LIBRATION • DICCIONARIO INGLES.COM • Definition of Libration

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noun

Libration n.

The act or state of librating.

(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.

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Etymology of 'Libration'

Collaborative International Dictionary of English 0.48

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"Libration" Quotes from Famous Books

... in the same direction, which is not strictly true, of course; but the reasons of the varying appearance are as clearly shown as if it were absolutely exact. The same may be said in regard to the phenomena of libration; the inclination of the moon's axis to the plane of her orbit is really small, but is purposely exaggerated in this apparatus in order to make the results apparent; in the position represented, it is quite ...

— Scientific American Supplement, No. 447, July 26, 1884 • Various

... World rotated more rapidly about its axis, thereby exposing the whole surface periodically to the deadly radiation of the Blue Sun, instead of having a rotation period that, combined with the eccentricity of the World's orbit, gave it just enough libration to expose only sixty-three per cent to the rays, leaving the remaining thirty-seven per cent in twilight or darkness. Or suppose the orbit were so nearly circular that there were no perceptible libration at all; one side would burn eternally, and the other side ...

— The Asses of Balaam • Gordon Randall Garrett

Words linked to "Libration" : variation, librate, uranology, astronomy, oscillation