North Star is a readily visible star that appears to be located almost directly above the North Pole. The term polestar is sometimes used for North Star. The North Star is presently Polaris, the brightest star in the constellation Ursa Minor. Polaris is located within one degree of the place where the northern extension of the earth’s axis pierces the sky. Because of its position, Polaris appears stationary, while other stars seem to revolve around the earth’s axis as the earth rotates. As a result, Polaris has served as a guide for navigators through the centuries. Polaris is a star of the second magnitude. The brighter a star is, the lower is its magnitude (see Star (Brightness of stars) ).
Polaris will not always be the North Star because the earth’s axis will not always point toward Polaris. The earth’s rotational axis changes direction in a circular motion called precession. Each end of the axis traces out a fictitious circle in the sky. One complete trip around the circle takes about 26,000 years. Thus, the brighter stars on or near the precessional circle above the earth’s North Pole each become the North Star for a certain period. For example, in about 12,000 years, the earth’s axis will point north to a spot near Vega in the constellation Lyra. In about 22,000 years, Thuban in the constellation Draco will become the North Star. About 26,000 years from now, Polaris will return to its present location relative to the earth’s axis, and will be the North Star.
