Shortly before Christmas 1499 Pope Alexander VI proclaimed that the following year would be a Jubilee, or Holy Year, in which a special indulgence would be granted to all pilgrims who came to Rome and visited the four principal churches of the city, beginning with St. Peter's, whose doors would be open night and day throughout that time. The celebrations went on throughout the year, and on Easter Sunday an estimated 200,000 pilgrims thronged St. Peter's Square for the pope's blessing. The pious monk Petrus Delphinus was led to exclaim “God be praised, who has brought hither so many witnesses to the faith.” And Sigismondo de’ Conti, the papal secretary, noted in his chronicle, “All the world is in Rome.”
Among the pilgrims was the young Nicholas Copernicus, who came to Rome around Easter and remained for a full year, giving lectures on astronomy and mathematics. The Italian Renaissance was in full bloom and Copernicus was in Rome at the height of its glory, before returning to his home in what he called “this remote corner of the earth,” in what was then Prussia but is now northern Poland.
Copernicus was born on 19 February 1473 at Torun, a town on the Vistula 110 miles northwest of Warsaw. His name was originally Niklas Koppernigk, which he Latinized as Nicholas Copernicus after he went to college. He was the youngest of four children of a prosperous merchant, the others being his brother Andreas and his sisters Barbara and Katherina. Their father died in 1483, whereupon the children were adopted by their maternal uncle Lucas Watzenrode, a priest who had studied at the universities of Cracow, Cologne, and Bologna.
In 1489 Lucas become bishop of Ermland, also known as Varmia, one of the four provinces into which Prussia was then divided. The bishop's palace was at Heilsberg (Lidzbark Warminski), 140 miles northeast of Torun, while the cathedral of the bishopric was at Frauenburg (From-bork), on the shore of the long lagoon east of Danzig (Gdansk). Nicholas and Andreas stayed with their uncle Lucas at his palace in Heilsberg, while Barbara entered a convent and Maria married a merchant in Cracow.
In the autumn of 1491 Nicholas and Andreas were sent by their uncle Lucas to the University of Cracow, where they enrolled in the faculty of arts. They remained there for three or four years, but left without earning a degree. During that time Nicholas is known to have taken courses in mathematics, astronomy, astrology, and geography, and his reading included Cicero, Virgil, Ovid, and Seneca.
The renowned Polish astronomer Albert Brudzewski was lecturing at the University of Cracow at the time and Nicholas would have read his works, although there is no record of their having met. Brudzewski had published a commentary on the planetary theory of Peurbach, in which he put forward his own theory that the celestial orbs are not spheres but circles. Brudzewski also used a mathematical method analogous to one employed by the Arabic astronomers Nasr al-Din al-Tusi and Ibn al-Shatir, similar to a model that Copernicus would later use in his heliocentric theory.
The textbooks Copernicus read in his courses in mathematics, astronomy, and astrology included works by Euclid, Ptolemy, Sacro-bosco, Peurbach, and Regiomontanus. The works of a number of Arabic astronomers were available in Cracow at that time, including those of Masha'allah, al-Farghani, al-Kindi, Thabit ibn Qurra, and Jabir ibn Aflah. Copernicus also bought a number of books in Johann Haller's bookshop in Cracow, including the Alphonsine Tables and the Tabulae Directionum of Regiomontanus, which he had bound together with parts of Peurbach's Tables of Eclipses and tables of planetary latitudes.
Nicholas and Andreas left Cracow early in 1496 to live with their uncle Lucas in the bishop's palace at Heilsberg. Lucas nominated Nicholas and Andreas to be canons of Frauenburg Cathedral, but at first his efforts were unsuccessful. Nicholas was finally made a canon in 1497, and Andreas was elected in 1499. Both of them were elected in absentia, for in the fall of 1496 Nicholas had gone off to study at the University of Bologna; Andreas joined him there two years later. They were both in the faculty of law and enrolled in the Natio Germanorum, the largest of the “nations” into which foreign students were organized at Bologna.
