Nicolaus Copernicus: The Canon Who Moved the Earth
Life and work of Nicolaus Copernicus: training, the heliocentric theory, De Revolutionibus, the Osiander preface, his death, and the slow spread of Copernicanism.
Nicolaus Copernicus: The Canon Who Moved the Earth
Few figures in this history are simultaneously so often invoked and so little read as Nicolaus Copernicus. His name is on every schoolbook account of the Scientific Revolution. He moved the Earth. He is associated with a clean break from the past, with the long shadow of Galileo and Newton, with modernity itself. The actual man is harder to see through this fog. He was a canon of a remote cathedral chapter in northern Poland, a trained canon lawyer, a physician to his uncle the bishop, an occasional economist, a competent but unspectacular astronomer, and a man who held his most consequential idea in manuscript form for more than thirty years before letting it see the light of day. He did not, by the standards of his own time, “start” a revolution; he wrote a book. The revolution came later, and most of the work of making it was done by others. This page is an introduction to that figure and to the book that bears his name. Three articles treat specific aspects in detail: What Did Copernicus Write in De Revolutionibus? examines the structure and content of the book itself, How Did Copernicus Change Astronomy? considers his longer-term influence, and Why Was Copernicus’s Theory Controversial? surveys the theological, philosophical, and physical objections it provoked. For the broader context in which Copernicus worked, see the page on the key figures of the Scientific Revolution and the heliocentrism and astronomy section in the discoveries section.
Early Life and Education
Nicolaus Copernicus was born on 19 February 1473 in the city of Toruń, in Royal Prussia, a region then part of the Kingdom of Poland. His father, also Nicolaus, was a wealthy merchant who had migrated from Kraków; his mother, Barbara Watzenrode, was the daughter of an important local family. The father died when the boy was about ten, and his uncle Lucas Watzenrode, then a canon at the cathedral of Frombork, helped to raise and educate him. The uncle was an ambitious churchman who became Bishop of Warmia in 1489 and would loom large in his nephew’s career. Copernicus was sent to the University of Kraków in 1491, where he studied the liberal arts and first encountered formal astronomy. The Kraków school was an unusually strong one for the period; it had produced a generation of astronomers, including Wojciech Brudzewski, who is sometimes credited with teaching Copernicus the first principles of Ptolemaic astronomy and also with introducing him to the Greek and Arabic criticisms of Ptolemy that prove decisive. Copernicus left Kraków around 1495 without a degree, in keeping with the custom of the day, and travelled to Italy. In Bologna, Padua, and Ferrara, he studied canon law, medicine, mathematics, and astronomy over roughly the next nine years. He earned a doctorate in canon law from the University of Ferrara in 1503, having also spent considerable time at Padua, where the medical faculty was one of the best in Europe. He had read Ptolemy’s Almagest in the original Greek by the time he returned to Poland. He had also read a number of Greek and Arabic critics of Ptolemy — Ptolemy himself had noted that his system was not the only way to “save the appearances,” and commentators from Proclus to al-Urdi had explored alternatives. By 1503, when he was elected a canon of the cathedral of Frombork, Copernicus was in possession of two things: a secure ecclesiastical position and a growing sense that the Ptolemaic system could be improved.
The Canon at Frombork
For the rest of his life, Copernicus lived and worked in and around Frombork, a small cathedral town on the Vistula Lagoon in northern Poland. His duties as a canon were mostly administrative: he sat on the chapter’s governing council, served as his uncle’s physician, and acted, on occasion, as the chapter’s representative to the regional diet. He wrote a short treatise on monetary reform, Monetae cudendae ratio (1519), in which he argued for the use of a unified currency in Royal Prussia. He was, in short, a competent and respected member of the local ecclesiastical establishment. He was also an astronomer. The tower of the cathedral’s north wing served as his observatory, and he made observations of the Sun, Moon, planets, and stars over several decades. His instruments were the standard ones of the pre-telescopic era: quadrants, armillary spheres, parallactic rules, and a triquetrum. With these, he could measure the altitude and azimuth of celestial bodies to an accuracy of perhaps ten arcminutes, which was competitive for the period but well below what Tycho Brahe would achieve a generation later. His observations of Mercury, in particular, are believed to have made it clear to him that the Ptolemaic model was not producing accurate predictions for that planet, and that an alternative arrangement of the spheres might.
The Commentariolus (c. 1510–1514)
Sometime around 1510, and probably by 1514, Copernicus circulated a short manuscript titled Nicolai Copernici de hypothesibus motuum coelestium a se constitutis commentariolus — the “Little Commentary on the Hypotheses of Celestial Motions Set Forth by Himself.” It was not published in his lifetime and survives in only a handful of manuscript copies. The Commentariolus did not yet contain the full mathematical apparatus of De Revolutionibus. Instead, it set out, in a few terse pages, the seven “postulates” on which the heliocentric system was to be built, and the qualitative consequences Copernicus believed followed from them. The seven postulates stated, among other things, that there is no single center for all the celestial spheres; that the Earth’s center is not the center of the universe; that all the spheres revolve around the Sun, which is therefore the center of the universe; that the ratio of the Earth’s distance from the Sun to the height of the firmament is less than the ratio of the Earth’s radius to its distance from the Sun, so that the firmament’s distance is immeasurably great; that the apparent daily motion of the heavens is really due to the Earth’s rotation; that the apparent annual motion of the Sun is really due to the Earth’s revolution around the Sun; and that the apparent retrograde motion of the planets is really due to the Earth’s motion relative to them. The Commentariolus made the rounds of European astronomers but did not, in itself, provoke much response. It was too sketchy to be tested mathematically, and its author was too cautious to push it. A letter survives from a Kraków friend, Wapowski, urging Copernicus to publish the full argument, and Copernicus’s reply asking for more time.
