Changing Seasons

StarDate: September 18, 2009

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The planet Uranus is putting in its best appearance of the year. It rises around sunset and is in the sky all night. It's brightest for the year, too. But it's so far away that you need binoculars to see it. It looks like a tiny star between Aquarius and Pisces.

Through a telescope, Uranus looks like a featureless blue-green disk. Methane in its atmosphere absorbs red light, allowing only the blue to shine through. So to see any storm clouds or other detail in its atmosphere, astronomers must filter out the hazy blue light.

When they do, they see that the atmosphere is changing.

Uranus lies on its side, so each pole receives 42 years of daylight followed by 42 years of darkness. The north pole just emerged into the sunlight a couple of years ago. As the northern hemisphere heats up, the atmosphere seems to be waking up.

In 2006, telescopes revealed a dark storm system as big as Europe in the planet's northern skies. At the same time, some bright features in the southern hemisphere were starting to fade.

Scientists aren't quite sure what to expect as the seasons continue to change on Uranus. The last time one pole moved into the light while the other moved into the darkness was almost half a century ago. The telescopes of the day provided poor views of the planet -- and almost no view through the haze. So they're watching something that no one has ever seen before: the awakening of half a planet after a long winter's nap.

Script by Damond Benningfield, Copyright 2009

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