Ask people how far is the moon and you will usually hear “about a quarter of a million miles.” That is close enough for a quiz show, but the honest answer is more interesting: the Moon never sits still, the gap is growing, and for most of human history nobody had a clue how to measure it.
The Short Answer
On average, the Moon is 238,900 miles (384,400 km) from Earth. That is the number NASA uses, and it is the one you should memorize if you only remember one figure. To put it in perspective, you could line up about 30 Earths end to end in that gap and still have room left over.
Light crosses the distance in 1.3 seconds. Radio waves take the same time, which is why Apollo astronauts always had a slight pause before Houston answered them.
Why the Number Keeps Changing
The Moon’s orbit is not a perfect circle — it is an ellipse, and Earth sits slightly off-center in it. So the distance swings every single month:
| Point in orbit | Distance from Earth | What you see |
|---|---|---|
| Perigee (closest) | ~225,700 miles / 363,300 km | “Supermoon” — looks ~14% bigger |
| Average | 238,900 miles / 384,400 km | — |
| Apogee (farthest) | ~252,100 miles / 405,700 km | “Micromoon” — noticeably smaller |
That is a swing of over 26,000 miles. It is why some full moons genuinely look bigger in photos than others — it is not just a camera trick.
How We Actually Measured It
Ancient Greek astronomers tried it with geometry. Hipparchus, around 150 BCE, used a lunar eclipse and some clever trigonometry to estimate roughly 59 Earth radii away. He was within about 5% of the real value — with nothing but his eyes and a brain.
Today we do something far more direct. During the Apollo missions, astronauts left retroreflectors on the lunar surface — basically mirrors angled to bounce light straight back where it came from. Observatories fire a laser at them and time the round trip. Since light speed is a known constant, the travel time gives the distance to within a few centimeters.
How Long Would It Take to Get There?
| How you travel | Time to the Moon |
|---|---|
| Light | 1.3 seconds |
| Apollo astronauts | About 3 days |
| Fastest unmanned probe | About 8-9 hours |
| Driving at 70 mph (nonstop) | Roughly 142 days |
| Walking at 3 mph (nonstop) | About 9 years |
The Moon Is Slowly Leaving
Here is the part that surprises most people: the Moon drifts about 1.5 inches (3.8 cm) farther away every year. The cause is tidal friction. Earth’s oceans bulge toward the Moon, Earth spins faster than the Moon orbits, and that bulge constantly drags the Moon forward, feeding it energy. A slightly more energetic Moon settles into a slightly wider orbit.
At the same time, Earth’s rotation slows — our days get about 1.8 milliseconds longer per century. Hundreds of millions of years ago, a day on Earth was closer to 20 hours.
Why Any of This Matters
Knowing how far is the moon is not trivia. The Moon’s distance is tuned in a way that makes total solar eclipses possible: the Sun is 400 times wider than the Moon but also 400 times farther away, so they appear almost exactly the same size in our sky. Change the Moon’s distance by much and that coincidence disappears — one of the best natural experiments in the solar system goes with it.
Keep Exploring
- What is a light-year? — the unit you need before any space distance makes sense
- Why do we have seasons? — the other astronomical thing people get wrong
- What is dark energy? — when distances grow for a much stranger reason
