The Moon’s distance in numbers
| Measure | Kilometers | Miles (approx.) |
|---|---|---|
| Average distance | about 384,400 | about 238,900 |
| Typical perigee (closest) | about 363,300 | about 225,700 |
| Typical apogee (farthest) | about 405,500 | about 252,000 |
These are center-to-center distances. The distance between the surfaces is smaller by the radii of Earth and the Moon, about 8,100 km in total. Individual perigees and apogees vary by several thousand kilometers from month to month, because the Sun’s gravity distorts the Moon’s orbit.
Perigee and apogee
The Moon follows an elliptical orbit around Earth. The closest point is called perigee, and the farthest is called apogee. The Moon goes from one perigee to the next in about 27.6 days, the so-called anomalistic month. That is a little shorter than the 29.5-day cycle of the moon phases, so the phase at perigee changes from month to month.
When a full Moon happens close to perigee, it is often called a supermoon. It looks a bit larger and brighter than an average full Moon, though most people would not notice the difference without a comparison.
Putting the distance into perspective
The average distance to the Moon is about 30 times Earth’s diameter. You could line up all the other planets of the solar system side by side in the gap between Earth and the Moon at average distance, with room to spare.
Light covers the distance in about 1.3 seconds. That is why radio conversations with the Apollo astronauts had a noticeable delay of about 2.5 seconds for a question and its reply.
The Apollo crews took about three days to travel from Earth to the Moon.
How the distance is measured
Early estimates used geometry. Ancient Greek astronomers, including Hipparchus, used eclipses and parallax to estimate that the Moon was roughly 60 Earth radii away, which is close to the modern value.
Today the distance is measured with lasers. Apollo astronauts and robotic Soviet landers left retroreflectors on the lunar surface. Observatories fire laser pulses at these reflectors and time how long the light takes to come back. This technique, called lunar laser ranging, measures the distance to within a few millimeters.
The Moon is slowly moving away
Lunar laser ranging shows that the Moon is drifting away from Earth by about 3.8 cm per year, roughly the rate at which fingernails grow.
The cause is the tides. The Moon’s gravity raises tidal bulges in Earth’s oceans. Because Earth spins faster than the Moon orbits, those bulges are carried slightly ahead of the Moon. Their pull speeds the Moon up a little in its orbit, which lifts it into a higher orbit. At the same time, the tides act as a brake on Earth’s rotation, so the day slowly gets longer.
Over millions of years this adds up. The Moon was much closer in the distant past, and it will continue to recede very slowly in the future.
Watching the Moon
To plan your observing, check the moonrise and moonset times for your location and the current moon phase. During a total lunar eclipse, the Moon passes through Earth’s shadow and can turn a coppery red.