Precession of the equinoxes
The precession of the equinoxes describes an astronomical phenomenon whereby the earth appears to wobble on its axis relative to the stars. This wobble is very slow, taking about 26,000 years to complete.[1] The result of this is that the position of stars and constellations overhead at any particular time gradually changes over the years. For example, the constellation that rises above the horizon at the spring equinox gradually cycles through the signs of the zodiac backwards. The star around which all the other stars seem to revolve (to an observer on Earth) also changes over time, meaning that Polaris, or the present North Star, has not always been the star closest to north, and will be replaced by other stars in the future. The Earth's axis pointed to the star Thuban in the year 3000 B.C., and it will point to the bright star Vega in the year A.D. 14,000. [2]
List of selected North Stars[3]
| Approximate year | Common name | Astronomical name |
|---|---|---|
| 3000 BC | Thuban | Alpha Draconis |
| 1000 BC | Kochab | Beta Ursa Minoris |
| 2000 AD | Polaris | Alpha Ursa Minoris |
| 4000 AD | Alrai | Gamma Cephei |
| 7500 AD | Alderamin | Alpha Cephei |
| 14000 AD | Vega | Alpha Lyrae |