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July 9, 2012

Most of us slow down a little as we age. And the same thing happens for stars — they spin more slowly as they get older. Compare, for example, the Sun and Vega, the brightest star of Lyra, the harp. The Sun is four-and-a-half billion years old, and it rotates about once a month. Vega’s about one-tenth of the Sun’s age, and it rotates twice a day.

Like the Sun, Vega is near the middle of its life. It’s “fusing” the hydrogen atoms in its core to make helium. Vega’s more than twice as massive as the Sun, though, so it consumes that fuel much more quickly, which makes Vega thousands of degrees hotter than the Sun.

Vega’s rapid rotation gives the star a pronounced “bulge” around the middle — it’s a lot bigger through the equator than through the poles.

The Sun probably looked somewhat similar when it was young. Newborn stars tend to rotate quickly. Over time, though, they slow down. A star’s magnetic field acts as a brake, slowing the star as the magnetic field interacts with the planets, gas, and dust around it. Vega is surrounded by a pretty thick disk of dust, which may also contain planets, so it, too, is likely to slow down. Vega won’t live nearly as long as the Sun will, though, so it’ll still be spinning in a hurry as it nears the end of its life.

Look for Vega high in the east at nightfall, and moving directly overhead later on. It’s one of the brightest stars in the entire night sky, so it’s hard to miss.

More about Vega tomorrow.


Script by Damond Benningfield, Copyright 2012


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