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August 15, 2010

The Moon passes by one of the scorpion's long lost claws tonight: the star Zubenelgenubi. It's a little above the Moon as darkness falls.

The name "Zubenelgenubi" means the "the southern claw." It tells us that thousands of years ago, it and a star that stands above it -- Zubeneschamali, the northern claw -- were part of Scorpius, the scorpion. But later, they were stripped away and assigned to a new constellation: Libra, the balance scales.

If you have clear skies and good eyesight, you might notice that Zubenelgenubi consists of two stars that are quite close together. The stars are bound to each other by gravity, so they travel through the galaxy as a pair.

What you can't see, though, is that each of these stars is actually a pair on its own. So the entire system consists of four stars. Three of them are bigger and hotter than the Sun, while the fourth is smaller and cooler. All four appear to be around 200 million years old.

A recent study says that the stars of Zubenelgenubi have one more companion, but it's a long way away. Known as KU Librae, the star is a lot like the Sun. Even though it's about three light-years from the stars of Zubenelgenubi, it appears to have a lot in common with them: it's about the same age, it has a similar composition, and it moves through space with them.

If KU Librae really is a member of the group, it would make Zubenelgenubi one of the most spread-out star systems in the galaxy.

Script by Damond Benningfield, Copyright 2010

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