How Earth’s pull slowed the Moon’s spin
The Moon did not always keep the same side facing Earth. Early on, it spun faster. Earth’s gravity pulled more strongly on the side of the Moon that was closer, stretching the young Moon slightly and creating a tidal bulge. As the Moon rotated, that bulge was repeatedly pulled out of alignment with the direction to Earth.
The Moon is not perfectly rigid, so its interior flexed as the bulge shifted. That flexing generated friction, which turned some of the Moon’s rotational energy into heat. Earth’s pull on the misaligned bulge then acted like a brake, slowing the spin over a long period.
A spin matched to an orbit
Eventually, the Moon settled into a stable rhythm: it rotates once on its axis in the same time it takes to travel once around Earth. This state is called synchronous rotation. Because the rotation and orbit keep pace, the same hemisphere remains turned toward us as the Moon circles Earth.
The Moon still rotates; it is not holding one side motionless in space. If it stopped spinning while orbiting, we would see different parts of its surface over the course of a month. Its matched spin is what keeps its near side facing Earth.
The far side still has days and nights
“Far side” means the hemisphere that generally faces away from Earth, not a region that never receives sunlight. As the Moon orbits, sunlight falls on different portions of its surface, creating lunar days and nights on both hemispheres. We rarely see the far side from Earth because the Moon’s synchronous rotation keeps it turned away—not because it is permanently dark.
