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Celestial Clock

January 31, 2011

The Big Dipper wheels around the North Star like an hour-hand on a giant clock, ticking off the hours of the night. And winter is an especially good time to watch it, because it's in good view pretty much all night long. Tonight, for example, the dipper stands clear of the northeastern horizon by an hour or two after sunset. It's standing on its handle, with the bowl highest in the sky.

Over the next few hours, the dipper wheels counterclockwise around and over the North Star. It's highest in the sky around 3 or 4 in the morning, stretching high across the north. The bowl is upside down, so it looks as though it's spilling its contents toward the northern horizon.

After that, the dipper begins its descent across the northwestern sky. It's still quite high in the sky at first light, with the leading edge of the bowl well above the height of the North Star.

As the Big Dipper turns across the sky, you can use its bowl to find the North Star. Line up the two stars that form the outer edge of the bowl, then extend the line away from the top of the bowl. The first moderately bright star you come to is the North Star, Polaris.

Despite its important position in the sky, the North Star isn't all that bright. So it's good to have some well-known stars to point the way -- the great hand of a celestial clock pointing back to clock's center as it ticks off the hours of a long winter's night.

Script by Damond Benningfield, Copyright 2010

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