from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. A very slow oscillation, real or apparent, of a satellite as viewed from the larger celestial body around which it revolves.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The act of librating.
  • n. The apparent wobble or variation in the visible side of the Moon that permanently faces the Earth, allowing observers on Earth to see, over a period of time, slightly more than half of the lunar surface.
  • n. A similar rotational or orbital characteristic of some other celestial body.

from the GNU version of the Collaborative International Dictionary of English

  • n. The act or state of librating.
  • n. A real or apparent libratory motion, like that of a balance before coming to rest.

from The Century Dictionary and Cyclopedia

  • n. The act of librating or balancing, or the state of being balanced; a state of equipoise; balance.
  • n. In astronomy, a real or apparent libratory or oscillating motion, like that of a balance before coming to rest.
  • n. libration in latitude, in consequenoe of her axis being inclined to the plane of her orbit, so that sometimes one of her poles and sometimes the other declines, as it were, or dips toward the earth
  • n. diurnal libration, which is simply a consequence of the lunar parallax. In the last case, an observer at the surface of the earth perceives points near the upper edge of the moon's disk, at the time of her rising, which disappear as her elevation is increased; while new ones on the opposite or lower edge, that were before invisible, come into view as she descends toward the horizon. If the observer were placed at the earth's center he would perceive no diurnal libration.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. (astronomy) a real or apparent slow oscillation of a moon or satellite


from The American Heritage® Dictionary of the English Language, 4th Edition

Latin lībrātio, lībrātiōn-, oscillation, from lībrātus, past participle of lībrāre, to balance, from lībra, balance.

from Wiktionary, Creative Commons Attribution/Share-Alike License

From Latin lībrātiō ("a hurling, swinging"), from lībrō ("poise, cause to swing").


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  • The moon really undergoes considerable libration, recalling the libration of

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  • This produces the phenomenon that is called libration, the result of which is that, along the border between the day and night hemispheres there is a narrow strip where the sun rises and sets once in each of her years, which are about two hundred and twenty-five of our days in length.

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  • Due to a slight "wobble" in the lunar motion called libration,

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  • But it would not rise or set: it would be fixed in the sky, and subject only to a minute oscillation to and fro once a month, by reason of the "libration" we have been speaking of.

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  • As the moon, except for the slight movement termed its "libration," always turns the same face to us, so that we see in all only about four sevenths of its surface, it has naturally been conjectured that the unseen side, which is probably some miles lower than that turned toward us, might have a different character from that which we behold.

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  • Now this increased action of the system, during the hot fit, by exhausting the sensorial powers of irritation and association, contributes to induce a renewal of the cold paroxysm; as the accumulation of those sensorial powers in the cold fit produces the increased actions of the hot fit; which two states of the system reciprocally induce each other by a kind of libration, or a plus and minus, of the sensorial powers of irritation and association.

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  • Yes, we don't like what we hear about the black libration theology.

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  • Democracy, libration, human rights, free speach, etc are code words used to sell wars! to uninformed or missinformed, or the do not want to be informed masses. lear k

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  • The Japanese Hiten space probe, which passed through the libration points to detect trapped dust particles, did not find an obvious increase in dust levels above the density in surrounding space.

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  • "in astronomy, is an apparent irregularity of the moon's motion, whereby she seems to librate about her axis, sometimes from the east to the west, and now and then from the west to the east; so that the parts in the western limb or margin of the moon sometimes recede from the centre of the disc, and sometimes move towards it, by which means they become alternately visible and invisible to the inhabitants of the earth. This libration is owing to her equable rotation round her own axis, once in a month, in conjunction with her unequal motion in the perimeter of her orbit round the earth."

    Falconer's New Universal Dictionary of the Marine (1816), 222

    October 12, 2008