As the position of the Earth's axis changes, it will point in slightly different directions and therefore at different stars. At the moment, it's northern end is ponting to within a degree of Polaris in Ursa Minor. In about 12,000 years from now, it will be pointing at a point some 12 degrees from Vega, the main star in the constellation of Lyra. The star Thuban (in Draco) was the star closest to the pole about 4500 years ago.

The precession of the Earth's axis is caused mainly by the gravitational pull of the Sun and Moon. There is a smaller component caused by the gravitational pull of the planets. The overall effect of precession is to move the axis of the Earth by just under 1 degree every 70 years or so. A star atlas needs to take account of this and needs regular updating if the positions of the stars and other objects are to be correct. A good star atlas such as Nortons will give the star positions for a particular time (referred to as the epoch). The current epoch for star catalogues is 2000 AD. Small corrections (given in tables supplied within these publications) need to be applied for dates other than the epoch date for precise work. For general work, they are accurate enough without alteration.



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