Libration of the moon

Also found in: Encyclopedia, Wikipedia.
Related to Libration of the moon: Libration in latitude, Lunar libration
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.

See also: Libration

References in periodicals archive ?
Joseph Louis Lagrange died; an Italian-French astronomer and mathematician; made investigations into the libration of the Moon, the planetary theory, and the theory of Jupiter's satellites.
Arthur Ernest Hodgson died; worked at the Natal Observatory; in 1908 he took a series of lunar photographs for a determination of the physical libration of the moon.
Both are important figures in the history of selenography, the former in connection with positional studies and lunar nomenclature, the latter with the figure and libration of the Moon.