precession of the equinoxes, motion of the equinoxes along the ecliptic (the plane of Earth’s orbit) caused by the cyclic precession of Earth’s axis of rotation.

In compiling his famous star catalog (completed in 129 bce), the Greek astronomer Hipparchus noticed that the positions of the stars were shifted in a systematic way from earlier Babylonian (Chaldean) measures. This indicated that it was not the stars that were moving but rather the observing platform—Earth. Such a motion is called precession and consists of a cyclic wobbling in the orientation of Earth’s axis of rotation with a period of 25,772 years. Precession was the third-discovered motion of Earth, after the far more obvious daily rotation and annual revolution. Precession is caused by the gravitational influence of the Sun and the Moon acting on Earth’s equatorial bulge. To a much lesser extent, the planets exert influence as well.


[link to www.britannica.com]


So, Britannica says it's 25,772 years...

Now what?