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Venus, in astronomyVenus, in astronomy, 2d planet from the sun; it is often called the evening star evening star or morning star, planet that becomes visible in the western sky shortly after sunset or in the eastern sky shortly before sunrise. It can usually be seen in twilight, when it is too light for the true stars to be seen...... Click the link for more information. or morning star and is brighter than any object in the sky except the sun and the moon. Because its orbit lies between the sun and the orbit of the earth, Venus passes through phases like those of the moon, varying from a large bright crescent when the planet is near inferior conjunction conjunction, in astronomy, alignment of two celestial bodies as seen from the earth. Conjunction of the moon and the planets is often determined by reference to the sun. ..... Click the link for more information. (nearest the earth) to a smaller silvery disk when it is at superior conjunction (farthest from the earth). Since its greatest elongation elongation, in astronomy, the angular distance between two points in the sky as measured from a third point. The elongation of a planet is usually measured as the angular distance from the sun to the planet as measured from the earth. ..... Click the link for more information. (the angle made between the sun, the earth, and Venus) is 47°, it can never be seen much longer than 3 hr after sunset or 3 hr before sunrise. Venus revolves around the sun at a mean distance of c.67 million mi (107 million km) in a nearly circular orbit, and its period of revolution is about 225 days. It comes closer to the earth than any other planet, being c.26 million mi (42 million km) away at inferior conjunction. Venus is often referred to as the sister planet of the earth, because it is only slightly smaller in both size and mass. Several important differences, however, exist between the two planets. Although Venus is covered with a thick blanket of clouds that hides its surface from view, much has been learned of the conditions on Venus from U.S. and Soviet space probes. These probes indicate a surface temperature of about 890°F; (475°C;) and an atmospheric pressure as great as 100 times that at the earth's surface. The thick atmosphere is composed mainly of carbon dioxide, with a slight amount of water vapor and a trace of nitrogen and other elements. The high surface temperature is assumed to result partly from the greenhouse effect; radiation passing through the atmosphere heats the surface, but the heat is blocked by the enveloping carbon dioxide from escaping back out through the atmosphere. The European Space Agency's Venus Express space probe began orbiting the planet in 2006; its instruments are designed primarily to study the Venusian atmosphere. Studies also indicate that Venus rotates on its axis in a retrograde direction (opposite to the direction of revolution about the sun) with a period of about 243 days. Despite this slow rotation there is little observed temperature difference between the lighted and unlighted sides of the planet. The surface of Venus is thought to be stormy. From 1990 to 1992 NASA's Magellan spacecraft mapped the Venusian surface using radar, revealing details of a continentlike feature, called Aphrodite Terra, that crosses the planet's equator and is marked by geologic faults. A second such feature, Ishtar Terra, straddles the north polar region. Magellan also observed many volcanic features, including immense lava plains and large shield volcanoes, and relatively few impact craters resulting from asteroids and comets. Compared to the number of craters on other bodies of the inner solar system, this suggests that the surface of Venus is only about 800 million years old. No strong magnetic field comparable to that of the earth has been detected. Venus, in Roman religion and mythologyVenus, in Roman religion and mythology, goddess of vegetation. Later, she became identified (3d cent. B.C.) with the Greek Aphrodite Aphrodite , in Greek religion and mythology, goddess of fertility, love, and beauty. Homer designated her the child of Zeus and Dione. Hesiod's account of her birth is more popular: she supposedly rose from the foam of the sea where Uranus' genitals had fallen after..... Click the link for more information. . In imperial times she was worshiped as Venus Genetrix, mother of Aeneas; Venus Felix, the bringer of good fortune; Venus Victrix, bringer of victory; and Venus Verticordia, protector of feminine chastity. The most famous representations of Aphrodite or