| Astrophysics (Index) | About |
Precession is a cyclical change in an astronomical body's rotation or orbit. The Earth's rotation precesses the direction that the poles point, aligning most closely with different stars as the precession progresses (the precession of the equinoxes, with a period of about 26000 years). In the case of planets or moons this type of precession is called axial precession.
Regarding an orbit's precession, an example of something other than axial precession, could be its apoapsis shifting to different directions over time. Other spinning objects besides astronomical bodies can precess, such as a spinning top's axis of rotation rotating so that its point at the top of the top moves in a circular path. Determining a planet's (axial) precession constant allows its moment of inertia to be calculated.