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rotation comparison table

Subject	has period	has definition
differential rotation		As an object rotates, different parts of it may move at different rates. The Galaxy rotates differentially.
libration		Variations in the orientation of the Moon's surface with respect to an observer on the Earth. Physical librations are due to variations in the rate at which the Moon rotates on its axis. The much larger optical librations are due to variations in the rate of the Moon's orbital motion, the obliquity of the Moon's equator to its orbital plane, and the diurnal changes of geometric perspective of an observer on the Earth's surface.
synchronous rotation	equal to orbital period	Rotation whose period is equal to the orbital period.

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