Hubble Classification
  • The generally-used classification of the galaxies into elliptical, spiral and barred spiral types, which is used to describe all but the most unusual types of galaxy. Within these overall headings are subdivisions. The ellipticals are classed as E0 to E7, becoming steadily more elongated as the number increases. Spirals are classed as Sa, Somebody or Sc, with the spirals less tightly wound for the later letters, and the same system is adopted for the barred spirals, which are classed as SBa, SBb and SBc. Type S0 indicates a regular ellipse apparently intermediate between the three categories. Galaxies which fall between the categories are sometimes classed as Sbc or some similar hybrid. It is important to note that the actual relation between the different types of galaxy may well be less neat than this family tree implies.

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