Moon in the Middle

StarDate: August 18, 2010

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Back in the 1960s, after a weak-sister team managed to beat his Longhorns, Texas coach Darrell Royal compared the other team to a cockroach. The problem isn't what the cockroach carries away, Royal said, but what it falls into and messes up.

It's not just the pending football season that brings the comment to mind -- it's a pesky object in the night sky: the bright Moon. Its glare fills the sky with light. It's not nearly as much light as the Sun, but it's enough to mess up the view of faint stars, galaxies, and other objects.

When there's a bright Moon in the sky, astronomers turn their telescopes toward relatively bright targets that shine through the glare. They have to wait until the Moon sets to go after fainter targets.

Telescopes in space don't have that problem. Most of them don't look directly at the Moon, but with no atmosphere to scatter the moonlight, they can look just about anywhere else. In fact, they don't have to worry about the Sun, either -- as long as they don't look right at it, they can continue their observations of the universe all day -- and all night.

Tonight, the bright gibbous Moon is near the "spout" of the teapot formed by the brightest stars of Sagittarius. It's surrounded by the Milky Way. But the Milky Way is so faint that it's tough to make out. Like many other faint wonders of the night sky, it's "messed up" by the glare of the bright Moon.

Tomorrow: the glare of a bright planet.

Script by Damond Benningfield, Copyright 2010

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