Copernicus and De Revolutionibus (1543): The Sun at the Centre

De revolutionibus orbium coelestium (“On the Revolutions of the Heavenly Spheres”), published in Nuremberg in 1543, set out Nicolaus Copernicus’s theory that the Earth and the other planets move around the Sun. Appearing in the year of its author’s death, the book challenged an Earth-centred view of the universe that had dominated for more than 1,400 years. Its ideas took decades to win acceptance, but they began what historians call the Copernican Revolution and helped launch the Scientific Revolution.

Background: the Earth-centred cosmos

Educated Europeans in 1500 followed a cosmos inherited from Aristotle and refined by the Greek astronomer Claudius Ptolemy in the second century AD. The Earth sat motionless at the centre. Around it moved the Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn, and beyond them the sphere of the fixed stars.

Planets do not move smoothly across the sky. Mars, Jupiter and Saturn sometimes appear to stop and travel backwards for a while, a motion called retrograde. Ptolemy explained this with a geometric system of circles moving on circles, called epicycles, plus off-centre points known as equants. The system predicted planetary positions reasonably well, but critics found the equant philosophically unsatisfying because it broke the ideal of uniform circular motion.

The idea of a moving Earth was not new. Aristarchus of Samos had proposed a Sun-centred arrangement in the third century BC, and medieval scholars such as Nicole Oresme had discussed the Earth’s rotation. No one, however, had built a complete mathematical astronomy around it.

Copernicus the man

Nicolaus Copernicus (Mikołaj Kopernik) was born in Toruń, in Royal Prussia under the Polish crown, on 19 February 1473. After his father died, his uncle Lucas Watzenrode, later Bishop of Warmia, oversaw his education. Copernicus studied at the University of Kraków from 1491, then in Italy at Bologna, where he lodged with and assisted the astronomer Domenico Maria Novara, and at Padua, where he studied medicine. In 1503 he took a doctorate in canon law at Ferrara.

Back in Warmia he became a canon of Frombork Cathedral, an administrative church post rather than a priestly one. He managed estates, practised medicine, wrote a treatise on currency reform and helped defend the town of Olsztyn during a war with the Teutonic Knights in 1520–1521. Astronomy was the work of his spare hours, carried out with simple instruments and many old observations.

From the Commentariolus to the book

Around 1510–1514 Copernicus circulated a short handwritten summary of his ideas, now called the Commentariolus (“Little Commentary”). It listed seven assumptions, among them that the Earth is not the centre of the universe, that the Earth rotates daily, that it orbits the Sun annually, and that the distance to the stars is immense compared with the Earth–Sun distance. A Kraków library catalogue of 1514 appears to mention it.

He then spent decades working out the full mathematics but hesitated to publish. In May 1539 a young mathematics professor from the Lutheran University of Wittenberg, Georg Joachim Rheticus, arrived in Frombork. He stayed about two years, studied the manuscript and in 1540 published the Narratio prima (“First Account”), a summary that tested reactions. Encouraged by Rheticus and by his friend Tiedemann Giese, Bishop of Chełmno, Copernicus agreed to let the book appear.

Rheticus took the manuscript to Nuremberg, to the printer Johannes Petreius. When Rheticus left to take up a post in Leipzig, the Lutheran theologian Andreas Osiander supervised the printing. Osiander added an unsigned note “To the Reader” stating that the theory need not be true, only a convenient basis for calculation. Copernicus’s own dedication to Pope Paul III, by contrast, defended the physical reality of his system. Copernicus had suffered a stroke in late 1542, and Giese later wrote that the printed book reached him only on the day he died, 24 May 1543.

What the book argued

De revolutionibus has six books. The first sets out the general picture: the Sun near the centre, the Earth as a planet with a daily rotation and an annual orbit, and the Moon orbiting the Earth. Later books cover spherical astronomy, a catalogue of stars, the motion of the Earth, the Moon, and the planets in longitude and latitude.

The Sun-centred arrangement immediately explained several puzzles. Retrograde motion became an effect of perspective, as the faster-moving Earth overtakes an outer planet. Mercury and Venus always stay close to the Sun because their orbits lie inside the Earth’s. Most strikingly, the model fixed the order of the planets and their relative distances from the Sun, something Ptolemy’s system could not do.

