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Northern Cross

December 25, 2011

The sky is decorated with some beautiful baubles for this Christmas night. Venus, the “evening star,” is low in the west as night falls. The Moon is below it, although it’s a whisker-thin crescent, and it sets before the sky gets completely dark. Jupiter, the next-brightest object in the night sky after Venus, is high overhead. And the Summer Triangle stands in the west, with its highest point marked by Deneb, the star at the tail of Cygnus, the swan.

When the swan stands high in the sky, it really does look like a graceful bird. As it noses toward the horizon, though, the pattern looks more like its other name: the Northern Cross. It’s just above the horizon around 8 or 9 o’clock, with the long axis standing straight up, and the cross parallel to the horizon.

Cygnus was first drawn thousands of years ago. But if the people who created it could look at the stars tonight, they wouldn’t notice any difference in its pattern at all.

The stars are all moving around the center of the galaxy at a good clip. And they’re at different distances from Earth, so their motions across the sky are different, too. So over time, the familiar patterns in the night sky will become distorted — and, eventually, unrecognizable. But on the human scale, “eventually” is a long time. The stars are all so far away that their drift across the sky is imperceptible even over the span of hundreds of lifetimes.

So Cygnus — and the Northern Cross — will continue to grace the night sky for millennia to come.


Script by Damond Benningfield, Copyright 2011


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