Definitions for "Libration"
A real or apparent libratory motion, like that of a balance before coming to rest.
(astronomy) a real or apparent slow oscillation of a moon or satellite; "the libration of the moon"
Libration is an oscillation in the apparent aspect of a secondary body (such as a planet or satellite) as seen from the primary object around which it revolves.
Keywords:  rocking, movement
a rocking movement
Keywords:  act
The act or state of librating.