How did Edwin Hubble categorized galaxies?

Astronomer Edwin Hubble classified galaxies into four major types: spiral, barred spiral, elliptical and irregular. Most of the nearby, bright galaxies are ... Spiral galaxies have a variety of shapes and are classified according to the size of the bulge and the tightness and appearance of the arms. read more

Edwin Hubble's arrival at Mount Wilson Observatory, California in 1919 coincided roughly with the completion of the 100-inch (2.5 m) Hooker Telescope, then the world's largest. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy. read more