libration
noun
li·bra·tion lī-ˈbrā-shən 
: an oscillation in the apparent aspect of a secondary body (such as a planet or a satellite) as seen from the primary object around which it revolves
librational
lī-ˈbrā-shnəl
adjective -shə-nᵊl
libratory
ˈlī-brə-ˌtȯr-ē
adjective 
Example Sentences
Recent Examples on the Web The discovery pivots on the detection of a curious libration—a wobble—in the rotation of Mimas. 
Jamie Carter, Forbes, 19 Jan. 2022
Jamie Carter, Forbes, 19 Jan. 2022 Word History
Etymology
Latin libration-, libratio, from librare to balance, from libra scales
First Known Use
1667, in the meaning defined above