COPERNICUS, Nicolaus

(1473-1543)

With On the Revolutions of the Celestial Spheres, Nicolaus Copernicus ini­tiated a shift in scientific thinking often now described as the ''scientific revo­lution.'' Although the details of the heliocentric theory of the universe were disproved long ago, its central claim that the earth is but one of many objects orbiting the sun without a doubt changed the theory and practice of astronomy and physics within the course of a single century.

The son of prosperous parents from Torun in Poland, Copernicus was edu­cated early both at home and elsewhere. At the age of twelve, following the deaths of his parents, he became the ward of his uncle Lucas Waczenrode, the bishop of Varmia. He first attended the cathedral school and later entered the University of Cracow in 1491. Upon the urging of his uncle, Copernicus was elected a canon to the cathedral chapter at Frombork in 1497. An eight-year educational sojourn in Italy solidified his training in law, medicine, mathematics, and astronomy. After study at the Universities of Bologna, Padua, and Ferrara, Copernicus returned to Varmia for good around 1504 and served the cathedral chapter with distinction for his remaining years.

Most of Copernicus's life was occupied by duties having little to do with his scientific achievements, but he is justly renowned for his heliocentric under­standing of the universe: ''The earth moves while the sun stands still.'' His scholarly output was limited, and even though he made no secret of his views, he opposed publication of his theory, bowing to the pressure of his friends only in the last years of his life. His delay can hardly be attributed to fear. He circulated a draft report of his new system as early as 1514, and by 1533 Pope Clement VII approved publication of his views. On the Revolutions of the Ce­lestial Spheres was complete by 1540, and the work appeared in 1543, the year of the author's death.

Although some ancient philosophers had posited heliocentricity, Copernicus was the first to elaborate upon it systematically. He did so in the face of sig­nificant resistance, since the strength of tradition and academic habits secured the dominant positions of Aristotle and Ptolemy within astronomy. In the second century, Ptolemy described a geocentric model of the universe by relying upon the basic tenets of Aristotle's Physics. Accordingly, the earth was the fixed center of the universe, and all bodies fell ''naturally'' to the earth. Since the heavens did not fall, they were of a qualitatively different substance than the earth, one that exhibited the qualities of perfection, not the least of which was perpetual and, therefore, circular (rather than linear) motion. But the problem for Aristotle was that the heavenly bodies displayed disturbingly irregular behavior to the observer on earth. They sometimes moved at different rates of speed or displayed varying degrees of brightness, and, in particular, they some­times moved in a retrograde fashion, that is, they sometimes went backward. Ptolemy elegantly tackled this problem in a theory that posited the existence of large and small circles. The planets moved first along the small circles positioned around imaginary points in space (equants) that were themselves moving along the large circles. Although inaccurate, this model, minus the equants, is in es­sence how modern astronomers understand the movement of moons around planets, in small orbits, and the sun, in large orbits. But centuries of observations had eroded the reliability of ancient thought on the heavens. The problem of explaining the speed, brightness, and retrograde motion of the planets remained.

Copernicus's own observations, along with those of others, led to his dissat­isfaction with received wisdom and to his desire to replace it with something simpler and more accurate. His central argument can be easily summarized, although the mathematics used to justify its claims cannot be. The earth rotated daily around an axis; furthermore, it circled annually around the sun. By impli­cation, the sun was the center of the universe around which the other heavenly bodies moved.

The chief significance of Copernicus's views lies not so much in his own conclusions as in the implications they raised—new problems that other astron­omers set themselves to solving. Copernicus was clearly right about the cen-trality of the sun, but he produced a model that was hardly less complex and barely more accurate than the accepted one. But he had vigorously attacked the Ptolemaic system and seriously challenged the physics of Aristotle underlying it. He had broken the traditional paradigm. In the following decades, like-minded philosophers of the natural world would follow. The empirical work of Galileo* would lay bare the physical nature of the heavens, and the theoretical work of Johannes Kepler* would accurately describe the complexities of planetary mo­tion. Both rightly acknowledged their debts to Copernicus.

Bibliography

H. Blumenberg, The Genesis ofthe Copernican World, 1987.

O. Gingerich, The Eye of Heaven, 1993.

Edmund M. Kern