2. The architecture of the heavens

During his studies, Copernicus learned three important details about celestial motions that would provide a fundamental foundation for his future astronomical work. First, the sun moves eastward in an annual path around the sky, tilted so that the sun travels higher in the sky in summer. Furthermore, the sun moves faster in winter than in summer. Second, the planets also move eastward, in approximately the same path as the sun, but occasionally they slow down, stop, and move westward for a while. Third, the stars themselves move very, very slowly eastward. ‘The architecture of the heavens’ describes the work of Mesopotamian, Babylonian, and Greek astronomers that was the starting point for Copernicus.

6. Rheticus

As Copernicus entered his sixties, he was still a busy canon, particularly with respect to his medical expertise. Martin Luther’s Reformation was gaining power at this time, and a young mathematician-astronomer from Wittenberg (home of Luther and his thriving university) became aware of Copernicus’s work. Georg Joachim Rheticus left Wittenberg early in May 1539 to travel to Varmia. Rheticus brought with him a gift: three technical books printed by Johannes Petreius in Nuremberg. He went on to assist Copernicus with observations of the planet Mercury and completion of De revolutionibus. In the autumn of 1541, Rheticus returned to Wittenberg armed with the manuscript of Copernicus’s magnum opus.

4. Canon days and the Little Commentary

Late in 1510, Copernicus’s passion for astronomy resulted in his leaving the Bishop’s Palace in Lidzbark Warminski for a residence in Frauenburg. Very little of his work over the next few years is dated, but two pages of random notes in one of his astronomy books supply tantalizing clues to his future theory. ‘Canon days and the Little Commentary’ considers these clues and the questions that Copernicus needed to answer. What kept the planets moving? How would he deal with Ptolemy’s equants? Copernicus’s Little Commentary, thought to have been written in 1514 or a little earlier, explained his new arrangement of the sun, the earth, the moon, and the other planets.

Prologue

In or around 1510 Nicolaus Copernicus, one of the sixteen directors of the northernmost Catholic diocese in Poland, invented the solar system. Wait a minute! you say. Wasn’t the sun always in the middle of the planets? But that wasn’t the way everyone else thought about it. Farmers, professors, priests, and school children all assumed the earth was solidly fixed in the middle of the cosmos. Every day the sun and stars revolved around the earth. The sun also moved, more slowly, in a path against the more distant stars so that it was higher in the sky in the summer and much lower in winter....

5. Competing with Ptolemy

In 1515, a full Latin translation of Ptolemy’s account of his geocentric cosmology was printed. Copernicus soon realized that his own radical cosmology would need a comparable book—with a full set of observed planetary positions—to be taken seriously. ‘Competing with Ptolemy’ explains how he spent more than two decades collecting the specific observations for his magnum opus, De revolutionibus. But how could he measure the position of a slowly moving planet? How would he deal with the precession of the equinoxes? This was the starting problem for Copernicus; he had to get precession under control before he could get into serious details of the planetary motions.

8. The book nobody read

An anonymous introductory essay was added to De revolutionibus. Rheticus was outraged by this unauthorized addition—later attributed to Andreas Osiander—as it suggested Copernicus’s work could be a safe recipe book for computing the positions of planets but should not be considered as actual physical reality. ‘The book nobody read’ describes the reactions of readers of the book, including Johannes Kepler and Galileo, who began to campaign for the Catholic Church to maintain an open position with respect to the heliocentric cosmology. The Vatican responded by placing De revolutionibus on the Index of Prohibited Books. It was not until 1835 that the Catholic ban on the book would be lifted.

7. De revolutionibus

Soon after his return to Wittenberg, Rheticus was appointed dean of the university. This delayed his travel to the printer in Nuremberg, but after a year of teaching he was granted leave. By early spring of 1542, the printing of the six books of De revolutionibus began, with Rheticus acting as a full-time copy reader until his appointment to a new professorship in Leipzig, when he was replaced by Andreas Osiander, a local clergyman well trained in Latin, Greek, and mathematics. ‘De revolutionibus’ outlines the complicated printing process involved with the technical material and the structure and breakdown of the six volumes.

3. Copernicus’s vision

The Ptolemaic system, created by Claudius Ptolemaeus around AD 150, for the first time in history introduced a comprehensive geometrical structure from which the positions of the planets (including the sun and moon) could be calculated for any time, past or future. It was a monumental achievement, and it held sway for 1,400 years. ‘Copernicus’s vision’ describes the basic structure of Ptolemy’s epicyclic system before explaining the heliocentric arrangement of Copernicus’s solar system. Copernicus’s sun-centered system automatically and unambiguously arranged the planets according to their periods of revolution around the sun. It also gave a logical explanation for the phenomenon of retrograde motion.

1. Copernicus, the young scholar

Nicolaus Copernicus was born in Torun, Poland, on February 19, 1473. When his father died in 1483, his maternal uncle, Lucas Watzenrode (who became bishop of Varmia in 1489), took over responsibility for him and his older brother. ‘Copernicus, the young scholar’ outlines Copernicus’ studies, which began at the Jagiellonian University in Cracow from 1491 to 1495 and included an astronomy course and introductions to Sacrobosco’s De sphaera, the Alfonsine Tables, and Euclid’s Geometry. In 1496, Copernicus was enrolled at Bologna University to study civil and canon law, and in 1497 he became one of the sixteen canons at Frauenburg in his uncle’s diocese. He went on to study medicine at Padua University in 1501.