Ordering the planets

Nicholas Copernicus (1473–1543)
De revolutionibus orbium coelestium
Nuremberg: Ioannes Petraeus, 1543

The teachings of the Church placed the Earth at the centre of all things; the sun, moon, planets and stars revolving around it. If this view were correct, the solar system should move in an orderly progression. Awkwardly, observations of the planets showed that they behaved differently – sometimes they appeared to go backwards. If it was the sun at the centre, though, the explanation became trivial. Copernicus was not the earliest thinker to propose this arrangement of the solar system but he was the first to publish the idea in our modern era.

F154.b.1.1, f. 10r

There is no evidence that Copernicus knew of the ideas of Aristarchus or Nicholas of Cusa and he apparently made very few astronomical observations but he was aware of the problem of retrograde motion in planetary orbits. Though not necessarily propounding that it reflected the actuality of nature, Copernicus realised that a much simpler explanation of observed planetary motion was to take the Sun as the centre of the system – the retrograde motion of, say, Jupiter would occur when the planet was opposite the Sun in its orbit as the Earth sped past far closer to the Sun, just as a racing car further from the curve of a racetrack bend would appear to go backwards in relation to a car closer to the curve.

In this celebrated woodcut Copernicus illustrates the solar system arranged with the Sun at the centre. In Copernicus’s original manuscript that today survives in Prague a hole in the paper at the Sun’s centre may be seen – where the point of the compass Copernicus used to inscribe the circles of the orbits punctured the paper. Though his ideas on heliocentricity had been maturing for decades and his manuscript was substantially completed in the 1530s, its author hesitated to commit himself to publication for ten years, well aware that demoting the Earth from the centre of the known universe would be contrary to Church doctrine. In the event Copernicus died in May 1543, just as De revolutionibus was finally published.

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