Moon

The Moon is the only natural satellite orbiting Earth. It orbits around Earth at an average distance of 384,399 kilometres (238,854 mi), a distance roughly 30 times the width of Earth, and completes an orbit in relation to Earth and the Sun (synodically) every 29.5 days. The Moon and Earth gravitationally pull on each other. The resulting tidal forces are the main drivers of Earth's tides, and have forced the Moon to face Earth with always the same near side, effectively synchronizing the Moon's rotation period to its orbital period. This makes the Moon tidally locked to Earth. Read more on Wikipedia