Moon and Regulus
A big carnival-ride of a star hovers close to the Moon tonight. They're high in the sky at nightfall, with the star a little to the Moon's left or upper left, and they set in the wee hours of the morning.
Regulus is several times bigger and more massive than the Sun. Yet it spins on its axis once every 16 hours, compared to about four weeks for the Sun. That means that a spot on the star's equator whirls around at an astounding 700,000 miles per hour.
If that makes it sound like you'd need to hold on for dear life, that's pretty much the case. Like all stars, Regulus is a big ball of gas. Its high-speed rotation causes its equator to bulge out, so the star is a good bit thicker through the equator than through the poles. In fact, it's spinning just about as fast it can without actually flying apart.
Since the poles are so much closer to the star's core, which is the source of its energy, the poles are thousands of degrees hotter than the equator. That means the poles are brighter than the equator, too.
The cause of this furious rotation may be a companion star. A small stellar corpse orbits Regulus. It's possible that as this star neared the end of its life, it puffed up so much that it dumped much of its outer layers of gas onto Regulus. As the gas rammed into Regulus's surface, it made the star spin faster, like aiming a fire hose at a water wheel.
Script by Damond Benningfield, Copyright 2011
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