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October 23, 2010

Anyone who's played chess knows that the king is a surprisingly weak piece. It's the same story in the sky: the king, represented by the constellation Cepheus, is a bit of a weakling, too.

Yet the king's brightest star, Alderamin, is intriguing. It spins so fast that it isn't round.

Alderamin looks nearly as bright as the North Star, Polaris. And like the North Star, it shines in the northern sky. In fact, it stands directly above Polaris around mid-evening at this time of year. It's a white star, and it's about 50 light-years from Earth.

Alderamin spins so fast that its equator whirls at more than half a million miles per hour. That makes the star puff out at the equator. Astronomers recently used an array of telescopes to measure Alderamin's shape. They found that the star is about 27 percent fatter through the equator than through the poles.

Because of that out-of-round shape, the star's poles are closer to its center than the equator is. As a result, the poles are thousands of degrees hotter than the equator. In contrast, the Sun has a pretty uniform temperature across its entire surface.

No one knows for sure why Alderamin spins so fast. It may have been born from a fast-spinning cloud of gas and dust. Or it may once have had a close companion star that dumped hot gas onto it, making it spin faster. Whatever the case, Alderamin's fast spin and odd shape set it apart from most of its stellar peers.


Script by Ken Croswell, Copyright 2010


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