Galaxies congregate in vast superclusters -- collections of many thousands of galaxies that are bound together by their mutual gravity. But it took a long time for astronomers to recognize this cosmic structure. In fact, the most famous astronomer of the early twentieth century, Edwin Hubble, thought that galaxies were evenly distributed across the sky.
The first clue that Hubble was wrong came in 1932. By then, Hubble himself had just proved that the universe consists of many individual galaxies.
Austrian astronomer Walter Bernheimer reported a concentration of galaxies stretching from Pegasus to Pisces and into Perseus -- a concentration he described as a supercluster.
Also in the 1930s, Clyde Tombaugh -- the astronomer who discovered Pluto -- was searching for distant planets. His photographic plates revealed many galaxies, and he noted the same supercluster that Bernheimer had seen.
Tombaugh tried to persuade Hubble that the universe of galaxies wasn't smooth. Hubble wasn't convinced, though, and other astronomers gave his opinions a lot of weight. Not until the 1970s did they begin to accept that superclusters are strung through the cosmos like luminous spider webs.
Today, the supercluster that Bernheimer and Tombaugh discovered is known as the Pisces-Perseus supercluster. It's one of the closest superclusters, even though it's a quarter of a billion light-years away.
We'll talk about a big gap between superclusters tomorrow.
Script by Ken Croswell, Copyright 2008
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