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Jumpy Stars

The celestial great bear is light on his feet. His paws are represented by three pairs of stars. And all three pairs have names that mean “leap” or “spring.”

The stars of the bear’s hind leg are known as Alula Borealis and Alula Australis. “Alula” is from an Arabic phrase that means “the first leap of the gazelle.” The other pairs of stars represent the second and third leaps.

Alula Borealis — the northern member of the pair — is the brighter of the two stars. It’s a giant star that’s passed the end of its “normal” lifetime. It’s going through a series of changes in its core. Those changes have caused the star’s outer layers to puff up like a giant balloon. The star is almost 60 times the Sun’s diameter, and almost 800 times its total brightness. That makes it easy to see even though it’s 400 light-years away.

Alula Australis — the southern star — is only about 30 light-years away. It actually consists of four stars, which are split into two pairs. The leading light of each pair is similar to the Sun. The two companion stars are much smaller and fainter than the Sun, so they don’t add much to the system’s brightness.

Alula Borealis and Australis are bright enough to see with the unaided eye, although not from light-polluted cities. At nightfall, they’re well to the right of the bowl of the Big Dipper — the bear’s body. They’ll rotate high above the dipper during the night, and stand to its lower left at first light tomorrow.

Script by Damond Benningfield

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