natural selenizza compared with petroleum bitumen has shown that the environmental impact of the selenizza is about half the impact of the road asphalt produced in oil refineries in terms of carbon dioxide emission. Recycling. Bitumen is a commonly recycled material in the construct...
During bitumen's early use in modern paving, oil refiners gave it away. However, bitumen is a highly traded commodity today. Its prices increased substantially in the early 21st Century. A U.S. government report states: The report indicates that an "average" 1-mile (1.6-kilometer)-long, four-lane highway would include ...
Health and safety. People can be exposed to bitumen in the workplace by breathing in fumes or skin absorption. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit of 5mg/m3 over a 15-minute period. Bitumen is a largely inert material that must be heated or diluted to a...
American National Standards Institute The American National Standards Institute (ANSI ) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organization also coordinates U.S. standards with...
Many ANSI regulations are incorporated by reference into United States federal statutes (i.e. by OSHA regulations referring to individual ANSI specifications). ANSI does not make these standards publicly available, and charges money for access to these documents; it further claims that it is copyright infringement for ...
According to Adam Stanton, the first permanent secretary and head of staff in 1919, AESC started as an ambitious program and little else. Staff for the first year consisted of one executive, Clifford B. LePage, who was on loan from a founding member, ASME. An annual budget of $7,500 was provided by the founding bodies....
Process. Although ANSI itself does not develop standards, the Institute oversees the development and use of standards by accrediting the procedures of standards developing organizations. ANSI accreditation signifies that the procedures used by standards developing organizations meet the institute's requirements for ope...
The institute is the official U.S. representative to the two major international standards organizations, the International Organization for Standardization (ISO), as a founding member, and the International Electrotechnical Commission (IEC), via the U.S. National Committee (USNC). ANSI participates in almost the entir...
Argument (disambiguation) In logic and philosophy, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion. Argument may also refer to:
Apollo 11 Apollo 11 was a spaceflight conducted from July 16 to 24, 1969, by the United States and launched by NASA. It marked the first time that humans landed on the Moon. Commander Neil Armstrong and Lunar Module Pilot Buzz Aldrin landed the Apollo Lunar Module "Eagle" on July 20, 1969, at 20:17 UTC, and Armstrong b...
After being sent to the Moon by the Saturn V's third stage, the astronauts separated the spacecraft from it and traveled for three days until they entered lunar orbit. Armstrong and Aldrin then moved into "Eagle" and landed in the Sea of Tranquility on July 20. The astronauts used "Eagle"s ascent stage to lift off from...
Background. In the late 1950s and early 1960s, the United States was engaged in the Cold War, a geopolitical rivalry with the Soviet Union. On October 4, 1957, the Soviet Union launched Sputnik 1, the first artificial satellite. This surprise success fired fears and imaginations around the world. It demonstrated that t...
Since the Soviet Union had higher lift capacity launch vehicles, Eisenhower's successor, John F. Kennedy chose, from among options presented by NASA, a challenge beyond the capacity of the existing generation of rocketry, so that the US and Soviet Union would be starting from a position of equality. A crewed mission to...
An early and crucial decision was choosing lunar orbit rendezvous over both direct ascent and Earth orbit rendezvous. A space rendezvous is an orbital maneuver in which two spacecraft navigate through space and meet up. In July 1962 NASA head James Webb announced that lunar orbit rendezvous would be used and that the A...
Project Apollo was abruptly halted by the Apollo 1 fire on January 27, 1967, in which astronauts Gus Grissom, Ed White, and Roger B. Chaffee died, and the subsequent investigation. In October 1968, Apollo 7 evaluated the command module in Earth orbit, and in December Apollo 8 tested it in lunar orbit. In March 1969, Ap...
Personnel. Prime crew. The initial crew assignment of Commander Neil Armstrong, Command Module Pilot (CMP) Jim Lovell, and Lunar Module Pilot (LMP) Buzz Aldrin on the backup crew for Apollo 9 was officially announced on November 20, 1967. Lovell and Aldrin had previously flown together as the crew of Gemini 12. Due to ...
Deke Slayton gave Armstrong the option to replace Aldrin with Lovell, since some thought Aldrin was difficult to work with. Armstrong had no issues working with Aldrin but thought it over for a day before declining. He thought Lovell deserved to command his own mission (eventually Apollo 13). The Apollo 11 prime crew h...
By the normal crew rotation in place during Apollo, Lovell, Mattingly, and Haise were scheduled to fly on Apollo 14, but the three of them were bumped to Apollo 13: there was a crew issue for Apollo 13 as none of them except Edgar Mitchell flew in space again. George Mueller rejected the crew and this was the first tim...
Capsule communicators. The capsule communicator (CAPCOM) was an astronaut at the Mission Control Center in Houston, Texas, who was the only person who communicated directly with the flight crew. For Apollo 11, the CAPCOMs were: Charles Duke, Ronald Evans, Bruce McCandless II, James Lovell, William Anders, Ken Mattingly...
