How big and how far is the Moon
About 30 Earths would fit side by side in the gap between Earth and the Moon.
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A small world next to a big one
Look at the full Moon and it seems about as large as the Sun, yet the two could hardly be more different. The Moon is a ball of rock with a mean radius of 1,737.4 km, so it is about 3,475 km across. Earth's mean radius is 6,371 km. Divide one by the other and the Moon comes out at 0.27 of Earth's width, a little more than a quarter. NASA puts it in coins: if Earth were the size of a nickel, the Moon would be about as big as a coffee bean.
Width hides how small the Moon really is. Volume grows with the cube of the radius, so the Moon's volume is only about 2% of Earth's: you would need about 49 Moons to fill Earth. Mass is smaller still. The Moon has 0.07346 × 1024 kg against Earth's 5.9724 × 1024 kg, so Earth is about 81 times heavier. The Moon is also less dense, 3,344 kg per cubic metre against Earth's 5,514, because its iron core is small. NASA gives the solid inner core a radius of only about 240 km.
Less mass means weaker gravity. A dropped object on the Moon speeds up by 1.62 metres per second every second, against 9.80 on Earth. That is 0.165 of Earth's pull, close to one sixth, which is why the Apollo astronauts seemed to bounce as they walked. A person with a mass of 60 kg weighs about 588 newtons on Earth and about 97 newtons on the Moon. Their mass does not change at all; only the pull on it does.
Measuring the distance
The average distance from Earth to the Moon is 384,400 km. Earth's mean diameter is 12,742 km, and 384,400 ÷ 12,742 ≈ 30.2, so about 30 Earths would fit in between. Light covers the distance in about 1.28 seconds. That number is not only a curiosity. Apollo 11 left a Laser Ranging Retroreflector on the surface in 1969, and stations on Earth still fire laser pulses at reflectors like it. The pulse comes back about 2.56 seconds later, and the timing gives the distance with great precision.
The Moon's orbit is an ellipse, not a circle. NASA's fact sheet gives a mean closest point (perigee) of 363,300 km and a mean farthest point (apogee) of 405,500 km, and over a year the distance ranges roughly from 357,000 to 407,000 km. NASA's visualisation team notes that the apparent size of the Moon at perigee and at apogee differs by more than 10%. Use the distance menu in the model: the readout shows the Moon's apparent width change from about 0.548° at mean perigee to 0.491° at mean apogee.
A few other numbers round out the picture. The Moon travels along its orbit at about 1.02 km per second and takes 27.32 days to go round once relative to the stars. It has almost no air, so its surface swings from about 127 °C in full sunlight to about −173 °C in darkness. NASA says it likely formed from debris after a Mars-sized body hit the young Earth.
| Moon | Earth | Moon ÷ Earth | |
|---|---|---|---|
| Mean radius (km) | 1,737.4 | 6,371.0 | 0.273 |
| Mass (10²⁴ kg) | 0.07346 | 5.9724 | 0.0123 |
| Mean density (kg/m³) | 3,344 | 5,514 | 0.606 |
| Surface gravity (m/s²) | 1.62 | 9.80 | 0.165 |
| Escape speed (km/s) | 2.38 | 11.2 | 0.213 |
| Average Earth to Moon distance | 384,400 km |
| Moon's mean radius | 1,737.4 km |
| Moon's surface gravity | 1.62 m/s², about 1/6 of Earth |
| Light time Earth to Moon | About 1.28 s |
| How fast the Moon drifts away | About 3.8 cm a year |
| Earth's mass compared with the Moon's | About 81 times |
- Earth's mean diameter is 12,742 km and the Moon is 384,400 km away. About how many Earths fit in the gap?
- The Moon's width is about what fraction of Earth's?
- A half
- A little more than a quarter
- A tenth
- Light travels 299,792 km per second. How many seconds does it take to reach the Moon? (one decimal)
- A laser pulse goes to an Apollo reflector and back. About how many seconds is the round trip? (one decimal)
- Surface gravity is 9.80 m/s² on Earth and 1.62 m/s² on the Moon. What is the weight in newtons of a 60 kg person on the Moon?
- Why is the Moon less dense than Earth?
- It is hollow
- Its iron core is small
- It is made of ice
- The Moon drifts away at 3.8 cm a year. How many metres farther is it after 100 years?
- Which is closest to the Moon's mean perigee distance?
- 363,300 km
- 384,400 km
- 405,500 km
- Earth's volume is 108.321 and the Moon's 2.1968 (in 10¹⁰ km³). About how many Moons would fill Earth?
- A 60 kg astronaut stands on the Moon. What happens to their mass?
- It stays 60 kg
- It drops to 10 kg
- It becomes zero
- Mean radius 1,737.4 km, about 0.27 of Earth's radius.
- Average distance 384,400 km, about 30 Earths; light takes about 1.28 s.
- Gravity 1.62 m/s², about one sixth of Earth's.
- The orbit is an ellipse: about 363,300 km to 405,500 km on average.
- The Moon drifts away by about 3.8 cm a year.
Sources for this course (16)
- NASA Moon Fact Sheet (nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html)
- NASA Moon facts (science.nasa.gov/moon/facts)
- NASA Moon phases (science.nasa.gov/moon/moon-phases)
- NASA Tidal locking (science.nasa.gov/moon/tidal-locking)
- NASA Tides (science.nasa.gov/moon/tides)
- NASA Moon eclipses (science.nasa.gov/moon/eclipses)
- NASA Eclipse types (science.nasa.gov/eclipses/types)
- NASA GSFC eclipse tables by Fred Espenak (eclipse.gsfc.nasa.gov/LEdecade/LEdecade2021.html, eclipse.gsfc.nasa.gov/SEdecade/SEdecade2021.html)
- NASA SVS Moon Wobble (svs.gsfc.nasa.gov/10836)
- NASA Apollo program (nasa.gov/the-apollo-program)
- NASA Apollo 11 mission overview (nasa.gov/history/apollo-11-mission-overview)
- NASA Apollo 12, 14, 15, 17 mission pages (nasa.gov/mission/apollo-12 etc.)
- NASA Moon walkers (science.nasa.gov/moon/moon-walkers)
- NASA Moon exploration (science.nasa.gov/moon/exploration)
- NASA Apollo samples (science.nasa.gov/science-research/planetary-science/astrobiology/nasas-apollo-samples-yield-new-information-about-the-moon)
- NASA Artemis II (nasa.gov/mission/artemis-ii, nasa.gov/news-release/nasas-artemis-ii-crew-eclipses-record-for-farthest-human-spaceflight, nasa.gov/gallery/artemis-ii-splashdown-and-recovery).
Checked: 2026-10-17