The American astronomer Carl Seyfert (1911–1960) is credited with the discovery of active galaxies. Seyfert’s general area of astronomical expertise was determining the spectroscopic properties, colors, and luminosities of stars and galaxies. In 1940, he went to work as a research fellow at the Mount Wilson Observatory in California, the same institution where Edwin Hubble made his most famous discoveries about galaxies. By 1943 Seyfert had discovered a number of spiral galaxies with exceptionally bright nuclei. These galaxies had unusual spectral signatures that had extremely strong and broad emission lines, indicating that very energetic activity was going on inside their nuclei. Today, those types of active galaxies are called Seyfert galaxies in his honor.