Nicolaus Copernicus, De revolutionibus orbium coelestium (Nuremberg, 1543)
Copernicus argued that the Sun rather than the Earth lies in the center of the universe. The Earth moves as a planet around the Sun. In 1543 little proof was available that the Earth moves; there were many reasons not to accept it. Ptolemaic astronomy, as represented in the Epitome of Regiomontanus, was neither overly complex nor inaccurate. The most important advantage offered by Copernicus was a vision of the universe as a coherent and integrated system, where all the planets move together in elegant harmony.
Why did Copernicus do this? Why did he believe it? How revolutionary was De revolutionibus?
The book begins with an unsigned preface “To the Reader, on the Hypotheses of this Work.” The preface suggests that one should read the book and instead of taking offense, interpret it hypothetically. Mathematical works were often regarded as hypothetical because one could “save the phenomena” with various mathematical devices, even with false ones. This same argument later repeatedly plagued Galileo. The preface was unsigned because this was the middle of the Reformation and the preface was written by a leading Lutheran theologian who served as the final editor of the manuscript. Copernicus was a Catholic who worked in a cathedral in northern Poland.
In a prefaced letter, Nicolaus Schönberg, a Cardinal, asked Copernicus to publish his book and even offered to pay for its printing. Although often overlooked, Copernicus had support from the highest levels of the Church. Indeed, Copernicus dedicated the book to none other than the pope. In his preface, he asserted that astronomy is a work of mathematics, for mathematicians. Theologians should understand, before they criticize, that the current system was no credit to the deity.
In Book I Copernicus laid out his basic assumptions, including that the universe is spherical and that the Earth is spherical. Ptolemy began the Almagest in the same way. Copernicus departed from Ptolemy by switching the positions of the Sun and the Earth, which the work of Regiomontanus had made theoretically possible.
In 1543 proof that the Earth moves could not come from observations. Nor was Ptolemaic astronomy overly complex: Copernicus used about the same total number of circles as Ptolemy. And in theory, a geocentric system may be updated to yield accurate predictions for any epoch, as occurs in any planetarium today with an observer-centered mechanical-optical star projector. When he conceived the heliocentric cosmos, Copernicus’ aim was not to account for new observations but to equal the Epitome in mathematical power.
The most important advantage offered by Copernicus was a vision of the universe as a coherent and integrated system, where all the planets move together in elegant harmony. In contrast, Ptolemy considered each planet in isolation. In the geocentric cosmos, each planet was explained separately by its own individual model, and the models did not even share the same center. Copernicus compared this fragmented portrait of the cosmos with a sculpture assembled piece-meal, more like a monster than the well-proportioned form of a man.
When the Counter-Reformation began in earnest after the Council of Trent, the Catholic reception of Copernicus became immensely complicated by the desire to avoid unsanctioned novelties. A Catholic astronomer once hailed by cardinals and popes now became suspect, associated with northern heretics. In 1616, this work by Copernicus was put on the Index of prohibited books, suspended until it could be corrected.
The OU copy of Copernicus is a “censored” copy. Notice how the heading on the page facing the cosmic section is emended. Where the original heading reads, “Demonstration of the triple motion of the Earth,” the handwritten correction states, “Demonstration of the hypothesis of the triple motion of the Earth.” This is one of the corrections mandated by the Inquisition in 1620 when it became permissible to read Copernicus again, following its suspension in 1616.
