Why do we see only one side of the Moon from Earth?

The Moon is tidally locked to Earth, meaning its rotational period equals its orbital period — both approximately 27.3 days. As a result, the same hemisphere always faces Earth. This is not a coincidence but the predictable outcome of gravitational forces acting over billions of years. Early in the Moon's history, Earth's gravity created a tidal bulge in the Moon's slightly non-rigid body. When the Moon rotated faster than it orbited, this bulge was pulled slightly ahead of the Earth-Moon line, creating a torque that gradually slowed the Moon's rotation. Over hundreds of millions of years, this braking effect brought the rotation rate into sync with the orbital period — a stable configuration called synchronous rotation. This state is energetically favorable and stable. Once achieved, any small perturbation that nudges the Moon slightly is corrected by the same gravitational torque, pulling it back into alignment. Many large moons in the solar system are similarly tidally locked to their parent planets, including the Galilean moons of Jupiter. It's worth noting that we actually see slightly more than 50% of the Moon's surface over time — about 59% — due to a phenomenon called libration. The Moon's orbit is slightly elliptical and tilted, causing it to appear to "wobble" from Earth's perspective, revealing small amounts of the far side around the edges at different times. The far side was completely unseen until 1959, when the Soviet spacecraft Luna 3 photographed it for the first time.