Copernicus, Nicolas (1473–1543)
Nicolas Copernicus, or Mikolaj Kopernick, was a Polish clergyman, physician, and astronomer, and the propounder of a heliocentric theory of the universe. He was born at Torun (Thorn) on the Vistula. He studied liberal arts, canon law, and medicine at the universities of Kraków (1491–1494), Bologna (1496–1500), and Padua (1501–1503) and received a doctorate in canon law from the University of Ferrara in 1503. Through the influence of his uncle, the bishop of Ermland, Copernicus was elected in absentia as a canon of the cathedral of Frauenburg in 1497. By 1506 he had returned to Poland, serving as physician to his uncle until 1512, when he took up his duties as canon. Copernicus's duties as canon involved him in the complex diplomatic maneuverings of the time and in the administration of the cathedral's large estates. In his own day he was more widely known as a physician than as an astronomer. He was one of the few persons in northeastern Europe to have a knowledge of the Greek language, and the one book he published without the urging of colleagues was a Latin translation of the poems of Theophylactus Simocatta, a seventh-century Byzantine poet. Copernicus's competence in economics was shown in some reports on money, presented to the Prussian diet, in which he anticipated a form of Gresham's law.
Copernicus's interest in astronomy was probably aroused at Kraków by the mathematician Wojciech Brudzewski and spurred on at Bologna by the astronomer Domenico Maria da Novara. Copernicus's first documented astronomical observation was made in Bologna in 1497. Twenty-seven such observations were used in his major treatise; others he recorded in the margins of books in his library. By 1514 he was so well known as an astronomer that he was asked by Pope Leo X to assist in the reform of the calendar, a task he declined because the motions of the sun and the moon had not yet been sufficiently determined.
Although Copernicus's major work, De Revolutionibus Orbium Coelestium Libri IV, was not published until 1543, the year of his death, he had been developing his theories at least from about 1512, the approximate date of his Commentariolus (a short outline of his system which he gave in manuscript copies to a few trusted friends). The first published account of his system was the Narratio Prima of his disciple and biographer (the biography is no longer extant), Georg Joachim Rheticus, in 1540. It was Rheticus who finally induced Copernicus to allow the publication of his major work.
Late Medieval Astronomy
The difference between Copernicus's theory and the then prevailing Ptolemaic system of astronomy can be stated briefly. The Copernican system was heliocentric rather than geocentric and geostatic; it placed the sun close to the center of the universe and Earth in orbit around the center, rather than postulating an immobile Earth at the center of the universe. But the full significance of this statement can be understood only via an examination of the ad hoc character of late medieval astronomy. Such late scholastic thinkers as Robert Grosseteste, Thomas Bradwardine, Jean Buridan, Nicholas Oresme, and Nicholas of Cusa had perceived the theoretical virtues and explanatory power of the heliocentric principle, as had Ptolemy himself long before. They understood the imperfections of the Ptolemaic techniques; yet they conceded that observational evidence did not clearly favor either theory—as was the case until the late sixteenth century. On scriptural grounds these thinkers accepted orthodox geocentrism; but they aired, more fully and deliberately than any of their predecessors, the arguments in support of terrestrial movement. They played advocatus diaboli with precision and imagination.
But prior to Copernicus astronomy was a piecemeal undertaking. Such problems as the prediction of a stationary point, or of an occultation, were dealt with one at a time, planet by planet. There was no conception that one planet's current stationary point might be related to another planet's later occultation. Techniques were employed as needed, and problem solving was not systematically integrated. Copernicus's theory changed this piecemeal approach forever. He effected a Kantian revolution in astronomy perhaps even more than Immanuel Kant effected a Copernican revolution in philosophy. Copernicus relocated the primary observational problem, that of explaining the apparent retrograde motions of the planets, by construing the motions not as something the planets "really" did "out there," but as the result of our own motion. Earth's flight around the sun makes other circling objects sometimes appear to move backward in relation to the fixed stars. Although either the Ptolemaic or the Copernican theory could be reconciled with sixteenth-century observations, Copernicus's view did not require investing those planets with queer dynamical properties, such as retrogradations-in-fact; a planet that actually halted, went into reverse, halted again, and then proceeded "forward" would be a strange physical object indeed. Rather, in Copernicus's view, all planets, including Earth, had the same kind of motion—a simple motion that explained the observed retrogradations.
