Nicolaus Copernicus

I

INTRODUCTION

Nicolaus Copernicus (1473-1543), Polish astronomer, best known for his astronomical theory that the sun is at rest near the center of the universe, and that the earth, spinning on its axis once daily, revolves annually around the sun. This is called the heliocentric, or sun-centered, system. See Astronomy; History of Astronomy; Solar System.

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EARLY LIFE AND EDUCATION

Copernicus was born on February 19, 1473, in Thorn (now Toruń), Poland, to a family of merchants and municipal officials. Copernicus's maternal uncle, Bishop Łukasz Watzenrode, saw to it that his nephew obtained a solid education at the best universities. Copernicus entered Kraków Academy (now Jagiellonian University) in 1491, studied the liberal arts for four years without receiving a degree, and then, like many Poles of his social class, went to Italy to study medicine and law. Before he left, his uncle had him appointed a church administrator in Frauenberg (now Frombork); this was a post with financial responsibilities but no priestly duties. In January 1497 Copernicus began to study canon law at the University of Bologna while living in the home of a mathematics professor, Domenico Maria de Novara. Copernicus's geographical and astronomical interests were greatly stimulated by Domenico Maria, an early critic of the accuracy of the Geography of the 2nd-century astronomer Ptolemy. Together, the two men observed the occultation (the eclipse by the moon) of the star Aldebaran on March 9, 1497.

In 1500 Copernicus lectured on astronomy in Rome. The following year he gained permission to study medicine at Padua, the university where Galileo taught nearly a century later. It was not unusual at the time to study a subject at one university and then to receive a degree from another—often less expensive—institution. And so Copernicus, without completing his medical studies, received a doctorate in canon law from Ferrara in 1503 and then returned to Poland to take up his administrative duties.

III

RETURN TO POLAND

From 1503  to 1510, Copernicus lived in his uncle's bishopric palace in Lidzbark Warminski, assisting in the administration of the diocese and in the conflict against the Teutonic Knights. There he published his first book, a Latin translation of letters on morals by a 7th-century Byzantine writer, Theophylactus of Simocatta. Sometime between 1507 and 1515, he completed a short astronomical treatise, De Hypothesibus Motuum Coelestium a se Constitutis Commentariolus (known as the Commentariolus), which was not published until the 19th century. In this work he laid down the principles of his new heliocentric astronomy.

After moving to Frauenberg in 1512, Copernicus took part in the Fifth Lateran Council's commission on calendar reform in 1515; wrote a treatise on money in 1517; and began his major work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), which was finished by 1530 but was first published by a Lutheran printer in Nürnberg, Germany, just before Copernicus's death in 1543.

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EARLY 16TH-CENTURY COSMOLOGY

The cosmology that was eventually replaced by Copernican theory postulated a geocentric universe in which the earth was stationary and motionless at the center of several concentric, rotating spheres. These spheres bore (in order from the earth outward) the following celestial bodies: the moon, Mercury, Venus, the sun, Mars, Jupiter, and Saturn. The finite outermost sphere bore the so-called fixed stars. (This last sphere was said to wobble slowly, thereby producing the precession of the equinoxes; see Ecliptic.)

One phenomenon had posed a particular problem for cosmologists and natural philosophers since ancient times: the apparent retrograde (backward) motion of Mars, Jupiter, and Saturn. From time to time the daily motion of these planets through the sky appears to halt and then to proceed in the opposite direction. In an attempt to account for this retrograde motion, medieval cosmology stated that each planet revolved on the edge of a circle called the epicycle, and the center of each epicycle revolved around the earth on a path called the deferent (see Ptolemaic System).

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THE COPERNICAN SYSTEM AND ITS INFLUENCE

The major premises of Copernicus's theory are that the earth rotates daily on its axis and revolves yearly around the sun. He argued, furthermore, that the planets also circle the sun, and that the earth precesses on its axis (wobbles like a top) as it rotates. The Copernican theory retained many features of the cosmology it replaced, including the solid, planet-bearing spheres, and the finite outermost sphere bearing the fixed stars. On the other hand, Copernicus's heliocentric theories of planetary motion had the advantage of accounting for the apparent daily and yearly motion of the sun and stars, and it neatly explained the apparent retrograde motion of Mars, Jupiter, and Saturn and the fact that Mercury and Venus never move more than a certain distance from the sun. Copernicus's theory also stated that the sphere of the fixed stars was stationary.

Another important feature of Copernican theory is that it allowed a new ordering of the planets according to their periods of revolution. In Copernicus's universe, unlike Ptolemy's, the greater the radius of a planet's orbit, the greater the time the planet takes to make one circuit around the sun. But the price of accepting the concept of a moving earth was too high for most 16th-century readers who understood Copernicus's claims. In addition, Copernicus's calculations of astronomical positions were neither decisively simpler nor more accurate than those of his predecessors, even though his heliocentric theory made good physical sense, for the first time, of planetary movements. As a result, parts of his theory were adopted, while the radical core was ignored or rejected.

There were but ten Copernicans between 1543 and 1600. Most worked outside the universities in princely, royal, or imperial courts; the most famous were Galileo and the German astronomer Johannes Kepler. These men often differed in their reasons for supporting the Copernican system. In 1588 an important middle position was developed by the Danish astronomer Tycho Brahe in which the earth remained at rest and all the planets revolved around the sun as it revolved around the earth.

After the suppression of Copernican theory occasioned by the ecclesiastical trial of Galileo in 1633, some Jesuit philosophers remained secret followers of Copernicus. Many others adopted the geocentric-heliocentric system of Brahe. By the late 17th century and the rise of the system of celestial mechanics propounded by the English natural philosopher Sir Isaac Newton, most major thinkers in England, France, the Netherlands, and Denmark were Copernicans. Natural philosophers in the other European countries, however, held strong anti-Copernican views for at least another century.