libration
noun
[ lʌɪˈbreɪʃ(ə)n ]
• 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.
Origin:
early 17th century (denoting an oscillating motion, or equilibrium): from Latin libratio(n- ), from the verb librare, from libra ‘a balance’.
