- noun a real or apparent oscillation in the orbit of one astronomical object, especially as observed in the orbit of the Moon from earth
- Effect whereby more than half of the Moon’s surface can be seen from the Earth despite its captured rotation. The slight ‘nodding’ and ‘rocking’ effects are caused by the fact that the Moon’s orbit is slightly tilted to the ecliptic and is eccentric, so that the Earth and the Moon alter their relative positions with time. Libration in longitude allows us to see around the eastern and western limbs of the Moon and libration in latitude shows us the regions beyond the Moon’s north and south poles.
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