It had been clear even to the ancients that the view that Earth was in the exact center of the universal system and that all celestial bodies moved about Earth in perfect circles could not generate predictions and descriptions even remotely close to the observed facts. In order to generate the right predictional numbers as well as tractable orbital shapes, the Ptolemaic astronomers made a number of ad hoc assumptions. They moved Earth from the exact center of the planetary array; they used the geometrical center of the system as a reference point from which to calculate planetary distances; and they invented a third point, the punctum aequans (a mere computational device without physical significance, a device that Copernicus described as "monstrous"), around which the centers of the planetary epicycles described equal angles in equal times. No mechanisms known in nature or in art, however, have one center from which distances are determined, another from which velocities are determined, and a third from which observations are made. Moreover, the location of all these points and the choice of angular velocities around them were fixed arbitrarily and ex post facto simply to cope with each new observation as it turned up.
Even had Ptolemaic astronomy achieved perfection in predicting and describing, it was still powerless to explain planetary motion. One might ask how a theory that could describe and predict perfectly could in any way lack explanatory power; but Copernicus would have distinguished between the mere capacity of a theory to generate accurate numbers, and its further ability to provide an intelligible foundation for comprehending the phenomena studied. Even had the Ptolemaic system been able to predict accurately any future position of each moving point of light, Copernicus would still have asked what these points of light were, and what systematic mechanical interconnections existed between them.
An imaginative scholar, aware of the many difficulties posed by the Ptolemaic system as it had been developed over the years, and knowing (as Copernicus did) the accounts of ancient heliocentric theorists, might have only been expected to continue to seek improvements within the Ptolemaic system by incorporating promising heliocentric devices from his Scholastic predecessors (if he knew them) and from the ancients. Any gifted astronomer of Copernicus's day bent on improving astronomy "from the inside" would thus have had to take heliocentrism seriously.
In fact, Copernicus's books and Rheticus's summary might be viewed as an articulate and systematic expression of much late medieval planetary thinking. The ties with fifteenth-century Scholastic thought are everywhere apparent. But the primary insight of De Revolutionibus, although not novel, was boldly carried out and very much sharpened in detail. It was a comprehensive attempt to make the science of that day work better; it was not explicitly a plan for a new science of tomorrow. The dramatic consequences, largely unanticipated by Copernicus, are a tribute to his thoroughness as a student of nature and not to any self-conscious desire to level the orthodoxy around him.
The Copernican Alternative
Copernicus was led to conclude that, in view of the plethora of epicycles required by the Ptolemaic system to account for the observed motion of the heavenly bodies, it must contain some basic error. He found that the assumption of a moving Earth, however absurd and counterintuitive it appeared, led to a much simpler and aesthetically superior system. Imagine yourself on the outer edge of a merry-go-round, sitting in a swivel chair. The constant rotation of the chair, when compounded with the revolution of the chair around the center of the merry-go-round, would generate—to say the least—complex visual impressions. Those impressions are compatible either with the motion as just described or with the supposition that it is the chair which is absolutely fixed and that all of the visual impressions stem from the motion of the merry-go-round about the chair-as-center and of a like motion of the walls of the building in which it is housed. The actual observations could be accounted for by either hypothesis. But what is easy to visualize in this example was extraordinarily difficult to comprehend in astronomical terms. That it was Earth that rotated and twisted, and revolved around the sun, seemed contrary to experience, common sense, and Scripture. Yet it was this simple alternative hypothesis that, for reasons demanded by astronomy, Copernicus espoused.
Fundamentally, then, Copernicus argued that the observational intricacies of planetary motion were not real, but merely apparent. This argument made planetary motion simpler to comprehend but our own motion more intricate and therefore harder to believe. That was the fundamental objection to Copernicus's innovation.
