Chasing Dogs

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A pair of "dog" stars chases each other across winter's night skies. But which star is chasing and which is being chased depends on your location.

The brighter star is Sirius, in the constellation Canis Major, the big dog. The other is Procyon, of Canis Minor, the little dog.

Sirius is the brightest star in the night sky. It shines about 20 times brighter than the Sun. But the main reason it looks so bright is that it's one of the closest stars, at a distance of just eight and a half light-years.

Sirius is actually a double star. Its companion is a white dwarf -- the hot, dense core of a star that was once like Sirius itself. At the end of its life, the star cast its outer layers into space, leaving only the core. The same thing will happen to Sirius when it reaches the end of its life.

Procyon is a little farther than Sirius, and it doesn't produce quite as much light. Still, it's the eighth-brightest star system in the night sky. And like Sirius, it also has a white-dwarf companion.

The name Procyon means "before the dog." From about 30 degrees latitude and points northward, it rises before Sirius. From Kansas City, for example, it climbs into the sky about 20 minutes earlier. The viewing angle is different from more southerly latitudes, so Sirius actually rises first.

Watch for Sirius rising in the east-southeast in mid evening, with Procyon well to its left. Both stars sail across the south in the wee hours of the morning.

Script by Damond Benningfield, Copyright 2004, 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.