The idea at the core of De Revolutionibus was that the Earth is not at the center of the universe, but that it and everything else moves in a circle around the center. The Sun has place of honour very near to the center. Copernicus’s reason for believing this is justified in philosophical terms:
Nikolaus Copernicus is commonly believed to be the father of the Solar System, the first brave soul to stand up to the orthodoxy and declare the Sun to be the centre of the universe and not the Earth. This isn’t quite true — the bulk of the credit should go to Johann Kepler, for providing a model that not only worked but was based on physical evidence — but he did make some very important observations and he does indeed deserve to be remembered.
Copernicus was born Mikolaj Kopernik on 19 Feb 1473 in Toruń, in what was then called Polish Prussia (Poland). He spent three years studying at the cathedral school of Wloclawek, after which he entered the University of Kraków. There he studied Latin, mathematics, geography, philosophy and astronomy, although the astronomy courses of the day were geared more to casting horoscopes and calculating the dates of holy festivals and didn’t have much in common with modern astronomy at all.
It was at this time that Kopernik began using the Latin form of his name: Copernicus. He left the university after four years, and returned home. When his uncle learned of his academic leanings, he advised him to enter the clergy, as this line of work would grant him the time and the resources to indulge his intellectual interests. To get the necessary qualifications, he moved to Italy and enrolled in the University of Bologna, for a degree in canon law. Happily for him, he managed to find accommodation with a professor of astronomy, and assisted him with his research and observations. Over the years he would return home, accept positions within the church, and return to study further, but never completed his religious studies and never graduated. He faced increasing pressure from the Church to qualify as a priest and do the work they were paying him for, and he continued to fob them off while pursuing his true passion as an astronomer. Even when they threatened to fire him and cut off his income, he found more excuses to allow him to continue observing and working on his new theories.
In 1514, he distributed copies of his Little Commentary, a handwritten book in which he explained his theory of the Universe, to his friends. The theory was summed up by the Seven Axioms, which stated:
1. There is no one centre in the universe.
2. The Earth’s centre is not the centre of the universe.
3. The centre of the Universe is near the sun.
4. The distance from the Earth to the sun is imperceptible compared with the distance to the stars.
5. The rotation of the Earth accounts for the apparent daily rotation of the stars.
6. The apparent annual cycle of movements of the sun is caused by the Earth revolving round it.
7. The apparent retrograde motion of the planets is caused by the motion of the Earth from which one observes.
Note that, in opposition to the modern scientific method, these axioms were not explained carefully from observed data. Instead, they were stated out at the beginning as a set of initial assumptions, and Copernicus then based the rest of the book on that foundation. He did include the following note, however: “Here, for the sake of brevity, I have thought it desirable to omit the mathematical demonstrations intended for my larger work”, referring to his lasting legacy: De Revolutionibus Orbium Coelestium
Although the Little Commentary was not widely distributed, he did manage to establish quite a reputation as an astronomer. When Pope Gregory appealed to experts to help bring the calendar back in line with the motions of the heavens (the old Julian calendar having slipped out of sync by more than a week by that point), Copernicus was one of those experts (He turned the offer down, though).
Sadly, Copernicus worked in isolation from other astronomers and was kept busy with earthly matters. As a result, his theories developed slowly and it wasn’t until shortly before he died that his famous De Revolutionibus Orbium Coelestium was finally published. In fact, were it not for the encouragement of one Georg Joachim Rheticus, a young professor of mathematics and astronomy at the University of Wittenberg, De Revolutionibus might never have been published at all. De Revolutionibus was a more complete treatment of Copernicus’s theories than what was in the Little Commentary, and included the mathematical proofs which had been promised in that volume
In a bizarre twist of fate, Rheticus was tasked to deliver the manuscript to the printers, but was unable to stay and supervise the process. He delegated the job to Andreas Osiander, a Lutheran theologian. Osiander seemed a good choice, since he had a lot of experience with printing mathematical texts, and had spoken with Copernicus for years about his work. Unfortunately, much of his correspondence was an attempt to save Copernicus from persecution from the peripatetics (followers of Aristotle) and theologians, by suggesting that he present the work as nothing more than a fanciful idea: Something clever, but not to be taken seriously. Copernicus always refused to take this advice, so when Osiander found the manuscript in his hands, he took the opportunity to write an introduction and insert it into the text as if it were part of the original manuscript. The introduction explained that the theories in the book weren’t meant to be taken as a truthful description of the universe, but merely a mathematical model which could be used to accurately calculate the motions of the planets. It would take 50 years for this deception to be publicly be revealed, but it seems likely that the book would have had a much harsher reception without it.
