Precession of the Equinoxes
The slow continuous conical rotation of Earth's rotational axis in space, taking ~25,800 years to complete one full cycle.
Governing formula
Precession Period T ≈ 25,772 years (Axial Wobble Rate ~ 50.3″/year)
SI unit
Years per Cycle (~25,800 years)
In depth
Caused by gravitational differential tidal torques exerted by the Sun and Moon on Earth's oblate equatorial bulge. Slowly changes North Pole star alignment and equinox dates along the ecliptic.
Examples in the real world
Polaris acting as Earth's North Star today, whereas Vega served as North Star 12,000 years ago.