An illustrator at the Manned Spacecraft Center (MSC) did the artwork, which was then sent off to NASA officials for approval. The design was rejected. Bob Gilruth, the director of the MSC felt the talons of the eagle looked "too warlike". After some discussion, the olive branch was moved to the talons. When the Eisenho...
Mementos. The astronauts had personal preference kits (PPKs), small bags containing personal items of significance they wanted to take with them on the mission. Five PPKs were carried on Apollo 11: three (one for each astronaut) were stowed on "Columbia" before launch, and two on "Eagle". Neil Armstrong's LM PPK contai...
Areas that appeared promising on photographs taken on Earth were often found to be totally unacceptable. The original requirement that the site be free of craters had to be relaxed, as no such site was found. Five sites were considered: Sites 1 and 2 were in the Sea of Tranquility ("Mare Tranquillitatis"); Site 3 was i...
One of the first versions of the egress checklist had the lunar module pilot exit the spacecraft before the commander, which matched what had been done on Gemini missions, where the commander had never performed the spacewalk. Reporters wrote in early 1969 that Aldrin would be the first man to walk on the Moon, and Ass...
The media accused Armstrong of exercising his commander's prerogative to exit the spacecraft first. Chris Kraft revealed in his 2001 autobiography that a meeting occurred between Gilruth, Slayton, Low, and himself to make sure Aldrin would not be the first to walk on the Moon. They argued that the first person to walk ...
The S-IVB third stage of Saturn V AS-506 had arrived on January 18, followed by the S-II second stage on February 6, S-IC first stage on February 20, and the Saturn V Instrument Unit on February 27. At 12:30 on May 20, the assembly departed the Vehicle Assembly Building atop the crawler-transporter, bound for Launch Pa...
Mission. Launch and flight to lunar orbit. An estimated one million spectators watched the launch of Apollo 11 from the highways and beaches in the vicinity of the launch site. Dignitaries included the Chief of Staff of the United States Army, General William Westmoreland, four cabinet members, 19 state governors, 40 m...
Saturn V AS-506 launched Apollo 11 on July 16, 1969, at 13:32:00 UTC (9:32:00 EDT). At 13.2 seconds into the flight, the launch vehicle began to roll into its flight azimuth of 72.058°. Full shutdown of the first-stage engines occurred about 2 minutes and 42 seconds into the mission, followed by separation of the S-IC ...
On July 19 at 17:21:50 UTC, Apollo 11 passed behind the Moon and fired its service propulsion engine to enter lunar orbit. In the thirty orbits that followed, the crew saw passing views of their landing site in the southern Sea of Tranquility about southwest of the crater Sabine D. The site was selected in part because...
As the descent began, Armstrong and Aldrin found themselves passing landmarks on the surface two or three seconds early, and reported that they were "long"; they would land miles west of their target point. "Eagle" was traveling too fast. The problem could have been mascons—concentrations of high mass in a region or re...
During the mission, the cause was diagnosed as the rendezvous radar switch being in the wrong position, causing the computer to process data from both the rendezvous and landing radars at the same time. Software engineer Don Eyles concluded in a 2005 Guidance and Control Conference paper that the problem was due to a h...
Armstrong found a clear patch of ground and maneuvered the spacecraft towards it. As he got closer, now above the surface, he discovered his new landing site had a crater in it. He cleared the crater and found another patch of level ground. They were now from the surface, with only 90 seconds of propellant remaining. L...
ACA was the Attitude Control Assembly—the LM's control stick. Output went to the LGC to command the reaction control system (RCS) jets to fire. "Out of Detent" meant the stick had moved away from its centered position; it was spring-centered like the turn indicator in a car. Address 413 of the Abort Guidance System (AG...
Armstrong acknowledged Aldrin's completion of the post-landing checklist with "Engine arm is off", before responding to the CAPCOM, Charles Duke, with the words, "Houston, Tranquility Base here. The "Eagle" has landed." Armstrong's unrehearsed change of call sign from "Eagle" to "Tranquility Base" emphasized to listene...
Lunar surface operations. Preparations for Neil Armstrong and Buzz Aldrin to walk on the Moon began at 23:43 UTC. These took longer than expected; three and a half hours instead of two. During training on Earth, everything required had been neatly laid out in advance, but on the Moon the cabin contained a large number ...
Apollo 11 used slow-scan television (TV) incompatible with broadcast TV, so it was displayed on a special monitor and a conventional TV camera viewed this monitor (thus, a broadcast of a broadcast), significantly reducing the quality of the picture. The signal was received at Goldstone in the United States, but with be...
Armstrong intended to say "That's one small step for a man", but the word "a" is not audible in the transmission, and thus was not initially reported by most observers of the live broadcast. When later asked about his quote, Armstrong said he believed he said "for a man", and subsequent printed versions of the quote in...

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