The Hubble-Sandage-de Vaucouleurs Classification

Two broad morphological types characterize most galaxies: elliptical and spiral forms. The remaining small percentage of galaxies that cannot be characterized in this way are generally relegated to the irregular class. The earliest classification schemes that have had a continuing influence on modern systems were independently developed by Lundmark [90] and Hubble [52]. Discussions of this early history of galaxy classifications: [14, 26, 49]. Modern reviews of the existing classification schemes: [30, 158 (L5), 195, 199].