The surface of the planet Venus is permanently concealed from direct view by clouds of sulfuric acid in its thick carbon dioxide atmosphere. Ultraviolet images, like this one taken by the HST on January 24, 1995, reveal distinctive cloud bands that cannot easily be seen in visible light. In particular, there is a horizontal Y-shaped feature near the equator. Similar features have been observed by the spacecraft Mariner 10, Pioneer Venus and Galileo. Ultraviolet light is absorbed by Earth's atmosphere so images such as this can only be taken from space.
The brighter regions near the poles may be due to a haze of small particles above the main cloud layers. Darker areas show where sulfur dioxide is more concentrated near the cloud tops. Such features travel east-to-west, along with Venus's prevailing winds, making a complete circuit round the planet in four days.
Less than half of the disk of Venus is illuminated by sunlight in this image. Viewed from Earth or near to the Earth as HST is - Venus goes through a cycle of phases similar to the Moon's because its orbit is nearer to the Sun than Earth's. As Venus gets closer to Earth during the course of its orbit, its disk appears larger overall, but the visible part of the illuminated side shrinks to a crescent. When this picture was taken, Venus was 113.6 million kilometers (70.6 million miles) away.
Though Venus's surface cannot be viewed directly, the Magellan spacecraft, operating in orbit around Venus between 1990 and 1994, used radar to map in detail the landscapes hidden beneath the clouds.
Camera: WFPC2 in PC mode.
Technical Information: False color has been used to enhance
cloud features.
Credit: L. Esposito (University of Colorado, Boulder), and NASA
