What is nutation in astronomy?
Nutation in astronomy describes an oscillation in the precession of the equinoxes.
Nutation was discovered by James Bradley, an English astronomer, in 1748. In essence, nutation is an irregularity in the slow wobbling of the earth as it spins. Nutation causes an oscillation with a period of 18.6 years and an amplitude of 9.2 seconds of arc.
Nutation occurs because the plane of the orbit of the earth around the sun is tilted about 5˚ from the orbit of the moon around the earth. The moon's plane precesses around the earth's every 18.6 years, causing an irregularity.