What is tidal locking?

Tidal locking occurs when an astronomical body (like a moon or a planet) always shows the same face to the object it is orbiting. This effect is the result of gravitational forces causing the rotating body's rotational period to match its orbital period. Neil deGrasse Tyson explains that the Earth's tidal forces have slowed down the Moon's rotation until it became tidally locked, always showing one face to Earth 1 2.

David Kipping highlights that tidal locking is common for moons and also possibly for close-in exoplanets. Such bodies are gravitationally influenced to maintain a stable orientation, often described with fluid dynamics influencing this process 3 4. Additionally, Neil deGrasse Tyson notes that Earth's rotation is gradually slowing due to tidal friction, which also causes the Moon to slowly spiral away from Earth 1.

This leads to a fascinating dynamic where, eventually, Earth and the Moon could enter a "double tidal lock," where one face of the Earth also continuously faces the Moon, akin to a cosmic dance of equilibrium 4.