LIBRATIONS
Noun
librations
plural of libration
Anagrams
• Bristolian
Source: Wiktionary
LIBRATION
Li*bra"tion, n. Etym: [L. libratio: cf. F. libration.]
1. The act or state of librating. Jer. Taylor.
2. (Astron.)
Definition: 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.
Source: Webster’s Unabridged Dictionary 1913 Edition