How Do We Know the Size of the Universe?

Imagine you're in a huge balloon, and you can only see the part of the balloon around you. To figure out how big the whole balloon is, you might measure how fast it's expanding or how far away other parts of the balloon are from you.

The Big Balloon

Scientists look at stars and galaxies like they're on a giant balloon, the universe. They see that everything is moving away from us, just like when you blow up a balloon. By measuring how fast things are moving apart, scientists can guess how big the whole universe might be.

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Examples

If you're on a balloon, and it's blowing up, everything else seems to move away from you, just like galaxies do in the universe.
Imagine measuring how far your friend is by how bright their flashlight looks from across the room.
A giant ruler made of stars helps scientists measure distances across space.

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Categories: Science · cosmology,universe,science