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. 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.

List of selected North Stars

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
10,000 AD	Deneb	Alpha Cygni
14000 AD	Vega	Alpha Lyrae

List of selected South Stars

Approximate year	Common name	Astronomical name
4000 BC	Achernar	Alpha Eridani
2000 AD	n/a	Sigma Octans
4200 AD	n/a	Gamma Chameleon
5800 AD	n/a	Omega Carinae
8100 AD	Aspidiske	Iota Carinae
9200 AD	n/a	Delta Velae
14000 AD	Canopus	Alpha Carinae
22000 AD	Achernar	Alpha Eridani