Hubble Classification of Galaxies

There are several schemes to desribe or classify a galaxy based on its physical appearance. The Hubble classification scheme, devised by Edwin Hubble in 1936, arranges most galaxies into one of three broad classes:

  • Elliptical Galaxies
  • Spiral Galaxies
  • Barred Spiral Galaxies

Within each of these broad classes, there are sub-classes to further categorize a galaxy. The Hubble scheme is illustrated in the diagram above in a fork-shaped arrangement. The elliptical galaxies arranged in 7 sub-classes from spherical (E0) to extremely elliptical (E7), followed by the lenticular galaxy class (S0). Beyond the lenticular class, the spiral (types Sa, Sb and Sc) and barred spiral (types SBa, SBb and SBc) galaxies are organized along two separate tines.

For more information, see Galaxy Morphological Classification (Wikipedia).

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