libration; oscillation of a celestial body
Technical term in astronomy for the apparent wobbling or oscillation of a celestial body, especially the Moon, as seen from another body.
Due to the Moon's libration, about 59% of its surface is visible from Earth.
Compound of 秤 (balance, scales) and 動 (motion), referring to the oscillatory motion resembling a balance. The term is a direct translation of the Western astronomical concept of libration.