Large Scale Structure
Up until the latter part of the 20th Century astronomers thought, in the words of the eminent astronomer Edwin Hubble, that the universe was "sensibly uniform." As a result of redshift surveys of large samples of galaxies we now know that the galaxies around us are distributed in an incredible tapestry of filamentary and sheet-like structures called the cosmic web. Massive clusters of galaxies lie at major "intersections" in this web. Galaxies like our own Milky Way are usually found in groups which often lie on the outskirts of clusters or superclusters. The first really large structure, the Great Wall, was discovered by CfA astronomers in the late 1980's and is approximately 300 million light-years across.
Emilio Falco, Dan Fabricant, Margaret Geller, Robert Kirshner, Mike Kurtz