Hubble Tuning Fork Diagram: Galaxy Classification
Hubble classified galaxies as elliptical or spiral. The elliptical
galaxies are designated with E and then a number indicating the elongation
of the galaxy: En, where n = 10(a-b)/a a = long
diameter, b = short diameter. The spiral galaxies are divided into
two major types, normal and barred. Both normal (designated with
S) and barred (designated with SB) are further divided into 3 subclasses:
a = largest bulge to disk ratio, most "wound" spiral structure; through
c = smallest bulge to disk ratio, least "wound" spiral structure.
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