libration
/laɪˈbreɪʃən/noun
- Astronomy an apparent or real oscillation of the moon, by which parts near the edge of the disc that are often not visible from the earth sometimes come into view【天文】天平动。
派生词
librate
verb词源
early 17th cent. （denoting an oscillating motion， or equilibrium）： from Latin libratio（n-）， from the verb librare, from libra 'a balance'.