This animation shows the geocentric phase, libration, position angle of the axis, and apparent diameter of the Moon throughout the year 2012, at hourly intervals. Until the end of 2012, the initial Dial-A-Moon image will be the frame from this animation for the current hour. The jagged, cratered, airless lunar terrain casts sharp shadows that clearly outline the Moon’s surface features for observers on Earth.
This is especially true near the terminator, the line between day and night, where surface features appear in high relief. Elevation measurements by the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) make it possible to simulate shadows on the Moon’s surface with unprecedented accuracy and detail.
The Moon always keeps the same face to us, but not exactly the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 12 seconds, as it is in this animation, our changing view of the Moon makes it look like it’s wobbling. This wobble is called libration.