Prior to the scientific revolution of the 17th century, Aristotle’s teachings that the universe centered around the Earth was believed by Europeans, especially churchmen. The system had some flaws, which included the occasional retrograde movement of Mars. Copernicus (1473-1543), however, thought he could disprove the old ideas because they were too full of errors. He promoted the belief that the sun was the center of the universe. Copernicus’ new idea of heliocentrism trumped the former belief of geocentrism because it had fewer flaws. Then Kepler (1571-1630) discovered that planets do not have perfectly circular orbits by analyzing other astronomer’s data and performing his own astronomical observations. This new idea removed most, if not all, of the flaws from Copernicus’ heliocentrism. Observing craters and mountains on the moon, Galileo (1564-1642) proved that celestial objects, as it turns out, are not perfect spheres. During his moments when he watched the sky with a telescope, Galileo also saw moons orbiting Jupiter, disproving the theory that the Earth would lose the moon if it was in motion. Several decades later, Issac Newton (1642-1726) was struck by an apple that fell from a tree. He postulated a theory of gravity which stated that every object attracts every other object in the universe. Previously people believed that Earth was affected by different laws of physics than outer space. Newton’s new idea applied to the entire universe. When Aristotle’s outdated teachings were discarded primarily by the work of these four ingenious men, Copernicus, Kepler, Galileo, and finally Newton, the flimsy old ideas were replaced by proven ones.