An infrared view from the Keck Telescope shows details in the atmosphere of Uranus, the third-largest planet in the solar system. In optical light, Uranus looks like a featureless blue-green marble, because methane in its upper atmosphere absorbs red wavelengths of light. Infrared peers through the methane haze, revealing belts of clouds plus bright storms that extend high above most of the surrounding clouds. These two views show the eastern and western hemispheres. They also reveal Uranus's narrow rings. [Lawrence Sromovsky, Univ. Wisconsin-Madison/W.M. Keck Observatory]
Like a giant waking from a long sleep, the planet Uranus shows signs of being a lot more active than it was just a few years ago. Bands of clouds are changing color, and big blobs of clouds are popping up -- apparently because of a change in seasons.
Like the seasons on Earth, the seasons on Uranus are caused by the planet's tilt on its axis. But while Earth is tilted just a little, Uranus is tilted on its side. So during the planet's 84-year-long orbit around the Sun, each pole has 42 years of sunlight, followed by 42 years of darkness.
In 2007, Uranus passed through an equinox, so the Sun was shining on its equator and illuminating the entire planet.
The change triggered changes in the planet's atmosphere.
A haze of methane, which absorbs red light, surrounds the planet, making it look blue-green. This haze masks the clouds below it, so Uranus looks like a featureless blob. Astronomers must look at it in wavelengths that are invisible to the human eye to see any detail.
Those wavelengths have revealed dramatic changes in the atmosphere. In fact, some of the changes are so dramatic that they're visible to the eye as well.
A ring of bright clouds near the south pole has turned dark, and a ring of clouds near the north pole has brightened. Giant storm systems thousands of miles across have flared up, too.
Astronomers are continuing to watch the planet to see how it responds to the changing seasons.
More about Uranus tomorrow.
Script by Damond Benningfield, Copyright 2010
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