Studying the line spectra produced by hot gases and absorbed by cooler gases allows us to identify the elements in stars. When a gas is very hot, it doesn’t emit all wavelengths of light.

Proceedings of the American Academy of Arts and Sciences, Vol. 42, No. 13 (Nov., 1906), pp. 235-260 (34 pages) ...

This causes line emission spectra to be produced, as shown below. This is not a continuous spectrum as only light of specific frequencies and specific colours are produced. Different types of ...