The Moon is the most familiar object in the night sky. Humans have watched its changing appearance for thousands of years, used its phases to mark the passage of time, and imagined faces and figures in the patterns across its surface.
Yet our nearest celestial neighbor is much stranger than it appears. Even some of its most familiar features have surprising explanations, while discoveries made by spacecraft and the Apollo missions continue to change what we know about this seemingly quiet world.
Ready to discover more? Here are ten fascinating facts about the Moon.
1. The “Man in the Moon” is made from ancient lava
Look at the full Moon and one feature immediately stands out: the large dark patches scattered across its surface. For thousands of years, people have imagined faces and figures in these markings, including the familiar “Man in the Moon.”
There is no official face, of course, and different cultures have interpreted the pattern in different ways. In the traditional Western version, large dark regions such as Mare Imbrium and Mare Serenitatis help form the most recognizable parts of the face, with other nearby dark plains contributing to the pattern, depending on how you see it.
These dark areas are known as the lunar maria, from the Latin word for “seas.” Early astronomers believed they might actually contain water, which is why names such as the Sea of Tranquility and Sea of Serenity survive today.
But the maria aren’t seas at all. They are enormous plains of dark volcanic rock.
Billions of years ago, huge objects struck the young Moon and blasted out vast impact basins. Later, lava from inside the Moon flooded many of these basins before cooling and solidifying into dark basalt.
So one of the most familiar patterns in the night sky is actually the result of colossal impacts and volcanic eruptions that occurred billions of years ago.
Many of these maria can easily be seen without a telescope. With binoculars or a small telescope, you can explore them in much greater detail in our guide to the top features on the Moon for stargazers.
2. We can actually see about 59% of the Moon
You’ve probably heard that we always see the same side of the Moon. That’s broadly true — but it doesn’t mean exactly half of the lunar surface is permanently hidden from us.
The Moon is tidally locked to Earth, meaning it rotates once on its axis in about the same amount of time it takes to complete one orbit around our planet. As a result, essentially the same hemisphere remains facing Earth.
But the Moon appears to rock slightly from side to side and nod up and down as we observe it over time. This effect is called libration.
Part of this apparent rocking occurs because the Moon travels in an elliptical rather than perfectly circular orbit. Its orbital speed therefore changes slightly during each trip around Earth, while its rotation remains much steadier. The Moon’s orbit is also tilted, allowing us to peer a little farther over its northern and southern edges at different times.
Together, these effects allow observers on Earth to see about 59% of the Moon’s surface over the course of time.
And despite the popular expression, there is no permanently “dark side of the Moon.” The far side receives sunlight just like the near side does. What changes throughout the month is how much of the Moon’s sunlit hemisphere faces Earth, producing the familiar phases of the Moon.
3. A day on the Moon lasts about a month on Earth
If you could stand on the Moon and watch the Sun cross the sky, you would need plenty of patience. From sunrise to sunset takes nearly two Earth weeks.
A complete lunar solar day — from one sunrise to the next — lasts about 29.5 Earth days. That means most locations on the Moon experience roughly two weeks of continuous daylight followed by about two weeks of darkness.
At first this seems strange because the Moon takes only about 27.3 days to orbit Earth. This is known as its sidereal month.
The Moon also takes about 27.3 days to rotate once on its axis — the same amount of time it takes to orbit Earth. Because these two periods are synchronized, the Moon keeps essentially the same hemisphere facing Earth.
So why does sunrise-to-sunrise take 29.5 days rather than 27.3?
While the Moon is orbiting us, Earth is also moving along its orbit around the Sun. After the Moon completes one orbit of Earth, it therefore has to travel a little farther before the Sun, Earth and Moon return to the same relative alignment.
That extra journey makes the cycle from one new Moon to the next about 29.5 days. This is called the synodic month, and it is also the cycle behind the Moon’s changing phases.
Those extremely long periods of daylight and darkness help produce the dramatic temperature swings experienced on the lunar surface — and create a major challenge for spacecraft designed to survive there.
4. The Moon has an atmosphere — just barely
The Moon is often described as an airless world, but that isn’t quite true. It does have an atmosphere — only an astonishingly thin one.
