Ursa Minor

Position in the Sky

Named Stars

The constellation Ursa Minor contains the group of stars commonly called the Little Dipper. The handle of the Dipper is the Little Bear's tail and the Dipper's cup is the Bear's flank. The Little Dipper is not a constellation itself, but an asterism, which is a distinctive group of stars. Another famous asterism is the Big Dipper in the constellation Ursa Major.

The most famous star in Ursa Minor is Polaris, the North Star. This is the star that is nearest to the North Celestial Pole. If you stood at the north pole, Polaris would be almost directly overhead. If you can spot Polaris in the sky, you can always tell which way is north. In addition, the angle of Polaris above the horizon tells you your latitude on the Earth. Because of this, Polaris was the most important star for navigating at sea.

To find Polaris, first find the Big Dipper. If you follow the two stars at the end of the cup upwards (out of the cup of the Big Dipper), the next bright star you will run into is Polaris. The distance to Polaris on the sky is about five times the angle between the two stars at the end of the cup of the Big Dipper. Because they are so useful for finding the all-important North Star, these two stars are known as the Pointer Stars. They are also called Dubhe and Merak (Merak is the one at the bottom of the cup).

Because the Earth's axis is precessing (like a spinning top wobbles around), Polaris is only temporarily at the North Pole. In about 14,000 years, Vega will be the North Star and another 14,000 years after that, it will be Polaris again. Precession is caused by the the gravitational attraction of the Sun and the Moon. It only happens because the Earth is not quite spherical.

See also Star Facts for June 1995

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