Galaxies, Page 82: [Previous Page] [Next Page] [Class Home Page] Textbook pages 423 - 431

The Classification of Distant Galaxies

Edwin Hubble took photographs (this was done on large glass plates) of tens to hundreds of galaxies. Just like Annie J. Cannon who classified stellar spectra, Hubble classified galaxies. This classification scheme is strictly morphological (based on physical appearance) and does NOT imply an evolutionary sequence. However, their physical appears do reflect differences in their content! Consider this image of a spiral galaxy, NGC 1512.

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: