During the European Renaissance, scientists finally began to replace the old ideas put forth by Aristotle and Ptolemy with new and remarkable theories of their own. Many of these theories would completely change our view of the universe and would lay the groundwork for the discovery of universal gravitation.The first, and perhaps the most important new idea of Renaissance astronomers was put forth by the Polish priest Nicolaus Copernicus (1473 AD-1543 AD). In short, he proposed that the Earth was not the center of the universe after all, but simply orbited around the Sun with the rest of the planets. This is called a heliocentric universe. This was a huge step forward for scientific thinking so it is not surprising that the idea was met by strong opposition, especially from the Catholic church which had used Ptolemy’s Earth centered model for over 1,000 years. In fact, it took well over half a century for other scientists to begin taking Copernicus’ theory seriously.
The Italian astronomer Galileo Galilei (1561 AD-1642 AD), was another major Renaissance thinker. Not only was he one of the first major supporters of Copernicus, for which he was punished by the Catholic church, but he also managed to score a second victory against the old ways of thinking when he disproved Aristotle’s belief that heavier objects fall faster than lighter ones.As the legend goes, Galileo climbed to the top of the Leaning Tower of Pisa where he simultaneously dropped a large and a small weight. Both weights hit the ground at the same time, thus proving that all objects, barring air resistance, fall at the same speed. However, the reason for this phenomenon would not actually be understood for another hundred years or so. For more on this discovery see Small Scale Effects Page 6.
A third Renaissance scientist, the German Johannes Kepler (1571 AD-1630 AD), capped off this age of discovery with his three laws of planetary motion. While Copernicus had given us a vague idea of what the solar system looked like by suggesting that the planets orbit around the sun, Kepler worked out the details of these orbits. His most famous law made the remarkable statement that the planets did not travel in perfect circles, as Copernicus had thought, but in slightly eliptical orbits instead. (An ellipse is an elongated circle.) Oddly enough, Kepler was not very fond of this idea himself and only used it because it seemed to match his observations very well. However, it ruined his hypothesis that orbits were caused by magnetic forces. For more on Kepler's laws see Large Scale Effects Page 6.
