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He died fighting for his King

On 2 June 1644 one of the biggest battles of the English Civil War took place on Marston Moor just outside of the city of York. The Parliamentary forces under Fairfax had, together with the Scottish Covenanters under the Earl of Leven had been besieging York, the principle Royalist stronghold in the North, the defence being led by the Marquess of Newcastle. Prince Rupert came to the aid of the beleaguered city with a substantial royalist army. Newcastle boke out of the city with his cavalry and joined Rupert and the two armies clashed on Marston Moor. The battle ended in a disastrous defeat for the royalist forces and marks a significant turning point in the war.

The Battle of Marston Moor 1644, by J. Barker Source: Wikimedia Commons

The Battle of Marston Moor 1644, by J. Barker
Source: Wikimedia Commons

This is all well and good but at first glance doesn’t appear to have a lot to do with the history of science. However if we zoom in a little closer Marston Moor actually has two connections with that history. William Cavendish, the Marquess of Newcastle, and his brother Charles were both actively engaged supporters of the new sciences developing at the time in Europe and having fled England following the royalist defeat, they eventually ended up in Paris as part of the court of Queen Henrietta Maria. Here the Cavendish brothers became part of a philosophical circle dedicated to the investigation of science that included Marin Mersenne, Kenelm Digby and Thomas Hobbes. In Paris William also met and married Margaret Lucas, one of Henrietta Maria’s chamber maids, who would later become notorious as Margaret ‘Mad Madge’ Cavendish, a female philosopher of science and extensively published author.

Our second history of science connection to the Battle of Marston Moor is a less happy one because amongst the 4 000 royalist soldiers who are estimated to have died there was the astronomer, inventor and instrument maker William Gascoigne (1612–1644). Gascoigne is today mostly only known to those interested in the fine details of the history of the telescope, something that hasn’t changed much since his own times when he only became widely known after his most important invention, the micrometer, was claimed by the Frenchman Adrien Auzout (1622–1691) in 1666, twenty two years after his untimely death.

Adrien Auzout's (1621-1692) Micrometer published in his book (1662) Source: Wikimedia Commons

Adrien Auzout’s (1621-1692) Micrometer published in his book (1662)
Source: Wikimedia Commons

Gascoigne was born into the landed gentry in the village of Thorpe-on-the Hill near Leeds. Little is known of his childhood or education, although he claimed to have studied at Oxford University, a claim that cannot be confirmed. Like many amateur astronomers Gascoigne was self taught and appears to have been a very skilled instrument maker as he made all of his telescopes himself, including grinding his own lenses. One of the problems of early telescopes was measuring the size of celestial objects viewed through them. There is no easy solution to this problem when using a Dutch or Galilean telescope, i.e. with a plano-convex objective and a plano-concave eyepiece, and Galileo soled the problem by attaching a metal grid to the side of his telescope and viewing the object under observation through the telescope with one eye whilst observing the grid with his other eye. A trick that is thought to have been possible for Galileo because of an optical peculiarity he seems to have been born with. This method could only produce rough approximate sizes.

The Keplerian or astronomical telescope, where both objective and eyepiece lenses are convex, provides a much simpler solution. The Focal plane is at the juncture of the two focal lengths of the lenses, which is inside the telescope tube, and here the Keplerian telescope produces a its image. It appears that Gascoigne was the first to utilize this fact. There is a story that Gascoigne was made aware of this phenomenon by a spider that had woven its web in his telescope tube in the crucial position allowing him to focus on what he was viewing and the spider’s web at the same time. The story is probably apocryphal bur astronomers continued to collect spider’s silk from the hedgerows to form the crosshairs in their astronomical telescope well into the nineteenth century. Whatever led Gascoigne to the discovery of the internal image, he soon went beyond the simple expedient of installing crosshairs into his telescopes.

Focal plane with image at (5) Source: Wikimedia Commons

Focal plane with image at (5)
Source: Wikimedia Commons

Gascoigne realised that this phenomenon would enable him to introduce a measuring device into the focal plane of his telescope and this is what he did. He produced a calliper the points of which could be moved towards or away from each other by means of turning a single screw. Along the base along which the calliper points moved was a measuring scale. Gascoigne could now make accurate measurements of the celestial objects he observed.

