Hubble defined three major classes of galaxies, called Ellipticals, Spirals and Irregulars. Spiral galaxies come in two varieties: Barred and Normal.

This elliptical galaxy, M59, is classified between E3 and E5.	M81 is an Sb galaxy 12 million light years away.	Can you identify two nuclei? This twisted mess of an IRREGULAR Galaxy is made up of NGC 4038 and NGC 4039.

Hubble went further to try and show the connectedness of these types by making a flow-chart, sometimes called a tuning fork because of its shape. This does NOT constitute an evolutionary sequence! It's based SOLELY on morphology. E stands for Elliptical, while S stands for Spiral: