Copernicus concluded that, in view of the many circles and their displacements from the center of the Earth that the Ptolemaic system required to account for the observed motions of heavenly bodies, a simpler, alternative explanation might be possible. In consequence, he read the works of many original Greek authors and found that, indeed, heliocentric ideas had been suggested. The idea of a moving Earth seemed absurd at first, but, when Copernicus applied this assumption, the result was an aesthetically superior, although not much simpler, system, even though, as might be expected, he still believed that the planets moved with uniform circular motion. After many years of mathematical calculations, he became convinced that his new idea was true, yet he made no attempt to publish.
From about 1510 to 1514, Copernicus prepared a short manuscript to summarize his new idea, De hypothesibus motuum coelestium a se constitutis commentariolus ("A Commentary on the Theories of the Motions of Heavenly Objects from Their Arrangements"), which he privately circulated among friends in 1514. Its main points were that the apparent daily motion of the stars, the annual motion of the Sun, and the retrogressive behaviour of the planets result from the Earth's daily rotation on its axis and yearly revolution around the Sun, which is stationary at the centre of the planetary system. The Earth, therefore, is not the centre of the universe but only of the Moon's orbit. As the years passed, he developed his argument with diagrams and mathematical calculations. Lectures on the principles expounded in the Commentariolus were given in Rome in 1533 before Pope Clement VII, who approved, and a formal request to publish was made to Copernicus in 1536. But he continued to hesitate. It was only through the efforts of his friends--in particular, his pupil and disciple Georg Joachim Rhoticus, who studied with him for two years--that he finally published his work. In 1540 Rhoticus was permitted to take the completed manuscript to Nьrnberg, Germany,
for printing. Because of opposition from Martin Luther, Philipp Melanchthon, and other reformers, Rhдticus left Nьrnberg and went to Leipzig, where he passed on the task of publication to Andreas Osiander. Apparently fearing criticism of a treatise that proposed an annual motion of the Earth around a stationary Sun, Osiander, on his own responsibility, inserted a preface emphasizing that the hypothesis of a stationary Sun was only a convenient means for simplifying planetary computations.
The Copernican system.
A careful examination of the text makes it clear, however, that Copernicus had really come to believe in the heliocentric system--rather, heliostatic, since he placed the Sun at some distance from the centre--as a true picture of the universe. He wrote On the Revolutions of the Celestial Spheres, in six sections, as a mathematical reinterpretation of Ptolemy. He wished to provide an alternative computational scheme that would make possible more accurate predictions that would be used in calendar reform and eclipses, and that would, at the same time, explain the troublesome variations of brightness, retrogressions, and velocity with a simpler geometric system of points and circles.
In the first section, Copernicus gave some basic mathematical rules, countered the old arguments about the fixity of the Earth, and discussed the order of the planets from the Sun. He could no longer accept the old arrangement--Earth, Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn--since this had been a consequence of a geocentric system. He found it necessary to adapt it to his heliocentric system and adopted the following order from the stationary Sun:
Mercury, Venus, Earth with the Moon orbiting around it, Mars, Jupiter, and Saturn. In the second section, Copernicus applied the basic mathematical rules of the previous section to the apparent motions of the stars and planets, and attributed the motion of the Sun to the motion of the Earth. The third section contains a mathematical description of the Earth's motion, including the precession of the equinoxes, which is caused by the gyration of the Earth's axis. Sections four, five, and six deal with the motions of the Moon and of the five remaining planets.
In his heliocentric theory, Copernicus found himself able to describe the movements of the Moon and planets in a more elegant way than Ptolemy in his geocentric system. To fit the observations, Ptolemy had been forced to offset the centres of regular motion a slight way from the centre of the Earth, and this Copernicus believed to conflict with the basic rule of true circular motion. In De revolutionibus the centres all lay at the centre of the Sun, but, because Copernicus still adopted circular motions at an unvarying speed, his system proved to be virtually as complex as Ptolemy's. Nevertheless, Copernicus believed that his system was aesthetically more satisfying and that it was a true picture of the divinely ordained cosmos.
A copy of the great work is believed to have been brought to Copernicus at Frauenburg on the last day of his life, May 24, 1543.
The Copernican system appealed to a large number of independent-minded astronomers and mathematicians. Its attraction was not only because of its elegance but also, in part, because of its break with traditional doctrines: in particular, it opposed Aristotle, who had argued cogently for the fixity of the Earth; furthermore, it provided an alternative to Ptolemy's geocentric universe. In Western Christendom both of these views had been elevated almost to the level of religious dogma; to many thoughtful observers, however, they stifled development and were overdue for rejection.
Scientifically, the Copernican theory demanded two important changes in outlook. The first change had to do with the apparent size of the universe. The stars always appeared in precisely the same fixed positions, but if the Earth were in orbit round the Sun, they should display a small periodic change. Copernicus explained that the starry sphere was too far distant for the change to be detected. His theory thus led to the belief in a much larger universe than previously
conceived and, in England, where the theory was openly accepted with enthusiasm, to the idea of an infinite universe with the stars scattered throughout space. The second change concerned the reason why bodies fall to the ground. Aristotle had taught that they fell to their "natural place," which was the centre of the universe. But because, according to the heliocentric theory, the Earth no longer coincided with the centre of the universe, a new explanation was needed. This re-examination of the laws governing falling bodies led eventually to the Newtonian concept of universal gravitation.
The dethronement of the Earth from the centre of the universe caused profound shock. No longer could the Earth be considered the epitome of creation, for it was only a planet like the other planets. No longer was the Earth the centre of all change and decay with the changeless universe encompassing it. And the belief in a correspondence between man, the microcosm, as a mirror of the surrounding universe, the macrocosm, was no longer valid. The successful challenge to the entire system of ancient authority required a complete change in man's philosophical conception of the universe. This is what is rightly termed "the Copernican Revolution." Nicolaus Copernicus
