How Far Away Is the Moon?

The Moon is an average of 238,855 miles (384,400 kilometers) from Earth. That is far enough that radio and light take about 1.28 seconds to make the trip one way, so a round-trip signal lags by roughly 2.5 seconds. The gap is also big enough to line up about 30 Earths side by side between us and the Moon.

Putting 238,855 miles in perspective

Numbers that big are hard to actually feel. So picture stacking Earths between us and the Moon: about 30 of them would fit neatly in the space.

Another way to grasp it: the gap is wide enough that you could, in principle, line up every other planet in the solar system in the space between Earth and the Moon. There is a lot more room out there than the night sky suggests.

The Moon looks close to us mainly because it is huge and bright, not because it is near. That bright disc is hanging a quarter of a million miles away.

For comparison, a commercial jet cruising at 500 miles per hour would need nearly 20 days of nonstop flight to cover the distance. The Moon feels like a neighbor, but it is a seriously long way off.

The distance is not fixed

The Moon's orbit is an ellipse, not a perfect circle, so the distance changes as it travels around Earth each month. At its closest point, called perigee, it sits about 225,600 miles away.

At its farthest, apogee, it stretches out to roughly 252,000 miles. That swing of nearly 27,000 miles is real and measurable.

It is also why some full moons look noticeably bigger than others. A full moon near perigee gets the supermoon label, even though the size difference is subtler than the headlines suggest.

The Moon is slowly leaving

Each year the Moon drifts about 3.8 centimeters farther from Earth, which is roughly the rate your fingernails grow. Tidal interactions between the two bodies are slowly handing the Moon extra orbital energy.

Over billions of years that tiny annual creep adds up enormously. In the deep past the Moon was much closer and loomed far larger; in the distant future it will hang noticeably smaller in our sky.

Eventually the Moon will be too far away to perfectly cover the Sun, which means total solar eclipses will become a thing of the past. We just happen to live in the era when the sizes match.

How we know so precisely

We are not guessing at any of this. Apollo astronauts and several uncrewed missions left mirrored reflectors on the lunar surface, and observatories on Earth fire lasers straight at them.

By timing how long the light takes to bounce back, scientists pin the distance down to within a few centimeters. That same technique is exactly how we measure the 3.8-centimeter yearly drift in the first place.

Bounce a laser off the Moon and you wait about 2.5 seconds for it to come home.

How long it takes to get there

Light makes the trip in 1.28 seconds, but spacecraft are nowhere near that fast. The Apollo missions took roughly three days to reach the Moon back in the late 1960s and early 1970s.

Faster modern probes have made the crossing in well under a day when they fly a direct path, while fuel-efficient missions sometimes spiral out over weeks or months to save propellant.

Driving there, hypothetically, would take about six months of nonstop highway speeds. The Moon is close in cosmic terms and very, very far in human ones, which is exactly why crossing it in days by rocket was such a staggering achievement.

It is worth sitting with that contrast. The fastest natural messenger in the universe, light, makes the trip in just over a second, while the fastest thing humans have ever built still needs the better part of a day. That gap is the whole story of why space travel is so hard.

Try It Yourself

Want to mess around with the ideas above? On whatifs.fun, Solar System, Size of Space and Gravity Playground all let you do exactly that — free, in your browser, no download.

Keep reading: what if the Moon vanished and how big the universe really is. Both go deeper on the same rabbit hole.