Galaxy Classification

Galaxies occur in three main varieties of shapes: Elliptical, Spriral and Irregular. Following is the so called "tuning fork" diagram, produced by Edwin Hubble in the 1920s. It was the first systematic attempt to quantify the morphology of galaxies.

• Elliptical galaxies are designated "E#," where # refers to their apparent flattening.
• Normal spiral galaxies are designated S? and barred spiral galaxies are designated SB?, where "?" is chosen from a, b or c, and was originally classified on the basis of the pitch angle of the spiral arms.
• Irregular galaxies are harder to classify.