Precession of the Equinoxes -- from Eric Weisstein's World of Physics

Equinoctial precession is a circular motion of Earth's

rotational axis with respect to the "fixed" stars, also known as lunisolar precession. It is caused by the torque of the Sun

and Moon

on the Earth's rotational bulge. The axis precesses with a period of approximately 25,770 y (Beatty et al. 1990). This corresponds to

or, equivalently,

in Epoch 2000, where years are measured in mean Julian years

(Astronomical Almanac, pp. B19 and K6; Lang 1992, p. 12). Lang (1992, p. 48) gives a table containing precessional values for all the planets, but the values for the Earth appear to be incorrect. The following table gives the components of precession for Epoch 1994.5 from the Astronomical Almanac (pp. B19), where

Beatty, J. K.; Petersen, C. C.; and Chaikin, A. (Eds.). The New Solar System, 4th ed. Cambridge, England: Cambridge University Press, p. 105, 1990.

Duffett-Smith, P. "Precession." §34 in Practical Astronomy with Your Calculator, 3rd ed. Cambridge, England: Cambridge University Press, pp. 56-59, 1992.

Lang, K. R. Astrophysical Data: Planets and Stars. New York: Springer-Verlag, 1992.

Montenbruck, O. and Pfleger, T. "Precession." §2.4 in Astronomy on the Personal Computer, 4th ed. Berlin: Springer-Verlag, pp. 20-25, 2000.

United States Government Printing Office. Astronomical Almanac for the Year 1997. Washington, DC: U. S. Government Printing Office, p. B18-B19, 1997.