Precession

Precession is the slow, long-term change in the orientation of the Earth’s rotation axis caused primarily by gravitational torques exerted by the Moon and the Sun on the Earth’s equatorial bulge. This motion results in a gradual shift of the celestial poles and the equinoxes over a period of approximately 26,000 years.

In geodesy, precession is a fundamental component of Earth orientation modeling and is essential for the precise transformation between terrestrial and celestial reference frames. Accurate precession models are required in space-geodetic techniques such as VLBI and GNSS to ensure consistent Earth rotation parameters, satellite orbit determination, and high-precision positioning.