Libration of the moon
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. [1913 Webster]

2. (Astron.) A real or apparent libratory motion, like that of a balance before coming to rest. [1913 Webster]

{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. [1913 Webster]


The Collaborative International Dictionary of English. 2000.

Look at other dictionaries:

  • libration of the moon — the combination of four libration effects that causes parts of the side of the moon turned to the earth to be alternately visible and invisible so that as much as 59 percent of the moon s entire surface can be observed from the earth * * *… …   Useful english dictionary

  • parallactic libration of the moon — diurnal libration of the moon caused by the observer s view over the upper limb of the moon when it is rising and setting …   Useful english dictionary

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  • 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. [1913 Webster] 2. (Astron.) A real or apparent libratory motion, like that of a balance before coming to rest. [1913 Webster]… …   The Collaborative International Dictionary of English

  • libration — [ librasjɔ̃ ] n. f. • 1547; lat. libratio ♦ Astron. Balancement apparent (d un astre, et spécialement de la Lune). « un capteur optique de la position angulaire du Soleil pour étudier la libration de Phobos » (Sciences et Avenir, 1988). ●… …   Encyclopédie Universelle

  • Libration — This article is about astronomical observations. For molecular motion, see Libration (molecule). Not to be confused with Liberation, Libation, or Vibration. Simulated views of the Moon over one month, demo …   Wikipedia

  • Moon — This article is about Earth s Moon. For moons in general, see Natural satellite. For other uses, see Moon (disambiguation) …   Wikipedia

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