Why does a star glow?

A star is so heavy that its own gravity squeezes it hard, most of all in the middle. Down there, tiny bits of hydrogen get crushed together so hard that they join up and become helium. Every join lets out a burst of energy. All those joins make the light and heat that a star shines with.

If stars are mostly hydrogen, where did everything else come from?

Big stars keep squeezing, joining small bits into bigger ones, like carbon and oxygen. Some of that stuff blows off into space, and some is flung out when big stars explode. It drifts into new clouds that become new stars and planets. So the carbon and oxygen in your body were made inside stars, long before the sun was born.

What are stars made of?

Zib answers for ages 8–11, then goes 2 steps deeper each time a child asks why.

Zib says

Our sun is the closest star, so it shows us what they're all like. It's a gigantic ball of hot, glowing gas. Most of that gas is hydrogen, with some helium mixed in. Every star you see at night is a ball like that, just much, much farther away.

For ages 8–10

Checked against Stars (NASA Science)
Why does a star glow?

A star is so heavy that its own gravity squeezes it hard, most of all in the middle. Down there, tiny bits of hydrogen get crushed together so hard that they join up and become helium. Every join lets out a burst of energy. All those joins make the light and heat that a star shines with.

For ages 9–11

Checked against Stars (NASA Science)
If stars are mostly hydrogen, where did everything else come from?

Big stars keep squeezing, joining small bits into bigger ones, like carbon and oxygen. Some of that stuff blows off into space, and some is flung out when big stars explode. It drifts into new clouds that become new stars and planets. So the carbon and oxygen in your body were made inside stars, long before the sun was born.

For ages 10–11

Checked against How are we made of star stuff? We asked a NASA expert (NASA)