De revolutionibus orbium coelestium

• 1. Introduction

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  De revolutionibus orbium coelestium arrived in print in 1543, in Nuremberg, just before its author died. Nicolaus Copernicus, who lived from 1473 to 1543, had built an alternative to the model of the universe handed down from Ptolemy. That older system put the Earth at the center, and it had been widely accepted since ancient times. Copernicus instead placed the Sun at the center and set the Earth in motion around it. The initial print run was 400 copies, and it failed to sell out. Demand was low, and the book was so technical that few could read it. Yet this single volume helped usher in the Scientific Revolution. How did an idea this radical reach print at all? Who pushed Copernicus past his own hesitation, who tried to soften the blow, and who fought over a single anonymous page added to the front of the book?

• 2. The Long Hesitation

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  A physician's library list from 1514 describes a manuscript matching the Commentariolus, the short, untitled, anonymous sketch Copernicus circulated among friends. So he must have begun his new system by that year. Most historians believe he wrote it after returning from Italy, possibly only after 1510. At that early stage he expected an easy reconciliation. He thought the Earth's motion could explain the planets with fewer motions than the Ptolemaic system then required.

  By the 1530s a substantial part of the larger book was complete, yet Copernicus held back. In 1536, Cardinal Nikolaus von Schönberg wrote to him and urged him to publish. A manuscript of De revolutionibus in Copernicus' own hand has survived, and scholars studied the different types of paper to reconstruct an approximate timetable for its composition. He appears to have started with a few astronomical observations to perfect his models, perhaps writing while still observing. The pressure to publish would soon come from a young visitor who had not yet arrived.

• 3. The Young Mathematician

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  In 1539, Georg Joachim Rheticus, a young mathematician from Wittenberg, arrived in Frauenburg, also called Frombork, to study with Copernicus. Rheticus read the manuscript and quickly wrote a non-technical summary of its main theories. He cast it as an open letter to Schöner, his astrology teacher in Nürnberg, and published it as the Narratio Prima in Danzig in 1540. His friend and mentor Achilles Gasser brought out a second edition in Basel in 1541.

  The friendly reception loosened Copernicus' caution. In 1542 he agreed to release a treatise on trigonometry drawn from the second book of the still unpublished work, which Rheticus published in Copernicus' name. Under strong pressure from Rheticus, Copernicus finally handed the book to his close friend, Bishop Tiedemann Giese. Giese was to deliver it to Rheticus in Wittenberg for printing by Johannes Petreius at Nürnberg. Copernicus also kept his own copy, which after his death was sent to Rheticus in an attempt to produce an authentic, unaltered version. That plan failed, but the copy resurfaced in the 18th century and now rests at the Jagiellonian University Library in Kraków, bearing the number BJ 10 000.

• 4. Eight Spheres

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  Copernicus argued that the universe comprised eight spheres. The outermost held the motionless, fixed stars, with the Sun standing still at the center. The known planets revolved about the Sun, each in its own sphere, in the order Mercury, Venus, Earth, Mars, Jupiter, Saturn. The Moon alone circled the Earth. What looked like the daily revolution of the Sun and stars was really the Earth turning on its own axis.

  The book divides into six "books," following closely the layout of Ptolemy's Almagest, which it updated and replaced. Book I gives a general vision of the heliocentric theory and his cosmology, with chapters on chord geometry and a table of chords. Book II sets out spherical astronomy and a catalogue of the fixed stars. Book III treats the precession of the equinoxes and the apparent movements of the Sun. Book IV covers the Moon, Book V the calculation of planetary positions with tables for the five planets, and Book VI their digression in latitude from the ecliptic.

  Copernicus held to one standard belief of his time, that celestial motions must be built from uniform circular motions. Because of this, he could not account for the planets without keeping a complex system of epicycles much like Ptolemy's. He had attached the Earth's axis rigidly to a Sun-centered sphere, which would have eliminated the seasons. To restore them he proposed a third motion, an annual contrary conical sweep of the terrestrial axis. The circles would not be abandoned until 1609, when Johannes Kepler replaced them with ellipses.

• 5. The Anonymous Preface

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  An unsigned letter, Ad lectorem de hypothesibus huius operis, stood at the front of the first edition, ahead of Copernicus' own dedicatory preface to Pope Paul III. Rheticus had left Nürnberg for a post in Leipzig, and Andreas Osiander, a Lutheran preacher living in Nuremberg, took over supervising the printing. His letter argued that the system was mathematics meant to aid computation, not a claim of literal truth. It said the astronomer cannot attain the true causes and will adopt whatever suppositions let the motions be computed correctly. "For these hypotheses need not be true nor even probable," it declared, warning the reader not to leave the study "a greater fool than when he entered."

