Belgian priest and astronomer Georges Lemaître died on June 20, 1966, at the age of 71. A pioneering astrophysicist, Father Lemaître was a professor in Louvain, Belgium and a lecturer at Harvard University. His most important contribution to science was the discovery of the expansion of the universe and the theory of the Primeval Atom, which would later come to be known as the Big Bang Theory. Born in Charleroi, Belgium in 1894, Father Lemaître studied mathematics, astronomy and philosophy at Catholic University of Louvain, graduating with undergraduate and master's degrees, and later earned a doctorate from MIT. After teaching in Louvain, he was appointed the director of the observatory at the Collège de Belgique in 1927. His work ushered in a new understanding of the universe, and earned him several honors and awards, including the Prix Janssen from the French Academy of Sciences and a nomination for the Nobel Prize in Physics. He published numerous books and articles during his lifetime, including the 1933 paper in which he proposed that the universe was expanding. His greatest contribution to science and cosmology continues to be acknowledged and celebrated.