tidal locking

Tidal locking occurs when an astronomical body, like the Moon, rotates on its axis at the same rate that it orbits another body, such as Earth. This means that the same side of the locked body always faces the larger body. The gravitational forces between the two create a tidal effect, causing the rotational speed of the smaller body to gradually slow until it matches its orbital period. As a result, the Moon takes about 27.3 days to complete both one rotation and one orbit around Earth, making the same lunar hemisphere visible from our planet.