Being a self taught amateur astronomer and living as he did in a small northern village in an age when long distance communication was difficult and unreliable one might be forgiving for thinking that Gascoigne was isolated and to some extent he was but not completely. He communicated by mail, for example, with William Oughtred inventor of the slide rule and mathematics teacher of several notable seventeenth century mathematicians. This contact seems to have been initiated by Gascoigne who was surprisingly well informed about actual developments in mathematics and astronomy and is known to have owned all of the relevant literature. Through Oughtred Gascoigne was also introduced to Kenelm Digby with whom he also corresponded.

Perhaps more significantly Gascoigne was in contact with the Towneley family of Towneley Hall near Burnley, landed gentry who took an interest in the actual developments in mathematics and astronomy.

Towneley Hall Source: Wikimedia Commons

Towneley Hall
Source: Wikimedia Commons

Christopher Towneley (1604–1674) introduced a group of northern astronomers to each other including William Milbourne of Christ’s College Cambridge (M.A. 1623), William Crabtree a merchant from Salford, Jeremiah Horrocks curate from Much Hoole near Preston and Gascoigne. Crabtree and Horrocks, famously, were the first astronomers to observe a transit of Venus. Crabtree and Gascoigne became good friends with Crabtree visiting Gascoigne to view and inspect his instruments and the two of them corresponding extensively on both Gascoigne’s instrumental novelties and the contemporary developments in astronomy, in particular the theories of Johannes Kepler, which both Crabtree and Horrocks accepted and Gascoigne under Crabtree’s influence came to accept. It was through this correspondence that we have Crabtree’s account of Horrocks’ death.

"Crabtree watching the Transit of Venus A.D. 1639" by Ford Madox Brown, a mural at Manchester Town Hall. Source: Wikimedia Commons

“Crabtree watching the Transit of Venus A.D. 1639” by Ford Madox Brown, a mural at Manchester Town Hall.
Source: Wikimedia Commons

All of this might have been lost following the deaths of Horrocks (1641), Gascoigne (1644) and Crabtree (1644) if not for the Towneleys. When the Royal Society announced Auzout’s invention of the micrometre screw gauge in 1666 it was Richard Towneley (1629–1704), Christopher’s nephew and a mathematician and astronomer in his own right, who piped up and said I beg to differ. John Flamsteed (1646–1719) (another northerner, later to become the first Astronomer Royal, who was a protégée of Jonas Moore (1617–1679), yet another Lancastrian and a pupil of William Milbourne) travelled up north to investigate Towneley’s claims. Towneley demonstrated his micrometer screw gauge based on Gascoigne’s design to Flamsteed and the two of them travelled to Salford where Crabtree’s widow gave them the Crabtree Gascoigne correspondence. Flamsteed made notes from the correspondence but the originals remained in the possession of the Towneley family.

Robert Hooke drew diagrams of Towneley’s version of Gascoigne’s micrometer, which were published in the Philosophical Transactions of the Royal Society thus establishing Gascoigne’s priority and his right to be acknowledged the inventor of the micrometer screw gauge.

Robert Hooke - A Description of an Instrument for Dividing a Foot into Many Thousand Parts, and Thereby Measuring the Diameters of Planets to a Great Exactness, &c. as It Was Promised, Numb. 25. In: Philosophical Transactions. Band 2, Nummer 29, 11.  Source: Wikimedia Commons

Robert Hooke – A Description of an Instrument for Dividing a Foot into Many Thousand Parts, and Thereby Measuring the Diameters of Planets to a Great Exactness, &c. as It Was Promised, Numb. 25. In: Philosophical Transactions. Band 2, Nummer 29, 11.
Source: Wikimedia Commons

As a small side note it was Richard Towneley together with Henry Power (1623–1668) who first discovered what is now known as Boyle’s Law, which Power published in his Experimental Philosophy, in three Books in 1664, an important early work on microscopy and the corpuscular theory.

