The Moon's centre of mass sits about two kilometres closer to us than its geometric centre, which is part of why it keeps the same face turned our way.

The near-side crust is thinner and the dense mare basalts are piled on that side, so the mass is not evenly spread. Earth's gravity gets a grip on that lopsidedness and holds it, the way a weighted ball always rolls heavy-side down. The offset was one of the first surprises from lunar orbiters in the 1960s.