Our Planet

Why does the Moon follow me?

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If you're riding in a car at night, it may look like the Moon is following you or chasing you, zooming behind the treetops to keep up with your car. The Moon isn't actually following you, though. It's just an optical illusion!

There are a couple reasons for the illusion. The first is that the Moon is huge! It's smaller than the Earth. About 50 Moons could fit inside the Earth, but it's still really huge! If a person stood as far away as the Moon is, we wouldn't be able to see him or her without a really powerful telescope!

The Moon's distance also helps it seem like it's following you. Things that are very far away stay in our fields of vision (what we can see) for longer! You can imagine your field of vision like a giant "V" coming out of your eyes. The pointed tip of the "V" is close to your eyes, and from there it expands outward. Nearby things that move across your field of vision, like a tree close to the road as your car drives past it, appear to move very quickly. They only have a short trip across your field of vision, through the thinnest part of the "V". Things that are far away, in the very widest parts of the "V," have farther to go across your field of vision. You see them for longer, and they appear to move more slowly. The Moon is so far away that it's almost always in your field of vision. And it's so very far away that it seems like it's always in the same part of your field of vision. Even as you vroom along in a car, the Moon appears to stay with you!

Exploration

Vehicle Visions

Next time you are a passenger in a car, on a bus, or on a train, look out the side window. Watch objects that are really close to the side of the road, like stop signs or mile markers. How quickly do those seem to go by as your car passes them? Look at objects farther back from the side of the road, like trees or houses. How fast do those seem to go by? Is it faster or slower?

Do mailboxes on the side of the road seem to pass by more quickly than the houses behind them? If you're lucky enough to see the Moon in the sky behind those houses, think about how slowly it seems to go by because it's so far away!