Henry Power, Experimental philosophy, in three books : containing new experiments microscopical, mercurial, magnetical ; with some deductions, and probable hypotheses, raised from them, in avouchment and illustration of the now famous atomical hypothesis. London, 1664 Source: NIH U.S:.National Library of Medicine

Henry Power, Experimental philosophy, in three books : containing new experiments microscopical, mercurial, magnetical ; with some deductions, and probable hypotheses, raised from them, in avouchment and illustration of the now famous atomical hypothesis. London, 1664
Source: NIH U.S:.National Library of Medicine

Much of Gascoigne’s original correspondence has become lost of time but enough has been recovered to give a vivid picture of this inventive and highly skilled astronomer and his contributions to the history of astronomy. More important the fragments of the Gascoigne story demonstrate very clearly that progress in science in not achieved through lone geniuses but through networks of researchers exchanging views and discoveries and encouraging each other to make further developments.






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The Goddess, her husband and his lovers

In recent days the science sections of the media have been full of the successful entering of orbit around Jupiter by the NASA probe Juno after its five-year, 2.8 billion kilometre journey from the Earth. Many of the reports also talk about the so-called Galilean moons, Jupiter’s four largest moons (there are currently 67 known moons of Jupiter), and Galileo’s discovery of them with the recently invented telescope in early 1610.


Montage of Jupiter’s four Galilean moons, in a composite image depicting part of Jupiter and their relative sizes (positions are illustrative, not actual). From top to bottom: Io, Europa, Ganymede, Callisto. Source: Wikimedia Commons

Juno was even carrying Lego models of the god Jupiter, the goddess Juno and Galileo holding a telescope.


With the notable exception of the New York Times none of the reports mentioned that the Ansbach court mathematicus, Simon Marius, independently discovered the Galilean moons just one day later than Galileo. However, whereas Galileo rushed into print with his telescopic discoveries in his Sidereus nuncius in 1610, Marius waited until 1614 before publishing his discoveries in his Mundus Iovialis.


Title page of Sidereus nuncius, 1610, by Galileo Galilei (1564-1642). *IC6.G1333.610s, Houghton Library, Harvard University

The four moons are named Io, Europa, Ganymede and Callisto after four of the lovers of Zeus, the Greek equivalent to Jupiter, and many people have made a joke about the fact that Juno, his wife, was on her way.


Once again what none of the reports, with the exception of the New York Times, mention is that the names were not given to the moons by Galileo. Wishing to use his telescopic discoveries to leverage a position at the Medici court in Florence Galileo wrote a letter to Grand Duke Cosimo’s secretary on 13 February 1610 asking if the Grand Duke would prefer the moons to be called Cosmania after his name or, rather, since they are exactly four in number, dedicate them to all four brothers with the name Medicean Stars (All heavenly bodies were referred to as stars in the Renaissance). The secretary replied that Cosimo would prefer the latter and so the moons became the Medicean Stars in the Sidereus nuncius.

The New York Times report attributed the names Io, Europa, Ganymede and Callisto to Simon Marius and they did indeed first appear in print in his Mundus Iovialis. However the names were not thought up by Marius.


Title page Mundus Iovialis Simon Marius 1614. Internet Archive

In the Mundus Iovialis Marius makes several naming suggestions. His first suggestion is to just number the moons I to IV, a system that was actually used by astronomers. His second suggestion follows Galileo in that he wishes to name them after his employer/patron the Margrave of Ansbach’s family and call them the Brandenberger Stars. Marius’ third suggestion is more than somewhat bizarre as he suggests naming them in analogy to the solar system planets, so the moon with the smallest orbit would be the Jupiter Mercury, the next the Jupiter Venus, the third the Jupiter Jupiter and the fourth the Jupiter Saturn. As I said bizarre. It is with Marius’ fourth suggestion that we finally arrive at Zeus’ lovers. After talking about Jupiter’s reputation for a bit on the side and describing his most notorious affairs Marius write the following:

 In Europa, Ganimedes puer, atque Calisto,

Lascivo nimium perplacuere Jovi.

