13.7: Classification of Galaxies
Edwin Hubble was the first to classify galaxies based on the shapes, which he observed. These observations included Elliptical galaxies, Spiral galaxies, and Irregular galaxies. This lead to his Hubble Galactic Tuning Fork (Hubble Sequence)—how Hubble thought galaxies evolved.
Astronomers now recognize four major groups of galaxies:
- Elliptical Galaxies
- Spiral Galaxies
- Irregular Galaxies
- Active Galaxies