libration
Pronunciation:
/laɪˈbɹeɪ.ʃən//laɪˈbɹeɪ.ʃən/noun
Definitions
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.
(by extension) A similar rotational or orbital characteristic of some other celestial body.
A vibrational degree of freedom whereby a group of atoms partly rotates back and forth, similar to the Moon's motion.