What is the galaxy classification?

The current galaxy classification is based on.

* The Hubble sequence is a morphological classification scheme for galaxies invented by Edwin Hubble in 1936 * The de Vaucouleurs system for classifying galaxies is a widely used extension to the Hubble sequence, first described by Gérard de Vaucouleurs in 1959. * The Yerkes (or Morgan) scheme uses the spectra of stars in the galaxy