Tidal locking arises when tidal torques drive a body's spin toward an orbital resonance. In the circular synchronous case, its rotation period equals the orbital period, so the same hemisphere continually faces its companion.
Synchronous rotation has spin period equal to orbital period. A synchronously rotating exoplanet on a circular orbit has a persistent illuminated hemisphere and a persistent dark hemisphere, making day-night heat redistribution crucial.
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Tidal locking is a phenomenon that occurs when an astronomical body, such as a moon or a planet, rotates on its axis in such a way that the same side always faces the body it is orbiting. This happens due to gravitational interactions between the two bodies, which create tidal forces that distort their shapes. In the case of a tidally locked moon, its orbital period around the planet matches its rotation period.