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September 4, 2010

If a bright light going off over your head means the birth of a bright idea, then we should all be thinking hard around 9 or 9:30 tonight. That's when a bright light will stand over all of our heads: Vega, the brightest star of Lyra, the harp. It'll cross high across the sky for the entire country, and from latitudes across the middle of the country, it'll stand directly overhead.

Vega is only about 25 light-years away, making it one of our closest neighbors. It shines pure white, which tells us that its surface is thousands of degrees hotter than the surface of the Sun.

Models of how stars age indicate that, like the Sun, Vega is about halfway through its "normal" lifetime -- the time when it "fuses" the hydrogen in its core to make helium. But stellar lifetimes aren't all the same. Vega is probably around one-tenth the age of the Sun, so it has only a few hundred million years to go, versus billions of years for the Sun.

The difference is the mass of the two stars. Vega's more than twice as "heavy" as the Sun, so it burns through its hydrogen much faster than the Sun does. So Vega will finish off its hydrogen, puff up to become a red giant, blow its outer layers off into space, and fade into obscurity as a white dwarf -- all while the Sun continues to shine much as it does today.

Again, look for Vega passing high overhead as the sky gets good and dark. It'll continue to crown the early evening sky for the rest of the month.


Script by Damond Benningfield, Copyright 2010


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