  This clashed directly with Copernicus' own claims for his theory. Even Osiander's defenders concede the letter expresses views at variance with the author. Copernicus' own preface had dedicated the work to Pope Paul III and appealed to the pope's skill as a mathematician to recognize its truth. The original title "Praefatio authoris" was kept on Copernicus' preface to signal that the unsigned letter was not his. Many came to view the addition as a betrayal.

• 6. Osiander On Trial

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  Bruce Wrightsman, a historian, defended Osiander as no enemy of science. Osiander held many scientific connections, including Johannes Schöner, Peter Apian of Ingolstadt University, Erasmus Reinhold, and Hieronymus Cardan. Wrightsman argued Osiander left the letter unsigned because he was a notorious Protestant reformer, infamous among Catholics, and a signature could have drawn hostile scrutiny onto the work of Copernicus, a loyal Catholic canon. Copernicus himself had voiced fears his work would be attacked by the "peripatetics and theologians." He had also been in trouble with his bishop, Johannes Dantiscus, over a former mistress and a friendship with the suspected heretic Alexander Scultetus.

  Osiander's own interest in astronomy was theological. He hoped to improve the chronology of historical events and sharpen apocalyptic readings of the Bible, sharing the awareness that the calendar disagreed with astronomical movement. In writing the Ad lectorem he drew on Pico della Mirandola's idea that humanity orders an intellectual cosmos out of a chaos of opinions. That influence was tempered by Nicholas of Cusa and his coincidentia oppositorum, which placed true understanding in divine inspiration rather than intellectual organization. Osiander concluded that in speculation there are "no heretics of the intellect," but past speculation the Bible is the ultimate measure.

• 7. Rheticus And The Fallout

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  Pico della Mirandola, in his Disputations, had mounted a devastating attack on astrology and on the astronomers it relied on. Pico held that astronomers who calculate planetary positions could not even agree among themselves, so their numbers could not be trusted. He noted they disagreed on where the Sun fell in the order of the planets, some placing it near the Moon, others among the planets. Rheticus reacted strongly against the Ad lectorem, and the historian Robert S. Westman locates the deeper source of his anger here. Osiander now portrayed astronomy as a discipline fundamentally incapable of knowing anything with certainty, echoing Pico's attack on the foundations of divinatory astrology.

  According to the notes of Michael Maestlin, Rheticus suspected Osiander had written the preface. If he could prove it, Rheticus declared, he would rough up the fellow so violently that in future he would mind his own business. Tiedemann Giese urged the Nuremberg city council to issue a correction, but none was made and the matter was forgotten. Jan Broscius, a supporter of Copernicus, despaired too, writing that Osiander "deceives much with that preface of his." Hieronymus Schreiber, who died in 1547, left a note about Osiander's authorship in his copy. That copy passed via Michael Mästlin to Johannes Kepler, who methodically demonstrated that Osiander had added the foreword.

• 8. The Book Nobody Read

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  Even before 1543, rumors of the book's central theses spread. In one of his Tischreden, Martin Luther was quoted in 1539 dismissing the "upstart astrologer" who wished to reverse astronomy, pointing to Joshua commanding the Sun, not the Earth, to stand still. In 1549, Melanchthon wrote against Copernicus and advocated "severe measures" against the impiety of Copernicans. Yet the work also won followers. Erasmus Reinhold hailed it in 1542 and by 1551 built the Prutenic Tables from Copernicus' methods. Those tables fed the calendar reform of 1582 under Pope Gregory XIII. In England, Robert Recorde, John Dee, Thomas Digges, and William Gilbert adopted his position, and a 1561 curriculum at the University of Salamanca let students choose between Ptolemy and Copernicus.

  Arthur Koestler called the book "The Book That Nobody Read" and "an all-time worst seller." Owen Gingerich disproved this across a 35-year project to examine every surviving copy of the first two editions. His census found 276 copies of the first edition and 325 of the second, and his study of the marginalia showed that nearly all leading mathematicians owned and read it. Most, though, ignored the cosmology at the front and cared only for Copernicus' equant-free models in the later chapters. The works of Copernicus and Diego de Zúñiga were placed on the Index of Forbidden Books by a decree of the 5th of March 1616, more than 70 years after publication. The book was withdrawn pending corrections, with nine sentences that stated heliocentrism as certain marked to be changed. It remained on the Index until 1758, when Pope Benedict XIV removed the uncorrected book.