The term “Cosmology” comes from the Greek κόσμος (kosmos, “world”) and –λογία (logia , “study of”). It is the study of the origin, evolution, and eventual fate of the universe, the study of the large scale properties of the universe as a whole. Like any field of science, cosmology involves the formation of theories or hypotheses about the universe, theories which make specific predictions for phenomena that should be testable with observations. The observations may cause the theories to be abandoned or to be revised to accommodate the data. For much of science’s history, the prevailing theory about the origin and evolution of the universe was the theory, dating back to Aristotle, that the universe was eternal, unchanging, not evolving, with neither beginning nor end. Observations in the 20th century caused that theory to be abandoned, and currently the prevailing theory about the origin and evolution of our Universe is the so-called Big Bang theory, first developed by Fr. Georges Lemaître in the 1920s.