The brothers seem to have stayed as paying guests in the house of Domenico Maria da Novara (1454-1504) of Ferrara, a professor of astronomy at the university. Nicholas believed that he was “not so much the pupil as the assistant and witness of observations of the learned Dominicus Maria,” as his friend Rheticus later relayed, quoting Copernicus. One of the observations at Bologna concerned a lunar occultation of the star Aldabaran, which Copernicus says they made “after sunset on the seventh day before the Ides of March, in the year of Christ 1497.”
Copernicus took his MA. degree in law at Bologna in 1499, after which he went to Rome for a year. According to Rheticus, while in Rome Copernicus “lectured on mathematics before a large audience of students and a throng of great men and experts in this branch of knowledge.” Copernicus observed a lunar eclipse in Rome on 6 November 1500. He compared it to an eclipse observed by Ptolemy at Alexandria in the “nineteenth year of Hadrian” (A.D. 136-137), his purpose being “to determine the positions of the moon's movement in relation to the established beginnings of calendar years.”
Nicholas and Andreas returned to Poland in May 1501. On 27 July of that year they made an appeal to the authorities of their chapter in Frauenburg, asking for a two-year extension of their leave so that they could complete their studies in Italy. The chapter accepted and in August they left Frauenburg for Italy, Andreas to complete his degree in canon law in Bologna and Nicholas to study medicine in Padua.
Nicholas enrolled at the University of Padua in the fall of 15 01, studying law as well as medicine. He interrupted his studies at Padua after two years to enroll at the University of Ferrara, where on 31 May 1503 he received the degree of doctor of canon law. He then returned to Padua to continue his study of medicine, but he left in 1505 without obtaining a degree.
After his return from Italy Copernicus joined his uncle Lucas at Heilsberg Castle, the official residence of the bishops of Ermland. During the next six years Copernicus served as private physician and secretary of state to his uncle. He also represented Ermland in the Polish diets, or parliaments, and served on diplomatic missions to the King of Poland in Cracow. Early in 1512 he accompanied his uncle to Cracow to attend the wedding of King Sigismund and the coronation of his bride. But on the way home Bishop Lucas died in Torun, on 29 March 1512, after which his body was brought back to Frauenburg and buried in the cathedral.
After his uncle's death Copernicus left Heilsberg and returned to Frauenburg, where he resumed his duties as a canon. His apartment there was at the northeast corner of the enclosure wall of the cathedral, in a turret that is still called the Tower of Copernicus, which also served as his observatory. The first observation he recorded there was on 5 June 1512, when he noted that Mars was in opposition—that is, the planet rose at sunset and set at sunrise, since it was diametrically opposite the sun in the celestial sphere. This was the first of at least twenty-five observations Copernicus would make at Frauenburg, where he also developed the mathematical methods that he used in his new astronomical theory.
Around this time Copernicus began writing a work entitled Nicolai Copernici de Hypothesibus Motuum Caelestium a Se Constitutis Commentariolus (Nicholas Copernicus, Sketch of His Hypotheses for the Celestial Motions). This came to be known as theCommentariolus, or Little Commentary, the first notice of the new astronomical theory Copernicus had been developing. He gave written copies of this short treatise to a few friends but never published it in book form. Only two manuscript copies have survived, one of which was first published in Vienna in 1878. The earliest record of the Commentariolus is a note made in May 1514 by a Cracow professor, Matthias de Miechow, who writes that he had in his library “a manuscript of six leaves expounding the theory of an author who asserts that the earth moves while the sun stands still.” Matthias was unable to identify the author of this treatise, since Copernicus, with his customary caution, had not written his name on the manuscript, for, as he later admitted, he feared that he would be censured and ridiculed for his revolutionary ideas. But there is no doubt that the manuscript was by Copernicus, because the author made a marginal note that he reduced all his calculations “to the meridian of Cracow, because… Fromberk [Frauenburg]… where I made most of my observations … is on this meridian as I infer from lunar and solar eclipses observed at the same time in both places.”
