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Nicolaus Copernicus (February 19, 1473 – May 24, 1543) began to write De Revolutionibus Orbium Coelestium (On the Revolution of the Heavenly Spheres) in 1506 and finished it in 1530, but did not publish it until the year of his death, in 1543. He believed that the Ptolemaic system was too complicated, and wanted to offer a simpler and more accurate explanation. The book was dedicated to Pope Paul III, and is divided into 6 volumes:
The first volume contains a general vision of the heliocentric theory, and a summarized exposition of his idea on the World.
The second volume is eminently theoretical and reports the principles of spherical astronomy and a list of stars (as a basis for the arguments developed in the following books).
The third volume is mainly dedicated to the apparent movements of the Sun and to related phenomena.
The fourth volume contains a similar description of the Moon and its orbital movements.
The fifth and the sixth volumes contain the concrete exposition of the new system.
De Revolutionibus starts with an anonymous foreword stating that the whole work was only a simple hypothesis, implying that it might only be fantastic speculation. It is misleading to understand hypothesis in its modern sense, a proposed law or principle that is to be tested by experiment; rather, the sense intended here was that this was a convenient bit of mathematics not necessarily related at all to reality. The foreword was generally regarded as Copernicus' own idea, until Johannes Kepler showed that it was an addition by the Lutheran philosopher Osiander.
In his system Copernicus argued that the universe was made up of eight spheres, with the sun motionless at the centre and the sphere of fixed stars motionless in the eighth sphere. The planets revolved around the Sun in the order of Mercury, Venus, the earth, Mars, Jupiter, and Saturn. The moon however, revolved around the earth. Moreover, acording to him, what seemed to be the movement of the Sun and fixed stars around the earth, was really explained by the daily rotation of the earth on its own axis. Even with all of his advances, he retained the circular orbits, because of which he was forced to also retain the epicycles of the Ptolemaic system to prove his calculations correct. Nevertheless, the shift from an earth-centered, to a sun-centered system was very important and raised serious questions about Aristotle's astronomy and physics, despite Copernicus' adherence to Aristotle.
The book caused only mild controversy at the time, and provoked no fierce sermons about contradicting holy scripture; Osiander's preface, therefore, may have had some success. In 1546, however, a Dominican, Giovanni Maria Tolosani, wrote a treatise denouncing the theory and defending the absolute truth of scripture. Tolosani also claimed that Bartolomeo Spina, the Master of the Sacred Palace, had intended to condemn the theory but had been unable to press the issue because of ill health.
It has been much debated why Copernicus' work should have come under serious attack only after sixty years. The alleged reasons range from the personality of Galileo Galilei to the availability of actual evidence (such as observations with the telescope) which could make it practical for the first time to settle the truth or falsity of the theory. Whatever the reason, in 1616 Cardinal Bellarmine gave Galileo an order from the Pope to take the position that the system was purely hypothesis. After that, De Revolutionibus was placed on the Index of Forbidden Books along with two less important works (but none of Galileo's, at that time). Formally, it was not banned but merely withdrawn from circulation pending corrections, so called, which would clarify the status of the theory as having nothing to do with reality. In fact, though such corrections were prepared by Francesco Ingoli and others, and were formally approved in 1620, the book was never reprinted with these changes, and was available in Catholic jurisdictions only by special request of suitably qualified scholars. It remained on the Index until 1835.
A few years after the death of Nicolaus Copernicus, Erasmus Reinhold developed the Prutenischen Tafeln (Prussian Tables), based on Copernicus' observations. Reinhold's Prussian Tables were used as a basis for the calendar reformation by Pope Gregory XIII. The tables were also used by sailors and sea explorers, who during fourteenth and fifteenth century had used the Table of the Stars by Regiomontanus.
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