libration

Plural: librations

Noun

• (astronomy) a real or apparent slow oscillation of a moon or satellite
  • "the libration of the moon"
• The act of librating.
• 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.
• A similar rotational or orbital characteristic of some other celestial body.
• The oscillation of an angle about a stable equilibrium point.
• A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.

Related Words

librate, libratory, nutation