Margaret Joan Geller (born 1947) discovered the existence of a Great Wall of galaxies in space that stretches at least 500 million light-years.

Margaret Joan Geller, an astronomy lecturer at Harvard University and a senior scientist at the Smithsonian Astrophysical Observatory, helped discover a "Great Wall" of galaxies in space stretching at least 500 million light-years. The existence of this structure, the largest ever seen in the universe, presents a conundrum for theorists dealing with the early universe. She has been mapping the nearby universe for the past sixteen years and has produced the most extensive pictures yet.

Geller was born in Ithaca, New York, on December 8, 1947, to Seymour Geller and Sarah Levine Geller. She received her bachelor's degree at the University of California at Berkeley in 1970, and was a National Science Foundation fellow from 1970 to 1973. Her M.A. followed at Princeton University in 1972, and her Ph.D. thesis, entitled "Bright...