Classification of galaxies according to their form, devised by astronomer Edwin Hubble in the 1920s; it is still used today.
Spherical or oval galaxy with no spiral arms.
Flat, lens-shaped galaxy with a large bulge but no arms.
barred spiral galaxy
Galaxy crossed by a bar of stars and interstellar matter; the spiral arms emerge from the ends of the bar.
normal spiral galaxy
Galaxy composed of a large nucleus from which spiral arms emerge.
type II irregular galaxy
Rare type of galaxy whose structure obeys no specific symmetry.
type I irregular galaxy
Rare type of galaxy that seems to possess spiral arms without displaying a specific symmetry.