The book was still conservative in important ways. Copernicus kept perfect circular motion and used epicycles of his own; the Sun was not exactly at the centre of the orbits. His predictions were not markedly more accurate than Ptolemaic tables, and his system was not dramatically simpler in its number of circles. Its strengths were coherence and harmony rather than practical advantage.

Key people

• Nicolaus Copernicus (1473–1543): astronomer, canon of Frombork and author of the book.
• Georg Joachim Rheticus (1514–1574): his only pupil, who persuaded him to publish and carried the manuscript to the printer.
• Andreas Osiander (1498–1552): theologian who oversaw the printing and added the anonymous preface.
• Johannes Petreius (c. 1497–1550): Nuremberg printer of scientific works.
• Tiedemann Giese (1480–1550): bishop and friend who urged publication and protected Copernicus’s reputation.

Reception

Early reactions were mixed. Astronomers valued Copernicus’s mathematics; Erasmus Reinhold of Wittenberg used it to compile the Prutenic Tables of 1551, which were widely adopted for calendars and almanacs. Many readers, however, treated the moving Earth as a calculating device rather than reality, as Osiander’s preface suggested. This cautious approach, sometimes called the Wittenberg interpretation, allowed Protestant and Catholic scholars alike to teach Copernican methods without committing themselves to a moving Earth. Martin Luther, in a table-talk remark recorded in 1539, reportedly dismissed the idea of a moving Earth as foolish, though the reliability of the record is debated.

The physical objections were serious in the sixteenth century. If the Earth moved, why did people not feel it, and why did falling objects not drop behind? If the Earth orbited the Sun, the stars should show an annual shift in position, called parallax, which nobody could detect. Copernicus answered that the stars were vastly far away, which turned out to be correct; stellar parallax was finally measured only in 1838.

A small number of thinkers embraced the system as physically true, including the English mathematician Thomas Digges in 1576 and the philosopher Giordano Bruno. Tycho Brahe proposed a compromise in which the planets circle the Sun while the Sun circles a stationary Earth.

From hypothesis to revolution

The decisive steps came in the early seventeenth century. Johannes Kepler, a convinced Copernican, used Tycho’s observations to show that planets move in ellipses; his laws of planetary motion made heliocentric astronomy far more accurate than any rival. In Astronomia nova (1609) he also revealed that Osiander, not Copernicus, wrote the cautious preface. Galileo’s telescopic discoveries from 1610, including the phases of Venus, undermined the Ptolemaic system.

In March 1616 the Catholic Congregation of the Index suspended De revolutionibus “until corrected”; corrections issued in 1620 required readers to amend about a dozen passages that presented the Earth’s motion as fact. The conflict deepened with the trial of Galileo in 1633. The book disappeared from the Index only in its 1835 edition. By then Isaac Newton’s theory of gravitation had long since explained why the planets orbit the Sun.

By the numbers

Myths and facts

• Myth: Copernicus was persecuted by the Church. Fact: he died before any controversy, dedicated his book to the pope and faced no proceedings; the 1616 decree came 73 years later.
• Myth: his system was much simpler and more accurate than Ptolemy’s. Fact: it still used many circles and gave predictions of similar accuracy; Kepler’s ellipses brought the real improvement.
• Myth: nobody read the book. Fact: Gingerich’s census found heavily annotated copies all over Europe.

Timeline

• 1473, 19 February: Copernicus born in Toruń.
• c. 1510–1514: the Commentariolus circulates in manuscript.
• 1539, May: Rheticus arrives in Frombork.
• 1540: Rheticus publishes the Narratio prima in Gdańsk.
• 1543: De revolutionibus printed in Nuremberg by Petreius.
• 1543, 24 May: Copernicus dies at Frombork.
• 1551: Reinhold’s Prutenic Tables based on Copernican calculations.
• 1609: Kepler’s Astronomia nova identifies Osiander as author of the preface.
• 1616, 5 March: the Congregation of the Index suspends the book until corrected.
• 2010: Copernicus’s remains, identified by DNA analysis, are reburied in Frombork Cathedral.

Why it matters

De revolutionibus moved the Earth out of the centre of the universe and made it one planet among several. Its method, building a physical picture from mathematical consistency and observation, became a model for modern science, and the shift it began changed humanity’s understanding of its place in the cosmos.