Io, Europa, the young Ganymede and Calisto

appealed all too much to the lascivious Jove

In the next paragraph Marius goes on to explain that the idea for using these names for the moons was suggested to him by Johannes Kepler[1] when the two of them met at the Imperial Parliament in Regensburg in October 1613. He then names Kepler as co-godfather of these four stars. Marius closes his list of suggestions by saying that the whole thing should not be taken too seriously and everybody is free to adopt or reject his suggestions as they see fit.

So as we now know it was Kepler’s suggestion which finally won the naming contest for the four largest moons of Jupiter but it should be noted that the names were first adopted by the astronomical community in the nineteenth century but they first became the official names of the Galilean Moons in 1975 through a decision of the IAU (International Astronomical Union)

Anybody who wants to learn more about Simon Marius can do so at the Simon Marius Portal or become a member of the Simon Marius Society (Simon Marius Gesellschaft e.V.) via the portal, membership is free!

Addendum 7 July 2016: My attention has been drawn to a delightful pop song about the lascivious Jupiter, his dalliances with his satellites and the impending arrival of his wife, She’s Checking In (The NASA Juno Song) by Adam Sakellarides  h/t Daniel Fischer (@cosmos4u)

[1] It should be noted that Johannes Kepler loved coining names and terms for all things scientific. It is to him, for example, that we owe the term satellite, coined specifically for the Jupiter moons, and also the term camera obscura, which in shortened form is our modern camera.


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Retraction of a Retraction – Turns out I wasn’t wrong after all!

Yesterday I deleted a post about Caroline Herschel, the Google doodle that had been posted for her birthday and the type of telescope that she had used to make he comet discoveries only hours after I had posted it. I went on to claim that I was mistaken in my claims and to apologies widely on the Internet to anybody I might have misled. In the cold grey light of dawn I realised that I had indeed made an error, however not in my original post but in retracting it. How this came about can be attributed to one or more of the following:

1) Extreme tiredness

2) Mental and physical confusion brought about by my first day of remedial orthopaedic treatment

3) A brain fart

4) Early signs of dementia

5) Congenital stupidity

6) An inability to read

7) Late repercussion of my substantial drug abuse in my misspent youth

8) Aliens!

9) Add your own reason!

In my post I had said that the Google Doodle was wrong because it displayed Caroline Herschel with a ‘normal’ refractor, i.e. with lenses, telescope whereas the Herschel used reflectors, i.e. telescopes with mirror, which they designed and constructed themselves. So far, so good. Then in the comments Tony Angel drew my attention to an interesting article about Caroline Herschel and her comet hunting. I hastily, and here is where the problems begin, skimmed the article and read the following quote from Caroline:

I found I was to be trained for an assistant-astronomer, and by way of encouragement a telescope adapted for ‘sweeping,’ consisting of a tube with two glasses, such as was commonly used as a ‘finder,’ was given to me.

 I read “a tube with two glasses” as being the description of a refractor with two lenses, thought ‘Oh FUCK!’ and in a state of confused panic deleted my post.

In fact, if I had read a few lines further I would have seen the following:

Table 1. The Parameters of Caroline’s two alt-azimuth

                 Newtonian reflecting sweepers.

 And on the following page there is even a diagram of the two telescopes with a caption that clearly states that they are Newtonian reflectors. So now being once again of sound mind and body I shall restore my post with a little bit of added information i.e. the illustration of Caroline’s reflector telescopes.







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I have deleted my previous  post on the Caroline Herschel Google Doodle because I was wrong! I will explain tomorrow.


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Blogging Hiatus

There will be a four-week blogging hiatus both here and at Whewell’s Gazette for two different reasons. Firstly I am going into hospital for three weeks, but have no fear this is a positive development not a negative one. I suffer from scoliosis and I’m going to get three weeks of intensive remedial orthopaedic treatment to try and improve my condition. Directly following my last day of treatment, I shall then fly to Britain for a meeting of the Christie Clan in a twelfth-century manor house in the Welsh marches. I shall not be entirely incommunicado, as I will only be a day patient during my treatment. So I will still pop up on Twitter and Facebook, from time to time, but I don’t think I shall be doing any blogging in this period and Whewell’s Gazette is definitely out.