Venus in sculpture are the Venus of Milo or Melos (Louvre); the Venus of Medici or Medicean Aphrodite (Uffizi); the Venus of Capua (national museum, Naples); and the Capitoline Venus (Capitoline Mus., Rome). The Venus of Milo is a Greek statue in marble, generally dated to the 2d or 1st cent. B.C. Found (1820) on the island of Melos, it was taken by the French ambassador to Turkey and was eventually presented by Louis XVIII to the Louvre. The Venus of Medici belongs to the 3d cent. B.C. It is probably derived from Praxiteles' Aphrodite of Cnidus, which was destroyed. VenusRoman goddess of cultivated fields and gardens, later associated with Aphrodite. She was the daughter of Jupiter and Dione, the wife of Vulcan, and the mother of Cupid. She was famous for her romantic intrigues and affairs with both gods and mortals, and she became associated with many aspects of femininity. The planet Venus, originally the star of Ishtar, came to be named for Venus through her association with Ishtar. She has been a favourite subject in art since ancient times, notably in the statue known as Venus de Milo (c. 150 BC)and in Sandro Botticelli's painting The Birth of Venus (c. 1485). VenusSecond major planet from the Sun. Named for the Roman goddess, Venus is, after the Moon, the most brilliant natural object in the night sky. Venus comes closer to Earth—about 26 million mi (42 million km)—than any other planet. Its orbit around the Sun is nearly circular at a distance of about 67 million mi (108 million km) and takes 225 days; its rotation, in retrograde motion, takes even longer (243 days). As viewed from Earth, Venus undergoes phase changes similar to the Moon's, going through one cycle of phases in 584 days. It is seen only near sunrise or sunset and has long been known as both the morning star and the evening star. Venus is a near twin of Earth in size and mass but is completely enveloped by thick clouds of concentrated sulfuric acid droplets. Its surface gravity is about 90% that of Earth. Its atmosphere is over 96% carbon dioxide, with a pressure about 95 times Earth's. The dense atmosphere and thick cloud layers trap incoming solar energy so efficiently that Venus has the highest surface temperature of any of the Sun's planets, more than 860 °F (460 °C). Radar imaging indicates that the surface is dry and rocky, consisting mostly of gently rolling plains, broad depressions, and two large elevated regions analogous to continents on Earth; Venus also has impact craters, extensive lava fields, and massive shield volcanos. The interior is thought to be similar to that of Earth, with a metal core, a dense rocky mantle, and a less-dense rocky crust. Unlike Earth, Venus has no intrinsic magnetic field. Venus1 1. the Roman goddess of love 2. mount of Venus See mons veneris Venus2 1. one of the inferior planets and the second nearest to the sun, visible as a bright morning or evening star. Its surface is extremely hot (over 400?C) and is completely shrouded by dense cloud. The atmosphere is principally carbon dioxide. Mean distance from sun: 108 million km; period of revolution around sun: 225 days; period of axial rotation: 244.3 days (retrograde motion); diameter and mass: 96.5 and 81.5 per cent that of earth respectively 2. the alchemical name for copper Venus [′vē·nəs] (astronomy) The planet second in distance from the sun; the linear equatorial diameter of the solid globe is 7521 miles (12,104 kilometers); the mass is about 0.815 (earth = 1). Venus bright planet, second from the Sun. [Astronomy: EB, X: 392] See : Brightness Venus goddess of love and beauty. [Rom. Myth.: Aeneid] See : Love Venus provided future protection for Aeneas, her son. [Rom. Myth.: Aeneid] See : Love, Maternal Venus goddess of this season. [Rom. Myth.: Hall, 130] See : Spring Venus the second planet in order from the sun and the nearest one to the earth in the solar system; astronomical symbol, ♀ . Venus has also been known by the names Morning Star, Hesperus, Vesper, Evening Star, Phosphorus, and Lucifer. Its mean distance from the sun is 108 million km (0.723 astronomical unit). The sidereal period measures 224 days, 16 hours, 49 minutes, and 8 seconds. To the observer on the earth, the angular distance from Venus to the sun does not exceed 48°, as a result of which the planet is visible only during a certain period after sunset (evening star) or shortly before sunrise (morning star). Venus is the brightest celestial object (after the sun and moon) in the terrestrial sky. At maximum brightness it attains a stellar magnitude of -4.4. The phases of Venus (discovered