| absolute zero | Theoretical temperature. Absolute zero is characterized by a complete absence of heat. It is equivalent to exactly –273.15°C (–459.67°F). |
| Adams, Ansel | American photographer. Adams (1902-84) is highly respected for his technical innovations and for his representations of mountainous terrain. Although originally his vocation was music and his avocation was photography, Adams became a professional photographer following publication of his first portfolio, Parmellian Prints of the High Sierras (1927). By 1935, following publication of Making a Photograph, Adams was being hailed as an historian of photography. In 1941, he began to produce photo-murals for the US Department of the Interior. Adams was an ardent conservationist who turned his personal activism into pro-activism by serving as the director of the Sierra Club from 1936. |
| AEB | See Brazilian Space Agency. |
| aerobraking | Decelerating a spacecraft by passing through planetary atmosphere. |
| aerospike engine | Originally developed for the X-33 space plane. Aerospike engines are unlike conventional engines that push a vehicle aloft by hot gases escaping from bell-shaped chambers. Instead, aerospike engines are designed so that one end of their exhaust plume runs along a ramp while the other end remains open to the atmosphere. This makes them more powerful and easier to steer than conventional engines. |
| Aesop | Greek author of fables. Aesop is almost certainly a legendary figure, although attempts were made by Herodotus and Plutarch to prove that Aesop actually existed. It is far more likely, however, that Aesop was simply a name invented to provide an author for fables centering on animals. Indeed, “a story of Aesop” is today seen to be synonymous with “fable.” |
| Agrippa | Lunar crater. According to the Gazetteer of Planetary Nomenclature, Agrippa was named for a Greek astronomer (died AD 92). However, when considered in its proximity to the crater Julius Caesar, it is as likely that this crater was named for Marcus Vipsanius Agrippa (63-12 BC), a Roman general and statesman. It was Agrippa who commanded Octavian’s fleet in the victory at Actium (31 BC) over the combined forces of the Roman general Mark Antony and Queen Cleopatra of Egypt—effectively ending their plot to overthrow Octavian. Earlier, in 36 BC, Agrippa had defeated Sextus Pompeius in two naval battles (Mylae and Naulochus), thus helping Octavian (the heir to Julius Caesar) become sole ruler of the Roman Empire. |
| AIDS | Acquired Immunodeficiency Syndrome. AIDS is the most severe manifestation of the Human Immunodeficiency Virus (HIV). The Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, list various opportunistic infections and neoplasms (cancers) that, in the presence of HIV, constitute an AIDS diagnosis. Individuals living with AIDS often have infections of the lungs, brain, eyes, and other organs. They also frequently suffer debilitating weight loss, diarrhea, and a type of cancer called Kaposi’s sarcoma. |
| Aitken, Robert Grant | American astronomer. Aitken (1864-1951) specialized in the study of double stars, discovering more than 3,000 of them. After serving as professor of mathematics and astronomy at the University of the Pacific in Stockton, California, Aitken joined the staff of the Lick Observatory, Mt. Hamilton, California, from which he retired in 1935. He is best known for his publications The Binary Stars (1918) and New General Catalogue of Double Stars Within 120° of the North Pole (1932). |
| albedo | Reflectivity of an object. Albedo is the ratio of reflected light to incident light. |
| albedo feature | Dark or light marking on the surface of an object (e.g., a planet or an asteroid). Note that an albedo feature might not be a geological or topographical feature. |
| ALH84001 | Martian meteorite found in Antarctica. ALH84001 is estimated to be approximately 4.5 billion years old, or about as old as Mars itself. Recently it has been established that inside a small fragment of the meteorite, chains of magnetite crystals, which could only have been left by living organisms, were detected. Magnetite crystal chains similar to these are seen here on Earth, in bacteria that live near the surface of shallow water sediments. Although magnetite crystals have been found in ALF84001 before, no clear images of the chain characteristics of bacteria had been previously seen. Despite this, warning voices are suggesting there is the possibility that the meteorite has been contaminated and that there is as yet no proof that life once existed on Mars. |
