Spectral Lines

Hot things like stars glow. The glow makes light in all the different colours of the spectrum.

However, atoms can emit (make) or absorb (destroy) light of very specific colours.

They make the same colours as they absorb, but only one at a time - when they are hot they make the light and when colder, they absorb it.

Different atoms make or absorb different sets of colours.

This means that astronomers can tell what atoms a star is made of by looking at the different colours that have been made or absorbed by the different atoms.