Moon and Uranus

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• 12 of 1970
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A hidden giant lurks in the darkness of the outer solar system -- the planet Uranus. It's the third-largest planet -- about four times wider than Earth. Yet it's so far from the Sun that it doesn't get a lot of light, so it doesn't shine very bright. And it's so far from Earth that it's not really visible without some help -- binoculars or a telescope.

But there's a big finder's aid quite close to the planet this evening -- the crescent Moon. At their closest, they'll be separated by about the width of a finger held at arm's length.

Uranus is about 20 times farther from the Sun than Earth is. At that distance, the Sun looks only about one four-hundredth as bright as it does from Earth. To put it another way, each square foot of Earth receives about 400 times more energy from the Sun than the same-sized patch of Uranus. That makes Uranus much colder and darker than Earth.

And at such a great distance, not much of the light that does hit Uranus is reflected back to Earth, so that makes the planet hard to see. Under really dark skies, when Uranus is at its brightest, the planet is just visible to people with sharp eyesight. But most of us need help to see this dark giant.

To get that help, use binoculars to scan a little to the left or lower left of the Moon after the sky gets good and dark. Uranus looks like a faint star, with a little bit of blue-green color. Uranus and the Moon drop from sight by around 10 o'clock.

Script by Damond Benningfield, Copyright 2007

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