What Is the Moon Like? Surface, Phases, and Orbit

What the Moon is

The Moon is a natural satellite: an object that orbits a planet. It is not a star, because it does not produce its own visible light through nuclear fusion. The bright Moon we see is sunlight reflected from its surface. It is also not a planet under the usual astronomical classification, because it orbits Earth rather than the Sun directly as a primary world. Earth and the Moon together orbit the Sun.

The Moon is roughly one-quarter Earth’s diameter and about 1/81 of its mass. Its gravity is weaker than Earth’s: an object’s weight at the lunar surface would be about one-sixth its Earth weight, although its mass would stay the same. The Moon is about 384,000 kilometers (239,000 miles) from Earth on average, but its distance varies because its orbit is slightly oval.

Scientists estimate that the Moon formed more than four billion years ago. The leading explanation is that a large body struck the young Earth, sending material into orbit that eventually gathered into the Moon. Details of its formation remain an active subject of research, so this is a scientific model rather than a witnessed event.

A surface of craters, plains, and dust

The Moon’s surface is rocky and covered in regolith, a layer of loose dust, broken rock, and impact debris. It has no oceans or broad, wind-shaped landscapes. Many craters formed when asteroids and smaller space rocks struck the surface. Because the Moon has almost no atmosphere to burn up incoming objects and little weather to erase marks, some ancient craters remain visible for billions of years.

The dark patches visible from Earth are called maria (singular: mare, Latin for “sea”). They are broad plains formed when lava flooded older impact basins and later cooled into rock. They are not water. The lighter, rougher highlands are generally more heavily cratered. The near side, which faces Earth, has more large maria than the far side, though both sides have extensive cratered terrain.

There is no breathable air at the lunar surface and no global weather system like Earth’s. The Moon does have an extremely thin exosphere, but it is so sparse that it cannot provide meaningful breathing air or protect the surface as Earth’s atmosphere does. Its sky looks black even in daytime because there is not enough air to scatter sunlight into a blue sky.

How the Moon’s phases work

The Moon does not make its own light, and Earth’s shadow does not cause the regular phases. At any moment, sunlight illuminates about half of the Moon. As the Moon moves around Earth, we see different portions of that sunlit half. The complete cycle of phases takes about 29.5 days, measured from one new moon to the next.

New moon: The Moon is roughly between Earth and the Sun, so its sunlit side mostly faces away from us.
First quarter: About half of the visible disk is lit as the Moon waxes, or appears to grow.
Full moon: Earth is roughly between the Sun and Moon, and the near side appears fully illuminated.
Third quarter: About half the disk is lit as the Moon wanes, or appears to shrink.

Phases progress through crescent and gibbous shapes between these main points. The geometry is not usually perfectly aligned, which is why the Moon does not pass through Earth’s shadow every month. A lunar eclipse occurs only when the Sun, Earth, and Moon line up closely enough for Earth’s shadow to fall on the Moon.

Orbit, rotation, and the far side

The Moon takes about 27.3 days to orbit Earth once relative to the distant stars. It also rotates once on its axis in about the same time. This synchronized rotation, called tidal locking, is why the same hemisphere generally faces Earth. It does not mean the Moon never rotates; it turns once during each orbit.

The hemisphere that usually faces away from Earth is called the far side, not the “dark side.” It receives sunlight during its day, just as the near side does. From Earth, observers can see a little more than half of the lunar surface over time because of small apparent rocking motions called libration. No single view from Earth reveals the entire far side.

The Moon’s orbit is tilted relative to Earth’s path around the Sun, and the Moon’s distance from Earth changes along its oval orbit. Those facts help explain why eclipses are occasional rather than monthly. They also mean the Moon can appear somewhat larger or smaller in the sky at different points in its orbit, though its apparent size remains modest.

Gravity, tides, and conditions on the Moon

The Moon’s gravitational pull is the main driver of Earth’s ocean tides, with the Sun also contributing. Tides are not simply a result of the Moon “pulling water upward” on one side: differences in gravitational pull across Earth, together with the Earth–Moon system’s motion, produce tidal bulges. Coastline shape, ocean depth, and local geography influence the timing and height of tides, so the pattern differs by location.

Conditions on the Moon are extreme compared with those on Earth. With virtually no atmosphere to hold or move heat, sunlit ground can become very hot, while nighttime or shadowed terrain becomes intensely cold. A lunar day-night cycle, measured from sunrise to sunrise at a given location, lasts about 29.5 Earth days. Permanently shadowed areas near the poles can preserve water ice, but that does not mean liquid water is lying across the open surface.

The lack of air also means sound cannot travel through the lunar environment as it does through Earth’s atmosphere. A person standing outside without a suitable spacesuit would have no breathable air or atmospheric pressure. The Moon is therefore not a place people can visit unprotected, despite its familiar appearance in the night sky.

Frequently Asked Questions

Why does the Moon shine?

It reflects sunlight. The amount of its sunlit side visible from Earth changes as it orbits, producing the phases.

Is the far side of the Moon always dark?

No. The far side receives daylight and nighttime in turn. “Far side” means the hemisphere usually turned away from Earth, not a permanently unlit region.

Does the Moon cause all ocean tides?

No. Lunar gravity is the strongest influence on tides, but the Sun also contributes. Local coast and ocean conditions shape the tides people experience.

Why are there so many craters on the Moon?

Impacts made them, and the Moon lacks substantial weather, flowing water, and active surface processes that would erase most of them. Its thin exosphere offers little protection from incoming space debris.

How long is a day on the Moon?

From sunrise to sunrise at one location, the lunar day lasts about 29.5 Earth days. The Moon’s rotation relative to distant stars takes about 27.3 days.

Further reading: NASA. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.