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lunar libration[′lü·nər lī′brā·shən]
The effect wherein the face of the moon appears to swing east and west about 8° from its central position each month. Also known as apparent libration in longitude.
The state wherein the inclination of the moon's polar axis allows an observer on earth to see about 59% of the moon's surface. Also known as libration in latitude.
The small oscillation with which the moon rocks back and forth about its mean rotation rate. Also known as physical libration of the moon.