Copernicus (1473 - 1543)
Copernicus was the son of a well-to-do merchant. After his father's death in 1483, he was brought up by his uncle, a prince-bishop, and thus had the advantage of a first-class education. Copernicus studied mathematics and painting at Cracow, which was then and for many years afterwards the intellectual center of Poland. In 1496 he traveled to Italy for a leisurely education that would turn out to last a decade, and studied medicine, canon law, and astronomy.
Italy at this time was a hotbed of intellectual ferment. The system of the Universe as propounded by Hipparchus and Ptolemy, in which all heavenly bodies rotated about the Earth, was almost preposterously complex -- and despite all the careful mathematics involved, was still not very useful for predicting the positions of the planets over long periods of time. The Alfonsine Tables, named after Alfonso X, were the best the previous centuries had produced, but they were already far off the mark. (Alfonso X is credited with the classic remark, "If God had consulted me before the creation, I should have suggested a simpler design." This sums up the problems with Earth-centered theories about as elegantly as one could want.)
It occurred to Copernicus as early as 1507 that tables of planetary positions could be calculated more easily if it were assumed that the Sun, rather than the Earth, were the center of the Universe. This would mean that the Earth itself, along with the other planets, would have to be considered as moving through space and revolving about the Sun. This was not a new idea within and of itself. Among the ancients, Aristarchus had suggested the notion, and not many years before the time of Copernicus, Nicholas of Cusa had made a similar suggestion.
Copernicus was to do more than suggest, however. Beginning in 1512, he set about working out the system in full mathematical detail to demonstrate how planetary positions could be calculated on this new basis. In doing this, he made little use of his own observations. Actual observation was not his forte, and he is reputed to have never seen the planet Mercury. (However, Mercury is the most difficult of the planets to observe because of its proximity to the Sun.) Still, his observations were good enough to enable him to determine the length of the year to within twenty-eight seconds.
The Copernican system explained some of the puzzling motions of the planets rather neatly. Mercury and Venus, for example, never move more than a certain distance away from the Sun as viewed from the Earth. This had no particular explanation within the Earth-centered theories, other than "that's just the way the epicycles work out". Within the Copernican system, it was natural that they were never more than a certain distance from the Sun, because their orbits lay between the Sun and the Earth. Similarly, since the Earth was in an inner orbit as compared to those of Mars, Jupiter, and Saturn, it would periodically overtake those planets and this would cause them to appear to be moving backward in the sky.
Both the limited motions of Mercury and Venus and the backward ("retrograde") motions of Mars, Jupiter, and Saturn had been thorns in the side of the Ptolemaic theory for 1000 years, and vast complications had been introduced to account for them. Now they were easily and simply explained. Furthermore, the degree to which a planet's motion was limited or went through retrograde motion could be used to measure its relative distance from the Sun, something that Earth-centered theories could not do even in principle. And as a final bonus, the phenomenon of the precession of the equinoxes, discovered by Hipparcus, could now be explained not by twisting the entire celestial sphere, but just by wobbling the Earth as it rotated on its axis. As for the celestial sphere of the stars, Copernicus held it to be a vast distance from the Earth, at least a thousand times as distant as the Sun. This meant that any apparent shift in the positions of the stars as the Earth moved (i.e., their "parallax") would be too insignificant to notice. (Nonetheless, the fact that the stars did not shift was used as an argument against Copernicus, and was not fully laid to rest until higher-precision measurements could be made three centuries later.)
So much was explained so well by the new Copernican system that it grew tempting to consider the system as more than a mere device to calculate planetary positions. Perhaps it described the actual situation, moving Earth and all. Copernicus, however, still kept the notion of perfectly circular orbits and had to retain thirty-four of the epicycles associated with the older theory. This was not corrected until the time of Kepler a half century later. Copernicus described his system in a book, but for years he hesitated to publish it, believing that any suggestion that the Earth moved would be considered heretical and might get him into trouble. This view was a natural and perhaps a prudent one in the light of the later troubles of Galileo.
In 1505 Copernicus returned to Poland where he served as canon, under his uncle, at the cathedral at Frombork (Frauenberg, in German), although he never became a priest. Copernicus never married. He also served as his uncle's doctor and fulfilled a variety of administrative duties, especially after his uncle's death. He was involved in diplomatic negotiations between the Poles and the Teutonic Knights of Prussia, for instance. In working on currency reform, he realized that that the appearance of debased currency drives good coins into hiding -- because people hoard the good money -- something later called "Greshams' Law", after an economist who was a younger contemporary of Copernicus.
Meanwhile, by 1530, Copernicus had prepared a summary of his ideas in manuscript and this circulated among Europe's scholars, creating considerable interest and enthusiasm. Finally, at the urging of the mathematician Rheticus, Copernicus permitted publication of his entire book, carefully dedicating it to Pope Paul III. Rheticus volunteered to oversee its publication.
Unfortunately, Rheticus had to leave town since he was involved in some rather uncomfortable doctrinal disputes and since he had a chance to accept a better position at Leipzig. He left a Lutheran minister, Andreas Osiander, in charge. Martin Luther was firmly against the Copernican theory, and Osiander played it safe by adding an unauthorized preface to Copernicus' book, to the effect that the Copernican theory was not meant to be a description of the actual facts but merely a device to facilitate the computation of planetary tables. This weakened the book and for many years compromised Copernicus' reputation, for it was long thought that he was responsible for the preface. It wasn't until 1609 that Kepler discovered the truth about the preface.
"Concerning the Revolutions of the Heavenly Bodies" was published in 1543 and the story has long persisted that the first copy reached Copernicus as he lay on his deathbed, suffering from a stroke. However, a copy of the book dated four weeks before his death has recently come to light, and it may be that Copernicus had a chance to see it. The book began to win converts at once, with at least one astronomer using it within a few years to publish new tables of planetary motion.
Copernicus helped begin the Scientific Revolution, which was to dethrone Greek science and set civilization on a new path. It reached its climax with Newton a century and a half later. Yet it was not until 1835 that Copernicus' book was removed from the list of those banned by the Catholic Church. In 1807 Napoleon's conquering career had brought him to Poland, and when he visited the house in which Copernicus was born, he expressed his surprise that no statue had been raised in his honor. In 1839 this omission was rectified, but when the statue to Copernicus was unveiled in Warsaw, no Catholic priest would officiate on the occasion.
Much is owed to Copernicus for demonstrating that something which had always been believed to be true -- indeed, which had been believed unquestioningly by untold millions for thousands of years, was only a shabby imitation of a much better view.This page is adapted from Michael Fowler's lectures and Web page at the University of Virginia, and Fred L. Wilson's lectures and Web page at the Rochester Institute of Technology.
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