If you are at a loose end and looking for something to do during this period, Afton, the excessively charming three-year-old daughter of my very good #histsci friend and colleague Michael Barton (@darwinsbulldog), suffers from epilepsy and has recently undergone neurosurgery. As they live in America this means big medical bills. Michael and his wife, Catherine, have set up an appeal on gofundme to help pay those bills, so you could do me and Afton a favour and make a small donation to help pass the time until I’m up and blogging again.







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Scientists and Saints’ Days

Friday 12 February was the birthday of Charles Darwin, which has now been celebrated by his acolytes for several years as Darwin Day. The British Society for the History of Science obviously thinks this is a good idea and asked the following question on Twitter, “Should other scientists have a day?” launching a poll with the usual suspects, Isaac Newton, Marie Curie, Galileo Galilei and the not so usual Rachel Carson. I for one have the feeling that in following this path the history of science community is running the danger of establishing a faux religion with Saints’ Days like the Catholic Church. Some of you may ask, well what’s wrong with that? Shouldn’t we honour the women and men who gave us our scientific worldview? I, as a historian of science, would answer; yes we should acknowledge them but not like that. So why do I object?

In the good old days what passed, as popular history of science (and not infrequently academic history of science) was a collection of inspiring stories about how lone, oft persecuted, geniuses fought against the ignorance of the masses to bring enlightenment into the world and to lead humanity into a glorious future. The Early Modern Period was a litany of great names and great moments: Copernicus/heliocentricity persecuted by the Catholic Church, Galileo/modern astronomy persecuted by the Catholic Church, Descartes/the rainbow killed of by Christina, Newton lone loony who invented the modern world. Starting around 1930 historians of science have been chipping away at this travesty deflating the great and bringing in the hordes of anonymous researchers who got left out of the picture. Having rehabilitated the lesser beings, who actually contributed most of the real work, they then moved on to the instrument makers, technicians and finally the women. Despite all their best efforts these advances in the story of science, and the way that we tell it, remain largely unknown to the public at large, as the media and all too many of the pop science writers insists on repeating the myths of old. However some progress has been made and more can be made if we keep up the pressure.

The concept of special days for selected scientists is a massive step in the wrong direction. It harks back to the great names great event model of the story of science that we actually need desperately to get rid of, once and for all. Are we going to have a calendar of the patron saints of science: 12 February is St Charles’ Day, patron saint of evolution, 14 February St Galileo’s Day patron saint of the telescope: St Isaac’s day poses a bit a problem, when do we celebrate the patron saint of gravity? On 25 December the day he was born under the Julian calendar or 4 January the corrected date on the Gregorian calendar? On 7 November, Saint Marie’s day, the patron saint of radiation do we all go down to the clinic for a dose of radiation therapy? You think I’m joking? On Darwin Day people were posting images of artefacts out of Charles Darwin’s life, his geological hammer, his death’s head walking cane, without links to articles or websites, like the medieval Christian Churches displaying relics of the saints. Will our science museums become shrines to the saints of science with reliquaries containing their bones? The Galileo Museum in Florence already had his middle finger on display in a gilded glass container.

In 2010 I posted a short post with the deliberately provocative title A Biological Birthday. Why provocative? Because most readers would expect a post about Charles Darwin, but 12 February is also the birthday of the Dutch anatomist, microscopist and natural historian Jan Swammerdam (born 1637). I wonder how many of the people posting accolades to Darwin on social media last Friday have even heard of Jan Swammerdam let alone know about the important contribution that he made to the life sciences.

12 February is also the birthday of Julian Schwinger (born 1918). Julian who I hear a chorus of Darwinites cry. Julian Schwinger, as well as being a frighteningly intelligent child prodigy, won the 1965 Nobel Prize for physics for his theory combing the theory of special relativity with quantum theory, one of the most important developments in twentieth-century physics.

