Galaxy morphological classification
There are several schemes in use by which galaxies can be classified according to their morphologies , the most famous being the Hubble sequence , devised by Edwin Hubble and later expanded by Gérard de Vaucouleurs and Allan Sandage . 
<triplet> Hubble sequence <subj> Edwin Hubble <obj> named after <triplet> Edwin Hubble <subj> Hubble sequence <obj> notable work