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February 22, 2011

The Big Dipper wheels high across the north on winter nights. It's low in the northeast in early evening, standing on its handle, and high in the northwest at first light. It's led by Dubhe, the star at the outer edge of the bowl, with Alkaid, the star at the end of the handle, bringing up the rear.

In the mythology of the sky, though, leaders and followers are all a matter of perspective. Alkaid, for example, is an ancient Arabic name that means "the leader." It represented the leader of a group of daughters -- the stars of the dipper's handle -- who were leading a platform containing a dead body.

Regardless of whether it's the leader or the tail, though, Alkaid is an impressive star. It's about six times as massive as the Sun, and when you add up all forms of energy, it's close to a thousand times brighter.

The star's great heft revs up the nuclear engine in its core, so Alkaid "burns" through its hydrogen fuel far more quickly than the Sun does. That makes the surface of Alkaid thousands of degrees hotter than the Sun. It also means that Alkaid will live a much shorter life than the Sun -- about a hundred million years, compared to more than 10 billion years for the Sun.

One other item of note about Alkaid is its distance: almost exactly 100 light-years. That means the light you see from Alkaid tonight actually left the star a century ago -- around the start of 1911.

We'll talk about Dubhe tomorrow.

Script by Damond Benningfield, Copyright 2010


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