Unit 6 Review Questions1.How was Edwin Hubble important to our understanding of galaxies?Edwin Hubblediscovered the existence of other galaxies besides our own. In one year, astronomers went frombelieving that the universe contained only the Milky Way to believing the universe holds billionsof galaxies.2.How are galaxies classified?Galaxies are classified by shape into three major groups: spiral,elliptical, and irregular. Spiral galaxies are, perhaps, the type of galaxies that you might think ofwhen you imagine what a galaxy looks like. These galaxies appear in a shape similar to that of aflying saucer. A spiral galaxy has four main parts: a halo, bulge, disk, and arms. Irregular galaxiesare galaxies that do not fit into the spiral galaxy or elliptical galaxy classifications. As their namesuggests, irregular galaxies have an irregular, or unorganized, shape. Ellipticalgalaxies arespherical clusters of stars that can appear condensed into a seemingly perfect circle or stretchedout like an oblong, oval sphere. These galaxies are usually extraordinarily bright within theircenters and contain very little dust and gas. These galaxies generally contain old stars, and allelliptical galaxies lack the material to form nebulae, the material that forms new stars.