Scroll to the Moon

The part nobody puts in the diagram

Every picture of the Earth and the Moon is a lie of composition. The two bodies are drawn large enough to see, which means they are drawn close enough to fit, and the gap between them gets whatever space is left over. It is almost never to scale, because to scale there is nothing in the gap worth drawing, and a diagram of nothing is a hard sell.

This page is that diagram with the compression taken out. Everything on it sits where it actually sits, at one consistent scale, which means most of it is empty and the emptiness is not filler. It is the finding.

The number you looked up is not the number on this page

If you search for the distance to the Moon you get 384,400 km. This page is 376,291.5 km tall. The difference is not an error, and it is worth a paragraph because it is the kind of thing that quietly breaks every scale model ever built.

384,400 km is what NASA's Jet Propulsion Laboratory calls a mean semi-major axis. A semi-major axis is a property of an orbit, and orbits are measured between centres — so that number runs from the middle of the Earth to the middle of the Moon. It passes through 6,371 km of rock to get out of here and another 1,737.5 km of rock to arrive.

You are not starting at the centre of the Earth. You are starting on the surface, which is where the scrolling begins, and you are stopping at the Moon's surface, which is where it ends. Subtract the two radii and the trip is 376,291.5 km. The 8,108.5 km you just discarded is twenty times the altitude the International Space Station orbits at — a rounding error taller than everything humans have ever routinely flown through.

The second thing about 384,400 is that the Moon is not there. NASA's own table defines the figure as the "average of minimum and maximum distances from an object to the body it orbits" — it is a midpoint by construction, the average of a nearest and a furthest, and the Moon spends almost all of its time at neither. It is also leaving: about an inch further away each year. This page picks the average and holds it still, which is the only way to draw a fixed thing, and is worth knowing as a choice rather than a fact.

Nobody agrees where space starts

Not far into the scroll you pass a band rather than a line. That is deliberate, and it is the most interesting thing on the way up.

Ask where space begins and the answer is 100 kilometres. NASA gives that number and, in the same sentence, says why you should not lean on it: "While there's really no clear boundary between where Earth's atmosphere ends and outer space begins, most scientists use a delineation known as the Kármán line, located 100 kilometers (62 miles) above Earth's surface, to denote the transition point, since 99.99997 percent of Earth's atmosphere lies beneath this point."

That is not a measurement. It is a convention that a large number of people found convenient, and conventions can be argued with. In 2018 Jonathan McDowell, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, published a paper doing exactly that, proposing "80 kilometers as a more appropriate boundary than the currently popular 100 km Von Kármán line".

Twenty kilometres of disagreement sounds academic until you notice what the line is load-bearing for. It decides who has been to space. McDowell points out that if the boundary is set at 100 km rather than 80, five X-15 pilots — Robert White, Robert Rushworth, Jack McKay, Bill Dana and Mike Adams — stop having been astronauts. Same flights, same altitudes, same men; a different convention, and the record reads differently.

Drawn to scale, the disagreement is 20 km wide on a journey of 376,291, and you will pass through the whole of it in well under a second. The atmosphere does not end. It thins out over hundreds of kilometres with no edge anywhere in it, and the line is a decision people made about where to stop arguing — a decision that determines an official record about specific named human beings. This is the useful shape to take away from the band: a number can be real, widely used, and correctly cited, and still not settle the thing everyone assumes it settles.

Everything worth seeing happens in the first minute

Scroll with determination and the Moon is eight to ten minutes away. Here is where the landmarks fall in that.

The edge of space, whichever edge you pick, is 0.02% of the way. The Space Station is 0.10%. The GPS satellites, which feel remote in the way that satellites do, are 5.37%. The geostationary ring — the furthest orbit anything routine occupies, where the weather satellites hang motionless over one spot — is 9.51%.

That is the whole tour. Every landmark on this page is behind you inside the first minute, and then there are eight more minutes of nothing at all. Not nothing as a gap between the interesting parts. Nothing as roughly ninety per cent of the distance between the Earth and the only other place people have ever stood.

The Space Station deserves a note on the way past, because it is the one landmark with no fixed altitude at all. NASA publishes a range — "between 370–460 km" — and explains why in the next breath: the station "falls towards Earth continually due to atmospheric friction and requires periodic rocket firings to boost the orbit". It is drawn here as a band for that reason. The ISS is not a place, it is a sag with a schedule.

Why it has to be this slow

The scale is the entire argument, so it cannot be cheated. Speed the scroll up past the empty parts and you have made another diagram with the gap taken out, which is the thing every other picture of the Moon already does.

There is an auto-cruise button, because nine minutes of thumb work is a real cost and wrists are not a joke. What there is not is a shortcut. The distance is the content. Anything that gets you there faster is editing the finding. If you would rather have your scale in one screen than in nine minutes, spending a trillion dollarsmakes a related point about a number nobody can picture.

Most people stop somewhere in the void, and that is a reasonable response to finding out how much of it there is. If you do reach the end there is a certificate, which roughly one in a thousand visitors will see.

Questions people ask