The introduction to the Commentariolus discusses the theories of Greek astronomers concerning “the apparent motion of the planets,” noting that the homocentric spheres of Eudoxus were “unable to account for all the planetary motions” and were supplanted by Ptolemy's “eccentrics and epicycles, a system which most scholars finally accepted.” But Copernicus took exception to Ptolemy's use of the equant, which led him to think of formulating his own planetary theory, “in which everything would move uniformly about its proper center, as the rule of absolute motion requires.”
Copernicus goes on to say that after setting out to solve “this very difficult and almost insoluble problem,” he finally arrived at a solution that involved “fewer and much simpler constructions than were formerly used,” provided that he could make certain assumptions, seven in number.
The assumptions are: that there is not a single center for all the celestial circles, or spheres; that the earth is not the center of the universe, but only of its own gravity and of the lunar sphere; that the sun is the center of all the planetary spheres and of the universe; that the earth's radius is negligible compared to its distance from the sun, which in turn is “imperceptible in comparison to the height of the firmament;” that the apparent diurnal motion of the stellar sphere is due to the rotation of the earth on its axis; that the daily motion of the sun is due to the combined effect of the earth's rotation and its revolution around the sun; and that “the apparent retrograde and direct motion of the planets arise not from their motion but from the earth's.” He then concludes that “the motion of the earth alone, therefore, suffices to explain so many inequalities in the heavens.”
Copernicus goes on to describe the “Order of the Spheres” in his heliocentric system, in which the time taken by a planetary sphere to make one revolution increases with the radius of its orbit.
The celestial spheres are arranged in the following order. The highest is the immovable sphere of the fixed stars, which contains and gives position to all things. Beneath it is Saturn, which Jupiter follows, then Mars. Below Mars is the sphere on which we revolve, then Venus; last is Mercury. The lunar sphere revolves around the center of the earth and moves with the earth like an epicycle. In the same order, also, one planet surpasses another in speed of revolution, accordingly as they trace greater or smaller circles. Thus Saturn completes its revolution in thirty years, Jupiter in twelve, Mars in two and one-half, and the earth in one year; Venus in nine months, Mercury in three.
Copernicus used the same system of epicycles that Ptolemy and all of his successors had employed in the geocentric model. He concludes the Commentariolus by summarizing the number of circles (i.e., deferents, or primary circles) and epicycles (secondary loops) required to describe all of the celestial motions in his heliocentric system: “Then Mercury runs on seven circles in all; Venus on five; the earth on three, and round it the moon on four; finally Mars, Jupiter and Saturn on five each. Altogether, therefore, thirty-four circles suffice to explain the entire structure of the universe and the entire ballet of the planets.”
The first indication that the new theories of Copernicus had reached Rome came in the summer of 1533, when the papal secretary Johann Widmanstadt gave a lecture entitled “Copernicana de Motuu Terra Sentential Explicani” (An Explanation of Copernicus's Opinion of the Earth's Motion) before Pope Clement VII and a group that included two cardinals and a bishop. After the death of Pope Clement, on 25 September 1534, Widmanstadt entered the service of Cardinal Nicholas Schön-berg, who as papal nuncio in Prussia and Poland had undoubtedly heard of Copernicus years before. Schönberg wrote to Copernicus on 1 November 1536—the letter may have been drafted by Widmanstadt—urging Copernicus to publish a book on his new cosmology and to send him a copy.
Despite this encouragement Copernicus made no move to publish his researches, but his attitude changed in the spring of 1539, when he received an unexpected visit from a young German scholar, Georg Joachim van Lauchen, who called himself Rheticus (1514-1574). Rheti-cus, who although only twenty-five was already a professor of mathematics at the Protestant University of Wittenberg, explained that he was deeply interested in Copernicus's new cosmology; Copernicus received him hospitably and permitted him to study the manuscript he had written to explain his theories. During the next ten weeks Rheticus worked with Copernicus in studying the manuscript, which he then summarized in a treatise entitled Narratio Prima (First Narrative), intended as an introduction to the Copernican theory. This was written in the form of a letter from Rheticus to his friend Johann Schöner, under whom he had studied at Wittenberg. The Narratio Prima was published at Danzig in 1540 with the approval of Copernicus, who is referred to by Rheticus as “my teacher” in the introductory section where he describes the scope of the Copernican cosmology.
