On a clear night, the Moon feels less like an object and more like a companion. It rises on schedule, changes its face as the weeks pass, and quietly turns ordinary streets into silver scenes. That familiarity can hide how strange it is: a rocky world with no weather, no breathable air, and a history written in scars.

Most scientists think the Moon formed about 4.5 billion years ago, shortly after Earth itself. The leading idea is the giant impact hypothesis. In that scenario, a Mars sized protoplanet struck the young Earth, blasting material into orbit. Over time, that debris gathered into a single body. Lunar rocks brought back by Apollo missions show chemical similarities to Earth’s mantle, which fits with the idea that the Moon was built from a mix of Earth material and the impactor.

The Moon orbits Earth at an average distance of about 384,400 kilometers (238,900 miles). It is 3,474 kilometers wide, roughly one quarter of Earth’s diameter. Gravity there is about one sixth of Earth’s, so a person’s weight would feel dramatically lower, even though their mass stays the same. The Moon is also tidally locked, meaning it rotates once in the same time it takes to orbit Earth, about 27.3 days. That is why we see nearly the same lunar face all the time. The phase cycle, from new to full and back, takes about 29.5 days because Earth is moving around the Sun while the Moon circles Earth.

Through binoculars you can spot the dark patches called maria, Latin for “seas.” They are not water. They are ancient lava plains that filled huge impact basins billions of years ago, when the Moon’s interior was hotter and more active. The brighter highlands are older, battered terrain, pocked with craters from impacts that never got erased by wind or rain. The surface is covered in regolith, a dusty mix of crushed rock and glassy fragments created by countless micrometeorite hits.

The lunar environment is extreme. In sunlight, surface temperatures can reach about 120°C (250°F). In darkness, they can drop near −170°C (−280°F). With no thick atmosphere to trap heat, the swings are brutal. Still, the Moon is not completely dry. Several missions have found evidence of water, including ice likely preserved in permanently shadowed craters near the poles, where sunlight rarely reaches.

The Moon’s pull shapes Earth, too. It drives ocean tides and slowly nudges Earth’s rotation, lengthening our days over geologic time. Many researchers think it also helps stabilize Earth’s tilt, which supports long term climate steadiness. For something that looks like a simple lantern in the night, the Moon is deeply connected to the story of Earth and to the way we live under its light.

Humanity has only visited it a handful of times, but robotic orbiters and landers add detail. The far side, first seen by spacecraft in 1959, has fewer maria and thicker crust. Future missions aim to study polar ice and use the Moon as a testbed for travel.