Earth's natural satellite
The Moon
Our constant companion
The Moon is Earth's only natural satellite and the fifth largest moon in the solar system. It most likely formed about 4.5 billion years ago when a Mars-sized body collided with the young Earth, throwing debris into orbit that clumped together. The Moon stabilizes Earth's wobble, which keeps our climate steadier, and its gravity drives the ocean tides. It is the only world beyond Earth that humans have walked on.
Quick facts
- Distance from Sun
- 384,400 km from Earth
- Diameter
- 3,475 km (0.27x Earth)
- Day length
- 27.3 Earth days (rotation)
- Year length
- 27.3 days (orbit around Earth)
- Avg. temperature
- -173 C night / 127 C day
What's it like there?
The Moon has no atmosphere, so its sky is black even in daylight and footprints can last for millions of years. Temperatures swing from 127 C in sunlight to -173 C at night. Gravity is one-sixth of Earth's, which is why Apollo astronauts bounded across the surface. The dark patches visible from Earth are ancient lava plains called maria; the bright regions are older, heavily cratered highlands. Water ice hides in shadowed polar craters.
Fun facts
The Moon always shows the same face to Earth (tidal locking).
The Moon is drifting away from Earth about 3.8 cm per year.
12 people have walked on the Moon, all between 1969 and 1972.
Moonquakes occur, caused partly by Earth's gravitational pull.
The Moon's gravity is the main driver of Earth's ocean tides.
Exploration history
Luna 2 1959
First spacecraft to reach the Moon's surface.
Apollo 11 1969
First crewed landing; Armstrong and Aldrin walked on the Moon.
Lunar Reconnaissance Orbiter 2009+
Mapping the Moon in high resolution.
Artemis program 2022+
NASA program to return humans to the Moon.
The Moon vs Earth
| Property | Earth | The Moon |
|---|---|---|
| Diameter | 12,742 km | 3,475 km |
| Gravity | 1 g | 0.17 g |
| Atmosphere | Nitrogen-oxygen | Essentially none |
| Day length | 24 hours | 27.3 Earth days |
Scientific Sources & Provenance
All data is verified against official space agency records (NASA, ESA, and IAU).
- NASA Science / Mission Datahttps://science.nasa.gov/moon/
- NASA Science / Mission Datahttps://www.nasa.gov/humans-in-space/artemis/