Tuesday, July 22, 2008

The Big Dipper


One of the most recognizable groups of stars in the sky is the Big Dipper in the constellation Ursa Major. Most people learn to find it as children. For those who missed that lesson, go outside after dark just as the stars are starting to come out and look to the northwest. The stars of the Big Dipper are fairly bright and should be one of the first ones to appear in the evening. See if you can recognize the shape from the chart above.

If you're having trouble finding it, remember that the Big Dipper is huge, spanning 25°. Hold your hand at arm's length against the sky with your thumb and pinky finger extended. The width between those two fingers is approximately 25°. Don't forget to try your planisphere, if necessary.

Once you've located the Big Dipper, look for Mizar, the second star from the end of the handle of the Big Dipper. It is a double star, meaning it is actually two stars even though it appears a single star to the naked eye. Alcor is its companion star. Mizar and Alcor are easy to split in binoculars. If your eyes are very sharp, you might be able to see both stars without binoculars.

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