In fact, the same volume of Earth’s atmosphere can contain around 100 trillion times as many molecules as the atmosphere close to the lunar surface. The particles around the Moon are so widely separated that they rarely collide with one another.
Scientists therefore usually describe this extremely tenuous envelope as an exosphere rather than an atmosphere like Earth’s.
Among the gases detected around the Moon are helium, neon and argon. Some particles arrive in the solar wind, while others are released from lunar rocks or produced when meteoroids strike the surface.
NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) mission, which orbited the Moon in 2013 and 2014, helped scientists investigate this environment in detail. Among its findings, LADEE confirmed that neon is an important component of the lunar exosphere and found evidence that micrometeoroid impacts continually create a thin cloud of dust around the Moon.
So the Moon isn’t completely airless after all. But standing on its surface would still feel essentially like being exposed to the vacuum of space.
5. Some of the coldest places in the Solar System are on the Moon
The Moon is far closer to the Sun than distant worlds such as Pluto, yet some places on its surface rank among the coldest ever measured in the Solar System.
They are found near the lunar poles.
Because the Moon’s rotational axis is only slightly tilted, sunlight strikes the polar regions at a very low angle. The floors of some deep craters therefore never receive direct sunlight at all.
These areas are known as permanently shadowed regions.
NASA’s Lunar Reconnaissance Orbiter has measured temperatures in some of these dark craters below −246°C (−411°F). In parts of Hermite Crater near the Moon’s north pole, temperatures measured by the Diviner instrument have fallen to about −249°C (−416°F).
That’s colder than the surface of Pluto.
But these dark craters hold another surprise: water ice.
With little or no sunlight to warm them, these regions act as natural cold traps, where volatile substances can remain frozen for extremely long periods. Spacecraft observations have confirmed water ice in permanently shadowed areas near the lunar poles.
That frozen water could become an important resource for future lunar explorers, potentially providing drinking water, oxygen and even ingredients for rocket fuel.
6. Earth raises tides in the solid Moon
The Moon’s gravity raises tides in Earth’s oceans — but the gravitational relationship works both ways.
Earth also raises tides on the Moon.
Unlike our planet, the Moon has no oceans for Earth to pull into large tidal bulges. Instead, Earth’s gravity actually deforms the solid lunar surface.
As the Moon travels around Earth, the strength and direction of Earth’s gravitational pull change slightly. The lunar crust responds by flexing, causing parts of the surface to rise and fall by roughly 10 to 15 centimeters (4 to 6 inches).
These movements are known as solid-body tides.
They are far too small to notice if you were standing on the Moon, but spacecraft and precise measurements can detect them. Studying this subtle flexing also helps scientists learn more about the structure of the Moon’s interior.
And these gravitational forces don’t just change the Moon’s shape. Earth’s tidal pull can also trigger deep moonquakes — although, as we’ll discover next, the Moon’s continuing contraction produces quakes of its own.
7. The Moon is shrinking — and it still has moonquakes
The Moon may look frozen and unchanging, but its interior has been slowly cooling for billions of years.
As it cools, the Moon contracts.
The effect is rather like a grape shriveling into a raisin. The Moon’s rigid crust cannot simply shrink smoothly, so sections of crust are pushed over one another, creating cliffs known as thrust faults or lobate scarps.
Scientists estimate that the Moon’s diameter has decreased by about 50 meters (164 feet) over the past several hundred million years. Images from NASA’s Lunar Reconnaissance Orbiter have revealed thousands of these relatively young scarps across the lunar surface.
The contraction also helps produce moonquakes.
Seismometers placed on the surface by Apollo astronauts detected thousands of seismic events. Some originated deep inside the Moon and are associated with Earth’s tidal forces, while shallower quakes can occur as the cooling lunar crust contracts and faults move.
The strongest shallow moonquakes detected during the Apollo era reached about magnitude 5.5, and some continued shaking for more than ten minutes.
Earthquakes usually die away much more quickly because water and fractured rock inside Earth help absorb seismic energy. The Moon is much drier and more rigid, allowing vibrations to reverberate for longer.
