Nicolas Copernicus (1473–1543) was the sixteenth-century priest and astronomer whose ideas finally led to the realization that the Earth is not fixed at the centre of the universe, but is just one of the planets revolving around the Sun.
AT THE TIME COPERNICUS WAS BORN, Europe was beginning to feel the effects of the Renaissance. Classical ideas and texts were appearing in Europe from the Arab world, and thinkers there were beginning to add to them ideas of their own. At this time the Roman scholar Ptolemy’s model of how the universe worked, described in his book Almagest (the Greatest), was still considered correct. In this model the Earth was still and fixed at the centre of the universe. Round the Earth were a series of invisible concentric spherical crystal shells in which the Sun, Moon, planets and stars revolved in perfect circles, one heavenly body in each, except for the stars.
Unfortunately for this model, actual observation showed that only the stars appeared to move in perfect circles. To account for this, Ptolemy suggested two main mechanisms – epicycles and equants. These explained the apparent motions of the planets while still keeping the idea of perfect circles. Epicycles were basically tiny circular motions inside each sphere, or wheels within wheels. Equants allowed the circles of the Moon and the planets to be slightly offset to turn around different points, called equant points, rather than all turning around the exact centre of the Earth.
This view of the universe as a series of nested crystal spheres turning round the Earth pretty much worked, in that it allowed astronomers to predict accurately the motions of the Sun, the Moon and the planets then known – Mercury, Venus, Mars, Jupiter and Saturn. But there were problems. In the 1490s, when Copernicus was in his twenties, the German astronomer Johannes Müller (better known by his Latin name Regiomontanus) published a summary of Ptolemy’s Almagest, along with a critical commentary called the Epitome. In the Epitome, Regiomontanus pointed out that one of the problems with the Ptolemaic system is that if the circle of the Moon is offset as the system says it is, then it should get larger and smaller as it moves closer to the Earth and further away – and yet it clearly doesn’t.
Another problem with the Ptolemaic system, as far as the young priest Copernicus was concerned, was that it seemed too elaborate and intricate. Surely God would have created something more simple and elegant? All these complications would disappear, Copernicus realized, if the Sun is at the centre and the Earth revolves around it, along with all the other planets. The only difficulty then was how to account for the fact that the Moon turned round the Earth. Although this ‘heliocentric’ (sun-centred) system had the great advantage of actually being true, it took more than a century for his idea to be widely known and even longer for it to be widely accepted (see here).
Mikolaj Kopernik
Copernicus was born in Torun on the Vistula River in northern Poland on 19 February 1473. His real name was Mikolaj Kopernik, and it was only later in life that he adopted the Latin version of his name, Nicolas Copernicus. His father, a well-to-do merchant, died when he was about 10, and so he was brought up by his uncle Lucas Waczenrode, soon to be bishop of Varmia. His uncle saw to it that he had the general education typical for those destined for a career in the Church.
At the age of 20, Copernicus went to the University of Krakow to study the liberal arts, including astrology and astronomy. Then, 5 years later, he went on to study in Bologna in Italy, where he lodged for a while in the house of the distinguished astronomer and astrologer Ferrariensis. It was Ferrariensis who really inspired Copernicus’s interest in the stars and introduced him to Regiomontanus’s Epitome. In 1497, Copernicus observed an eclipse of the Moon in Bologna.
By the time Copernicus had finished his doctorate in canon law in 1503, he was well grounded in astronomy and already beginning to develop his ideas about a heliocentric universe. His uncle arranged for him to become canon at Frombork (Frauenberg) Cathedral in Poland, a post which allowed him plenty of free time both for studying astronomy and for pursuing various other tasks. He worked for the community as a doctor, for instance, and developed a plan for reforming the currency. In 1519 he was pressed into military service to command the defence of the castle of Allenstein against invading Teutonic Knights.
The great idea
In the meantime, he took advantage of his position in the cathedral to consolidate his ideas. Most of his astronomy was entirely on paper or in his head, but sometimes he climbed the cathedral tower at Frombork, and also at Allenstein and Heilsberg, to gaze at the night sky. Unlike later scientists, Copernicus had no interest in verifying his ideas by observation or experiment.
In 1514, Copernicus published a little handwritten book for his friends. Called Commentariolus, it gave the first outline of his revolutionary theory. In Commentariolus Copernicus included not just the idea that the Earth moved around the Sun, and that the stars are very, very far away, but the suggestion that this arrangement explains a number of phenomena, such as the retrograde motion of the planets. Ptolemy had explained retrograde motion – the fact that the planets appear to loop back on themselves every now and then – by means of complicated epicycles. But if it is accepted that the Earth is moving around the Sun with the planets, no such elaborate explanation is needed; retrograde motion is simply due to the changing view of the planets from the Earth.
Copernicus also suggested in Commentariolus that the time taken for each planet to complete its cycle through the night sky might increase the further it is from the Sun. Mercury’s cycle takes 88 days, which makes it the nearest planet to the Sun. Venus takes 225 days, Earth 1 year, Mars 1.9 years, Jupiter 12 years and Saturn 30 years. It was thus easy for Copernicus to work out the order of the planets.
