Adjacent Words

Libration definitions

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Webster's 1828 Dictionary

LIBRA'TION, n.
1. The act of balancing or state of being balanced; a state of equipoise, with equal weights on both sides of a center.
2. In astronomy, an apparent irregularity of the moon's motions, by which it seems to librate about its axis.
Libration is the balancing motion or trepidation in the firmament, whereby the declination of the sun and the latitude of the stars change from time to time.
3. A balancing or equipoise between extremes.

WordNet (r) 3.0 (2005)

n
1: (astronomy) a real or apparent slow oscillation of a moon or satellite; "the libration of the moon"

Merriam Webster's

noun Etymology: Latin libration-, libratio, from librare to balance, from libra scales Date: 1667 an oscillation in the apparent aspect of a secondary body (as a planet or a satellite) as seen from the primary object around which it revolves • librational adjective • libratory adjective

Oxford Reference Dictionary

n. an apparent oscillation of a heavenly body, esp. the moon, by which the parts near the edge of the disc are alternately in view and out of view. Etymology: L libratio f. librare f. libra balance

Webster's 1913 Dictionary

Libration Li*bra"tion (l[-i]*br[=a]"sh[u^]n), n. [L. libratio: cf. F. libration.] 1. The act or state of librating. --Jer. Taylor. 2. (Astron.) A real or apparent libratory motion, like that of a balance before coming to rest. Libration of the moon, any one of those small periodical changes in the position of the moon's surface relatively to the earth, in consequence of which narrow portions at opposite limbs become visible or invisible alternately. It receives different names according to the manner in which it takes place; as: (a) Libration in longitude, that which, depending on the place of the moon in its elliptic orbit, causes small portions near the eastern and western borders alternately to appear and disappear each month. (b) Libration in latitude, that which depends on the varying position of the moon's axis in respect to the spectator, causing the alternate appearance and disappearance of either pole. (c) Diurnal or parallactic libration, that which brings into view on the upper limb, at rising and setting, some parts not in the average visible hemisphere.