Physics

You have only ever seen one side of the Moon

You see one face because the Moon turns exactly once every time it circles us: 27.3 days for both. Earth's gravity stretched the young Moon slightly, then dragged on that stretch, braking its spin until the two clocks matched. It still rotates. It just never gets ahead of its own orbit.

Sources & further reading

NASA ScienceTidal LockingNASA's plain-language explainer of the locked state and how Earth's pull braked the Moon's spin into it.NASA Scientific Visualization StudioThe Moon's RotationConfirms the Moon's turn takes the same time as its orbit, and visualises it.NASA ScienceMoon FormationThe giant-impact origin: a Mars-sized body struck the young Earth and the debris gathered into the Moon.NOAA Ocean ServiceGravity, Inertia, and the Two BulgesWhere the two ocean bulges come from, which is the same stretching that shaped the Moon's rock.NOAA NESDISWhat Causes Tides?Reader-facing summary of why the Moon raises our tides.NASA Goddard Space Flight CenterMeasuring the Moon's Distance (Apollo Laser Ranging)How the retroreflectors left by Apollo crews are used to time a laser pulse and measure the distance.NASALaser Beams Reflected Between Earth and Moon Boost ScienceModern confirmation of the 3.8 cm a year drift, with the fingernail comparison.NASA ScienceFirst Photo of the Lunar Far SideNobody had seen the far side until the Luna 3 probe photographed it in October 1959.