Copernicus, Nicolaus

I

Introduction

Copernicus, Nicolaus (1473-1543), Polish astronomer, best known for his astronomical theory that the Sun is at rest near the centre 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-centred, system. (See Astronomy; Solar System.)

II

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 the University of Kraków 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 Poland, 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 at 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 Warmiński, 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. Some time 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 (1515); wrote a treatise on money (1517); and began his major work, De Revolutionibus Orbium Coelestium (On the Revolutions of the Celestial Spheres), which was finished by 1530 but first published by a Lutheran printer in Nuremberg, Germany, just before Copernicus's death on May 24, 1543.

IV

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 centre 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, Saturn, and, finally, the finite outermost sphere bearing 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, or backward, motion of Mars, Jupiter, and Saturn. From time to time the 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 in a circle called the epicycle, and the centre of each epicycle revolved around the Earth on a path called the deferent (see Ptolemaic System).