What stars are made of?

And we do know! And yet we can’t scoop up some of the star stuff and take it to the laboratory. But we can look at the light from the stars (and our sun is also a star).

Different elements, when heated give off light of a particular color or sets of color. By passing the emitted light through a prism you can see the individual colors being emitted. If you pass white light through that same gaseous element you’ll see light being absorbed at those same colors. These are called emission and absorption spectra. Below is the absorption and emission spectrum for hydrogen.

When you look at the sun (DON’T!) you just see white light. But, again, if you pass the light through a prism you see the constituent colors emitted by the sun. It’s nearly a continuous spectrum from red to violet with some strange black lines. Those lines show colors that are being absorbed as the light leaves the sun and that is the fingerprint of certain elements

You can find the fingerprint of hydrogen, helium and other elements in the sun's spectrum

It’s actually a pretty big deal to find out that using terrestrial methods (spectroscopy) you find the terrestrial elements in the sun. Mostly hydrogen and helium with a smattering of heavier elements. It’s not so exciting what the elements are but that we KNOW what they are. There is a precise map of where those black lines are and what element is causing them.

AND the same can be done with star light. It takes a longer exposure but the method is exactly the same. And from looking at thousands of stars in the sky we find that the good old earth bound periodic table of the elements is actually the UNIVERSE’S  periodic table. ALL the stars are mostly hydrogen and helium with a smattering.

Again of course the devil (if he existed) is in the details. But what’s important is that the testable IDEA that light can be broken up into colors as everyone has seen with a prism or even a rainbow leads directly to a method for identifying elements. We don’t have to be able to calculate  the wave lengths ourselves to understand the one to one correspondence between colors (or missing colors in this case) and elements.