But one must be quite clear about the nature of the theory. It was not a celestial dynamics, even in the sense that Johannes Kepler's theory of the causes of planetary motion (in terms of primitive spokes of force radiating from the sun) was a celestial dynamics. Copernicus, like his predecessors, was no astrophysicist; he was concerned with positional astronomy—the kinematics of planetary appearances, the motions of stellar lights against the black bowl of the sky and the underlying geometry that would, with a minimum of ad hoc assumptions, make those motions intelligible. So, both the Almagest and the De Revolutionibus were concerned with plantetary kinematics exclusively—the latter in a systematic way, the former in the manner of a recipe collection. And even as a kinematic theory, Copernicus's theory was less adequate than those of Tycho Brahe and Kepler. He believed that the planets moved in perfect circles, an assumption shattered by Kepler's discovery of elliptical orbits. There is nothing in Copernicus to compare with Kepler's second law—that planets sweep out equal circumsolar areas in equal times. Nor is there anything to compare to Kepler's third law, correlating the time a planet requires to circle the sun with its distance from the sun. (And only when Kepler's three laws were added to the Galileo-Descartes law of inertia, and Isaac Newton's law of universal gravitation, was there developed a genuine celestial mechanics.) Copernicus's contributions consisted in a redeployment of the established elements of Ptolemaic positional astronomy. It is in this sense that he has been, and should be, viewed as the last great medieval astronomer.
Simplicity of Copernicus's Theory
Copernicus's theory was not psychologically simpler than competing systems. A moving Earth, and a sun and stars that do not "rise" and "circle" us, seemed contrary to experience. Also, a theoretical apparatus that linked all astronomical problems instead of leaving them to be faced one at a time could not constitute an easier system of calculation. Indeed, in the sixteenth century, heliocentrism was psychologically far more complex than the theories men were accustomed to.
Was Copernicus's conception perhaps simpler in that, as a formal theoretical system, it did not require primitive new ideas for each new problem or for the times when old problems led to difficulties? It invoked nothing like a punctum aequans ; that is, it invoked fewer independent conceptual elements (primitive terms) merely to explain aberrant calculations than did other astronomies. But this point is insufficient to explain the sense in which Copernicus's system manifests "simplicity." Computational schemes had been proposed by Caelio Calcagnini and Geronimo Fracastoro that were simpler in that they were built on smaller sets of primitive notions. But they were so inadequate to the observational tasks of astronomy that it would have been as idle to stress their simplicity as it would be today to press for the theoretical adoption of John Dalton's atom because of its simplicity; the issue of simplicity does not arise except between theories that are comparable in explanatory and predictional power.
It has been urged that Copernicus's theory was numerically simpler, in that it required only 17 epicycles to the Ptolemaic 83. But the Ptolemaist, because he addressed his problems singly and without regard for the configurational complexities of taking all planets at once, never had to invoke 83 epicycles simultaneously. The number was usually no more than 4 or 5 per individual calculation.
This error is analogous to that involved in referring to a Ptolemaic "system" at all. Such a system results only from taking all individual calculating charts for the separate planets, superimposing them, running a pin through the centric "Earthpoint," and then scaling the orbits up or down so they do not collide. This scaling is determined by a principle of order wholly unconnected with any part of the Ptolemaic epicycle-on-deferent technique. In contrast, Copernicus's system locates the planets in a circumsolar order such that their relative distances from, and their angular velocities around, the sun are in themselves sufficient in principle to describe and predict all stationary points, retrograde arcs, occultations, and the brightening and dimming of the planetary lights. Thus, since Copernicus linked all planets, and invented systematic astronomy, he had to invoke all the epicycles his theory needed en bloc. The number of epicycles in any calculation would tend to be greater, not less, than that required in a corresponding Ptolemaic problem.
Copernicus's scheme is systematically simpler. It required more independent concepts than some others, but these were deductively interlocked. Copernicus was astronomy's Euclid. He constructed out of the disconnected parts of astronomy as he found it a systematic monument of scientific theory. The De Revolutionibus is psychologically and quantitatively more complex than anything that had gone before, but it was deductively simpler. What Euclid had done for geometry, and what Newton was later to do for physics, Copernicus did for positional astronomy.
