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Star Wheel

May 1, 2013

Two of the night sky’s most prominent star pictures wheel around the Pole Star, Polaris, like a giant carnival ride. When one of them is high in the sky, the other is quite low, sitting right atop the northern horizon.

The “high-low” contrast is on good display this month. During the evening hours, the stars of the Big Dipper stand highest in the sky, with the bowl pouring its contents down upon Polaris. At the same time, W-shaped Cassiopeia, the queen, is directly below the Pole Star. It perches just above the horizon for most American skywatchers, but some or all of its stars dip below the horizon for those in the southern parts of the country.

All of the stars in the celestial northern hemisphere appear to wheel around the star that marks the north pole. That’s because Earth spins on its axis — one full turn against the starry background every 23 hours and 56 minutes. So as the night progresses, the stars appear to rotate across the sky.

The stars rise and set about four minutes earlier each night. So as the seasons go by, each star appears at a different spot in the sky for the same time of night.

Most of the stars spend part of the year below the horizon and out of sight. But stars like those of the Big Dipper and Cassiopeia are so close to the pole that, from mid- and high-northern latitudes, they never set — they’re in view every night of the year.

So watch these stars as they continue their never-ending circle around the celestial north pole.


Script by Damond Benningfield, Copyright 2013

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