Rheticus then goes into each of the books in detail, adding an astrological prediction of his own after his account of the Copernican theory in “The Eccentricity of the Sun and the Motion of the Solar Apogee.” Rheticus believed that world history followed the same cycle as the eccentricity of the sun's orbit (observed from the earth), and that the completion of its next cycle would coincide with the downfall of the Muhammadan faith, following which, he said, “We look forward to the coming of our Lord Jesus Christ when the center of the eccentric reaches the other boundary of mean value, for it was in that position at the creation of the world.”
Rheticus does not mention the heliocentric theory until after the section entitled “General Considerations Regarding the Motions of the Moon, Together with the New Lunar Hypotheses.” There he says that the new model explains the retrograde motion of the planets “by having the sun occupy the center of the universe, while the earth revolves instead of the sun on the eccentric.”
The Narratio Prima proved to be so popular that a second edition was printed at Basel the following year. But Copernicus still hesitated to publish his manuscript, which he sent for safekeeping to his old friend Tiedemann Giese, the bishop of Culm. Finally, in the autumn of 1541, Giese received permission from Copernicus to send his manuscript to Rheticus, who was to take it to the press of Johannes Petreius in Nuremberg for publication. The title chosen for the book was De Revolutionibus Orbium Codestium Libri VI (Six Books Concerning the Revolutions of the Heavenly Spheres). The title stems from the fact that Copernicus believed the celestial bodies to be embedded in the same crystalline spheres—or, rather, spherical shells—as those first proposed by Aristotle, though he had them revolving around the sun rather than the earth.
Toward the end of the following year Copernicus suffered a series of strokes that left him half paralyzed, and it was obvious to his friends that his end was near. Tiedemann Giese wrote on 8 December 1542 to George Donner, one of the canons at Frauenburg, asking him to look after Copernicus in his last illness. “I know that he always counted you among his truest friends. I pray therefore, that if his occasions require, you will stand by him and take care of the man whom you, with me, have ever loved, so that he may not lack brotherly help in his distress, and that we may not appear ungrateful to a friend who has richly deserved our love and gratitude.”
Meanwhile, Rheticus had taken a leave of absence from the University of Wittenberg in May 1542 to supervise the printing of De Revolutionibus in Nuremberg. Five months later he left Nuremberg to take up a post at the University of Leipzig, leaving responsibility for the book in the hands of Andreas Osiander, a local Lutheran clergyman. Osiander took it upon himself to add an anonymous introduction entitled “Ad Lec-torem” (To the Reader), which was to be the cause of considerable controversy regarding the Copernican theory.
De Revolutionibus finally came off the press in the spring of 1543, with the publisher's blurb, probably also written by Osiander, printed directly below the title. “You have in this recent work, studious reader, the motion of both the fixed stars and the planets recovered from ancient as well as recent observations and outfitted with wonderful new and admirable hypotheses. You also have most expeditious tables from which you can easily compute the positions of the planets for any time. Therefore buy, read, profit.”
The first printed copy of De Revolutionibus was sent to Copernicus, and according to tradition it reached him a few hours before he died, on 24 May 1543. Tiedemann Giese described the last days of Copernicus in a letter to Rheticus: “He had lost his memory and mental vigor many days before; and he saw his completed work only at his last breath upon the day that he died.”
