Another important fact of gas spectroscopy is that a gases emission and absorption spectrum are the same. Gas spectroscopy has a number of uses, one of which is to determine the composition of stars. We can't go to neighboring stars and take a sample of the gases inside, so instead we can measure what wavelengths are absorbed when the light emitted from the star pass through the far cooler gases surrounding it and approximate the star's composition. 1: If we measure this absorption spectrum from a nearby star:

And here is a chart of absorption bands:

Select all that apply:
Hydrogen
Helium
Sodium
Lithium