The document discusses the history of astronomy from ancient Greek astronomers to Isaac Newton. It describes how Ptolemy first proposed the geocentric model which was believed for over 1500 years. Copernicus later proposed the heliocentric model which placed the Sun at the center. Kepler took Tycho Brahe's data and developed his laws of planetary motion, showing their orbits were elliptical not circular. Galileo made important astronomical observations with his telescope that supported the heliocentric model, such as the phases of Venus and moons orbiting Jupiter. Finally, Newton explained gravity and inertia as what kept the planets in orbit around the Sun.