HENCOUP & MARTEN / SCIENCE PHOTO LIBRARY HENCOUP & MARTEN / SCIENCE PHOTO LIBRARY
Galaxy classification. A selection of galaxies chosen by American astronomer Edwin Hubble to illustrate his classification of galaxies. Hubble proposed it in 1925 and, although it has been revised since, it is still widely accepted. Galaxies were broadly divided into 3 classes: elliptical, irregular, and spiral. The first two classes are represented here. Elliptical galaxies were grouped into eight types according to their degree of flattening, ranging from E0 (NGC 3379), which is almost circular, to the spindle-shaped E7 (NGC 3115). At bottom, M82 and NGC 4449 represent galaxies Hubble placed in the irregular group, because they have no obvious symmetry.
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