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Lunar Libration

Libration in latitude is due to the Moon's axis being slightly inclined relative to the Earth's. From our angle we can at one time peek over the north pole of the Moon and later in the lunar month we peek over the south pole. Over the four week cycle it gives the the effect of the Moon slowly "nodding its head yes."

Diurnal (daily) libration is due to the observer viewing from the western edge of the Earth as the Moon is rising and up to four thousand miles away to the east as the Moon is setting, due to the rotation of the Earth. The difference in perspective between the rising and setting of the Moon appears as a slight turning of the Moon first to west and then to east, as though "shaking its head no."
Lunar Libration,

Libation is the term for any change in the face as viewed from Earth. In this 'normal' description of the change in the Moon's face there is no description of what has been seen and photographed, that the face becomes cocked such that the chin is up where the left ear was, for instance, a 90 degree cocking during the night, or in the case of the photo on the Mar 29, 2005 Gentile monthly review, a 40 degree turn in just 3 hours.