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March 2, 2013

The big dog ambles across the southern sky this evening. It’s easy to spot because its brightest star is the Dog Star, Sirius, which is the brightest star in the night sky.

But the constellation has an abundance of stars that are even more impressive than Sirius -- stars that look fainter only because they’re much farther away.

An example is Adhara, which represents one of the dog’s hind legs. It’s below Sirius as night falls. To the eye, it looks only a fraction as bright as Sirius. But if you moved it up to the same distance as Sirius -- about eight-and-a-half light-years -- Adhara would shine almost 200 times brighter than Sirius.

That’s because Adhara is both a good bit bigger than Sirius and a good bit hotter. It’s so hot that it radiates most of its energy not as visible light, but as ultraviolet light. When you add up all the forms of energy it produces, Adhara is probably about 20,000 times brighter than the Sun.

The star is also much heavier than the Sun. That greater heft means the star will live only a fraction as long as the Sun will. In fact, it’s already entering the final stages of life. A series of complex changes in its core will cause it to puff like a giant balloon, getting much brighter as it does so.

Eventually, Adhara will explode as a supernova, sending its outer layers racing through the galaxy at a few percent of the speed of light. Only the star’s dead core will remain - a tiny remnant of a once-mighty star.


Script by Damond Benningfield, Copyright 2013

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