by Galileo in 1610) may be observed with the naked eye by persons with exceptionally good vision. The planet’s angular diameter at inferior conjunction reaches 64″. According to terrestrial radar observations, its average radius is 6,050 ± 0.5 km and its deviation from sphericity, ± 3 km; its mass is 1/408,522 ± 3 that of the sun and 0.9528 that of the earth. Observed from the earth, Venus appears to be covered by a dense cloud cover having high reflectance (spherical albedo, 0.6) and lacking permanent markings. Using a few dark and bright markings noticeable on the cloud cover, principally in the wavelength range of 300-400 nanometers (3,000-4,000 angstroms), a rotation period of approximately four days has been established. (The direction of rotation is retrograde, that is, contrary to the motion of the planets around the sun.) The rotation period of the solid body of the planet, determined from radar observations, is 243 ± 0.18 days (the direction of rotation is also retrograde), while the axis of rotation is inclined to the plane of the orbit at an angle no greater than 2°. It is possible that the observed four-day rotation period of the cloud layer may be explained by atmospheric currents having an approximate velocity of 100 m/sec, which in the earth’s atmosphere is typical for altitudes of 50-60 km. The existence of the Venusian atmosphere was first established by M. V. Iomonosov from observations of the transit of Venus across the disk of the sun in 1761. The presence of carbon dioxide (C02) in the Venusian atmosphere has been reliably established by spectroscopic means. Carbon monoxide (CO), steam (H20), oxygen (02), hydrogen chloride (HCl), and hydrogen fluoride (HF) possibly exist in the layer above the clouds. It is supposed that the planet’s clouds consist of aqueous ice crystals. Information on the atmospheric layer below the clouds, obtained from terrestrial optical observations, is practically nonexistent. According to observations in the radio-frequency and infrared regions of the spectrum, Venus’ brightness temperature is strongly dependent on the wavelength in which observations are conducted (see Table 1).
Measurements in the infrared region of the spectrum pertain to the upper layers of the cloud cover. Maximum temperatures are apparently near the wavelength λ = 6 cm; around λ = 70 cm, the temperature, slowly changing, approaches 500-450° K. (In all cases, the temperature is averaged over the disk.) The phase change is small in the millimeter range (amplitude, approximately 10 percent) in the centimeter and decimeter ranges, it is within the limits of measurement error. The most widespread explanation for the distribution of the brightness temperature over the spectrum is the notion of the planet’s hot surface (approximately 600-700° K), whose radiation in the short and long waves is absorbed by the atmosphere. It is presumed that the high temperature of the surface is due to the greenhouse effect created by the Venusian atmosphere. Direct measurements, first made on Oct. 18, 1967, in the lower atmosphere by the Soviet unmanned interplanetary probe Venera 4 and confirmed by measurements of stations Venera 5, Venera 6, and Venera 7 (May 16, 1969, May 17, 1969, and Dec. 15, 1970), have shown that the temperature increases as the surface is approached by a gradient close to that of the adiabatic curve, and that the pressure at the surface exceeds several meganewtons/m2 (several tens of kilograms-force/cm2). According to direct investigations, the Venusian atmosphere consists principally of carbon dioxide gas, with an admixture of a small quantity of water (approximately 0.1 percent) and oxygen. A model of the atmosphere constructed according to the data obtained from the earth as well as direct measurements leads to the conclusion that the average temperature on the surface of Venus is approximately 750° K at a pressure of approximately 10 meganewtons/m2 (100 kgf/cm2). The surface of the planet is apparently solid; it is somewhat less pitted than that of the moon. Radar observations reveal isolated areas of increased reflectance, perhaps associated with the topography of the surface. REFERENCESSharonov, V. V. Planeta Venera.Moscow, 1965.Kuz’min, A. D. Radiofizicheskie issledovaniia Venery.Moscow, 1967. Moroz, V. I. Fizika planet.Moscow, 1967. Brandt, J., and P. Hodge. Astrofizika solnechnoi sistemy.Moscow, 1967. (Translated from English.) G. A. LEIKIN Want to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit the webmaster's page for free fun content. |
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