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May 29, 2010

If you rode a merry-go-round that started spinning at thousands of miles per hour, it would throw you off in a hurry.

Some stars have the same problem. They spin so fast that they try to throw some of their gas out into space. As a result, they're no longer round.

One example is the brightest star in Ophiuchus, a large but unspectacular constellation that's visible in the early evening hours in late spring and early summer. Ophiuchus is the serpent bearer, and its brightest star is Rasalhague -- Arabic for "head of the snake charmer."

The star is about 48 light-years away. It's a bit hotter than the Sun, and about 30 times brighter. But what makes it remarkable is its rapid spin: Astronomers estimate that the star's equator rotates at half a million miles an hour -- a far cry from the thousand-miles-per-hour speed at which Earth's equator rotates.

Because of the fast spin, Rasalhague isn't round. Astronomers recently determined its shape by using an interferometer -- a device that combines the light of more than one telescope to provide sharp views of the stars. The new work found that Rasalhague is 20 percent bigger through the equator than through the poles. And since the poles are closer to the star's center than the equator is, they're also hotter -- by 3300 degrees Fahrenheit.

Rasalhague's shape and temperature distribution may seem a little strange, but then we on Earth orbit a round star: the slow-spinning Sun.

Script by Ken Croswell, Copyright 2010

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