a fan wanted to know more. but see my father how from iraq wants to know. how do scientists determine the chemical composition of faraway stars. by the light they emit split into its color components light forms a continuous spectrum. when light impinges on atoms or molecules a portion of it is absorbed that creates black lines at distinct frequencies. in some ways it's like a fingerprint. all the elements in a star leave their fingerprint in the light spectrum that it emits. these spectra can differ greatly that's because the cocktail of elements that make up a star changes over time. this is what the spectrum produced