The Long Preparation of De Revolutionibus
From roughly 1515 until the early 1530s, Copernicus worked on what would become his life’s main publication, the De Revolutionibus Orbium Coelestium — “On the Revolutions of the Celestial Spheres.” The book was the first full mathematical elaboration of the heliocentric theory, in six books, modeled closely on Ptolemy’s Almagest but with the Earth removed from the center and the Sun installed there instead. The work went through several phases of composition. Copernicus had the broad outline by the late 1520s, but he continued to revise the details. A 1530 letter from a Nuremberg astronomer, Johannes Schönberg, urged him to publish; the work circulated in progressively fuller manuscript form among a small circle of European readers, including the young Rheticus. The eventual publication, in 1543, was arranged not by Copernicus himself but by Rheticus, who arranged with a Nuremberg printer, Johannes Petreius, for the book to appear in print. The full structure of De Revolutionibus is described in detail in What Did Copernicus Write in De Revolutionibus?. Briefly, the book retains many features of Ptolemaic astronomy — uniform circular motion, epicycles, eccentrics — but reorganizes them around a Sun-centered universe. Copernicus was, by the standards of Kepler half a century later, mathematically conservative. He did not dare to break entirely with the perfect-circle orthodoxy of the Greek astronomers, and so the mathematical predictions of his system were not, in the end, significantly more accurate than those of Ptolemy. What he did, instead, was to relocate the center of the cosmos and to argue, on physical as well as aesthetic grounds, that the heliocentric system was more economical and more harmonious.
The Osiander Preface
Copernicus’s most famous literary encounter is one in which he himself played no part. The De Revolutionibus was published in Nuremberg in 1543 with an unsigned preface addressed “to the reader, concerning the hypotheses of this work.” The preface is now universally attributed to Andreas Osiander, a Nuremberg Lutheran pastor and amateur astronomer who had overseen the printing while Rheticus was away supervising the final stages. The preface presented Copernicus’s theory as a convenient calculating device, not as a description of physical reality: “It is not necessary that these hypotheses should be true, or even probable; it is sufficient that they lead to a computation which agrees with the observations.” Whether Osiander added the preface on his own initiative or at the instigation of others has been debated for centuries. The “Ad lectorem” preface delayed the full impact of the heliocentric theory in several ways. It gave cautious readers a fig leaf: they could use Copernicus’s tables and not commit to the cosmology. It also outraged readers, including the eventual editors of the De Revolutionibus, who felt that the preface misrepresented the author’s intent. Copernicus himself is said to have been distressed by it, on what evidence we have of his final weeks, though whether he ever saw the printed book is uncertain. The story is treated in Why Was Copernicus’s Theory Controversial?.
Death and the Slow Publication
Copernicus died on 24 May 1543 in Frombork. The traditional story, originating with a sixteenth-century biographer, is that the printed De Revolutionibus was brought to him on his deathbed, and that he was able to touch it before expiring. The story is touching and probably apocryphal. For the next sixty or seventy years, the heliocentric theory existed in a peculiar limbo. The De Revolutionibus was, of course, available, and so were the De Revolutionibus–based tables that Erasmus Reinhold compiled in 1551, the Prutenicae Tabulae, which became the standard astronomical tables of the second half of the sixteenth century. Yet the cosmological claim of the book — that the Earth moves — was, for most working astronomers, an open question. Tycho Brahe proposed a hybrid system that incorporated the heliocentric ordering of the planets without the moving Earth. The Catholic Church did not formally proscribe the book until 1616, but Catholic astronomers in the late sixteenth century mostly avoided endorsing it. It was a teaching aid, a set of tables, an interesting hypothesis. It became a cosmology only in the generation of Kepler and Galileo.
