Ancient Astronomers time line By shannongibbs21 240 BCE Eratosthenes is most famous for making the first good measurement of the size of Earth 150 Ptolemy first major astronomical work the Almagest was completed 1543 Copernicus publishes his major astronomical work 'Six Books Concerning the Revolutions of the Heavenly Orbs,' 1572 Brahe made the observations of a supernova 1611 Kepler made the famous Keplerian telescope 1666 Newton developed his theories of gravitation 1905 Einstein created the Theory of General Relatively