Shrinking Star 
One of the biggest stars in the galaxy seems to be slimming down a bit. Over the last 15 years or so, its diameter has shrunk by about 15 percent. Even so, it's not exactly skinny: It may be up to a billion miles across. At that size, if it took the Sun's place in our solar system, it would extend all the way to Jupiter, the fifth planet out.
Betelgeuse marks the shoulder of Orion, the hunter. It's high in the southeast at nightfall, above the band of three stars that marks Orion's Belt. It's quite bright, and it has a distinctly orange color, so it's easy to pick out.
Betelgeuse is classified as a red supergiant. It's not only bigger than the Sun, it's far more massive, too. That great heft means that Betelgeuse is doomed to explode as a supernova, probably within the next few million years -- a blink of an eye on the astronomical timescale.
Over the last couple of decades, scientists at the University of California at Berkeley have watched the star with an array of telescopes at Mount Wilson Observatory. The combined telescopes allow them to precisely measure the star's size. And they've found that its diameter has decreased by more than a hundred million miles. Yet its brightness hasn't changed at all.
So far, there's no explanation for the change. But the astronomers will continue to keep an eye on Betelgeuse to see if it continues its disappearing act.
We'll talk about another supergiant star in Orion tomorrow.
Script by Damond Benningfield, Copyright 2009