Dog Stars

StarDate: January 16, 2010

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A pack of dogs bounds across the southern sky on winter nights -- the stars of Canis Major, the big dog. Tonight, they climb into view in the southeast by around 9 o'clock.

The leader of the pack is Sirius, the brightest star in the night sky. The other members stretch below or to the right of Sirius as the constellation climbs into view.

Sirius is larger, hotter, and brighter than the Sun. But one of the reasons it looks so bright is because it's close by -- less than nine light-years away.

Although they don't look as bright as Sirius, some of the other stars of Canis Major are actually more impressive. If its second-brightest star were as close as Sirius, for example, it would look about 200 times brighter.

The star is known as Adhara. It's well below Sirius, at the end of one of the dog's legs. The star puts out more than a thousand times more visible light than Sirius does, which is why it looks so bright across a distance of about 425 light-years.

The surface of Adhara is extremely hot, so the star puts out more ultraviolet energy than visible light. If our eyes were tuned to the ultraviolet, Adhara would outshine every other star in the night sky.

The bright star to the right of Sirius, known as Mirzam, would look just about as bright. It's similar to Adhara, but it's farther, so it looks a little fainter.

Watch both of these "dog" stars as they keep pace with Sirius, bounding across the southern sky.

Script by Damond Benningfield, Copyright 2006, 2009

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