 Nutation

Variation in the inclination of a rotating body's axis, distinguished from its azimuthal precession. For a heavy symmetric top, the cyclic angular momenta reduce the motion to ${\dot{\mu }}^2=F(\mu )$ with $\mu =\cos \theta$ and $F$ cubic. Its admissible interval and turning points describe the nutation.

Nutation is a term used in astronomy to describe a small oscillation or irregularity in an astronomical body's axis of rotation. Specifically, it refers to the periodic variations in the orientation of the Earth's rotation axis due to gravitational interactions, primarily with the Moon and the Sun. The primary effect of nutation is the change in the Earth's axial tilt and its position relative to distant stars.