Precession

Precession is a motion phenomena which is caused by the gravitational pull of the Moon and the Sun on the Earth's equatorial bulge. The Earth's precession can be seen as its axis of rotation traces out a circle in the sky.

As the Earth precesses, the north celestial pole slowly traces out a circle among the northern constellations. At present, the north celestial pole is near the moderately bright star, Polaris, which serves as the North Star.