The introduction to De Revolutionibus, the “Ad Lectorum” written by Osiander, is addressed “To the Reader Concerning the Hypotheses of This Work.” It says that the book is designed as a mathematical device for calculation and not as a real description of nature. The “Ad Lecto-rum” was intended to deflect criticism of the heliocentric cosmology by those who thought that it contradicted the Bible, particularly the passage in the Book of Joshua that says, “The sun stood still in the middle of the sky and delayed its setting for almost a whole day.” Martin Luther, referring to the Copernican theory, had already been quoted as remarking, “People give ear to an upstart astrologer who strove to show that the earth revolves, not the heavens, or the firmament, the sun and the moon. This fool wishes to reverse the entire science of astronomy, but sacred Scripture tells us that Joshua commanded the Sun to stand still and not the Earth.” Copernicus himself had been worried about such criticism, as evidenced by his statement in the preface of De Revolution-ibus, which he dedicated to Pope Paul III: “I can reckon easily enough, Most Holy Father, that as soon as certain people learn that in these books of mine which I have written about the revolutions of the spheres of the world I attribute certain motions to the terrestrial globe they will immediately shout to have me and my opinion hooted off the stage.”
The Copernican heliocentric theory, De Revolutionibus, 1543.
The first eight chapters of Book I of De Revolutionibus give a greatly simplified description of the Copernican cosmology and its philosophical basis. Copernicus begins with arguments for the spherical nature of the universe; the sphericity of the earth, moon, sun, and planets; and the uniform circular motion of the planets around the sun. He shows how the rotation of the earth on its axis, together with its revolution about the sun, can easily explain the observed motions of the celestial bodies. The absence of stellar parallax he explains by the fact that the radius of the earth's orbit is negligible compared to the distance of the fixed stars. All of the arguments on physical grounds against the earth's motion are then refuted, using in most cases the explanations given by Nicholas of Cusa.
Chapter 9 is entitled “Whether Many Movements Can Be Attributed to the Earth, and Concerning the Center of the World.” Here Copernicus abandons the Aristotelian doctrine that the earth is the sole source of gravity and instead takes the first step toward the Newtonian theory of universal gravitation, writing, “I myself think that gravity or heaviness is nothing except a certain natural appetency implanted in the parts by the divine providence of the universal Artisan, in order that they should unite with one another in their oneness and wholeness and come together in the form of a globe.”
Chapter 10 is entitled “On the Order of the Celestial Orbital Circles.” Here Copernicus removes the ambiguity concerning Mercury and Venus, which in the Ptolemaic model were sometimes placed “above” the sun and sometimes “below.” The Copernican system has Mercury as the closest planet to the sun, followed by Venus, Earth, Mars, Jupiter, and Saturn, surrounded by the sphere of the fixed stars, and with the moon orbiting the earth. This model is simpler and more harmonious than Ptolemy's, for all of the planets revolve in the same sense, with velocities decreasing with their distance from the sun, which sits enthroned at the center of the cosmos.
In the center of all the celestial bodies rests the Sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time. As a matter of fact, not unhappily do some call it the lantern, others the mind and still others, the pilot of the world…. And so the sun, as if resting on a kingly throne, governs the family of stars which wheel around.
Chapter 11 is “A Demonstration of the Threefold Movement of the Earth,” while the remaining three chapters of Book I are concerned with the application of plane and spherical geometry and trigonometry to problems in astronomy. The three motions to which Copernicus refers are the earth's rotation on its axis, its revolution around the sun, and a third conical motion, which he introduced to keep the earth's axis pointing in the same direction while the crystalline sphere in which it was embedded rotated annually. The period of this supposed third motion he took to be slightly different from the time it takes the earth to rotate around the sun, the difference being due to the very slow precession of the equinoxes.
Book II is a detailed introduction to astronomy and spherical trig onometry, together with mathematical tables and a catalog of the celestial coordinates of 1,024 stars, most of them derived from Ptolemy, adjusted for the precession of the equinoxes.
Book III is concerned with the precession of the equinoxes and the movement of the earth around the sun. Here the theory is unnecessarily complicated, since Copernicus, besides combining precession with his “third motion” of the earth, inherited two effects from his predecessors, one of them spurious. The first effect was the mistaken notion, stemming from the trepidation theory, that the precession was not constant but variable; the other was the variation in the inclination of the ecliptic.