At the middle of all things lies the sun. As the location of this luminary in the cosmos, that most beautiful temple, would there be any other place or any better place than the center, from which it can light up everything at the same time? Hence the sun is not inappropriately called by some the lamp of the universe, by others its mind, and by others its ruler.
The orthodox model at the time was that which Ptolemy had compiled from existing tradition some 1500 years earlier: That the Earth was a perfect sphere, fixed at the centre of the universe. The Sun, Moon and Planets moved in perfect circular orbits around the Earth, roughly aligned to the plane of the Ecliptic, and the stars were much further away still, moving together as if fixed on the inside of a great sphere. The orbits of the planets were complicated by the addition of a secondary orbit around a point in the primary orbit (known as epicycles), to explain their occasional retrograde motions. The wonderful thing about Copernicus’s model was that retrograde motion could be explained without all this trickery. Unfortunately, he adhered to the Platonic view of physics, in which the only natural motion is a circular one. This meant that he not only had to explain why the Earth didn’t rotate in sync with its revolution around the Sun (Plato taught that a body would naturally turn to match the curve of its circular motions), but he also had to find ways to explain the seasons, the variations in the Moon’s orbit, tides, the varying speeds of the planets (apart from retrograde motion), and all the other ways in which our Solar System varies from a system of perfect regular circles. The system he ended up with was a bit of a mess. To quote George Forbes in his History of Astronomy:
Such was the theory advanced by Copernicus: The earth moves in an epicycle, on a deferent whose center is a little distance from the Sun. The planets move in a similar way on epicycles, but their deferents have no geometrical or physical relation to the Sun. The moon moves on an epicycle centered on a second epicycle, itself on a deferent, excentric to the earth. The earth’s axis rotates about the pole of the ecliptic, making one revolution and a twenty-six thousandth part of a revolution in the sidereal year, in the opposite direction to its orbital motion.
In other words, it is the Ptolemaic system of spheres and epicycles, with the centre of rotation moved away from the Earth and a whole lot of extra complicated bits added to tie it all together. This new system was much more complicated than Ptolemy’s, and didn’t offer any convincing proof to an observer. Instead, devastatingly, astronomers of the day noted that if the Earth was moving then we would expect to see the stars shift their apparent position as our viewpoint changed from one side of the Sun to the other. There was no such shift (Actually there was. It’s just that the stars are so much further away than they ever imagined, making those parallax shifts far too small to detect without specialized equipment that would only be invented centuries later). It’s no wonder that hardly anybody took it seriously.
Copernicus wasn’t the first to consider that the Earth might not be the centre of all motion in the universe — the ancient Egyptians believed that Mercury and Venus revolved around the Sun — but he was the first person in over a thousand years to seriously consider that the Earth might be in motion. We must also remember that he was not blind to the problems with his theory: He repeatedly states throughout the text of De Revolutionibus that the reader does not have to accept that his system shows the actual motions of the planets and that it doesn’t even matter whether they are true. What mattered to him was that he offered a method to compute tables from which the positions of the planets could be predicted. He even adds that anybody not satisfied with this explanation must simply accept being told “Mathematicis mathematica scribuntur” (mathematics are for mathematicians).
But all those disclaimers and reservations aside, he remained absolutely religiously certain about one fact: The Earth moves. Sadly he couldn’t offer the slightest scrap of evidence to prove it, but he believed it anyway, and based his life’s work upon it. He wasn’t afraid of criticism for speaking his mind either, as this excerpt from the original intended preface shows:
Perhaps there will be babblers who, although completely ignorant of mathematics, nevertheless take it upon themselves to pass judgement on mathematical questions and, badly distorting some passages of Scripture to their purpose, will dare find fault with my undertaking and censure it. I disregard them even to the extent as despising their criticism as unfounded.
That one single idea, that Creation is not centered upon us and our planet, was absolutely huge. The philosophical and religious implications alone have been implicated in such huge historical events as the Reformation, although perhaps this is putting the cart before the horse. Whatever, the fact remains: it was Copernicus who started dismantling the ancient and persuasive theory of a geocentric universe, and he can rightly be called the first of the modern astronomers and his work led to the foundation of the modern scientific method. He may not have done what we remember him for, but he deserves to be remembered nonetheless.
Written by Allen Versfeld
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