The side closest to the moon.
The same side of the Moon always faces Earth. The “dark side” isn’t really dark, it has day and night cycles, just like most places on Earth; the “far side” is a more accurate term. The reason one side is never visible from Earth is because it spins once on its axis in exactly the same amount of time it takes to spin around Earth. If their speed of rotation were slightly different from their speed of revolution, those on Earth would eventually be exposed to the entire surface of the moon. However, these two intervals have been the same throughout recorded history and probably have been for millions of years or more.
Through their mutual gravitational attraction, the Earth and the Moon create tidal bulges with each other.
This strange phenomenon can be explained in terms of a subtle effect generated by gravitation and friction called tidal lock. Through their mutual gravitational attraction, the Earth and the Moon create tidal bulges on top of each other, with one bulge facing toward the other body and the other facing away from it. These bulges generate heat through the friction of the rock against itself and also become a greater orbital force for the Moon, meaning that it continually moves away from Earth. Over time, they absorb energy from the rotational moment of both bodies, producing a braking effect.
The so-called dark side of the moon actually receives frequent sunlight.
As the mass of the Earth dominates the Earth-Moon system, the Moon experiences the greatest braking effect. Over time, its rotation progressively slowed until the rate of rotation matched the rate at which the tidal bulge moves around the body. Today, the lunar tidal bulges are in a constant position with respect to the Moon’s rotation, meaning a kind of balance has been achieved.
The rotation taxa of Terra also decreased as the tempo due to the forces of the seas, but the braking effect is much less – to be perfectly synchronized with Lua, Terra would need to rotate only once per lunar cycle, or approximately every 29 ,5 days . So the Moon would always be in the same place in the sky and visible from only one side of the Earth, but this is not the case. In certain planetary systems, such as the dwarf planet Pluto and its satellite Charon, the two bodies are joined.