Figure 36.10 Venus's cloud cover.

Ultraviolet image of Venus's clouds from the Pioneer Venus Orbiter. Seen in visible light, the clouds are almost featureless. Reflected ultraviolet light reveals their structure and patterns. The thick cloud cover traps heat from the Sun, creating an extreme greenhouse effect. These clouds circle Venus in about 4 days, much faster than the 243-day rotation period of Venus itself, indicating that the atmosphere is in high-speed motion. Although they resemble Earth's clouds, Venus's clouds are not made of water droplets. They are very dry and are composed of droplets of sulfuric acid. (NASA/JPL)

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