Hubble’s classification

Classification of galaxies according to their form, devised by astronomer Edwin Hubble in the 1920s; it is still used today.

elliptical galaxy

Spherical or oval galaxy with no spiral arms.

lenticular galaxy

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.