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The information at this web site reflects my personal interests in amateur astronomy. There are features here for newcomers, for do-it-yourselfers, for deep sky observers, and for astrophotographers. Your comments are always welcome.

Clear skies,
Jeff DeTray
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Circumpolar Constellations
The sky is always in motion. Or, to be more precise, the sky appears to be in motion due to the rotation of the Earth on its axis.

Just as the hands of a clock rotate around the center of the clock's face, so the sky appears to rotate around the Celestial Pole. The star Polaris, the North Star, lies very near the North Celestial Pole. Because of this, the entire northern sky appears to rotate slowly and majestically in an enormous circle with Polaris at its center. If you were to stay up all night, you would certainly notice that the positions of the constellations and their stars had changed, but like watching the hands of a clock, the motion is difficult to perceive over the course of a just a few minutes.

The animated sky map below shows a time-lapse view of the northern sky and the motion of its constellations and stars. An entire night of movement is compressed into less than 30 seconds, beginning at 7:00 p.m. on December 15, 2012, and ending at 6:00 a.m. the next morning. The time is noted in the lower-right corner of the map. The animation pauses when it reaches 6:00 a.m., then repeats itself, starting again at 7:00 p.m.

Note how Polaris at the center of the map remains nearly stationary while the rest of the sky swings around it. Polaris barely moves because it lies so close to the North Celestial Pole. Also notice that some constellations, such as Perseus, Draco, Camelopardalis, Cepheus and Cassiopeia, never drop below the horizon. These constellations are said to be circumpolar, because they are visible all night long as they swing around Polaris.

How many constellations are circumpolar depends entirely on your distance from the North Pole. The map below shows the view from about 40 degrees north latitude. The farther north you travel, the more constellations will be circumpolar from your point of view. In fact, when you are standing at the Earth's North Pole, Polaris will be directly overhead, and every constellation you can see will be circumpolar.

North Circumpolar Sky Map



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