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Red Rivals

July 11, 2010

The largest stars in the universe are bright, cool stars known as red supergiants. If placed at the center of the solar system, the mightiest of these would engulf all the planets out to Jupiter and beyond.

The two brightest red supergiants that are visible from Earth appear on opposite sides of the sky. One, which is in view in winter, is Betelgeuse, in Orion, the hunter. The other, blazing like a ruby in the south tonight, is Antares, in Scorpius. Both are among the brightest stars in the night sky.

In mythology, the home constellations of these stars are rivals: Scorpius was the scorpion that stung and killed Orion. But the stars themselves appear to be near twins.

From the reddish-orange colors of the stars, astronomers have long known that they have the same surface temperature. But astronomers had thought that Betelgeuse was the weaker star.

But recent research indicates that Betelgeuse is 640 light-years from Earth. That's farther than earlier measurements. So to appear as bright as it does in our sky, Betelgeuse must emit more light into space than had been thought.

When astronomers work out the numbers, they find that Betelgeuse and Antares each emit about 20,000 times more light than the Sun. So these two brilliant red rivals are twins -- shining on us from opposite sides of the sky.

Look for Antares fairly low in the south at nightfall, at the "heart" of the scorpion. It sets in the wee hours of the morning.

Script by Ken Croswell, Copyright 2010

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