The Precession of the Earth's Axis

  • The Earth's axis rotates (precesses) just as a spinning top does. The period of precession is about 26,000 years.

  • Therefore, the North Celestial Pole will not always be point towards the same starfield.

  • Precession is caused by the gravitational pull of the Sun and the Moon on the Earth.

  • Hipparchus first estimated the precession of the Earth's axis around 130 B.C. The period of precession is about 26,000 years.

    While the Pole Star in the northern hemisphere is now Polaris, in 3000 B.C., the north celestial pole coincided with Thuban, a star in the constellation of Draco. In 14,000 A.D. Vega, in Lyra, will be the northern pole star.


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