| Almaz | Precursor to Mir. Almaz was conceived in the early 1960’s as the military twin to the Soyuz. In its initial form, the 20-ton Almaz was intended to operate for 2 to 3 years at a time, taking reconnaissance photographs the while. But after the death of Nikita Khruschev, who had championed the project, Almaz fell behind schedule. It was cancelled in July 1969. |
| Alpha Centauri |
Star 4.3 light years away from the Earth. Excluding our Sun, Alpha Centauri is the nearest bright star to Earth. |
| Altman, Scott | American astronaut. Altman (b. 1959) was chosen as a member of the 1995 astronaut-candidate group. He has flown twice—on STS-90 (1998) and STS-106 (2000)—and has spent in excess of 27 days in space. Education: BS in aeronautical and astronautical engineering, MS in aeronautical engineering. |
| amine | Any of a class of organic compounds that is derived from ammonia by replacing hydrogen with one or more alkyl groups. |
| Amundsen, Roald | Norwegian explorer. Amundsen (1872-1928) led the first expedition to reach the South Pole (December 14, 1911), beating Robert Scott’s expedition there by a matter of days. He is also credited with being the first explorer to make a ship voyage through the Northwest Passage and one of the first to fly across the Arctic. Amundsen is considered one of the greatest figures in polar exploration. His books include The South Pole (1912) and, with American adventurer Lincoln Ellsworth, First Crossing of the Polar Sea (1927). |
| andesite | Intermediate volcanic rocks containing 54 to 62% silica and moderate amounts of iron and magnesium. Andesite is an aphanite in texture and usually medium-dark in color. It commonly includes plagioclase and hornblende, with lesser amounts of mica, pyroxene, and various accessory minerals. Andesites occur in composite volcanic cones associated with convergent plate margins. |
| Andromeda | Great, spiral galaxy and the Earth’s nearest external galaxy. The Andromeda galaxy, which is believed to be a twin to the Milky Way, is one of the few galaxies visible to the unaided eye. About 2,000,000 light years from Earth, Andromeda is approximately 200,000 light years in diameter. First mentioned in AD 965—in the Book of Fixed Stars by Al-Sufi, an Islamic astronomer—and rediscovered in 1612 by the German astronomer Simon Marius, the Andromeda galaxy was seen as a component of the Milky Way. Only in the 1920’s did American astronomer Edwin Hubble determine that Andromeda was in fact a galaxy separate from the Milky Way, one surrounded by a number of satellite galaxies and globular clusters. |
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anorthosite |
Intrusive igneous rock. Anorthosites consist primarily of calcium-rich plagioclase feldspar. While those found on Earth are made up of coarse crystals, some samples of lunar anorthositic rock are finely crystalline. |
| antimatter | Particle with exactly the opposite properties to those of its matter counterpart. For example, a positron—the antimatter counterpart of an electron—has a positive charge, one that is equal in strength to the negative charge of the electron. Antimatter is created by pair production. When antimatter contacts its matter counterpart, the two particles are instantly annihilated. Their rest mass then turns into energy and is released as two-photon electromagnetic radiation. |
| aphanite | Dark rock. Aphanite has such a close texture that its separate grains are invisible to the naked eye. |
| aphelion | Point in orbit in which a planet is most distant from the Sun. Compare aphelion to perihelion. |
| Aphrodite | Greek goddess of sexual love and beauty. Aphrodite was also worshiped as the goddess of the sea and seafaring as well as the goddess of war, particularly in Sparta and Thebes. She was identified with Venus by the Romans. Phobos and Deimos were Aphrodite’s sons by the god Ares. The statue of Aphrodite, carved by the 4th-century BC Greek sculptor Praxiteles, served as the model for the Venus de Milo. |
| apogee | Point in orbit farthest from the Earth. Compare apogee to perigee. |
| Apollo | Greek god of divine distance. Phoebus Apollo was the most revered and influential of Greek gods. Also known as the god who made men aware of their guilt and purified them of it, he presided over religious law and the constitutions of cities, and he communicated his knowledge of the future and the will of his father, Zeus, to humans through prophets and oracles. His forename, Phoebus, means “bright” or “pure.” |