What primary visual categories define the Hubble Classification Scheme developed by 1926?
Answer
Elliptical or spiral
By 1926, after observing a growing number of external galaxies, Edwin Hubble formalized a system to organize them based on their visual appearance, resulting in the Hubble Classification Scheme. This system initially divided galaxies into two main, broad categories: elliptical galaxies and spiral galaxies. The spiral category was further refined into sub-classes based on the tightness of their spiral arms, designated from Sa to Sc, and also accounted for barred spirals (SBa to SBc) and lenticular (S0) and irregular (Ir) types. Although Hubble initially theorized this sequence represented an evolutionary track, the categorization itself remains fundamental for describing galactic morphology.
Related Questions
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