How far away is the Moon right now?

The Moon is Earth's only natural satellite: a ball of rock 3,474.8 kilometres wide that circles our planet about once a month. Earth is about 3.7 times as wide. The Moon has no air and makes no light of its own. What we see is sunlight bouncing off its grey dust and rock.

It is the only other world people have walked on, and it is close enough to shape our days. Its pull raises the tides in the oceans.

Its distance is never quite the same. The Moon's path around Earth is a slightly stretched loop, not a circle, so in every orbit it swings in to its closest point and out to its farthest. The Sun's pull tugs on that loop too. It stretches it more in some months than in others, and slowly turns it around. That is why the number at the top of this page never stands still.

Astronomers call the closest point of each orbit perigee, and the farthest apogee. They are not the same from month to month. Between 2016 and 2035, the Moon comes closest on 25 November 2034, at 356,445 kilometres. It was farthest in March 2020, at 406,692 kilometres.

A Moon at perigee looks a little bigger and brighter than a Moon at apogee. When a full Moon falls near perigee, people call it a supermoon. It is not an official term in astronomy. NASA uses it for a full Moon that comes close to perigee, and a few happen each year, one after another.

The difference is real but gentle. Side by side in two photos, a supermoon is clearly larger than a full Moon at apogee. Alone in the night sky, with nothing to compare it with, few people could tell.

Light is the fastest thing there is. It moves at 299,792.458 kilometres every second, fast enough to go around Earth's equator in 0.13 seconds.

Even light needs a moment to reach the Moon. Right now the trip takes 1.22 seconds. So the Moon you see tonight is the Moon of a moment ago. The light that reaches you from the Sun left it minutes ago, and the light of the stars left them years or ages ago. Of all the worlds in the night sky, the Moon is the one we see almost as it is now.

That small delay was easy to hear during the Apollo missions. Every word between Houston and the Moon crossed the gap at the speed of light, there and back, so each answer came after a short pause.

How do we know the distance so well? The astronauts of Apollo 11, 14 and 15 left mirrors on the Moon: panels of glass corner cubes that send light straight back to where it came from. Two Soviet rovers, Lunokhod 1 and 2, carry smaller ones.

Observatories on Earth fire laser pulses at them and time the echo. The beam spreads out on the way, and only a tiny few of its photons make it back. But that is enough. The round trip takes twice the light time at the top of this page, and timing it tells us the distance to within millimetres, about the thickness of an orange peel.

The mirrors need no power, and they have been in use since 1969. They are the last Apollo experiment still running. In 2025 a new reflector reached the Moon on the Blue Ghost lander.

Those laser pulses found something remarkable: the Moon is slowly moving away from us. Each year it is about 3.8 centimetres farther from Earth. NASA compares it with the speed at which your fingernails grow.

The cause is the tides. The Moon's pull raises bulges in Earth's oceans, and Earth's spin carries them slightly ahead of the Moon. Their gravity tugs the Moon forward along its orbit, and it spirals outward. In return, Earth's spin slows down very slightly, so our days are slowly getting longer.

There is nothing to fear in it. Over a lifetime the change is far too small to see. But it means the Moon in your sky is not quite the Moon your grandparents saw, and the mirrors on its surface notice the difference every year.

A famous picture shows all the other planets lined up in the space between Earth and the Moon. Does it work? Add up the widths of Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune, and you get 387,943 kilometres.

The gap itself is a little shorter than the distance from centre to centre, because Earth and the Moon take up some of it. At the average distance, the planets don't quite fit. They fit when the Moon is near apogee, the far part of its orbit, which it reaches in every orbit. So the picture is nearly right, and true for part of every month.

It also shows how empty space is. Seven worlds, two of them giants, laid side by side, and they barely fill the space between us and our nearest neighbour.