While we’re observing these stars, we can use a spectrometer, the device that separates wavelengths, to reveal the star’s absorption spectrum and its elemental composition.
But when we study very distant bodies, we find that their absorption spectrum is slightly different from what we’d expect, given our knowledge of typical star compositions.
But when we study very distant bodies, we find that their absorption spectrum is slightly different from what we'd expect, given our knowledge of typical star compositions.