Far side of the Moon

The lunar hemisphere that permanently faces away from Earth because the Moon rotates once per orbit. It is distinct from the permanently dark side: sunlight reaches it during its lunar day.

Synchronous rotation: Rotation in which a body's spin period matches its orbital period around another body. The Moon's synchronous rotation keeps the same hemisphere facing Earth.
Luna 3: The Soviet spacecraft that returned the first photographs of the Moon's far side in 1959. Its images first showed what the hidden hemisphere looked like.
Radio astronomy: The study of celestial objects by detecting radio waves they emit or reflect. The far side can shield instruments from many Earth-generated radio signals.
Dark side of the Moon: An informal phrase often used for the lunar hemisphere facing away from Earth, though that hemisphere receives sunlight. The phrase misleadingly conflates the far side with permanent darkness.
Tidal locking: A state in which tidal forces synchronize a body's rotation with its orbit. Lunar tidal locking is the physical reason the far side continually faces away.
Chang'e 4: The Chinese lunar mission that made the first soft landing on the Moon's far side in 2019. Its landing demonstrated direct exploration of the hemisphere beyond Earth's line of sight.
Dark Ages Radio Explorer: A proposed lunar-orbiting mission designed to observe low-frequency radio signals from the early universe. Its planned observations use the Moon to reduce terrestrial radio interference.
Lunar terminator: The boundary between the sunlit and unlit halves of the Moon. The terminator moves across both hemispheres, showing that the far side has day and night.
Lunar libration: The apparent rocking of the Moon that reveals small portions beyond its usual visible hemisphere. Libration lets observers glimpse a little more than half of the Moon over time.
Von Kármán crater: A large impact crater in the Moon's South Pole–Aitken basin. Chang'e 4 landed on its floor to study far-side geology.

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