It's tempting to think of stars as great fireballs. I mean, just looking at the image of our sun above, it certainly looks like it's burning. Stars aren't actually big balls of flaming gas and they don't burn in the conventional sense. They are mostly made up of hydrogen in its "plasma" state, which is a gas that is so hot that it ionises. The sheer gravitational force of the star's own mass heats it up to such extreme temperatures that the nuclei of the hydrogen atoms, which consist of a single proton, have enough energy to overcome the electrical charge that prevents them from smashing into each other. So that's exactly what they do, they smash into each other. The two hydrogen nuclei fuse together to make a helium nucleus in a process called nuclear fusion. This process releases a massive amount of energy, way more than simple chemical combustion by a significant amount. We call this energy "sunshine". These nuclei can even continue to fuse into even heavier elements all the way up to iron. When the star eventually dies, these heavy elements are ejected into space and become the building blocks of everything else in it. The elements on Earth, including the ones in your body, will have all have been forged in the heart of an enormous ancient star. Which is cool as all hell.
