Henry Norris Russell developed the Hertzsprung-Russell diagram. The diagram distinguished the lifespan of stars and popularized the idea of different types of stars based on their life spans.
Norris was able to formulate the life of stars by analyzing the amount of light that they emitted. He was able to determine that some stars were newborn while others were nearing the end of their life spans. He was also able to confirm an earlier theory that stars were primarily composed of hydrogen. Russell is sometimes referred to as the "Dean of American Astronomers" due to his important contributions to the world of astronomy.