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  • Writer's pictureMichal J A Paszkiewicz

Copernicus, Galileo, Kepler... they all lacked proof

Updated: Nov 27, 2023

Despite being born in England, I was brought up as a Pole. A Polish identity often includes a pride in Polish history, which would definitely include a love of Copernicus, or Mikołaj Kopernik, as he is known in Poland. I remember correcting people at school that it was Copernicus, and not Galileo, who proved the Earth went around the Sun.


But the reality is quite different.


Copernicus was certainly a trailblazing mathematician, who for the first time in human history built a serious mathematical model out of Heliocentric assumptions. Before this, the Geocentric Ptolemaic model had ruled for over a millennium with little to no competition.

A diagram of the Simplistic Ptolemaic Model
The Simplistic Ptolemaic Model

The Ptolemaic model and the shift to the Heliocentric model is probably covered in most school textbooks these days. But the details and genius of the Ptolemaic model remains hidden, no doubt because of the lack of understanding of it amongst teachers. Diving into the details of the Ptolemaic Model brings out a mathematical beauty, which is something that scientists will often strive for, even if it may only be subconsciously. This beauty can be seen in, for example, the pattern that the model of Venus made orbiting the Earth.

A model of Venus orbiting the Earth
The orbit of Venus in the Ptolemaic Model

This beautiful pattern came from the fact that planets in the Ptolemaic model followed a path that was composed of a circle and an epicycle (a second spinning circle centred on the edge of the first). The Epicycle for some of the planets was comparatively large to the first circle.


Then of course Copernicus built his model with the Sun at the centre. It is a very common misconception amongst people that Copernicus' model removed the need for epicycles. Or that this model was simpler and therefore proved true by Occam's razor. These claims turn out to be false. Copernicus used more circles, and also fiddled with some complex ideas such as the Tusi Couple. But there are a variety of reasons why these myths are so popular. Perhaps the main one today is the fact that textbooks will only usually include the simplistic diagrams of the models.

The Simplistic Copernican Model
The Simplistic Copernican Model

Despite not being simpler, the Copernican model gained interest even during Copernicus' lifetime. First a text called the Commentariolus was circled around academia with some basic ideas of the model. Copernicus' student Rheticus then drafted a new text called the Narratio Prima and propagated it. Pope Clement VII himself approved the Copernican model in 1533, a decade before Copernicus finally publish the De Revolutionibus. The model had grown and become more complex than he had intended it to be in his first texts.


But the Copernican Model was also useful. Some Astronomers found it to lead to more accurate measurements, and some people considered the mathematics to be easier. Jesuit Priests sent as missionaries to India and China would teach the Copernican Theory.


But the new model was hardly a proof of Heliocentrism being necessarily true. Copernicus' publish Osiander highlighted this in a preface where he stated that the model was a mathematical curiosity rather than a claim of reality being different. The biggest objections to the idea were the fact that no movement was felt, and that no stellar parallax was seen, despite the model claiming that one could take two observations on either side of the Sun. This meant that the distance to the stars had to be far greater than the distance considered to be the scientific consensus.


At the end of the 16th century, Tycho Brahe built a new model that was mathematically equivalent to the Copernican Model, except that the Sun orbited the Earth while the other planets orbited the Sun. Tycho Brahe also ran an observatory that could be compared in scale then to something like NASA in our time. He was hugely influential and made vast amounts of observations that allowed an improvement in planetary predictions.

The Tychonic Model
The Tychonic Model

Tycho's model was adopted as the scientific consensus in academic circles, largely due to his influence. He wrote hundreds if not thousands of letters to Astronomers across Europe.


When Galileo published his observations of the phases of Venus and the moons of Jupiter, evidence of a Heliocentric system would have to not only disprove the Ptolemaic model, but also the Tychonic model. The phases of Venus worked just as well in Tycho's model as they did in the Copernican model. The moons of Jupiter on the other hand were considered by Astronomers to be evidence that celestial bodies indeed moved according to epicycles. His observations of Sunspots could similarly be modelled in Tycho's system.


Galileo himself seemed to think that one of his best pieces of evidence for Heliocentrism was his model of the Tides. But his model was a step back in a way. Sailors had known for a long time that tides change due to the motion of the Sun and Moon. Galileo wanted to reject this concept that he considered to be Astrological. His proposed alternative would have been rejected by anyone with an inkling on the subject.


The Roman Inquisition found Galileo to be teaching Heliocentrism as Truth despite no convincing scientific evidence to support it. For them it was worse that despite this lack of evidence, he was trying to jump the gun and reinterpret scripture without a scientific reason. We know from Cardinal Bellarmine's letter to Foscarini that he would have similarly interpreted scripture, if there was actual evidence to support the Earth's motion. The Roman Inquisition tried to censor Heliocentric books and modify them to state that Heliocentrism was only a hypothesis. Owen Gingerich documented well in his The Book that Nobody Read that the censor was barely enacted anywhere across Europe.


Long after University, and before I started studying Riccioli, I was already aware of these facts. But I myself shared another myth with a variety of people I met. This myth was the claim that Kepler proved the Heliocentric system.


Kepler introduced elliptical orbits. These replaced epicycles and made the actual Astronomical models start to look like the simplistic representations we see in the classroom. But he had not solved the lack of observed parallax, and he did not solve a new problem with observed star sizes.


When Riccioli published the Almagestum Novum in 1651, he listed 77 arguments against Heliocentrism, and the Copernican answers to the problems. A new fascinating argument that he introduced, was the introduction of the Coriolis force. The Coriolis force must be observable on a spinning sphere, but Riccioli could not measure it. This was for him clear evidence that the Earth was not in motion. It would be over a century later before the Coriolis force could actually be measured.


In 1665 Riccioli published a Geocentric model that incorporated Kepler's elliptical orbits in his Astronomia Reformata. At this point, anyone convinced of Heliocentrism had to go on faith alone.


But scientific consensus isn't something that is always global. English Astronomers loved and were persuaded by the work of Kepler, perhaps ignoring the arguments against it, and expanded on it. Jeremiah Horrocks notably improved the model of the Moon and was the only Astronomer to predict the 1639 transit of Venus. The work of Horrocks set the stage for Newton and a considerably different approach to Astronomy.


 

Front cover of the new translation of Riccioli's Almagestum Novum

New Book!


Michal is a Software Developer with over a decade of experience, the majority of which he has worked on complex Transport systems. In his spare time he translates Ancient Science texts - doesn't everyone?


If you learnt anything here, or enjoyed reading this, please support Michal by buying his new translation of Riccioli's Almagestum Novum.


Some of his other writing and interactive content on Science and Transport can also be found on his blog.

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