We Only Ever See One Side of the Moon — the Other Was Hidden Until 1959

Go outside on any clear night, this year or in a decade, and look at the Moon. You will always see the same face — the same craters, the same dark patches. For all of human history, until surprisingly recently, nobody had ever seen the other half.

This is because of tidal locking. The Moon spins on its own axis in exactly the same time it takes to orbit the Earth — about 27 days. The two motions are perfectly synchronized, so one hemisphere is permanently turned toward us and the other permanently turned away.

It isn’t a coincidence. Billions of years ago the Moon spun faster, but Earth’s gravity gently tugged on the slight bulge in the Moon’s shape, acting like a brake, until the spin settled into this locked rhythm. Most large moons in the solar system are tidally locked to their planets the same way.

The hidden hemisphere is often called the “dark side of the Moon” — but that name is misleading. It gets just as much sunlight as the side we see; it’s simply the side we can never observe from Earth. “Far side” is the accurate term.

Humanity got its first glimpse only in 1959, when the Soviet probe Luna 3 swung around the Moon and beamed back grainy photographs of the far side. The images revealed something odd: the far side looks strikingly different — rugged, cratered, and almost entirely lacking the large dark plains (called maria) that form the familiar “face” we see from Earth. Why the two halves are so different remains an active area of research.

In 2019, China’s Chang’e-4 became the first spacecraft ever to land on the far side — a place no human eye had seen at all until within living memory.