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The Dragon

June 21, 2010

Draco, the dragon, slithers high across the northern sky on summer nights. It's high in the sky as darkness falls, wrapping around the North Star.

Draco is relatively faint. So like many other constellations, most of its stars are difficult to see from light-polluted cities and suburbs. The problem is compounded because Draco is a big, winding constellation -- it makes two big loops that wrap halfway around the celestial north pole.

Almost 5,000 years ago, one of the stars of Draco actually marked the pole. The star is called Thuban, which is the Arabic word for the dragon.

Today, a star called Polaris marks the celestial pole. The north pole of Earth points in that direction, so as the planet spins on its axis, Polaris appears to stand still, while all the other stars turn around it.

But Earth slowly wobbles on its axis like a spinning top. Over a period of about 26,000 years, the north polar axis draws a big circle on the sky. That gives us different pole stars at different times. About 5,000 years ago, the pole aimed at Thuban, making it look like the hub of the sky. And the star will regain that status about 21,000 years from now. We'll have more about Thuban tomorrow.

Look for Draco in the northeastern quadrant of the sky at nightfall. It's about mid way between the Big Dipper, which is high in the northwest, and the bright stars Vega and Deneb, which form part of the Summer Triangle low in the northeast.

Script by Damond Benningfield, Copyright 2003, 2006, 2010

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