Say it like this

Everything there is, including you. Most of it is empty space.

For the grown-up

The universe is the whole of space, time, matter and energy. Current estimates put it at roughly 13.8 billion years old. The overwhelming majority of its volume contains essentially nothing, which is the fact children find most startling and therefore most memorable.

The easy mistake

Careful here. Whether there is an edge is not a silly question and it does not have a simple answer. It is fine, and better, to say so.

The full explanation

What Is the Universe?

A glossary entry is the short version. This one has the child explanation, the grown-up explanation, the questions and an activity.

Read it

Words next to this one

Galaxy An enormous group of stars travelling together. Ours has a couple of hundred billion in it. Star An enormous ball of burning gas, so far away it looks like a dot. Our sun is one. Gravity The pull that everything with weight has on everything else. Bigger things pull harder. Orbit Going round and round something because it keeps pulling you in and you keep missing it.