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You have probably heard
Polaris called the North Star. Why is this so? Well, the axis of rotation of
the Earth points to the north celestial pole (NCP) and polaris is less than a degree away
from the NCP. Thus if you find Polaris in the night sky you will have also
discovered which direction is north in the process.
This situation arises due to the fact that the Earth is not a perfect sphere. In fact the Earth is ellipsoidal in shape. The equatorial diameter of the Earth is 43 kilometers larger than the diameter measured pole to pole. This is frequently called the Earth's equatorial bulge. |
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However Polaris has not always been the north star. In fact in 2000 B.C.
the star Thuban in the constellation of Draco was the north star, and in 14,000AD the star
Vega in Lyra will be the north star.