An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Mechanics: A wobbling motion of a spinning → rigid body, such as a top, as it → precesses about its vertical axis.
2) Astro.: A slight nodding motion of the Earth's axis of rotation, which has a principal period of 18.6 years. It is primarily caused by lunar → perturbations, and is superimposed on the → precession of the equinoxes and moves the equinox as much as 17'' ahead of or behind its mean position.

Fromm L. nutation-, from nutat(us), p.p. of nutare "to wobble, to sway, to nod repeatedly," from nu "nod" + -ta frequentative suffix + -tus p.p. ending + -ion a suffix denoting action or condition.

Kaltâv, from Kermâni keletow, Malâyeri kallatow "wobbling," from kal, kalleh "head" + tâv, tow, tâb "swing, twist," from tâbidan "to twist, to spin."

Same as → equation of the equinoxes.

→ nutation; → right ascension.