Cosmology Timeline By Scrasms: The Timeline Cru 1501 Copernicus develops the Heliocentric Theory 1572 Tyco Brahe discovers supernovas 1609 Kepler proposes the three laws of planetary motion 1687 Isaac Newton develops the theory of gravity 1773 Pierre-simon Laplace applies Newton's theory of gravity to the entire solar system 1781 William Herschel discovers Uranus and develops the theory of stellar evolution 1905 Percival Lowell predicts the existence of Pluto and begins looking for it 1905 Albert Einstein develops the theory of relativity 1912 Henrietta Leavitt develops the period-luminosity theory 1917 Willem de Sitter makes a model of the universe using Eintein's theory of relativity 1919 Harlow Shapley determines the overall shape of our universe and the position of our solar system 1927 Georges Lemaitre proposes the Big Bang theory 1929 Edwin Hubble proves our universe is expanding and the existence of other galaxies 1957 Fred Hoyle publishes his book that proves the stellar nucleosynthesis theory 1964 Arno Penzias and Robert Wilson discover Cosmic Background Radiation (CBR)