The Moon has two distinct sides and one is always facing Earth. Why?
One reason is that the moon
exhibits very slight oblateness with the fact that the “side” of the
moon that faces Earth is bit larger than the side turned away from us.
This is enough to cause this side to have greater mass, hence greater
gravitational pull
towards Earth.
Another factor to consider is the fact that
when
a Mars-sized object, dubbed Theia, smashed into Earth over four billion
years ago, it sent massive amounts of debris into space from both
Theia's and the Earth's crust and mantle which had to have different
densities. As the moon coalesced, the side facing the Earth received
heat from our planet that was still radiating energy resulting from the
collision and from the Earth's now exposed molten innards. This kept the
near side of the moon from cooling as fast as the far side, thus
resulting in the crust of the near side being thinner than the far
side's. Then when large meteors impacted the moon on the near side,
large lava flows occurred (which are not found on the far side). Crust
is lighter than mantle or core material.
In
short, the near side of the moon is larger and is denser than the far
side. Hence it has the greater gravitational pull than the far side
does.