Gravity isn’t uniform. Denser planets and objects in space — that is, things with more mass to them — experience a stronger pull of gravity. But even if you zoom in to the level of a single planet (or, in this case, our Moon), gravity isn’t uniform all the way around. That’s because the mass of the Moon isn’t uniform, either. It varies, along with the topography. In some places, the Moon’s crust is thicker. Those places have more mass, and thus, more gravitational pull.
via Boing Boing
February 19, 2013