The Moon is Earth’s only natural satellite, a rocky world 3,474.8 km (2,159 mi) across that orbits Earth at an average distance of 384,400 km (238,855 mi). It is about 4.5 billion years old, has about one-sixth of Earth’s surface gravity and always turns the same face toward Earth.
Key facts
- The Moon is 27% as wide as Earth and the fifth-largest moon in the solar system.
- Its distance ranges from about 356,400 km at perigee to 406,700 km at apogee.
- It turns once per orbit, so the same near side always faces Earth.
- Water ice survives in permanently shadowed craters near the poles.
- Twelve astronauts walked on the Moon in 1969–1972; Artemis II flew a crew around it in April 2026.
Moon facts at a glance
These are the Moon’s key numbers, measured by spacecraft, lunar laser ranging and samples brought back by Apollo astronauts.
- Diameter
- 3,474.8 km (2,159 mi), 27% of Earth's
- Mass
- 7.342 × 10²² kg (1.2% of Earth's)
- Surface gravity
- 1.62 m/s² (about 1/6 of Earth's)
- Average distance
- 384,400 km (238,855 mi)
- Perigee / apogee
- ≈ 356,400–370,400 km / ≈ 404,000–406,700 km
- Orbit (sidereal month)
- 27.32 days
- Phase cycle (synodic month)
- 29.53 days
- Orbital tilt to the ecliptic
- 5.14°
- Surface temperature
- +120 °C (250 °F) to −130 °C (−208 °F)
- Age
- about 4.5 billion years
- Moving away from Earth
- 3.8 cm (1.5 in) per year
- Light travel time to Earth
- ≈ 1.3 seconds
Each value is explained below, from size and distance to water ice, moonquakes and missions.
How big is the Moon?
The Moon is 3,474.8 km (2,159 mi) wide, 27% of Earth’s diameter, and has 1.2% of Earth’s mass.
About 49 Moons would fit inside Earth by volume. The Moon’s mass is 7.342 × 10²² kg, so about 81 Moons would balance one Earth. No other planet has a moon this large compared with its own size.
The Moon is the fifth-largest moon in the solar system. Four moons of Jupiter and Saturn are larger, and Jupiter’s Europa is slightly smaller.
| Moon | Planet | Mean diameter |
|---|---|---|
| Ganymede | Jupiter | 5,262 km |
| Titan | Saturn | 5,150 km |
| Callisto | Jupiter | 4,821 km |
| Io | Jupiter | 3,643 km |
| The Moon | Earth | 3,475 km |
| Europa | Jupiter | 3,122 km |
How far away is the Moon?
The Moon is 384,400 km (238,855 mi) from Earth on average, measured center to center, and the distance swings between about 356,400 km at the closest perigees and 406,700 km at the farthest apogees.
The distance changes because the Moon’s orbit is an ellipse. The Moon takes 27.55 days to go from one perigee to the next. Light covers the average distance in about 1.3 seconds. A car driving nonstop at 100 km/h (62 mph) would need about 160 days to get there.
A full moon close to perigee is a supermoon. It can look up to about 14% larger and 30% brighter than a full moon near apogee.
The Moon is also moving away from Earth by about 3.8 cm (1.5 in) per year. Scientists measure the change by timing laser pulses bounced off reflectors left on the surface by Apollo astronauts and Soviet Lunokhod rovers. Earth’s tides slowly transfer energy from Earth’s spin to the Moon’s orbit, which pushes the Moon outward and very gradually lengthens Earth’s day.
How does the Moon orbit and rotate?
The Moon orbits Earth once every 27.32 days relative to the stars and spins on its axis in exactly the same time, so the same side, the near side, always faces Earth.
This match is called synchronous rotation. NASA describes Earth and the Moon as tidally locked: Earth’s gravity slowed the young Moon’s spin until one face stayed toward Earth. A slight rocking motion called libration lets observers see 59% of the surface over time.
The phases repeat every 29.53 days, two days longer than one orbit. Earth moves along its own orbit during that time, so the Moon needs extra time to return to the same angle from the Sun. Our page on the lunar cycle explains the two kinds of month.
