libration

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.

(dynamics) The oscillation of an angle about a stable equilibrium point.

(chemistry) A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.