Moon and Regulus

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Moon and Regulus

Like a mixed litter of puppies, sibling stars don’t necessarily look alike. That can make it hard to figure out which stars are related to each other.

One example is Regulus, the heart of the lion. It’s close to the left or lower left of the Moon as darkness falls.

To the eye alone, Regulus looks like a single bright star. Instead, it’s a system of four stars — two pairs of stars that are separated by a third of a light-year.

What we see as Regulus is the brightest of the four stars. Known as Regulus A, it’s much bigger, heavier, and brighter than the Sun. It’s paired with a star that’s so faint, and so close to Regulus A, that we can’t actually see it, even with the largest telescopes. It reveals its presence only to special instruments. It’s probably a stellar corpse — a white dwarf.

The other pair is known as Regulus BC. Both of its stars are smaller, less massive, and fainter than the Sun. One of them, in fact, is less than one percent of the Sun’s brightness.

Despite the differences in the four stars, there’s evidence that they’re all siblings. They’re all about the same distance away, for example — about 79 light-years. The pairs are close enough to each other for their gravity to hold them together. And the stars move through the galaxy in the same direction, and at the same speed — indications that they’re members of a stellar family.

Script by Damond Benningfield

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