Book IV deals with the motion of the moon around the earth; Books V and VI study the motions of the planets. Here, as with the motions of the sun, Copernicus used eccentrics and epicycles just as Ptolemy had done, though his conviction that the celestial motions were combinations of circular motion at constant angular velocity made him refrain from using the Ptolemaic device of the equant. Because of the complexity of the celestial motions, Copernicus was forced to use about as many circles as had Ptolemy, and so there was little to choose from between the two theories so far as economy was concerned, and both were capable of giving results of comparable accuracy. The advantages of the Copernican system were that it was more harmonious; it removed the ambiguity about the order of the inner planets; it explained the retrograde motion of the planets as well as their variation in brightness; and it allowed both the order and the relative sizes of the planetary orbits to be determined from observation without any additional assumptions.
Copernicus mentions some of the Arabic astronomers whose observations and theories he used in De Revolutionibus, namely al-Battani, al-Bitruji, al-Zarqali, Ibn Rushd (Averroës), and Thabit ibn Qurra. But he does not mention Nasr al-Din al-Tusi or Ibn al-Shatir, although recent research shows that he used a mathematical method that had been developed by them. This is the so-called al-Tusi couple, which Copernicus used in Book III, Chapter 4 of De Revolutionibus There is no definite evidence that Copernicus knew of al-Tusi or al-Shatir, but current opinion is that he was aware of their works, which were known to some of his contemporaries.
Copernicus refers to Aristarchus of Samos thrice in De Revolutionibus, twice regarding his predecessor's measurement of the inclination of the ecliptic and once concerning his measurement of the length of the solar year. But nowhere does he mention that Aristarchus had, in the mid-third century B.C., proposed that the sun and not the earth was the center of the cosmos. Copernicus had referred to the heliocentric theory of Aristarchus in his original manuscript, but he'd deleted it from the edition of De Revolutionibusprinted in 1543. The suppressed passage, which had been in the last paragraph of Book I, Chapter 11, reads:
Though the courses of the Sun and the Moon can surely be demonstrated on the assumption that the Earth does not move, it does not work so well with the other planets. Probably for this and other reasons, Philolaus perceived the mobility of the Earth, a view also shared by Aristarchus of Samos, so some say, not impressed by that reasoning which Aristotle cites and refutes.
Copernicus is known to have possessed a copy of George Valla's Outline of Knowledge, printed by Aldus Manutius at Venice in 1501, which included a translation of a work by Aetius (Pseudo-Plutarch) containing two references to Aristarchus. One has Aristarchus “assuming that the heavens are at rest while the earth revolves along the ecliptic, simultaneously rotating about its own axis;” the other says that in his theory the earth “spins and turns, which Seleucus afterwards advanced as an established opinion.”
Copernicus was almost certainly familiar with Archimedes’ Sand Reckoner, which contains the earliest reference to the heliocentric theory of Aristarchus. There Archimedes says that Aristarchus explains the lack of stellar parallax in his heliocentric theory by supposing that the radius of the earth's orbit around the sun is negligible compared to the distance of the stars. This is essentially the same explanation given by Copernicus in his Commentariolus, where in the fourth of his assumptions he states that “the distance from the earth to the sun is imperceptible in comparison to the height of the firmament.” Copernicus uses this same argument in De Revolutionibus, where at the end of Book I, Chapter 10, he contrasts the retrograde motion of the planets with the unchanging array of the stars, noting, “How exceedingly fine is the godlike work of the Best and Greatest Artist!”
Thus it would seem that Copernicus was aware of Aristarchus's heliocentric theory and that he chose to suppress mention of it in De Revolutionibus, perhaps so as not to lessen the importance of his own life's work, setting the celestial orbs in motion around the sun rather than the earth.
Cosmology would never again be the same after the publication of De Revolutionibus The world picture was now irrevocably changed, an intellectual revolution started by an obscure canon working alone in what he called a “remote corner of the earth,” reviving a theory that had first been proposed eighteen centuries before by an almost forgotten Greek astronomer.