Outshining the Dog

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The brightest star in the night sky sweeps across the south this evening. It stands due south around 8 o'clock, and sets after midnight.

The star is Sirius. It's known as the Dog Star because it's in the constellation Canis Major, the big dog.

Sirius is several times brighter than the Sun. But one reason it looks so bright in our sky is that it's close by -- less than nine light-years away. Few stars are closer.

If you lined up all the stars that outline the dog at the same distance, though, Sirius wouldn't be even close to brightest. In fact, it would look positively pale compared to three other stars in the constellation.

The stars are Aludra, Wezen, and Adhara. They form a triangle that represents the dog's back end. All three of them are hundreds or even thousands of times brighter than Sirius. They appear fainter only because they're much farther away.

All three stars are giants or supergiants. That means they're much bigger than the Sun, and they're much later in life. The stars are so massive that they've burned through their nuclear fuel much faster than the Sun has. So even though they're younger than the Sun, they're undergoing the final stages of their evolution. In fact, two of the stars may be getting close to exploding as supernovae -- blasts that will outshine billions of normal stars.

Look for these three bright stars forming a triangle below Sirius as the big dog trots across the southern sky.

Script by Damond Benningfield, Copyright 2005, 2008

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