StarDate: August 25, 2009

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The tail of the swan recently got closer. It didn't actually move, mind you. Instead, we got a better yardstick for measuring how far away it is.

The tail of the swan is represented by the star Deneb, which soars high overhead on summer nights. It's one of the 20 brightest stars in the night sky -- and farther away than any of the others on the list.

But just how far has been tough to figure out.

The best way for measuring a star's distance is a technique called parallax. To see how it works, hold a finger in front of your face and look at it with one eye at a time. As you blink back and forth, the finger appears to move against the background of more-distant objects.

In astronomy, this is accomplished by looking at a star when Earth is on opposite sides of the Sun. The star appears to move back and forth a little against the background of other stars.

The technique works best for stars that are close -- which isn't the case with Deneb. Various studies found that it was as near as 1500 light-years, or as far as 3,000 or more.

But astronomers recently reanalyzed the data from a satellite that measured the parallaxes of many stars. According to the new figures, Deneb is a little less than 1500 light-years away.

That means that Deneb isn't as big and bright as astronomers had thought. Even so, it's still close to 20 times as massive as the Sun, and more than 60,000 times brighter. So Deneb is still one of the galaxy's giants.

Script by Damond Benningfield, Copyright 2009

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