Importance of the Theory
It has been argued that, as formalizations, the Copernican and Ptolemaic theories were strictly equivalent (D. J. de S. Price 1959), geometrically equivalent (A. R. Hall), even "absolutely identical" (J. L. E. Dreyer). But characterizing the theory as no more than "an alternative frame of reference plus some anti-Aristotelian philosophy" obscures the sense in which the heliocentric system and the geocentric systems of the sixteenth century were really equivalent. They were not equivalent in the sense that every consequence of the one was also derivable from the other. Even when construed as mere geometrical calculations on paper, what the Ptolemaist would generate within his theory as corresponding to a stationary point in Mars's orbit is not congruent with what the Copernican would generate. The orbits were accorded different shapes in both theories, so points on those shapes, although viewed at the same angle from Earth, will not be superimposable. Nonetheless, every line-of-sight observation inferable within the one theory is completely inferable in the other. As positional astronomy, the two theories were observationally equivalent; no astronomer then could distinguish the two by comparing them with known facts. (Even today the Nautical Almanac is virtually a textbook of geocentric observation-points.) But the theories were neither formally equivalent nor physically equivalent, and certainly not absolutely identical. This is a difference that should make a difference to a philosopher.
With Sigmund Freud, man lost his Godlike mind; with Charles Darwin his exalted place among the creatures on Earth; with Copernicus man had lost his privileged position in the universe. The general intellectual repercussions of this fact are more dramatic than any consequences within technical astronomy, where one can speak of the Keplerian "revolution" but of not more than a Copernican "disturbance."
For the broad history of ideas, however, the implications of Copernicanism can hardly be exaggerated. Even religious revolutionaries such as Martin Luther and Philipp Melanchthon came to view Copernicus's position with abhorrence. His views challenged the literal interpretation of Scripture, the philosophical and metaphysical foundations of moral theory, and even common sense itself. The result was a massive opposition, learned and lay, to the reported ideas of Copernicus. It was the slow, sure acceptance of the technical De Revolutionibus by natural philosophers that ultimately quieted the general clamor against heliocentrism. Without the riotous reaction against it, Copernicus's book might have been but a calm contribution to scholarship somewhat like Pierre Simon de Laplace's Mécanique céleste. In the sixteenth and seventeenth centuries, however, the name Copernicus became a battle cry against the establishment in religion, in philosophy, and in natural science. It was a cry amplified in the world of wider scholarship and theology—far beyond Copernicus's original pronouncements. For Copernicus epitomized the well-trained, thorough, and rigorous sixteenth-century natural philosopher. He sought to make the theories he had inherited work better than when he found them. The history of ideas is charged with such figures. The difference is that Copernicus was presented with a theory that was incapable of further internal revision and improvement. The only recourse was fundamental overhaul—the consequences of which we still feel today.
See also Bradwardine, Thomas; Buridan, Jean; Darwin, Charles Robert; Freud, Sigmund; Grosseteste, Robert; Kant, Immanuel; Kepler, Johannes; Laplace, Pierre Simon de; Luther, Martin; Melanchthon, Philipp; Nicholas of Cusa; Oresme, Nicholas.
works by copernicus
Edward Rosen is the editor and translator of Three Copernican Treatises (New York: Columbia University Press, 1939), which contains a translation of the Commentariolus, a "Letter against Werner," and Rheticus's Narratio Prima.
De Revolutionibus Orbium Coelestium Libri IV is available in a facsimile text and a Latin printed text edited with notes by S. Kubach (1944). The translation by C. G. Wallis in Great Books of the Western World, Vol. 16 (Chicago: Encyclopaedia Britannica, 1952) is to be used with caution.
works on copernicus
Armitage, Angus. Copernicus, the Founder of Modern Astronomy. London: Allen and Unwin, 1938.
Hanson, N. R. "Contra-Equivalence." Isis 55 (1964).
Hanson, N. R. "The Copernican Disturbance and the Keplerian Revolution." Journal of the History of Ideas 22 (1961): 169–184.
Kuhn, Thomas. The Copernican Revolution. Cambridge, MA: Harvard University Press, 1957.
Price, D. J. de S. "Contra-Copernicus." In Critical Problems in the History of Science, edited by Marshall Clagget. Madison: University of Wisconsin Press, 1959.
Prowe, Ludwig. Nicolaus Coppernicus, 3 vols. Berlin, 1883–1885.
Rudnicki, J. Nicholas Copernicus. Translated by B. W. A. Massey. London: Copernicus Quatercentenary Celebration Committee, 1943.
Norwood Russell Hanson (1967)
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