Tidal locking (also called
gravitational locking or
captured rotation) occurs when the
gravitational gradient makes one hemisphere of a revolving
astronomical body constantly face the partner body. This effect is known as
synchronous rotation. A tidally locked body takes just as long to rotate around its own axis as it does to revolve around its partner. For example, the same side of the
Moon always faces the
Earth. Usually, only the
satellite is tidally locked to the larger body. However, if both the mass difference between the two bodies and the distance between them are relatively small, each may be tidally locked to the other; this is the case for
Pluto and
Charon. This effect is employed to
stabilize some artificial satellites.