Precession

Precession is a change in the orientation of the rotationalaxis of a rotatingbody. If the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the secondaxis. In an appropriate referenceframe it can be defined as a change in the first Eulerangle, whereas the third Eulerangle defines the rotation itself. A motion in which the second Eulerangle changes is called nutation. In physics, there are two types of precession: torque-free and torque-induced.

In astronomy, precession refers to any of several slow changes in an astronomicalbody's rotational or orbital parameters. An important example is the steady change in the orientation of the axis of rotationof the Earth, known as the precessionof the equinoxes.