Often known popularly as the ‘evening star’ or ‘morning star’, Venus when observed from Earththe is the brightest of all the planets visible in the nighttime sky. The early Ancient Greeks once thought Venus was in fact two separate celestial objects, being the evening star Hesperus, and the morning star, Phosphorus, while the early Ancient Romans thought it was both Vesper and Lucifer. Babylonians adorned this planet as the goddess of beauty and love, with the name Ishtah meaning the lovely “light-bringer”. These same ancient peoples were first to realise that both objects were the indeed same. The Greeks were soon to adopted this too, which they named after the now solitary Greek goddess, Aphrodite. Even later, the Romans named the planet Venus.
Terms like “Venusian atmosphere” derive from the genitive, Veneris, but fortunately we have not use the traditional terms for planets as we do for stars and constellations. Else Venus would have to have an “Aphrodisiac atmosphere” certainly giving the wrong connotation and impression!
VENUS DATADiscoverer : Prehistoric Satellites : None DIAMETER Equatorial : 12 103.6 km Polar : 12 102.4 km Period (P) : 224.701 days Synodic Period : 583.92 days Orbital Velocity : 35.03±0.26kms-1 Eccentricity (e) : 0.0067 Inclination (i) : 3.39° Mean Density : 5.243 g.cm-3 Mean Distance : 108.21±0.73×106 km Sidereal Rotation : 243.02 days Day Length : 116.75 days Maximum Diameter : 66.0 arcsec Minimum Diameter : 9.7 arcsec Maximum Magnitude : -4.7 |
Of similar size to Earth, Venus is some 12 104 km across. Closer to the Sun than us, its almost circular orbit takes 224.7 days to complete at the mean solar distance of 0.72 A.U. (108 million kilometres). Like Mercury, Venus is a so-called inferior planet and experiences both inferior and superior conjunctions. Never drifting very far from the Sun, the maximum angle reaches only 47°. Each full cycle of lunar-like phases, over the called the synodic period, takes 1.60 years or 583.9 days, with its apparent size changing anywhere between 9.6 arcsec to 66 arc seconds (1.1′). Venus has the geocentric distance from us may change anywhere between 38 and 261 million km. (M.km.), with its visual brightness varying between -4.7 and -3.5 magnitude. Transits across the solar disk do occur, but because of the slight orbital inclination of 3.4°, they are quite rareand coming in pairs once every 127 years or so. We last obsevered a series in 1874 and 1882, with the most recent one on 8th June 2004. The next awaited transit, well placed for sourthern Australian observers is on 6th June 2012.
Venus is a total cloud-shrouded world that was mysteriously hidden until the 1960’s. It was once considered Earth’s twin, and quite fancifully by some imagined likely a prehistoric version of the Earth. This in including dinosaurs and other primitive life-forms, while other considered intellegent creatures often portrayed as beautiful maidens. When first explored by the Mariner 2 spacecraft in 1962, these views were quickly dispelled. Venus is actually a hellish world. The ground atmospheric pressure is ninety-two times that of Earth, whose thick hot and corrosive atmosphere contains 90% carbon dioxide (CO2). This is mixed with smaller quantities of nitrogen, sulphur dioxide, sulphuric acid, argon and only very minute traces of water. Fast upper winds move once around Venus every 4.3 days, and this spreads evenly the oven hot 460°C surface temperature on both the dark and sunlit sides of the planet. This internal heat is partly due to the proximity of the Sun, but it has become much hotter because the CO2 has trapped the sunlight via the runaway Greenhouse effect. This is even more remarkable because Venus only spins in a retrograde direction once every 243.7 days and opposite to all the other Solar System planets.
Many spacecraft have visited Venus and each have gathered a wealth of information. Radar observations by the Pioneer Venus Orbiter and Magellan spacecraft found e vidence of cratering, recently active volcanoes, plate tectonics, and several unknown geological features not seen on Earth. Venera 9 also obtained surface pictures in October 1975, showing that the ambient light is similar to the sky brightness of a full moon. No suggestion of any magnetic field has been found, so that core of Venus must be quite different in composition than that of the Earth.
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