The Moon’s orbit is tilted 5.14° to Earth’s orbit around the Sun. Because the Moon moves east along its orbit every day, it rises about 50 minutes later each day on average; our page on why the moon rises later each day shows how the delay changes through the year.
What does Earth look like from the Moon?
From the Moon’s near side, Earth hangs in almost the same place in the sky all the time, because the Moon keeps one face turned toward Earth.
Earth looks about 3.7 times wider from the Moon than the Moon looks from Earth. It goes through phases too, opposite to the Moon’s: when we see a new moon, an astronaut on the near side would see a full Earth. From the far side, Earth never rises at all.
How does the Moon’s gravity affect Earth?
The Moon’s surface gravity is 1.62 m/s², about one-sixth of Earth’s, and its pull on Earth raises most of the ocean tides.
The Moon pulls hardest on the side of Earth facing it and least on the far side. That difference stretches the oceans into two tidal bulges. Most coasts therefore get two high tides about every 24 hours 50 minutes, the time the Moon takes to return to the same place in the sky.
The Sun raises smaller tides of its own. At new and full moon, the two pulls line up and produce larger spring tides. At the quarter moons, they partly cancel and produce smaller neap tides.
What is the Moon’s surface like?
The Moon’s surface is a mix of dark lava plains called maria and bright, heavily cratered highlands, all covered by a layer of dust and broken rock called regolith.
- Maria: Latin for “seas.” NASA describes them as impact basins that filled with lava between 4.2 and 1.2 billion years ago. They are made of dark basalt and lie mostly on the near side.
- Highlands: the bright areas, made of older, lighter rock rich in a mineral called anorthosite. They are covered with overlapping craters.
- Craters: without wind, rain or plate tectonics, impact craters last for billions of years. The vast South Pole–Aitken basin on the far side is one of the largest known impact structures in the solar system.
- Regolith: a rubble layer of charcoal-gray, powdery dust and rocky debris that covers nearly the entire Moon.
Under the surface, the Moon has a crust about 40 km (25 mi) thick on the near side and up to about 60 km (37 mi) on the far side. Below it lie a rocky mantle and a small iron-rich core, solid at the center and surrounded by liquid iron.
How bright is the Moon?
The full moon shines at an apparent magnitude of about −12.7, which makes it by far the brightest object in the night sky, even though its gray rock reflects only a small part of the sunlight that reaches it.
Brightness rises steeply toward full moon. A first quarter moon looks half lit but gives only about a tenth of the full moon’s light. At quarter phase, sunlight strikes the surface at a low angle and craters cast long shadows; at full moon the light falls straight down and the shadows almost vanish.
When the Moon is a thin crescent, the dark part often glows a faint gray. This earthshine is sunlight reflected from Earth onto the Moon and back to our eyes.
How hot and cold does the Moon get?
Temperatures on the Moon range from about +120 °C (250 °F) in sunlight to about −130 °C (−208 °F) at night, and fall to −240 °C (−400 °F) or colder in permanently shadowed polar craters.
Each spot on the Moon has about two weeks of daylight followed by about two weeks of darkness. A full day-and-night cycle lasts one synodic month of 29.5 days. With no real atmosphere to hold heat, the surface cools fast once the Sun sets.
How old is the Moon, and how did it form?
The Moon is about 4.5 billion years old, and rock samples brought back by Apollo give ages of about 4.46 to 4.51 billion years.
Most scientists favor the giant-impact hypothesis. In this model, a large body, perhaps the size of Mars and often called Theia, struck the young Earth. Debris from the collision collected in orbit and formed the Moon.
The main evidence comes from Apollo samples. Their oxygen isotopes match Earth rocks too closely to be a coincidence. The samples also show that the young Moon was covered by a deep ocean of magma. NASA notes that the details are still debated, including whether one impact or a series of impacts formed the Moon.
Is there water on the Moon?
Yes, water ice exists in permanently shadowed craters near the Moon’s poles, where the warmest temperatures never rise above about −157 °C (−250 °F).
