An
animation of the
phases of the Moon. As the Moon revolves around the
Earth, the
Sun lights the Moon from a different side, creating the different phases. In the image, the Moon appears to get bigger as well as "
wobble" slightly.
Tidal locking synchronizes the Moon's
rotation period on its axis to match its
orbital period around the earth. These two periods nearly cancel each other out, except that the Moon's orbit is
elliptical. This causes its orbital motion to speed up when
closer to the Earth, and slow down when farther away, causing the Moon's
apparent diameter to change, as well as the wobbling motion observed.
Image: Tom Ruen