Copernicus’s Cosmology in Context
To understand what Copernicus was doing, it helps to see him against the background of the late-medieval astronomy he had been trained in. The Ptolemaic system that dominated European astronomy was, in 1500, a richly elaborated apparatus of circles upon circles: the basic sphere carrying a planet around the Earth, with epicycles, eccentrics, equants, and a complex business of deferents all designed to match the apparent motions of the planets. It worked — to a degree. It had been refined by Arabic astronomers, in particular by the Maragha school of the thirteenth and fourteenth centuries, who had attacked the “equant” point, a violation of the principle of uniform circular motion that Ptolemy himself had introduced. The aesthetic objections to the Ptolemaic system were not new, but they sharpened in the fifteenth century, partly because of the influence of the Maragha astronomers, partly because of the recovering of more Greek texts, and partly because of the increasing realization that the available tables were drifting away from the actual positions of the planets. Copernicus was not the only astronomer who felt that the system needed replacing. He was, however, the only one who replaced it in the radical way he did: by demoting the Earth from the center of the universe to a mere planet, and installing the Sun in its place. His reasons for this are worth lingering on, because they are not, at bottom, observational. Copernicus’s heliocentric system was, observationally, not more accurate than the Ptolemaic. His reasons were largely aesthetic and quasi-physical. He was bothered by the equant, the violation of uniform circular motion that the Maragha astronomers had also attacked. He was bothered by the fact that Ptolemy’s system required different schemes for each planet, with no unifying principle linking them. He was struck by the elegance of an arrangement in which the apparent retrograde motions of the planets fell out naturally as a consequence of the Earth’s motion, and in which a single scheme could explain the ordering of the planets by their periods. The heliocentric system was, in his view, more harmonious. It pleased the mind. This aesthetic and quasi-physical argument, more than any direct observation, is what made the heliocentric system stick. For the long-term consequences of Copernicus’s relocation of the Earth, see How Did Copernicus Change Astronomy?.
The Spread of Copernicanism
The “Copernican Revolution” — the slow conversion of European natural philosophy to heliocentrism — is conventionally dated to the century after 1543. It went through roughly three phases. The first phase, in the generation after Copernicus, was largely mathematical. Astronomers in Wittenberg, including Erasmus Reinhold, used the De Revolutionibus as a tool for computing better tables. They were, however, careful to keep their distance from the cosmology. George Joachim Rheticus, the only student Copernicus is known to have had, defended the heliocentric theory more openly. Giordano Bruno, an Italian Dominican friar who spent the late 1570s and 1580s wandering Europe, gave the heliocentric theory a more metaphysical spin, claiming that the stars were other suns with their own inhabited planets, and that the universe was infinite. Bruno was burned at the stake in Rome in 1600, though the reasons for his execution are more theological than astronomical. The second phase, beginning around 1600, was empirical. Tycho Brahe’s observations gave Kepler the data he needed to derive the elliptical orbits, and the publication of the Astronomia Nova in 1609 made the heliocentric system, in its Keplerian form, mathematically more accurate than any rival. Galileo’s telescopic discoveries, beginning in 1610, gave the heliocentric theory direct observational support: the phases of Venus could not be explained by the Ptolemaic system, the moons of Jupiter showed that there were centers of motion other than the Earth, and the moons of Jupiter and the surface of the Moon showed that the heavens were not the unchanging perfection of Aristotelian cosmology. The third phase, beginning in the 1630s, was methodological. Descartes’ mechanical philosophy, Newton’s Principia, and the work of the new scientific societies made the heliocentric system the default assumption of European natural philosophy, not a controversial hypothesis. By the end of the seventeenth century, the heliocentric theory was no longer a topic of serious debate in learned circles; it was a foundational fact. The detailed reception of the theory, and the famous trial of Galileo, are treated in the Galileo page and in the article on Why Was Galileo Put on Trial?.
What Copernicus Was Not
Copernicus was not a “scientist” in the modern sense. He did not perform controlled experiments. He did not, on the whole, observe more accurately than his contemporaries. He was a mathematically skilled astronomer working in a tradition — the Ptolemaic tradition — that was a thousand years old. He was also a working churchman, a competent physician, a man of affairs. The phrase “Copernican Revolution,” coined in the eighteenth century by Immanuel Kant, can be misleading. It suggests a single decisive turn. In fact, the work Copernicus began was a long process, the work of generations, and the final consolidation of the heliocentric theory is generally credited to Newton, in the Principia of 1687, more than a century after Copernicus’s death. The word “revolution” can also suggest that Copernicus was a revolutionary in temperament, which he was not. He was a cautious and rather conservative man who, late in life, allowed a book to be published that other people would have to defend. What Copernicus did, in the end, was to provide a target. He put the heliocentric theory on the table, in full mathematical form, in a book that the world would argue about for the next century and a half. That is enough.
Sources and Further Reading
The most useful modern biography of Copernicus is Jack Repcheck, Copernicus’ Secret: How the Scientific Revolution Began (Simon & Schuster, 2007). The standard scholarly treatment of the De Revolutionibus is Owen Gingerich, The Book Nobody Read: Chasing the Revolutions of Nicolaus Copernicus (Walker, 2004), which traces the actual reception of the book through a survey of the surviving copies. The standard account of the Copernican Revolution as an episode in the history of ideas is Thomas Kuhn, The Copernican Revolution: Planetary Astronomy in the Development of Western Thought (Harvard University Press, 1957). The classic older account is Angus Armitage, Copernicus: The Founder of Modern Astronomy (Thomas Yoseloff, 1957); the definitive older scholarly treatment is the relevant volume of the Studia Copernicana series. The Osiander preface is treated in detail in Robert S. Westman, “The Osiander-Gesner Letters” (Isis 86, no. 1, 1995), and the wider context of the 1543 publication is in Robert S. Westman, The Copernican Question: Prognostication, Skepticism, and Celestial Order (University of California Press, 2011).