What Is the Moon? A Kid-Friendly Guide to Our Moon

What the Moon is

The Moon is a large, rocky object that orbits Earth. An object that travels around a planet in this way is called a natural satellite. Earth has one natural satellite: the Moon. Other planets can have many moons, while some have none.

The word moon is the standard English name for Earth’s natural satellite. It is not slang or a nonstandard term. The word comes from Old English mōna, related to older Germanic words for the Moon. In a sentence, you might say, “The Moon is visible above the trees tonight.” When people mean Earth’s Moon, they often capitalize Moon in scientific or educational writing; everyday writing also commonly uses lowercase moon. The same word can describe natural satellites of other planets, as in “Jupiter has many moons.”

Earth’s Moon is not a star, planet, or cloud. It does not make its own visible light like the Sun. It is a world with a solid surface, and it is much smaller than Earth, though it appears prominent in our sky because it is relatively close to us.

Why the Moon shines and changes shape

Sunlight shines on half of the Moon at any given time. The Moon reflects some of that sunlight toward Earth, so we can see it. As the Moon moves along its orbit, the positions of the Sun, Earth, and Moon change. From Earth, we see different portions of the Moon’s lit half. These familiar appearances are called phases.

New moon: The Moon’s sunlit side mostly faces away from Earth, so it is difficult to see.
Waxing crescent and first quarter: The visible lit portion grows; at first quarter, it looks roughly half lit.
Full moon: The side facing Earth appears fully lit.
Waning phases: The visible lit portion shrinks until the next new moon.

The Moon’s shape does not actually change during these phases. Nor is Earth’s shadow making the everyday phases. Earth’s shadow causes a lunar eclipse, which happens only when the Sun, Earth, and Moon line up in a particular way. During an eclipse, Earth’s shadow falls across the Moon.

How the Moon moves

The Moon travels around Earth while Earth travels around the Sun. It takes about 27.3 days for the Moon to complete one orbit relative to distant stars. But the time from one new moon to the next is about 29.5 days, because Earth has also moved along its orbit around the Sun. The Moon has to travel a little farther for the Sun-Earth-Moon arrangement to repeat.

The Moon also rotates, or spins, on its axis. Its rotation takes about as long as its orbit around Earth, which is why the same general side faces us most of the time. This is called synchronous rotation. It does not mean the Moon never turns; it turns once as it travels once around Earth.

People sometimes call the side we do not usually see the “dark side.” That phrase can mislead: the far side receives sunlight too. It is called the far side because it faces away from Earth, not because it is always dark.

What the lunar surface is like

The Moon’s surface has dusty plains, highlands, mountains, valleys, and many impact craters. Most craters formed when space rocks struck the surface. The broad, darker-looking plains visible from Earth are called maria (the Latin plural of mare, meaning “sea”). They are not oceans; they are ancient solidified lava plains.

A layer of loose, broken rock and dust covers much of the surface. The Moon has no thick atmosphere like Earth’s to burn up most small incoming space rocks or to create familiar weather. It has no liquid-water oceans or Earth-like weather system. Temperatures at the surface can become extremely hot in sunlight and extremely cold in darkness, so the Moon is a harsh environment, not a place where people can simply go without specialized equipment.

There is water on the Moon in the form of ice in some permanently shadowed polar regions, along with small amounts of water or water-related molecules elsewhere. This does not mean the Moon has lakes or rivers. Its surface conditions and lack of a breathable atmosphere make it very different from Earth.

How the Moon affects Earth

The Moon’s gravity is a major cause of Earth’s ocean tides. Its pull helps create bulges in the oceans; as Earth rotates, many coastlines pass through changing high and low tides. The Sun’s gravity also affects tides. Local coastlines, ocean depth, and other factors influence the exact tide pattern, so the Moon’s phase alone does not tell you the tide at a particular beach.

The Moon also helps steady the direction of Earth’s rotation axis over long periods. Its gravity does not make Earth’s daily rotation stop, and the Moon is not responsible for ordinary changes in the weather. The Moon’s phases can be seen from Earth, but they do not cause the Moon to grow or shrink.

Seeing the Moon safely

You can observe the Moon with your eyes, binoculars, or a telescope. Its craters and light-dark patterns are especially easy to notice when it is partly lit, because shadows near the boundary between day and night on the Moon make surface features stand out. The Moon is also visible during daytime on many occasions; it is not only a nighttime object.

Looking at the Moon with your unaided eyes is safe. Never look directly at the Sun through binoculars or a telescope: concentrated sunlight can cause severe eye injury. If you use an optical instrument, follow its safety instructions and use a proper solar filter only when observing the Sun.

Frequently Asked Questions

Is the Moon a planet or a star?

No. The Moon is Earth’s natural satellite. It does not produce its own light like a star, and it orbits Earth rather than the Sun directly like a planet.

Why can I see the Moon during the day?

The Moon can be above the horizon in daylight, and its reflected sunlight can be bright enough to see against the blue sky. Whether it is visible depends on its position, phase, and the sky conditions.

Does the Moon make its own light?

No. Sunlight illuminates the Moon, and its surface reflects some of that light toward Earth. The Moon’s appearance changes as its position changes, not because its light switches on and off.

Why do we usually see the same side of the Moon?

The Moon rotates once on its axis in about the same time it takes to orbit Earth. This synchronized motion keeps the same general hemisphere facing us, while the far side still receives sunlight.

Is there water on the Moon?

Yes, evidence shows water ice in some permanently shadowed areas near the lunar poles, as well as small amounts of water-related material. There are no open oceans or rivers on the Moon.

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.