Nicolaus Copernicus:

A major contribution to Western thought was the publication in 1543 of De revolutionibus orbium coelestium, libri VI (Eng. trans., On the Revolutions of the Celestial Spheres, 1952; Latin reprint, 1965) by Copernicus, Polish astronomer, who is noted for the Copernican theory of the heavens. By attributing to the Earth a daily motion around its own axis and a yearly motion around the stationary Sun, Copernicus developed an idea that had far-reaching implications for the rise of modern science. Henceforth, the Earth could no longer be considered the centre of the cosmos; rather, as one celestial body among many, it became subject to mathematical description.

Nicolaus Copernicus (in Polish Mikolaj Kopernik, in German-Prussian dialect Niklas Koppernick) was born on February 19, 1473, at Torun, near the Vistula River in eastern Poland, where his father was a merchant of social standing. In 1491 Copernicus entered the University of Kraksw, where he became interested in the study of astronomy; he probably returned home in 1494 (or 1496). His maternal uncle, Lucas Waczenrode, newly elected bishop of Ermeland, wanted him to enter the canonry of Frauenburg in order to secure lifelong financial independence. While waiting for a vacancy to occur, he was sent by his uncle in 1497 for further training to the University of Bologna, where he associated himself with the German students. For three and a half years Copernicus studied the Greek language, mathematics, and the writings of Plato; he also became further acquainted with the astronomical thought of the day. In Bologna he also made his first recorded observation of the heavens, an occultation (overlapping, or eclipse) of the star Aldebaran by the Moon on March 9, 1497; the light of the former was shut off by the Moon. The same year he was elected (by proxy) a canon of Frauenburg. He travelled to Rome in 1500 for the great jubilee celebration and may have given informal lectures in mathematics there. In 1501 he briefly visited Frauenburg to claim his post on the cathedral staff, returning promptly to Italy under special leave of absence to continue his studies at the University of Padua. There, enrolled with other Polish students, he studied both law and medicine. Except for a short interruption in 1503, when he was granted the degree of doctor of canon law by the University of Ferrara, he spent almost four years in Padua.

On returning to Poland in 1503, he visited Kraksw and later acted as adviser to his uncle until the latter's death in 1512. Copernicus settled permanently at Frauenburg, where he acted as representative of the cathedral chapter, his medical skill being used particularly in aid of the indigent.

As a result of his studies in Kraksw and Padua, Copernicus may be said to have mastered all the knowledge of the day in mathematics, astronomy, medicine, and theology. Copernicus appears to have planned a systematic program of astronomical work. Although he did not make extensive observations, he did enough to enable him to recalculate the major components of the supposed orbits of the Sun, Moon, and planets around the Earth. He published 27 such observations made during the years 1497-1529, and a few others have been found entered in books in his private library. He also published for his uncle in 1509 a Latin translation of Greek verses of Theophylactus, a Byzantine poet of the 7th century AD, and from 1519 to 1528 prepared an exposition of the principles of currency reform for certain Polish provinces; the latter was not published in Warsaw, however, until 1816.

Copernicus' fame as an industrious student of astronomy rapidly increased, and in 1514 he was invited to give his opinion on calendar reform, which was then being considered by the Lateran Council, a general meeting of the church authorities. He refused to express any firm views, for he felt that the positions of the Sun and Moon were not known with sufficient accuracy to permit a proper reassessment.

Yet, as his studies progressed, Copernicus became increasingly dissatisfied with the Ptolemaic system of astronomy. He was not alone in this dissatisfaction; indeed, he himself said that the many divergent views prevalent in his day gave him cause for profound thought. Ptolemy's system, which contained not only original work but also a synthesis of the views of previous Greek philosophers, was basically geocentric and circular in conception. By the 16th century this geocentric interpretation of the heavens had become firmly entrenched in astronomical thought, virtually as an article of faith. Although certain Greek philosophers had suggested, as far back as the 3rd century BC, that the Sun--and not the Earth--was the centre of the universe, their ideas had not been widely accepted. Difficulties had arisen when ancient astronomers sought to account for the accumulated observations of the Sun, Moon, and planets. Accordingly, Ptolemy in the 2nd century AD had devised an elaborate geocentric model of the heavens composed of large circles, called deferents, and small circles, called epicycles. Each planet rode on the circumference of an epicycle, the centre of which revolved on the deferent. Ptolemy used this system to account for observed irregularities of the planets, such as changes in brightness, and particularly for their puzzling retrogressive motions, when they seemed to stop and move backward and forward in a loop. Moreover, to account for observed variations in velocity, Ptolemy introduced the equant, which was an imaginary point in space where uniform, circular speed would indeed be observed. This system enabled astronomers to account for the phenomena and to make predictions. As observations in succeeding centuries became more accurate, however, it became increasingly difficult to compute the future positions of the heavenly bodies, and much of the flexibility and elegance of the Ptolemaic system was thereby lost.

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 the centre not 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 Rhdticus, who studied with him for two years--that he finally published his work. In 1540 Rhdticus was permitted to take the completed manuscript to N|rnberg, Germany, for printing. Because of opposition from Martin Luther, Philipp Melanchthon, and other reformers, Rhdticus left N|rnberg 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.

A careful examination of the text makes it clear, however, that Copernicus really had 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, 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 reexamination 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."

Excerpt from the Encyclopedia Britannica without permission.