libration


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libration

(lÿ-bray -shŏn) The means by which 59% of the Moon's surface is made visible, over a 30-year period, to the terrestrial observer despite the lunar day being of the same length as the sidereal month (see synchronous rotation). Physical libration is a real irregularity in the Moon's rotation, arising from minor distortions in shape. Geometrical librations, including diurnal librations, are apparent oscillations due to the Moon being observed from slightly different directions at different times. A geometrical libration in longitude of 6°9′ (mean value) results from the inconstancy of the Moon's orbital velocity, which follows from the eccentricity of the Moon's orbit and Kepler's second law. This libration reveals part of the eastern or western farside limbs at different times during one month. In addition the 5°9′ inclination of the Moon's orbital plane to the ecliptic, plus the 1°32′ tilt of the Moon's equator to its orbital plane, produces a monthly geometrical libration in latitude of 6°41′. This makes the Moon's north and south polar regions more readily observable during one month.

libration

[lī′brā·shən]
(physics)
Any oscillatory rotational motion, such as that of the moon, or of a molecule in a solid which does not have enough energy to make full rotations.
References in periodicals archive ?
Il a en outre salu les sacrifices consentis par les "enfants de l'Arme nationale populaire (ANP), hriti?re de l'Arme de libration nationale (ALN), et des diffrents corps de scurit.
Libration point orbit spacecraft relative motion diagram is shown in Figure 2.
In order to illustrate the effectiveness of the method introduced in this paper, we design a constellation around the Earth-Moon L1 libration point which includes four Lagrangian satellites.
The two movements in a joint statement issued after the meeting of the delegation of the Libration and Justice chaired by Dr.
Antoniadi mentions and illustrates the idea of libration zones in his classic work, The Planet Mercury, (2) showing that the considerable orbital eccentricity of Mercury would lead to a total libration in longitude of some 47[degrees].
Asif Ali Zardari said that libration from Indian occupation and exploitation is a basic and democratic right of Kashmiri people.
Caption: Yellow dots indicate which part of the Moon's limb is tipped the most toward Earth by libration.
L'anniversaire du dclenchement de la rvolution du 1 e novembre 1954 ne peut pas se f?ter sans voquer l'quipe de football du front de libration nationale (FLN).
conducted an experimental study to investigate the effect of gravity for the libration of tethered satellite system by delayed feedback control [6].
They survey thousands of trajectories for transferring spacecraft between the Earth and various locations near the Moon, including lunar libration orbits, low-lunar orbits, and the lunar surface.
Development and libration parliamentary bloc member Yassin Jaber praised the army's step to enhance its presence in the South because "building on security factor reflects positively on stability, economy and civil peace." MP Jaber remarks came in a statement issued on Thursday in which he congratulated army on the occasion of its 65th anniversary.
The Plato 'hook', as it is often described, (2) is not readily observed, since its appearance is critically dependent upon a particular combination of selenographic colongitude, libration and topography.