The Hubble Classification

While working at the Mount Wilson Observatory, Edwin Hubble developed a galaxy classification system.  The "tuning fork" diagram above shows us three of the four shapes used to distinguish the various galaxies, E0 and E6 represent variables Elliptical galaxies, while Spiral Galaxies are represented by S0, Sa, Sb, and Sc, and Barred Spirals by SBa, SBb, and SBc. The other classification, Irregular Shaped galaxies are not represented on the graph.