Assiniboin, placating the spirit of a slain eagle, photograph by Edward S. Curtis, 1908; from The North Ameri¬ can Indian
COURTESY OF THE NEWBERRY LIBRARY, CHICAGO, AYER COLLECTION
Astaire in Top Hat, 1935
CORBIS-BETTMANN
© 2006 Encyclopaedia Britannica, Inc.
aster ► astronomy I 121
and Elath. Astarte shared many qualities, and perhaps a common origin, with her sister Anath. The goddess of love and war, Astarte was worshiped in Egypt and in Canaan, as well as among the Hittites. Her Akkadian counterpart was Ishtar. She is often mentioned in the Bible under the name Ashtaroth; Solomon is said to have worshipped the goddess, and Josiah destroyed the shrines dedicated to her. In Egypt she was assimilated with Isis and Hathor; in the Greco-Roman world she was assimilated with Aph¬ rodite, Artemis, and Juno.
aster Any of various chiefly fall-blooming, leafy-stemmed herbaceous plants (Aster and closely related genera) in the composite family, often with showy flowers. Included among the asters are many perennial wildflow- ers and hundreds of garden varieties.
asteroid Any of the many small rocky objects found mainly in a flat ring, or belt, between the orbits of Mars and Jupiter. It is thought that the gravitational influence of what became Jupiter kept the asteroids from aggregating into a single planet while the solar system was forming. Also called minor planets, asteroids are smaller than any of the nine major planets; only about 30 are more than 125 mi (200 km) across. Ceres is the largest known asteroid. Millions of boulder-sized asteroidal fragments are thought to exist in the solar system. Asteroids or their fragments regularly strike Earth, plunging through the atmosphere as meteors to reach its sur¬ face (see meteorite). Asteroids appear to be composed of carbonaceous, stony, and metallic (mainly iron) materials. See also Earth-crossing aster¬ oid; Trojan asteroids.
asthenosphere \as-'the-n3-,sfir\ Zone of the Earth’s mantle lying beneath the lithosphere, believed to be much hotter and more fluid than the lithosphere. The asthenosphere is thought to extend from about 60 mi (100 km) to about 450 mi (700 km) below the Earth’s surface.
asthma Vaz-mo\ Chronic disease with attacks of shortness of breath, wheezing, and coughing from constriction and mucous-membrane swell¬ ing in the bronchi (air passageways in the lungs). It is caused primarily by allergy or respiratory infection. Secondhand smoke can cause asthma in children. Asthma is common and runs in families; predisposition may be hereditary. In established asthmatics, exercise, stress, and sudden changes in temperature or humidity can bring on attacks. Attacks usually last from a half hour to several hours; severe attacks can be fatal. Corti¬ costeroids can control asthma; injections of epinephrine can relieve acute attacks. Prevention involves avoiding exposure to allergens.
astigmatism No-'stig-mo-.ti-zonA Lack of symmetry in the curvature of the cornea or, rarely, the lens of the eye. The unequal curvatures spread light rays, preventing them from being sharply focused at a point on the retina, causing blurring of part of the image. The effect of astigmatism can also be produced by misalignment of the lens. Astigmatic vision is corrected by means of lenses (see contact lens, eyeglasses) that refract the light rays to the proper degree in the opposite direction of that produced by the defects in curvature.
Astor, John Jacob orig. Johann Jakob Astor (b. July 17, 1763, Waldorf, Ger.—d. March 29, 1848,
New York, N.Y., U.S.) German-born U.S. fur magnate and financier. After emigrating from Germany at age 17, he opened a fur-goods shop in New York c. 1786. By 1800 he was a leader in the fur trade, and he estab¬ lished the American Fur Co. He con¬ trolled the fur trade with China (1800-17) and in the Mississippi and Missouri valleys (in the 1820s) before selling his interests in 1834.
His investment in New York City real estate became the foundation of the family fortune. At his death, Astor was the wealthiest person in the U.S.; he willed $400,000 to found what became the New York Public Library.
His son, William B. Astor (1792- 1875), greatly expanded the family real-estate holdings, building more than 700 stores and dwellings in the city.
Astrakhan Vas-tr3-,kan\ City (pop., 2002: 506,400), southwestern Rus¬ sia. It is situated on several islands in the delta of the Volga River. It was the capital of a Tatar khanate that became independent of the Golden Horde in the 13th century, and its location on caravan and water routes made it a trading centre. Ivan IV (the Terrible) conquered Astrakhan in 1556, giving Russia control of the Volga. The Turks burned the city in 1569. It served as the base for the campaign of Peter I (the Great) against Persia and later was given special trade privileges. Sites of interest include a fortress and a cathedral.
astrolabe Type of early scientific instrument used for reckoning time and for observational purposes.
Astrolabes can be traced to the 6th century ad; they came into wide use in Europe and the Islamic world in the early Middle Ages and were adopted by mariners by the mid-15 th century. One widely used variety, the planispheric astrolabe, can be regarded as a rudimentary analog computer. It enabled astronomers to calculate the positions of the Sun and prominent stars with respect to both the horizon and the meridian.
astrology Divination that consists of interpreting the influence of stars and planets on earthly affairs and human destinies. In ancient times it was inseparable from astronomy. It originated in Mesopotamia (c. 3rd millennium bc) and spread to India, but it developed its Western form in Greek civilization during the Hellenistic period. Astrology entered Islamic culture as part of the Greek tradition and was returned to European cul¬ ture through Arabic learning during the Middle Ages. According to the Greek tradition, the heavens are divided according to the 12 constella¬ tions of the zodiac, and the bright stars that rise at intervals cast a spiri¬ tual influence over human affairs. Astrology was also important in ancient China, and in imperial times it became standard practice to have a horo¬ scope cast for each newborn child and at all decisive junctures of life. Though the Copernican system shattered the geocentric worldview that astrology requires, interest in astrology has continued into modem times and astrological signs are still widely believed to influence personality.
astronaut Person trained to pilot a spacecraft, operate any of its sys¬ tems, or conduct research aboard it during spaceflights. The term com¬ monly refers to those participating in U.S. space missions; cosmonaut is the Russian equivalent. Extensive training, including classroom study of technical subjects as well as practice in computer-controlled simulators and full-sized mock-ups of spacecraft to experience free fall, prepares astronauts physically and psychologically for space missions. Astronauts also learn to use the control, communication, and life-support systems of any given spacecraft and conduct difficult flight operations. See also Edwin Aldrin; Neil Armstrong; Guion S. Bluford, Jr.; Yury A. Gagarin; John H. Glenn, Jr.; Mae Jemison; Sally Ride; Alan B. Shepard, Jr.; Valentina Teresh¬ kova.
astronomical unit (AU) Length of the semimajor axis of Earth’s orbit around the Sun, 92,955,808 mi (149,597,870 km), often defined simply as the average distance from Earth to the Sun. Direct measurement through the parallax method cannot be used for accurate determinations, because the Sun’s glare blots out the light of the background stars nec¬ essary to make the measurement. The most precise values have been obtained by measuring the distance from Earth to other objects orbiting the Sun. This indirect method requires an accurate proportional math¬ ematical model of the solar system; once the distance to one planet or other object is determined, then the distance to the Sun can be calculated.
astronomy Science dealing with the origin, evolution, composition, distance, and motion of all bodies and scattered matter in the universe. The most ancient of the sciences, it has existed since the dawn of recorded civilization. Much of the earliest knowledge of celestial bodies is often credited to the Babylonians. The ancient Greeks introduced influential cosmological ideas, including theories about the Earth in relation to the rest of the universe. Ptolemy’s model of an Earth-centred universe (2nd