Almost 3000 years after the Babylonians began recording motions in the heavens and 1300 years after Ptolemy's geometrical explanation of those motions, Nicolaus Copernicus revived Aristarchus's heliocentric concept launching astronomy, and consequently science, on a new road to understanding motion. On Copernicus's heels followed Tycho Brahe with new and better observations of the motions of planets and Johannes Kepler with his ingenious laws describing planetary motion. Briefly stated, Kepler's first two laws are that the orbits of the planets are ellipses, not circles as Plato had wanted, and their variable motion is due to their changing distances from the Sun. His third law establishes the relationship between the planets' orbital periods and their mean distances from the Sun. Kepler's laws are universal in that they apply to any two bodies gravitationally bound to each other, whether in the Solar System or elsewhere in the Universe.
Close behind Copernicus and Kepler came a fascinating personality and the architect of a new perception of motion in the person of Galileo Galilei. The 200-year period spanned by Copernicus, Kepler, and Galileo can be thought of as a dividing line between an old science, which had seen only minor changes since its invention by the Greeks, and a new science in which the methods of observation and experimentation would play an increasingly more profound role. There is, however, in this transition period no abandonment of the basic elements of scientific thinking as first laid down by the Greeks.
From the third century B.C. until the latter part of the seventeenth century, cosmological thought was pretty much that of the Greeks, with some mathematic refinements but no conceptual innovations. Halfway through the thirteenth century, knowledge of astronomy had spread throughout Europe as Greek manuscripts, having come by way of an earlier Arabic science, were translated into Latin in the newly founded European universities. The Renaissance blossomed in the next two centuries, ending the dominance of ecclesiastical concerns in medieval thought and beginning the development of a broader range of intellectual considerations. Renaissance scientists initiated a new era in picturing the physical world. In doing so they paved the way for important changes in scientific thought and outlook. For astronomy the most important advances were Kepler's, Galileo's, Descartes's, and Newton's concepts of motion, gravity, space, and time. After Copernicus, Kepler, and Galileo, Newton's conceptual framework introduced a a whole new era in cosmological thought. Let us examine these events leading up to Newton closer.