precession

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precession

Phenomenon associated with the action of a gyroscope or a spinning top and consisting of a comparatively slow rotation of the axis of rotation of a spinning body about a line intersecting the spin axis. It arises as a result of external torque acting on the body. One example of precession is the smooth, slow circling of a spinning top (the uneven wobbling is called nutation). Precession of the Earth's axis of rotation is the reason that the positions of celestial bodies appear to drift systematically with the passage of time. See also precession of the equinoxes.

This entry comes from Encyclopædia Britannica Concise.
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