libration

1. (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.countableuncountable

2. (by extension) A similar rotational or orbital characteristic of some other celestial body.broadlycountableuncountable

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

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