relative to the stars also varies with different periods, and these motions--caused by the tidal forces of the Moon and Sun--are also called nutations, except for the slowest, which are precessions of the equinoxes.

Predictions

The existence of Earth's free nutation was predicted by Isaac Newton in Corollaries 20 to 22 of Proposition 66, Book 1 of the Philosophiæ Naturalis Principia Mathematica,

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