How it began
Nicolaus Copernicus was born in 1473 in Toruń, a city on the Vistula River in north-central Poland, and studied liberal arts, including astronomy, at the University of Cracow before further study in Italy. He returned to serve as a church canon in Warmia, with duties that were largely administrative and medical, and did his astronomy in his spare time. Britannica states that he probably reached his main idea between 1508 and 1514 and wrote it up in a manuscript known as the Commentariolus. The final version, De revolutionibus, was printed in 1543, the year he died at Frauenburg, now Frombork, Poland.
Before it existed
Before Copernicus published, people generally agreed that the Moon and the Sun orbited a motionless Earth and that Mars, Jupiter and Saturn lay beyond the Sun. This geocentric picture was set out in the Ptolemaic system. Astronomers disagreed about the order of the planets, a weakness that critics of astrology had pointed out in Copernicus's student years.
How it works
The model takes the Sun as the fixed point to which the motions of the planets are referred. Earth is treated as a planet that orbits the Sun once a year and also turns once a day on its own axis. Very slow changes in the direction of that axis account for the precession of the equinoxes. Copernicus kept some elements of the older system, such as epicycles.
Who pushed back
Copernicus did not print the final theory until the end of his life. His disciple Rheticus took the manuscript from Frauenburg to arrange publication. A preface added to the 1543 book by Andreas Osiander presented the theory as purely hypothetical, which Britannica says helped keep the work off the Index of Forbidden Books until the next century. Galileo's support for the model led to his trial before the Inquisition in 1633.
What lasted
De revolutionibus became a standard reference for advanced problems in astronomical research, valued especially for its mathematical techniques. Britannica describes the theory as having important consequences for Galileo, Kepler, Descartes and Newton, and the book as the opening of the Scientific Revolution.
