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Directional Stars

May 2, 2010

The North Star is just that -- a star that stands due north in the sky. But its proper name doesn't specifically refer to its direction. The name "Polaris" tells us that the star marks the celestial pole, but it doesn't say which pole.

But many other stars don't have that problem. Their names include directions -- north or south. That's because they're members of "double" stars -- two stars of roughly equal brightness that appear close together. The stars aren't actually related, they just happen to line up in the same direction in the sky.

Two examples are in Ursa Major, the big bear, which is high in the northern sky this evening. The bear's body and tail are outlined by the Big Dipper. His feet are represented by three pairs of stars. Two of those pairs are known as Tania Borealis and Australis, and Alula Borealis and Australis.

Tania and Alula come from Arabic names that mean the first and second leaps, because the pairs of stars represented the leaps of a gazelle. And each pair has a star called borealis -- a word that means "northern" -- and one called australis, which means "southern."

Libra, which is climbing up in the east as night falls, also has northern and southern stars. Two of its brightest stars originally represented the claws of Scorpius, the scorpion. To help tell them apart, they were called the northern and southern claws -- giving us two of the best names in all the night sky: Zubeneschamali and Zubenelgenubi.

Script by Damond Benningfield, Copyright 2010

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