libration noun. [lʌɪ'breɪʃ(ǝ)n] E17.
[Latin libratio(n-), formed as LIBRATE verb: see -ATION.]
1. The action of librating; (a) motion like that of the beam of a balance oscillating upon its pivot; the state of being balanced or in equilibrium. E17.

2. Astronomy. A real or apparent oscillating motion; spec. an irregularity of the moon's motion which makes it possible to see more than about 59 per cent of its surface from the earth. M17.

3. The action of weighing. M17-L18.

■ librational adjective of or pertaining to (the moon's) libration L19.

[TahlilGaran] English Dictionary ▲