General astronomy freak and eclipse chaser Daniel Fischer drew my attention to an online manifesto from the International Astronomical Union, Call to Protect the Dark and Quiet Sky from Harmful Interference by Satellite Constellations, posted 14 March 2024. Dan asked about the historical accuracy of a statement in it about Copernicus, so I thought I would take a look and wish I hadn’t.
The whole of this section on pre-twentieth century astronomer is horribly ahistorical and inaccurate:
Likely influenced by criticism of the Ptolemaic cosmology by the Persian and Syrian astronomers, Al-Urdi, Al-Tusi and Ibn al-Shatir – all members of the Maragheh observatory funded in what was then Mongolia, now Iran – Copernicus revived the idea that the Earth orbits around the Sun and not vice versa. Kepler’s laws of the motions of the planets were the first mathematical description of a physical phenomenon, subsequently bolstered by Galileo’s first observations of the heavens through a telescope. Newton developed a whole branch of mathematics to connect those motions to physical laws.
We start with the simple historical fact that whereas al-Tusi (1201–1274) and al-Urdi (d. 1266) both worked in the Maragheh observatory, Ibn al-Shatir (1304–1375) didn’t. He studied astronomy in Cairo and Alexandria and then worked as muwaqqit (timekeeper) of the Umayyad Mosque in Damascus. A major point of the criticism of the astronomy of Ptolemy was his use of the equant point, a bone of contention for many astronomers over the centuries. Al-Tusi developed the so-called Tusi-couple, a mathematical device to help eliminate the equant point. Ibn al-Shatir presented a radical reform of the Ptolemaic planetary models in his kitab nihayat al-sul fi tashih al-usul (The Final Quest Concerning the Rectification of Principles) in which he incorporated the so-called Urdi lemma, which allowed an equant in an astronomic model to be replaced with an equivalent epicycle (the Tusi-couple) that moved around a deferent centred at half the distance to the equant point.
We now turn to Copernicus. The only motivation the Copernicus gave for his attempts to reform Ptolemaic astronomy was like al-Tusi, al-Urdi, Ibn al-Shatir, and many others, the removal of the equant point. We know that this reform led him to replacing the geocentric model of Ptolemy with a heliocentric model. Although there are numerous speculations over it, we don’t actually know what led him to take this step. In De revolutionibus, Copernicus uses the Tusi-couple in several places including his model of Mercury and in his theory of trepidation, which of course doesn’t exist. Once again although there has been much speculation on the topic there is no known link between Copernicus and those Islamic astronomers, who used the Tusi-couple and certainly absolutely no evidence that that Copernicus was likely influenced by their criticism of the Ptolemaic cosmology.
Kepler’s laws of the motions of the planets were the first mathematical description of a physical phenomenon is simply a mindbogglingly false statement. Archimedes would like a quite word with the author of the piece as would the Oxford Calculatores, as well as several others who provide mathematical descriptions of physical phenomenon before Kepler was even born. Kepler would like to point out that his own law of the spreading of light from a point source predates his laws of planetary motion.
I find the very generalised statement that Kepler’s laws of planetary motion were subsequently bolstered by Galileo’s first observations of the heavens through a telescope rather strange. The telescopic discovery of the Moons of Jupiter, independently by both Galileo and Simon Marius, and the subsequent determination of their orbits, showed that they too conformed with Kepler’s laws. But the rest of the early telescopic astronomical observations made by Galileo and others did nothing to bolster those laws.
The simple sentence, Newton developed a whole branch of mathematics to connect those motions to physical laws, contains a whole collection of historical myths. The reference here is, of course, to calculus but as I have explained in an earlier blog post, Newton and Leibniz did not develop, invent, or discover[1] calculus but rather collated about two thousand years’ worth of work on the topic by numerous predecessors. Secondly, Newton’s work on collating the elements of the calculus had nothing to do with the motions of the planets.
The next is something I have constant battles on social media about with people who “know better,” Newton did not used calculus either in the preparatory work for, or in the final presentation of his Principia, having lost faith in quality of proof using the analytical method. The whole work in done in tradition Euclidian geometry. I have a blog post on this, too.
I do wish that if scientists are going to make statements about the history of science, they would take the time and make the effort to check their facts first.
[1] Choose your own term according to your preferred philosophy of mathematics.
The Renaissance Mathematicus 
This is probably just a confusion on my part, but is it accurate to say that the Oxford Calculatores provided mathematical descriptions of physical phenomena? I’d always read that their mathematical treatment of motion was done in the abstract, without any application to the real world (even if their results were later used by Galileo, Beeckman, et al. for that purpose).
Their work is theoretical but what they are describing mathematically is a real physical process!
I had a run-in with the IAU leadership some years ago when they were promoting this silly idea of a Hubble-Lemaitre renaming. It turned out that they had NEVER bothered consulting their colleagues in the historical division since it turned out one of the leadership council members had been “teaching History of Astronomy for several year.” So I can’t say I’m in any way surprised.
Generally, such renamings are not a good idea, whether or not the ideas behind them are. However, the Hubble-Lemaître renaming is, compared to others (in astronomy and elsewhere) relatively harmless.
I feel immense sympathy for Michael Wav’s comment. In a different environment, I also have to deal constantly with people who imagine that calling themselves ‘scientists’ means they don’t need to bother learning much about the process involved in addressing historical questions; that there’s more to it than collecting data-points.