In 2009, NASA’s LCROSS impactor struck a shadowed crater near the south pole and detected water in the debris it threw up. In 2018, NASA’s Moon Mineralogy Mapper on India’s Chandrayaan-1 spacecraft gave direct evidence of ice at the surface. The ice sits in the darkest and coldest parts of the polar regions.
Polar ice is one reason NASA’s Artemis program plans to land crews near the lunar south pole. Ice could one day supply water and oxygen for explorers.
Does the Moon have an atmosphere?
The Moon has no breathable atmosphere, only an extremely thin exosphere of scattered atoms and molecules.
Without a real atmosphere, the lunar sky is black even in daylight. No weather wears down the surface, and sound cannot travel through the near-vacuum. The Moon also has only a weak magnetic field, so the solar wind and cosmic rays reach the surface directly.
Does the Moon have earthquakes?
Yes, the Moon has moonquakes, which seismometers placed by Apollo astronauts recorded in the 1970s.
NASA groups them into four kinds:
- Deep moonquakes, hundreds of kilometers down, triggered by Earth’s tidal pull.
- Moonquakes at moderate depth, about 20–30 km down, linked to the Moon cooling and shrinking.
- Impact tremors, from meteoroids hitting the surface.
- Thermal moonquakes, from surface rock expanding and contracting between day and night.
Shallow moonquakes are the strongest. NASA reports that they can reach magnitude 5.5 and last for more than 10 minutes, because the dry, rigid Moon keeps vibrating long after a quake.
Who has explored the Moon?
The Moon is the only world beyond Earth that people have visited, and robotic missions from several countries have studied it since 1959.
| Year | Mission | Milestone |
|---|---|---|
| 1959 | Luna 2 (USSR) | First spacecraft to reach the Moon’s surface |
| 1959 | Luna 3 (USSR) | First photographs of the far side |
| 1966 | Luna 9 (USSR) | First soft landing |
| 1968 | Apollo 8 (USA) | First crew to orbit the Moon |
| 1969 | Apollo 11 (USA) | First crewed landing, July 20, 1969 |
| 1970 | Luna 16 (USSR) | First robotic sample return |
| 2019 | Chang’e 4 (China) | First soft landing on the far side |
| 2023 | Chandrayaan-3 (India) | Lander and rover on the surface |
| 2024 | Chang’e 6 (China) | First samples from the far side |
| 2026 | Artemis II (USA) | First crew to travel to the Moon since 1972 |
Between 1969 and 1972, six Apollo missions landed and 12 astronauts walked on the Moon. They brought back 382 kg (842 lb) of lunar rock and soil, which scientists still study. Apollo 17, in December 1972, was the last crewed landing.
Chang’e 6 landed in the Apollo basin, inside the far side’s South Pole–Aitken basin, on June 1, 2024, and its capsule returned to China on June 25, 2024. Artemis II launched on April 1, 2026 and carried four astronauts around the Moon before splashing down on April 10, 2026.
Why does the Moon have phases and eclipses?
The Moon has phases because we see different parts of its sunlit half as it orbits Earth, and it causes eclipses when it lines up exactly with the Sun and Earth.
The Sun always lights one half of the Moon. As the Moon circles Earth, more or less of that lit half faces us, which produces the eight phases of the moon. Our explainer on why the moon has phases shows the geometry step by step. The moon phase today page shows the current phase, and the moon phase calendar shows every phase by month.
The phases also explain when you can see the Moon. A crescent or quarter Moon is often up in daylight, which is why you can see the moon during the day.
When a full moon passes through Earth’s shadow, the result is a lunar eclipse. When a new moon passes in front of the Sun, the result is a solar eclipse. Both need the Moon to sit close to the plane of Earth’s orbit, which is why they do not happen every month. The date of the next full moon shows the next chance for a lunar eclipse.
Why does the Moon look different from the Southern Hemisphere?
From the Southern Hemisphere the Moon appears rotated by about 180° compared with the northern view, because observers there face north instead of south to see it.
The same near side faces everyone on Earth, so the features are identical. Only their orientation changes: the “man in the moon” stands on his head, and a waxing crescent is lit on the left instead of the right. Our page on why the moon looks upside down in the southern hemisphere compares the views from London, Singapore and Sydney.