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Moon and Regulus

March 23, 2013

Most stars are fairly round, like balls. But the star that represents the heart of the lion is shaped more like a pill - a disk that’s much wider through the equator than through the poles.

Regulus, the brightest star of Leo, stands to the left or lower left of the Moon as night falls this evening, and trails along behind the Moon during the night.

Regulus is sculpted by its rotation. Its equator spins at about 700,000 miles per hour - more than a hundred times faster than the Sun. That pushes the gas at its equator outward, so Regulus is about a third wider through the equator than through its poles. And that’s about as wide as it can go. If the star were to spin just 10 percent faster, it would fly apart.

The spin is probably the result of interactions between Regulus and a companion star. The companion was originally much heavier than Regulus, so it aged more rapidly. As it neared the end of its life, it puffed up and dumped some of its gas on the surface of Regulus, spinning it up. Today, all that’s left of the companion is its hot but dead core, a white dwarf.

Because the gas at Regulus’s poles is so much closer to the core than the gas at the equator, the poles are thousands of degrees hotter than the equator, so they look much bluer. They’re also much brighter.

Again, look for Regulus to the left of the Moon this evening. It’ll stand above the Moon tomorrow evening. We’ll have more about Regulus and the Moon tomorrow.


Script by Damond Benningfield, Copyright 2013

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