Venus-the Clouded Planet
Venus, our nearest planetary neighbour, only 40 million km away, has its surface hidden from view by a dense yellowish-white cloud, which extends to 80 km above the surface (Fig). Venus appears to be the third brightest object in the sky after the Sun and the Moon, because of its short distance from us and because the white cloud reflects almost 76 per cent of the sunlight that falls on it. Venus appears so bright at times that, under ideal atmospheric conditions, it may be seen with the unaided eye in daytime. Venus can be best seen about three hours after sunset when it is a night object or about three hours before sunrise when it is a morning obiect. As you have read in Unit 9, Venus appears to go through phases, quite hke those oi the Moon. It requires almost 20 months for an observer to see Venus in all its phases. As revealed from the space probes, Venus has turned out to be a broiling hot planet. The surface temperatures of Venus are around 480°C. The atmosphere of Venus is made up of 96 per cent carbon dioxide gas and clouds of sulphuric acid withsmall quantities of hydrochloric and hydrofluoric acid. There we small traces of water vapour, nitrogen, argon, sulphur dioxide and carbon monoxide gases. The atmospheric pressure is 90 times the pressure we feel from the Earth's atmosphere. With its searing heat, crushing pressures and poisonous gases, Venus seems less the goddess of love of mythology and more an incarnation of hell! Life cannot survive on Venus. The high surface temperat%e of Venus comes about through what is known as the greenhouse effect. Sunlight passes through the clouds and atmosphere of Venus, and reaches its surface. The suqace on being heated, gives out infrared radiations. The carbon dioxide in the atmosphere of Venus does not let the infrared radiation escape. Thus, the heat of the Sun is efficiently trapped with only very little being able to escape. As a result, the surface temperature rises.