Copernicus was a Polish mathematician, physician, canon lawyer, cleric and astronomer. Much of his early adult life was spent in studies in Italy, the center of the Renaissance movement. He returned to Poland to serve in the church, practice medicine and to apply mathematics to his increasingly favourite pursuit – astronomy.
It must be remembered that Copernicus was living in the days before the invention of the telescope. Thus all his observations (done from a turret in the cathedral where he lived and worked) were accomplished using only the unaided eye.
For well over a thousand years, people had believed that the Earth was the center of the universe – that all the planets and stars, the sun and the moon revolved around the Earth. This was a geocentric model. It fit well with the ancient and medieval theological idea that if God had made humankind special by creating us in His image, then we must be living on the central planet – the cradle of the universe. The Earth was seen as solid and immovable. The universe indeed did revolve around us.
While in essence this concept was in harmony with Western religion, it had actually arisen during the time of the ancient Greeks among such prominent men as Hipparchus and Aristotle. However, it was a second century Egyptian astronomer who first popularized this notion and detailed its contours. His name was Ptolemy. His system was based in a Greek philosophical commitment to the superiority of the sphere and in a precise mathematics in harmonious work in the heavenly realms. Thus he was predisposed to maintain the circular motion of the planets and constant speed along their orbits. Along with his ancient counterparts, Ptolemy fixed the Earth centrally. He devised a rather complex system to account for some challenging occurrences. The foremost of these were seeming variations in planetary speed and the backwards (retrograde) movements of planets on the outer range of our system – Mars, Jupiter and Saturn.
Ptolemy developed a system in which each planet moved along a circular orbit (a deferent) in still smaller circles (epicycles), in a manner much like a whirling chair on a spinning carnival wheel. This helped to explain both of these problems. He needed 70 circles to accommodate the data.
Copernicus grew increasingly uneasy about Ptolemy’s explanations. The other Greek philosophical assumption which still held sway in the psyche of even medieval people was that the universe was simple as well as orderly. Ptolemy’s system was just too cumbersome, too complex. Copernicus redesigned it by putting a stationary sun at the center (a heliocentric model) and the Earth and other planets in orbit around it. This helped to explain both the speed variation and the occasional seeming backwards movement of some planets. It also reduced the complexity which Ptolemy had of necessity to build into his system to account for all the variables.
Both men’s drawings look like bull’s eyes – concentric circles each representing a planet in its orbit. Ptolemy placed the Earth at the center. Copernicus placed the sun at the center and the Earth in the third ring. Thus, as the Earth moved along a smaller circle than the outer planets (Mars, Jupiter and Saturn), it appeared as though they were slowing down, perhaps even going backward. (Think of a slot car racetrack.) This also explained why sometimes a planet such as Mars looked brighter on occasion – because Earth was getting closer to overtaking it.
However, Copernicus did have to explain why an Earth in motion didn’t fling its contents and inhabitants into space. This question of course never arose in Ptolemy’s system where the Earth was fixed and immovable. Copernicus suggested that a static Earth and a rotating universe would be in even greater jeopardy of spinning apart.
Now Copernicus’ system was still not perfect, although he had righted the fundamental flaw in Ptolemy’s system. Copernicus still tried to maintain the circular orbits and constant speeds. In the next century, Johannes Kepler would propose alternative theories which would further improve upon the understanding and accuracy of astronomy. These included elliptical orbits and variation in planetary speed according to the planet’s relative distance to the sun at any particular point in its orbit. With Kepler’s contribution, we finally reach today’s accepted theory of planetary motion.
Copernicus was reluctant to have his material published because it challenged centuries old beliefs and the authority of the church which upheld it. Earlier, he had written a manuscript which was circulated among his astronomer colleagues. However, tradition relates that it was while he was on his deathbed that the first published copy of his major work, On the Revolution of the Celestial Bodies (1543), was delivered to him. This publication was significant in marking the beginnings of the modern era of science.
