- The act of librating.
- (astronomy) The apparent wobble or variation in the visible side of the Moon that permanently faces the Earth, allowing observers on Earth to see, over a period of time, slightly more than half of the lunar surface.
- (by extension) A similar rotational or orbital characteristic of some other celestial body.
- (chemistry) A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.
act of libration
astronomy: apparent wobble of the moon