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August 16, 2010

Winter is still a long way away, but one of its signature star patterns is already in view in the early morning sky. Orion, the hunter, clears the eastern horizon a couple of hours before sunrise, and is fairly high in the sky at first light. Look for Orion's Belt -- a short line of three stars -- aiming straight up from the horizon. Betelgeuse is to its left, with slightly brighter Rigel to its right.

If you look carefully, you'll see that Betelgeuse looks orange, while Rigel is blue-white. Despite the different colors, though, they share a common fate: each will destroy itself as a supernova. Betelgeuse is probably closer to that final cataclysm, but Rigel won't be far behind.

Rigel is a blue supergiant. It's probably around 65 times wider than the Sun, and around 65,000 times brighter. But the number that seals its fate is its mass: around 17 times the mass of the Sun. Such heavy stars burn through their nuclear fuel at a furious rate, converting lighter-weight elements to heavier ones in their cores. Eventually, this process stops, the core collapses, and the layers around the core explode.

Even though Rigel is close to 800 light-years away, its demise -- sometime in the next few million years -- will create quite a show. At its peak, it might shine a quarter as bright as the full Moon. It would remain the second- or third-brightest object in the sky for weeks or even months before beginning a long fade from sight.

Script by Damond Benningfield, Copyright 2010

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