Copernicus' Writings

Copernicus' De Revolutionibus

Title page of Copernicus' On the Revolutions

Title page of Copernicus' "On the Revolutions" (De revolutionibus orbium coelestium). The book was published in 1543 in Nuremberg as Copernicus lay on his deathbed,and was dedicated to Pope Paul III. The second edition was printed in Basel in 1566, and the third in Amsterdam in 1617.

Copernicus's book did not create controversy in the years following its publication. Its main idea has been in circulation among astronomers for over 30 years, and a preview of the book's content, the "Narratio Prima" of Georg Joachim Rheticus, had been published in 1540. The "Copernican planetary model" was absorbed and commented upon in the contemporary technical astronomical literature, notably by Michael Maestlin and the leading Jesuit astronomer, Christoph Clavius. In 1551 Erasmus Rheinhold (1511–1553) published the "Prutenic Tables" of planetary positions, which were based on the Copernican model and enjoyed quite a bit of success.

Religious authorities at first did not react to book's publication. This was likely due, at least in part,to the addition of an anonymous preface, written by the publication's overseer Andreas Osiander (1498–1552), to the effect that Copernicus' "planetary model", (see below), should be treated as an hypothesis to facilitate the computation of planetary positions. This situation was to change once Galileo began his so-called Copernican Crusade. "De Revolutionibus" was suspended pending minor corrections following the 1616 Roman decree against Copernicanism. Following the controversy over the world systems, culminating with the publication of Galileo's "Dialogues" and his subsequent "trial by the Roman Inquisition", the book was banned, and remained on the Index of prohibited books until 1835.

Bibliography:
Copernicus, N., On the Revolutions, edited and translated by E. Rosen, The Johns Hopkins University Press, 1992.
Kuhn, T.S. 1957, The Copernican Revolution, Harvard University Press.
Gingerich, O. 1993, The Eye of Heaven, American Institute of Physics.

 

The Copernican Planetary Model

A diagram that shook the world, in chapter 10 of Book Iof Copernicus' On the Revolutions

A diagram that shook the world, in chapter 10 of Book Iof Copernicus' "On the Revolutions" (De revolutionibus orbium coelestium). In the Copernican system the Earth is given three distinct motions: A daily axial rotation, an annual rotation about the Sun, and a third motion related to precession. As acknowledged by Copernicus himself in the introduction of his book, the heliocentric hypothesis goes back to antiquity, in fact with Aristarchus of Samos (ca. 310-230 BC); In "De Revolutionibus" Copernicus mentions Philolaus, in reference to the Pythagorean school in general), and the hypothesis of the Earth's axial rotation at least to Heraklides of Pontus (ca. 388-310 BC).

The Copernican model has two observational consequences that were not observed at the time, which greatly bothered Copernicus. First, because of the Earths motion about the Sun, the stars should show an annual parallax; in fact they do, but the distance to the stars is so much larger than believed in Copernicus' days that the effect is only detectable telescopically. Second, because Mercury and Venus orbit the Sun they should show phases similar to the Moon's. Again they do, but observational confirmation of this had to await Galileo Galilei and the telescope.

Contrary to a common opinion still perpetuated today in some introductory astronomy textbooks, Copernicus did not eliminate Ptolemy's epicycles from planetary theory; he did eliminate the primary epicycles used to reproduce the apparent retrograde motions of the upper planets, but in fact his mathematicalmodel of planetary motion contains about as many epicycles as the version of the ptolemaic model in use at the time. More importantly, Copernicus eliminated the equant, so that his model involved only perfectly regular circular motions. As a consequence his model was not particularly more accurate than Ptolemy's at predicting planetary positions. It was Johannes Kepler who brought the heliocentric system to its modern form.

Bibliography:
Copernicus, N., On the Revolutions, edited and translated by E. Rosen,The Johns Hopkins University Press, 1992.
Kuhn, T.S. 1957, The Copernican Revolution, Harvard University Press.
Gingerich, O. 1993, The Eye of Heaven, American Institute of Physics.