Copernicus, Nicolaus (1473-1543)

Believing that the theories of Ptolemy regarding the Earth as the centre of the universe were too complicated, Copernicus turned to earlier Greek astronomers such as Aristarchus and Hipparchus. His deduction that the Earth is a moving planet was developed by later astronomers such as Kepler and Galileo.

Polish astronomer who believed that the Sun, not the Earth, is at the centre of the Solar System, thus defying the Christian church doctrine of the time. For 30 years, he worked on the hypothesis that the rotation and the orbital motion of the Earth are responsible for the apparent movement of the heavenly bodies. His great work De Revolutionibus Orbium Coelestium/On the Revolutions of the Heavenly Spheres was the important first step to the more accurate picture of the Solar System built up by Tycho Brahe, Kepler, Galileo, and later astronomers.

Copernicus proposed replacing Ptolemy's ideas with a model in which the planets (including the Earth) orbited a centrally situated Sun. He proposed that the Earth described one full orbit of the Sun in a year, whereas the Moon orbited the Earth. The Earth rotated daily about its axis (which was inclined at 23.5° to the plane of orbit), thus accounting for the apparent daily rotation of the sphere of the fixed stars.

This model was a distinct improvement on the Ptolemaic system for a number of reasons. It explained why the planets Mercury and Venus displayed only ‘limited motion’; their orbits were inside that of the Earth's. Similarly, it explained that the planets Mars, Jupiter, and Saturn displayed such curious patterns in their movements (‘retrograde motion’, loops, and kinks) because they travel in outer orbits at a slower pace than the Earth. The movement of the Earth on its axis accounted for the precession of the equinoxes, previously discovered by Hipparchus.

Copernicus's model represents a complete reformation of astronomy by replacing the anthropocentric view of the universe with the heliocentric viewpoint. Unable to free himself from the constraints of classical thinking, however, Copernicus was able to imagine only circular planetary orbits. This forced him to retain the system of epicycles, with the Earth revolving around a centre that revolved around another centre, which in turn orbited the Sun. Kepler rescued the model by introducing the concept of elliptical orbits. Copernicus also held to the notion of spheres, in which the planets were supposed to travel. It was Brahe who finally rid astronomy of that concept.

Copernicus was born in Toruń, on the River Vistula, Poland. After the death of his father in 1483, he was adopted by his uncle, Lucas Watzelrode, afterwards bishop of Ermland. He studied mathematics, astronomy, classics, law, philosophy, and medicine at Kraków and various universities in Italy. In 1500 he lectured in mathematics in Rome with great success. On his return to Poland in 1506 he became physician to his uncle, the bishop of Varmia, at the castle of Heilsberg. His uncle had also secured for him the post of canon at Frombork, enabling him to intersperse astronomical work with the duties of various civil offices.

Copernicus began to make astronomical observations in 1497, although he relied mainly on data accumulated by others. Where observational facts failed he found them himself, but he was essentially a thinker rather than an observer. In about 1513 he wrote a brief, anonymous text entitled Commentariolus, outlining the material he later discussed in De Revolutionibus. He had been at work for more than 30 years before at last agreeing to the publication of his major work. This was not, as is often supposed, because he feared that it would be seen as heretical, but because his idea was at that time so incredible that only those with an intimate knowledge of astronomy could be expected to consider it.

Copernicus was at last persuaded to publish by friends and by his young pupil Rheticus, who issued an account of the new system under the title Narratio Prima de Libris Revolutionum. This was the first printed work on the theory, and as it was received with less ridicule than Copernicus had feared, he consented to the publication of his own work. Pope Paul III accepted the dedication of the work to himself. Andreas Osiander, a Lutheran minister, oversaw the publication and inserted a preface (without permission) stating that the theory was intended merely as an aid to the calculation of planetary positions, not as a statement of reality. This served to compromise the value of the text in the eyes of many astronomers, but it also saved the book from instant condemnation by the Roman Catholic Church.

The book's immediate effects in the sphere of philosophy and theology were not conspicuous. The reaction was favourable among Roman Catholics but antagonistic among Lutherans. There was no question of persecution, and it was only when new philosophies began to develop from it that De Revolutionibus was denounced by Luther. It was placed on the index of forbidden books in 1616, and was removed in 1835.