Clusters of galaxies, and clusters of clusters of galaxies, called superclusters, make up the structures in the geography of the universe. In this section, we'll explore these structures and take a look at our address on these scales. Galaxies are titanic swarms of tens of millions to trillions of stars. Between the stars, there can be vast interstellar clouds of gas and dust.
Spiral galaxies have a thin, pancake-shaped disk, with a spherical bulge at the center.
Within the disk, the brightest stars trace out the characteristic spiral pattern. Elliptical galaxies are shaped roughly like watermelons, some round and some elongated. In rather plain fashion, the smallest galaxies are called dwarfs while the largest are called giants. Our Milky Way Galaxy is one of three large galaxies in the Local Group of Galaxies. Also in the Local Group are a couple dozen dwarf galaxies.