So although the Moon has no moving tectonic plates like Earth, it isn’t completely geologically inactive. Its cooling interior continues to deform its crust — and occasionally makes the Moon tremble.
8. New craters are still appearing on the Moon
Most of the craters covering the Moon formed billions of years ago, but crater formation didn’t stop in the distant past.
New ones are appearing even today.
Earth’s atmosphere destroys many small incoming space rocks before they reach the ground. The Moon has almost no atmosphere, so meteoroids can strike its surface at enormous speeds.
There is also no rain, flowing water or wind to rapidly erase the scars they leave behind. As a result, lunar craters can remain visible for extraordinarily long periods.
NASA’s Lunar Reconnaissance Orbiter has given scientists a remarkable way to track this ongoing bombardment. By comparing before-and-after images of the same areas taken between 2009 and 2016, researchers identified 222 newly formed impact craters, ranging from about 3 to 43 meters (10 to 140 feet) across.
The impacts also disturbed the surrounding lunar soil, creating bright patterns extending well beyond the new craters themselves.
Most of these impacts are far too small to create the enormous basins visible from Earth, but they provide a striking reminder that crater formation is not merely something that happened during the Moon’s violent youth.
The Moon is still being reshaped by impacts, one new crater at a time.
9. The Sun and Moon look almost perfectly matched in our sky
The Sun is vastly larger than the Moon, yet from Earth they can appear almost exactly the same size in the sky.
That remarkable coincidence is what makes total solar eclipses possible.
The Sun is roughly 400 times wider than the Moon, but it is also about 400 times farther away. Those two differences almost cancel each other out when we view them from Earth, giving the Sun and Moon very similar apparent sizes.
During a total solar eclipse, the Moon can therefore pass directly in front of the Sun and cover its brilliant visible surface while revealing the faint solar corona around it.
The match isn’t always perfect.
Both Earth’s orbit around the Sun and the Moon’s orbit around Earth are elliptical, so their apparent sizes vary slightly. Sometimes the Moon appears large enough to cover the Sun completely. At other times it appears a little too small, leaving a brilliant ring of sunlight around it during an annular eclipse.
It’s an extraordinary piece of celestial geometry: a Moon only about 3,475 kilometers (2,159 miles) wide can completely hide a Sun roughly 1.4 million kilometers (865,000 miles) across.
But this remarkable alignment won’t last forever.
That’s because the Moon’s distance from Earth is slowly changing — which brings us to our final fact.
10. The Moon is slowly moving away from Earth
The Moon is gradually drifting away from us at a rate of about 3.8 centimeters (1.5 inches) per year.
That may sound impossibly small, but scientists can measure the distance between Earth and the Moon with remarkable precision.
We know this partly because of laser reflectors placed on the Moon by Apollo astronauts. Scientists can fire laser pulses toward these reflectors and measure how long the light takes to return to Earth, allowing tiny changes in the Moon’s distance to be detected.
The reason the Moon is receding is connected to the tides.
The Moon’s gravity raises tidal bulges on Earth, while Earth’s rotation carries those bulges slightly ahead of the Moon’s position. Their gravitational interaction transfers a small amount of rotational energy from Earth to the Moon.
As a result, Earth’s rotation is gradually slowing while the Moon gains orbital energy and moves into a slightly larger orbit.
Over a human lifetime, the difference is tiny. Over hundreds of millions of years, however, it becomes significant.
And that means the remarkable coincidence described in the previous fact won’t last forever either. As the Moon moves farther away, it will gradually appear smaller in our sky. Eventually it will no longer be large enough to completely cover the Sun during an eclipse.
That doesn’t mean we’re slowly losing the Moon altogether. But according to NASA, in more than 600 million years, the Moon will appear too small for total solar eclipses to occur.
So we happen to live during a remarkable period in Earth’s history: a time when our slowly retreating Moon can still perfectly cover the Sun.
Keep exploring the Moon
There’s much more to discover about our nearest celestial neighbor. Learn how to recognize the Moon’s phases, explore some of its most interesting craters, mountains and other surface features, or discover more about the Apollo missions that first carried humans to another world.
