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Encyclopedia > Libration
The animation shows a set of simulated views of the Moon over one month.

Although the Moon's rotation on its axis is synchronously locked with its revolution around Earth, these librations permit a terrestrial observer to see slightly differing halves of the Moon's surface at different times. This means that a total of 59% of the Moon's surface can be observed from Earth. Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ...

There are three types of libration. Libration in latitude is a consequence of the Moon's axis of rotation being slightly inclined to the normal to the plane of its orbit around Earth. Its origin is analogous to the way in which the seasons arise from Earth's revolution about the Sun. Libration in longitude is a consequence of the Moon's orbit around Earth being somewhat eccentric, so that the Moon's rotation sometimes leads and sometimes lags its orbital position. Finally, there is a small effect called diurnal libration. This is a consequence of Earth's rotation, which carries an observer first to one side and then to the other side of the straight line joining Earth's center to the Moon's center, allowing the observer to look first around one side of the Moon and then around the other. A surface normal, or just normal to a flat surface is a three-dimensional vector which is perpendicular to that surface. ... Two intersecting planes in three-dimensional space In mathematics, a plane is a two-dimensional manifold or surface that is perfectly flat. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... This article or section is in need of attention from an expert on the subject. ... In astrodynamics, under standard assumptions any orbit must be of conic section shape. ...

• J. D. Mulhollan, E. C. Silverberg (1972). "Measurement of Physical Librations Using Laser Retroreflectors". Earth, Moon, and Planets 4: 155-159.

Results from FactBites:

 WWU Planetarium - Lunar Libration (355 words) The lunar libration in latitude is due to the Moon's axis being slightly inclined relative to the Earth's axis. The diurnal (daily) libration of the Moon is due to the observer first viewing from the western edge of the Earth as the Moon is rising, and then later from up to four thousand miles away to the east as the Moon is setting. Libration of longitude is an effect of the Moon's varying rate of travel along its slightly elliptical orbit around the Earth.
 Libration - Wikipedia, the free encyclopedia (334 words) In astronomy a libration (from the Latin verb libro -are "to balance, to sway", cf. Libration in latitude is a consequence of the Moon's axis of rotation being slightly inclined to the normal to the plane of its orbit around Earth. Libration in longitude is a consequence of the Moon's orbit around Earth being somewhat eccentric, so that the Moon's rotation sometimes leads and sometimes lags its orbital position.
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