Despite the fact that I follow a large part of the online history of science community on social media the number of people honouring Schwinger’s birthday was a small fraction of those honouring Darwin’s and I think I was the only person to acknowledge Swammerdam.

The claim made by the supporters of Darwin Day is that the theory of evolution by natural selection is the most important scientific theory ever discovered and that is why it should have a special celebration. Putting aside all of the plentiful arguments against quantifying the importance of scientific theories relative to each other, I think, for example, that for the bridge designing engineer the Newtonian theory of gravity is more important than the theory of evolution, if you are going to have a special day for the theory of evolution then celebrate the theory of evolution and not Charles Darwin. Celebrate all the early evolutionary theorists Maupertuis, Monboddo, Lamarck; Erasmus Darwin, Wallace and Charles Darwin, we can even give a nod to Patrick Matthew and a handful of other minor figures. We shouldn’t forget the geologists, whose theories of deep time allowed for the possibility of evolution in the first place Cuvier, Hutton, Smith, Sedgwick, Buckland, Lyell and all the ones I don’t know not being a historian of geology. We should forget the natural historians and palaeontologists whose work laid much of the foundations on which the theory of evolution was built, a list of names I am not qualified to write. Science is a collaborative enterprise let us demonstrate this in our historical acknowledgements and get away from the type of hagiographic hero worship engendered by concepts such as Darwin Day.

I am not alone in having doubts about Darwin Day. Already in 2012 the philosopher of biology Michael Ruse published an essay in The Chronicle of Higher Education entitled, Why I Am Not Celebrating “Darwin Day”. Last week on Twitter Jon Phillips (@jowiph) a doctoral student of the history of science at Johns Hopkins tweeted the following:

Every year I think I get a little less comfortable with the idea of “Darwin Day.” Treating scientists as objects of veneration feels off. I get the impulse. Evolution is a powerful theory, Darwin was a hugely important figure, and both have been at the center of a culture war. But I spend so much time reading people who invoke science—and evolution in particular—in support of often extreme political agendas I worry that treating Darwin as a secular saint emphasizes the talismanic quality that makes evol. a useful framing device for racists, etc – Jon Phillips (@jowiph)

Also last week Alexander Hall (@Green_Gambit) a post doc “researching & thinking at the interface of science, religion, & the environment” at Newman University (@Newman_Uni) posted the stimulating essay Darwin Day: Celebrating Without Deifying on the website Science & Religion: Exploring the Spectrum.

Maybe it’s time for all of us to take a step back and seriously ask if we should follow the BSHS suggestion for even more scientific “Saints Days”!














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A misleading illustration.



The difference between an easy model and a complicated one.

The gif above, from Malin Christersson’s  Website, has been making the rounds of the Internet to much acclamation but it is in my opinion severely misleading in what it claims to represent. Some people have pointed out that the heliocentric model is false because the orbits should be elliptical. This is my opinion an irrelevance because the eccentricity of the planetary orbits, that is the degree by which the ellipses differ from a circle, is so small that in a diagram of this sizel it wouldn’t be really detectable. In fact illustrations of the heliocentric system tend to exaggerate the eccentricity to make it clear that the orbits are in fact ellipses. My problem is another. The two models are presented side by side as if they were directly comparable but in fact they are two radically different representations.

The heliocentric system is displayed from a bird’s eye, or perhaps a god’s eye, view from a position directly above the sun perpendicular to the plane of the planetary orbits somewhere a couple of billion kilometres out in space. One should point out the sizes of the orbits are not to scale. Opposed to this the presentation of the geocentric system is not something one could actually view in reality. It is a fictitious birds eye view of the system as reconstructed by the astronomers in antiquity based on the activities they saw in the heavens and herein lies the crux of the problem.

