( astronomy) a real or apparent slow oscillation of a moon or satellite; " the libration of the moon"

The act or state of librating.

A real or apparent libratory motion, like that of a balance before coming to rest.

Balancing: a state of equipoise: a slight swinging motion.

The act of balancing; state of being balanced or in equipoise; vibratory motion, as of a balance before it comes to rest.

The act of balancing or state of being balanced, as a balance before coming to rest; in astron., the balancing motion or trepidation in the firmament whereby the declination of the sun and the latitude of the stars change from time to time; an apparent irregularity in the moon's motion.

First comes a research into the libration of the moon. – Pioneers of Science by Oliver Lodge

One- seventh of it is seen in those movements of libration Barbicane spoke of. – The Moon-Voyage by Jules Verne

And lunar- like in their libration are some of his melodies- glimpses, mysterious and vast, as of a strange world. – Chopin: The Man and His Music by James Huneker

Or suppose the orbit were so nearly circular that there were no perceptible libration at all; one side would burn eternally, and the other side would freeze, since there would be no seasonal winds blowing first east, then west, bringing the warmth of the Blue Sun from the other side. – The Asses of Balaam by Gordon Randall Garrett

Discovered the moon's libration. – Pioneers of Science by Oliver Lodge

Libration of the Earth's satellite - p. – COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 by Alexander von Humboldt

This turning is called a libration, and it should be borne in mind that the moon librates not only in the direction above measured, north and south, but also at right angles to this, east and west, so that we are able to see a little farther around every part of the moon's edge than would be possible if it turned toward us at all times exactly the same face. – A Text-Book of Astronomy by George C. Comstock

Inequalities, occasioned by sight variations in the revolution, give rise to fluctuations of from 6 degrees to 8 degrees, or to an apparent libration in longitude as well as in latitude. – COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 by Alexander von Humboldt

And in her walk there is also a serpentine elegance, a sinuous charm: the shoulders do not swing; the cambered torso seems immobile;- but alternately from waist to heel, and from heel to waist, with each long full stride, an indescribable undulation seems to pass; while the folds of her loose robe oscillate to right and left behind her, in perfect libration, with the free swaying of the hips. – Two Years in the French West Indies by Lafcadio Hearn

He also executed a chart of the Moon's surface, wrote a description of the lunar spots, and discovered the Libration of the Moon in Longitude. – The Astronomy of Milton's 'Paradise Lost' by Thomas Orchard

One more astronomical discovery also he was to make- that of the moon's libration. – Pioneers of Science by Oliver Lodge