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June 1, 2010

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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