Keeping quiet
Copernicus made it clear in this little book that he was planning a major work to expound his theory in full, writing, ‘Here, for the sake of brevity, I have thought it desirable to omit the mathematical demonstrations intended for my larger work.’ This larger work, the famous De Revolutionibus Orbium Coelestium (On the revolutions of the heavenly spheres) was not published for a further 26 years, by which time Copernicus was on his deathbed. This delay was perhaps due to the religious view of the universe at the time: Copernicus may have thought it simply too dangerous to publicize his ideas. Others have suggested Copernicus delayed because he had not developed his ideas and proofs sufficiently.
The daring young man
Whatever the truth, the final spur Copernicus needed to finish his great book came when he acquired a disciple in the form of Georg von Lauchen, known as Rheticus, a young professor of mathematics from Wittenberg. Rheticus came to Frombork to learn more about Copernicus’s ideas, and when he realized their importance he was determined that Copernicus should publish his work.
The Planisphaerium Copernicanum – the heliocentric planetary system of Copernicus. Taken for granted in the modern era, this was a revolutionary view in Copernicus’s day.
In 1540, Rheticus published a curtain-raiser. Called Narratio Prima de Libtus Revolutionum Copernici (First account of the revolutionary book of Copernicus), it summarized Copernicus’s main idea that the Earth moves around the Sun. This seems to have done the trick: Rheticus wrote to a friend on 9 June 1541, he ‘had finally overcome [Copernicus’s] reluctance to release his volume for publication’. By August of that year, De Revolutionibus Orbium Coelestium was ready. Rheticus undertook to see it printed and took it to Johann Petreius, the best printer in Nuremberg. Unable to see the printing through personally, Rheticus deputed the task to a Lutheran minister called Osiander.
Although the story only emerged gradually, it seems that Osiander took it upon himself to write an unsigned preface saying that Copernicus’s ideas were in no way intended to describe reality; they were simply a mathematical model to help with calculations. Osiander even changed the title to make it sound less definitive. Osiander was clearly worried about how people would react to Copernicus’s revolutionary ideas. When Rheticus discovered this, he was livid, scrawling a huge red cross through the preface in his copy of the book.
What Copernicus thought about all this, no one quite knows, for he died of a stroke shortly after publication of the new book in 1543. It is said that he was handed the new book for the first time when he briefly recovered consciousness, and that he died with it in his hands: one cannot but hope the story is true.
Moving the Earth
It is not clear whether Osiander’s preface to De Revolutionibus succeeded in limiting the outrage that might have been caused by Copernicus’s ideas. The plain fact is that few people took much notice at first. Many of the original edition of 400 copies were left unsold, and there was certainly no clamour from the Catholic Church for Copernicus to be burned at the stake. In fact the only protest came from the Protestants Osiander had tried to appease in his preface. It seems likely that few people appreciated the real implications of Copernicus’s ideas at first. Those who did understand them often remained quiet about it, and so no fuss was made.
One of those who did understand Copernicus was the English astronomer Thomas Digges, who wrote the first explanation of the Copernican system in English in 1576. Digges actually went further than Copernicus, suggesting that the universe around the solar system is infinite, with a multitude of stars in all directions.
The famous Danish astronomer Tycho Brahe (1546–1601) did not accept the Copernican model himself, yet his meticulous observations slowly built up a pile of evidence in favour of it – not least of which was the observation of a new star, a supernova, in 1572 which showed that the stars were not perfect and unchanging after all, whatever the Church and Ptolemy said.
One of the reasons why Brahe could not accept Copernicus’s model was because he was a very precise observer – and Copernicus’s model did not precisely fit the facts. This is where Brahe’s assistant Johann Kepler (1571–1630) comes in. Unlike Brahe, Kepler did accept the Copernican model, and what is more, in a brilliant feat of mathematical inspiration, he found a way to make it fit the facts, using Brahe’s observations. If the orbits of the planets and the Earth are elliptical, not circular, Kepler realized, then the Copernican system fits the facts perfectly.
Kepler’s ideas were finally published in full in 1619 in his book Harmonice Mundi (Harmony of the world), but by that time another astronomer, Giordano Bruno, had been burned at the stake. Because Bruno was a Copernican, and because like Digges he believed in a universe filled with infinite stars, people assume he was burned for his dangerous astronomical ideas. in fact, he was condemned by the Inquisition for his ‘blasphemous’ Arian beliefs and his practice of magic.
All the same the Catholic Church began to associate Copernicanism with the widespread threat of the Protestant Reformation. In 1610, Galileo saw through his telescope the clinching evidence that Copernicus was right – moons circling Jupiter and moonlike phases for Venus. As Galileo began to publicize his ideas – right from the heart of Catholic Europe, in Florence – the Church finally decided to take action.
In 1616, 73 years after its first publication, they banned De Revolutionibus. That same year, the cardinals summoned Galileo to Rome and forbade him to talk about Copernicanism. Galileo persisted, and in the end the Cardinals had to threaten him with torture to shut him up. But of course the battle was lost. The Copernican revolution was in full swing all over Europe. However, it would be another 200 years before the Catholic Church lifted its ban on De Revolutionibus.