While the Greeks and the Babylonians and others in the region made serious and interesting astronomical observations, they had really no overriding authoritative understanding of how the universe worked. Why did the stars shine? Why were they so incredibly distant from the sun, moon and the planets? Did the sun revolve around the Earth or did the Earth and the other planets revolve around the sun? What the scholars of antiquity did have was a growing understanding of algebra and geometry and even more complex forms of mathematics.
Since the Earth was the observational platform from which everything in the heavens was viewed, most of Greek science favored the idea of an Earth-centered geocentric universe, even though the idea of a sun-centered or heliocentric universe had been proposed notably by the Pythagoreans and by Aristarchus of Samos. Aristotle and Ptolemy had favored the geocentric model and Ptolemy had worked out many of the details. Many fell into line even when it became clear that the relative motions of the planets gave them very complex orbits when the Earth was the observational platform. Each of the planets had both forward and backward (retrograde) motions. The orbits of each of the planets were not perfectly circular with respect to the Earth. This was the “little” problem that needed to be fixed. The solution came in the form of the suggestion that there were secondary perfectly circular motions (epicycles) that overlapped the main circular motion around the Earth. This was a mathematical adjustment that was meant to save the geocentric model of Ptolemy–but it made little physical sense. The minor problem that seemed not to be addressed was that there was no basic underlying principle to create a solution other than the “perfect nature of the circle” for assuming that this adjustment was based on anything other than the psychological or philosophical need to view all motions as somehow circular–the faith that the circle was the natural motion for all things in the heavens.
In time this became a kind of religious certainty and when Galileo made observations with simple telescopes that seemed in conflict with the underlying motion of the heavenly bodies, now regarded as sacrosanct by the church, he was visited by members of the Inquisition, and eventually went through a trial and punished for his heretical views. Eventually, of course, matters were worked out by Copernicus and Kepler and the planets shown to follow perfectly elliptical orbits around the sun. Gradually the geocentric model gave way to the heliocentric, because the latter were predictable and even calculable by the underlying mathematics of Newton’s laws of motion and of universal gravitation.
Newton’s laws of motion showed that objects moved or accelerated when forces were brought to bear on them and thus the motions of planets around stars could be plotted, indeed calculated by Newton’s laws of motion. Mercury, Venus, Earth, Mars, Jupiter and Saturn were all satellites that fell into stable elliptical orbits around the sun due to the force of gravitational attraction. Each orbit would remain stable unless acted upon by really large outside forces, which might indeed send them careening into the sun or alternatively might somehow allow them to escape orbit around the sun sending the planet on a long and perilous journey toward an alternative distant star.
At the time Newton’s laws created a basic way of understanding motion in the real world on Earth and the heavens. A new world of basic physics was created. The world would never be the same again.