If you go outside at night in Fall or Winter and look at the sky, the most impressive constellation is undoubtedly Orion, the mighty hunter of the stars. His right shoulder is marked by a bright star, visibly red even with the naked eye. That's Betelgeuse. Enjoy it now, before it goes away.
Betelgeuse is a giant, massive star -- it has 20 times the mass of the Sun, and it fills a space as big as the orbit of Jupiter. It's so big that telescopes on Earth can resolve it as a visible disc even though it's more than 600 light years away.
Oh, and it's shrinking. Betelgeuse's diameter has shrunk by 15 percent since 1993. This may be part of some long-term fluctuation -- the star pulsates and huffs and puffs constantly -- or it could be the beginning of the end. Massive stars like Betelgeuse don't live long. They shine brightly and burn through their hydrogen fuel at a terrific rate. As they run out of hydrogen they swell, turning into huge red giants. Kind of like Betelgeuse is now. And then they start fluctuating, blowing off material. Kind of like Betelgeuse. And then . . .
Bang!
We'll all know if it happens. Betelgeuse will outshine everything but the Sun for a time. Right now Orion is next to the Sun in the sky, drowned out by sunlight, but a supernova would be visible even during the day. The last naked-eye supernova was Kepler's Star in 1604, and that was 50 times more distant. Fortunately Betelgeuse is too distant to sterilize the Earth with a blast of deadly gamma radiation, but the storm of particles released by a dying giant might be as bad as a big solar flare event -- bright auroras, communications interference, maybe even radiation damage to electronic systems on the ground. So be sure to back up your files on a CD-ROM soon, and keep watching the skies!
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