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Moon and Regulus

StarDate: 
June 9, 2016

The heart of the lion beats near the Moon this evening. Regulus, the bright heart of Leo, stands to the upper left of the Moon at nightfall. The Moon moves closer to Regulus before they set, after midnight.

Regulus is much bigger, brighter, and heavier than the Sun. And it spins about 15 times faster — more than 700,000 miles per hour at the equator.

Regulus whirls around so rapidly because it “stole” a lot of gas from a nearby companion star. As the hot gas poured in, Regulus twirled faster and faster. Today, it spins so fast that it bulges outward at the equator, so it looks like a severely squashed beachball.

If Regulus were to spin just 10 percent faster, it would rip itself apart. That’s unlikely to happen because it’s already pulled in all of the available gas from its companion. But some other stars are seen to spin much closer to that edge. Gas squirts away from such a star’s equator, forming a disk around it.

As the gas moves away from the star, it can condense to form tiny grains of dust. The dust absorbs some of the star’s light — especially blue light. That can make the star look much redder than it really is. In the 1800s, for example, astronomer John Russell Hind watched as one star changed from red to blue in a matter of weeks. The most likely explanation is that the star had spun off a shell of gas and dust, making it look red. The shell dissipated, though, allowing the star’s true color to shine through.

Script by Damond Benningfield

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