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Dog Days

August 17, 2013

The leading light of winter’s evening skies is climbing into view in the morning sky. According to tradition, that dawn appearance brings an end to the “dog days” of summer.

Sirius is the brightest star of Canis Major, the Big Dog, so it’s known as the Dog Star. It’s also the brightest star in the entire night sky. For the last couple of months, it’s been rising and setting at about the same time as the Sun, so it’s been lost in the daytime glare.

The ancient Greeks and Romans blamed that proximity to the Sun for the oppressive heat of summer. So they called this time of year the dog days.

Sirius doesn’t actually contribute anything to the heat of summer. Despite its brightness, it’s almost nine light-years away, so there’s no way for it to warm our planet. Its appearance during the hottest part of the year is just a coincidence.

But it’s one that won’t last forever. Thanks to a “wobble” in Earth’s rotation, the stars move through the seasons. As a result, the time that Sirius rises and sets with the Sun is moving later into the year. And over the millennia it will move even later. So perhaps the people of the distant future will associate the “dog days” not with the heat of summer, but with the cold of winter.

For now, look for Sirius just peeking into view in the south-southeast shortly before sunrise. The brilliant star will climb a little higher into the sky each day — eventually working its way into the cold evening skies of winter.


Script by Damond Benningfield, Copyright 2013

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