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June 23, 2010

Some constellations are a challenge to find. One example is Draco, the dragon. Draco does actually look like its namesake. But it has a long, faint, and difficult-to-see tail that winds between the Big and Little Dippers.

One star in Draco is easy to see and makes a good starting point. It's called Eltanin -- an Arabic name that means "the serpent." The star is Draco's brightest -- it shines as brightly as the North Star. So if you can see the North Star, you can see Eltanin.

Eltanin is in Draco's head, which lies close to the brilliant star Vega, in the neighboring constellation Lyra.

Eltanin itself is an orange giant -- a star that's nearing the end of its life. It's somewhat cooler than the Sun, but about 250 times brighter.

Right now, the star is about 150 light-years from Earth. But it's moving toward us in a hurry. In a million and a half years, it'll pass less than 30 light-years away, making it one of the brightest stars in the night sky.

Eltanin is one of a trio of orange-giant stars in the northernmost sky. The Big Dipper, which is just south of Draco's long tail, has another one, named Dubhe. And the Little Dipper, which is just north of Draco's tail, has an orange giant named Kochab. By coincidence, all three -- Eltanin in Draco, Dubhe in the Big Dipper, and Kochab in the Little Dipper -- are nearly the same distance from Earth, so they look equally bright in our sky.

We'll talk about a prominent dying star in Draco tomorrow.

Script by Ken Croswell, Copyright 2010

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