Mercury in the Evening

StarDate: January 3, 2009

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The planet Mercury puts in a meek appearance the next few nights. It's quite low in the southwest as the sky begins to darken, so it's tough to find.

Mercury is tough to study, too. It's the innermost planet in the solar system, so it always stays quite close to the Sun in our sky. Through the glare, telescopes reveal little more than a fuzzy blob.

In fact, we knew almost nothing about Mercury until the Space Age.

Until a half-century ago, scientists thought that the same side of Mercury always faced the Sun, just as the same side of the Moon always faces Earth. But using satellite-tracking antennas as giant radar guns, they found that that's not the case. Instead, Mercury rotates in such a way that the same side faces Earth each time the planet is closest to us.

We didn't see any details on Mercury until Mariner 10 flew past it in the 1970s. It revealed a landscape that resembles the Moon.

In recent decades, radio telescopes have mapped more of Mercury, and found possible deposits of ice inside craters at its poles.

And just last year, the Messenger spacecraft flew past Mercury twice, photographing regions that Mariner couldn't see. Messenger will enter orbit around Mercury in two years, and give us our most complete look at the elusive planet.

Look for Mercury beginning about a half-hour after sunset. It looks like a moderately bright star, but you'll need a clear horizon to spot it, and binoculars will enhance the view.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.

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