Karl Schwarzschild was a contributor to the field of astronomy in the 20th-Century. His work included developing precise methods of photographic photometry, establishing the link between spectral type and color of a star, and recognizing the role of radioactive processes in the transport of heat in stellar atmospheres.
In addition to his work in astronomy, Karl Schwarzchild made contributions to physics and relativity. He is credited with helping to develop the theory of atomic spectra. He also developed rules for quantization and proposed a theory of the effect of an electric field on light, known as the Stark effect. Finally, he was a pioneer in the quantum theory of molecular spectra.