Venus

Venus, the second planet from the Sun, is the brightest object in the Solar System after the Sun and Moon. Because of its prominence in the evening sky after sunset and its brightness at dawn Venus also is known as the Evening Star and the Morning Star. Venus (Latin) also was known as Aphrodite (Greek), the Goddess of Love. The planet was known as Astarte to the Phoenicians, as Ishtar to the Babylonians, and as Tai-pe (the Beautiful One) to the Chinese. Observations of the planet go back as far as 1900 B.C. when they were recorded by the Babylonians on the cuniform Venus Tablets (Saunders and Carr 1984). With the aid of a telescope Galileo determined in A.D. 1610 that Venus had lunar-like phases, lending support to the Copernican Sun-centered concept of the Solar System (Greeley 1985, p. 132). Some early observers using a telescope reported that Venus was featureless, but others later noted that the planet displayed bright patches. These patches were used to determine the length of a venusian day. In 1897 Lowell even published a map of canals that he believed he saw on Venus (Saunders and Carr 1984). Another feature noted by Father Johannes Riccoli during the seventeenth century was the Ashen Light. This faint phosphorescence of the night hemisphere when Venus appears as a thin crescent is believed to be due to extensive twilight or to electrical phenomena. Early observers were particularly interested in timing the transit of Venus across the Sun; the most famous attempt probably is the one made by Captain James Cook of HMS Endeavour, and he was given the responsibility for making these measurements by the Royal Society. The observations were made on 3 June 1769 from Tahiti; Bligh, future captain of HMS Bounty, was a member of Cook’s crew. Speculations regarding a possible atmosphere on Venus go as far back as 1796 (Schroter in Saunders and Carr 1984). During the midnineteenth century astronomers noted that Venus displayed a dark halo when silhouetted against the Sun, an observation that led Lomonosov to infer that the planet had an atmosphere. Visual and photographic spectroscopic data obtained during the third decade of the twentieth century led to the conclusion that the principal component of the venusian atmosphere is carbon dioxide. Infrared measurements by Kuiper (1962) showed nearly 40 carbon dioxide absorption bands, and 300 times the concentration of the gas in the venusian atmosphere than in the Earth’s atmosphere; thus, Venus is in a stage of experiencing an intense greenhouse effect.