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axis motion comparison table

Subject	has rate	has definition
nutation		A small, irregular oscillation in the precessional motion of Earth's rotational axis, caused primarily by lunar perturbations. It has a principal period of 18.6 years, and moves the equinox as much as 17" ahead of or behind its mean position.
polar motion		The irregularly varying motion of the Earth's pole of rotation with respect to the Earth's crust. (See celestial ephemeris pole.)
precession		The uniformly progressing motion of the pole of rotation of a freely rotating body undergoing torque from external gravitational forces. In the case of the Earth, the component of precession caused by the Sun and Moon acting on the Earth's equatorial bulge is called lunisolar precession; the component caused by the action of the planets is called planetary precession. The sum of lunisolar and planetary precession is called general precession. (See nutation.)

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