You're previewing the Bennett demo family. Numbers, schedule, and kids are sample data.Start your own

Why the Moon Looks Like It's Following You

Space · 4 min

Why the Moon Looks Like It's Following You

You go for a drive at night and the Moon comes too. It stays right outside your window the whole way. It is not chasing you — and there is a way to prove it.

It comes with you

You are in the back of a car at night. The Moon is out.

The car goes fast. Everything outside whips past — fences, bins, parked cars, gone, gone, gone.

But the Moon stays.

You turn a corner. It's still there. You drive for half an hour. Still there, right outside your window.

It really does look like it is coming with you.

So is it following you?

Lots of people think so when they are small. It's a good guess. It looks exactly like that.

But here is how you can tell it isn't.

Right now, somebody else is driving the other way down the same road. And they are looking out of their window thinking the Moon is following me.

And somebody in the next town. And a boat out at sea. All at once. All in different directions.

One Moon cannot chase all of them at the same time. So it isn't chasing anybody.

Everybody, everywhere, all at the same time, sees the Moon come with them. Something that happens to everyone at once cannot be about you.

Check yourself

You are in a moving car. Which one of these goes past your window the FASTEST?

Close things whoosh. Far things don't.

Watch out of a car window and you'll see it.

A fence post right by the road? Gone in a blink.

A house a bit further off? It takes a moment longer.

A big hill far away across the fields? That one takes ages. You watch it slide slowly by while the fences fly.

The further away something is, the slower it goes past. Every single time.

And the Moon is very, very far

The Moon is further away than anything you have ever been to.

It is further than the hill. Further than the mountains. Further than a whole day of driving.

So when your car moves, you do not really get any closer to it, and you do not leave it behind. Not even a little bit.

That means you always have to look the same way to see it. Out of your window. Where it was before.

That's it. That's the whole answer. The Moon is not keeping up with you. You never got anywhere near it.

Try it with your thumb

You can do this indoors right now.

Hold your thumb up in front of your face. Pick something far away behind it — a tree out of the window, or a wall at the end of a long room.

Now move your head slowly, side to side.

Your thumb jumps about all over the place. The far away thing hardly shifts at all.

Your thumb is the fence post. The far away thing is the Moon.

(The Moon does move, by the way. It goes slowly round us. But it takes weeks, so you will never catch it doing that from a car.)

One car ride, looking out of the window

Here is the same drive, thing by thing. Press to see how long each one stays in your window.

A fence postGone in a blink

an arm's length from the car, basically

0 of 4

Whooshes past, or stays with you?

You are in the car again. Put each thing in the right box.

Tap an item, then tap where it belongs

Whooshes past

Stays with you

Check yourself

Your friend is in a different car, driving the OTHER WAY. They say the Moon is following them too. Why are you both seeing that?

Three things to keep

01Close things go past fast. Fence posts, bins, parked cars. Blink and they are behind you.
02Far things go past slowly. A hill miles away takes minutes to slide by. Try it out of the window.
03The Moon is so far it never goes past. Your car never gets near it and never leaves it behind. So it stays in your window — for you, and for everybody else, all at once.

Keep going

Checks answered: 0 of 2

You’re previewing as a parent — nothing here is recorded.

That’s the last one in this channel for now. More are on the way.

Back to all episodes

Where these figures come from

The effect is parallax: as an observer moves, nearby objects appear to shift position quickly against the background while distant objects appear to shift very little. The apparent shift shrinks as distance grows (NASA Science; Las Cumbres Observatory, 'Parallax and Distance Measurement'). The Moon orbits at an average distance of about 384,400 km (roughly 238,900 miles) from Earth, so any journey a car can make in an evening is a negligible change in the observer's position relative to it — the direction you must look to see the Moon is effectively unchanged (NASA Science, 'Earth's Moon: Facts'). Because the effect depends only on distance, it applies to every very distant object: the Sun and the stars appear to 'follow' a moving observer in exactly the same way (Las Cumbres Observatory; standard observational astronomy). The Moon genuinely does move around Earth, completing an orbit in about 27 days, far too slowly for its orbital motion to be visible during a car journey (NASA Science, 'Earth's Moon: Facts'). The thumb demonstration is the standard classroom illustration of parallax: holding a thumb at arm's length and shifting the head makes the thumb appear to jump against a distant background, which barely moves (Las Cumbres Observatory, 'Parallax and Distance Measurement').