Viewed from the earth the moments of the celestial bodies is not the lovely regular circles depicted in the heliocentric model above but a bizarre dance of confusing movements. The sun appears to go around the earth once a year and the moon once every approximately twenty-nine days. The so-called inner planets mercury and venus both also appeared to take a year to orbit the earth never wandering far from the sun, at times to one side and at other times on the other. Often both disappeared for periods of time. This behaviour led some people in antiquity to speculate that they orbit the sun and not the earth, the so-called Egyptian or Heracleidian model. It is however the so-called outer planets mars, jupiter and saturn that display the most puzzling behaviour. They role along in one direction for a lengthy period of time and then appear to stand still for a short period before turning tail and heading back in the opposite direction after a short time remaining stationary again before resuming in the original direction. These apparent loops in the planets progress are known technically as retrograde motion. We now know that this is an illusion created within the heliocentric system as the earth moving faster overtakes one or other of the outer planets. Given the seemingly stationary condition of the earth this was a difficult conception leap for astronomical observers to make. In fact in two thousand or more years of astronomy only two people appear to have made that leap, Aristarchus of Samos in the third century BCE and Copernicus in the fifteenth century CE. Both of these visionaries still had to cope with the very obvious empirical evidence that the earth doesn’t move.

The gif above creates a false impression because it seems to imply that the simplicity of the heliocentric system makes its an obvious choice over the geocentric model but as should be obvious from my description of what you actually see as an observer on the earth, and all observers in the past were on the earth, making that choice is anything but simple or obvious. The creator of the gif includes a short history of the journey from geocentricity to heliocentricity, which unfortunately contains various errors and misconceptions, which I will now highlight.

≈ 350 BC, Aristotle 

Aristotle a pupil of Plato, becomes the tutor of Alexander the Great. Aristotle’s views of the world shape science for centuries. His influence lasts until the enlightenment. In his book On the Heavens (part 14), Aristotle asserts that:

From these considerations then it is clear that the earth does not move and does not lie elsewhere than at the centre.

Aristotle is just one of many scholars from antiquity whose views influenced the future views of the world. He in fact inherited and modified the homocentric geocentric views and models of Eudoxus and Callippus. These models could explain retrograde motion fairly well but not the observable variation in brightness of the planets. This was not the system that medieval Europe inherited from antiquity. See below Ptolemy.

 ≈ 250 BC, Aristarchus

Aristarchus estimates the size of the sun to be much larger than the size of the earth. Based on this observation he then presents the heliocentric model.

The geometrical text, which is attributed to Aristarchus, is for determining both the distance of the sun from the earth and its size relative to the moon. It is a purely geocentric text and has nothing to do with his speculation about a heliocentric cosmos. There are no direct accounts of Aristarchus’ heliocentric model so we don’t actually know what caused him to adopt it.

 ≈ 250 BC, Archimedes

In The Sand-Reckoner, Archimedes estimates the number of sand corns in the universe using the heliocentric model of Aristarchus.

In the Sand Reckoner Archimedes wishes to demonstrate his system for recorded extremely large numbers. He uses Aristarchus’ heliocentric model, which he sketches, because Aristarchus argued that the stars were much further away than hypothesised in the normal geocentric model in order to explain why there was no observable stellar parallax. Archimedes used this model because it would require many more grains of sand to fill thus giving him a much greater number to express with his system. It is only one of two accounts of Aristarchus’ heliocentric system both of which are uninformative.

≈ 150 AD, Ptolemy

In his book Almagest, Ptolemy introduces so called epicycles to explain planetary motions, based on the assumption that the earth is at the centre and does not move. Almagest is considered to be one of the most influential scientific works in history.

The epicycle system of planetary motion, used extensively by Ptolemy in the Almagest in the second century CE, was first introduced by Apollonius of Perga in the third century BCE and used extensively by Hipparchus of Rhodes in the second century BCE.

1543, Nicholaus Copernicus

Just before his death, Copernicus publishes the book De Revolutionibus Orbium Coelestium (On the Revolutions of the Heavenly Spheres) in which he places the sun rather than the earth at the centre of the universe. This book is the beginning of the Copernican Revolution.

