The technique of spectroscopy allows astronomers to study the composition of stars. The star light is split up into its rainbow colors. But little bits of colors are actually missing in there. Different atoms within the surface layers of the star have absorbed this missing light. This allows astronomers to figure out what elements and how much of them are present in the star.
Associated Book Chapter from Searching for the Oldest Stars: Ancient Relics from the Early Universe
- Chapter 7: Tales Told by Light