In English it’s Nicolaus (no ‘h’) Copernicus and in De revolutionibus the sun is not at the centre of the universe but somewhat off centre. Viewed strictly Copernicus’s system is heliostatic but not heliocentric.

1572, Tycho Brahe

Tyco Brahe observes a star being born and publishes his observation in De nova stella. Brahe’s observation refutes the commonly held view at the time, a view which dates back to Aristotle, that the stars are fix and never changing at the outskirts of the universe. Since Brahe couldn’t observe a stellar parallax, he concluded that the earth did not move. He proposed a model where the planets move around the sun, and the sun moves around the earth. (It was later shown that it wasn’t a star being born Brahe had observed, but the supernova SN 1572, i.e. a star exploding.)

In the first half of this paragraph we have an oft-repeated semi-myth. Although Tycho did indeed observe the nova of 1572 and it did contradict Aristotle’s cosmological theory of an immutable heaven this story is a myth for three different reasons. Firstly Aristotle’s concept of a an immutable heaven had already been seriously challenged in the sixteenth century by several leading astronomers based on their observations of several comets in the 1530s, so the nova of 1572 was not the first problem for Aristotle’s cosmology. Secondly Tycho was by no means the only astronomer to observe and comment on the 1572 nova and Michael Maestlin’s and Christoph Clavius’ acceptance that the nova was supralunar had more impact than Tycho’s. The attribution of this impact to Tycho alone is a version of the lone genius myth and historically false. Thirdly the refutation of Aristotle’s theory of the immutability of heaven actually has no real relevance for the geocentricity/heliocentricity discussion.

1609, Johannes Kepler

Using the observational data collected by Tycho Brahe, Johannes Kepler introduces his first two laws of planetary motion in Astronomia nova. The first law: the planets move in elliptical orbits with the sun at one focus.

Given that it was actually Kepler’s work that led to the acceptance of heliocentricity our author gives him rather short shrift in his chronology. What about the other two laws of planetary motion or the Rudolphine Tables?

 1616, Roman Inquisition

On 24 February 1616 a team of eleven consultants for the Roman Inquisition condemns the Copernican System, stating that the heliocentric system is “foolish and absurd in philosophy and “formally heretical”.

It should be pointed out that the Pope never confirmed the heretical status of heliocentricity thus it never was heretical.

 1633, Galileo Galilei

Galileo Galilei stands trial on suspicion of heresy “ for holding as true the false doctrine taught by some that the sun is the centre of the world”. At the trial he is found guilty and sentenced to formal imprisonment. Galileo spends the rest of his life under house arrest.

 1687, Isaac Newton

Sir Isaac Newton publishes Philosophiæ Naturalis Principia Mathematica (Principia). In Principia, Newton explains Kepler’s laws of planetary motion in terms of universal gravitation. Newton doesn’t consider the sun to be at rest, instead he uses the center of gravity of the solar system.

A small point, but one that irritates me. The man who published the Principia in 1687 was not ‘Sir’ Isaac Newton but just plain Isaac Newton who didn’t get knighted until 1705.

1838, Friedrich Bessel

Friedrich Bessel is the first to accurately measure a stellar parallax. In 1838 he announces that the star 61 Cygni has a parallax of 0.314 arcseconds.

Friedrich Bessel was not the first to accurately measure stellar parallax that honour goes to the Scottish astronomer Thomas Henderson, who measured the parallax of Alpha Centauri. Friedrich Bessel, however, was the first to publish.

1992, Roman Catholic Church

Pope John Paul II closes a 13-year investigation into the church’s condemnation of Galileo in 1633 by declaring that Galileo was right:

 Thanks to his intuition as a brilliant physicist and by relying on different arguments, Galileo, who practically invented the experimental method, understood why only the sun could function as the centre of the world, as it was then known, that is to say, as a planetary system. The error of the theologians of the time, when they maintained the centrality of the earth, was to think that our understanding of the physical world’s structure was, in some way, imposed by the literal sense of Sacred Scripture.

This final paragraph is just a horrible mess. Galileo did not practically invent the experiment method. Also the claim that he “understood why only the sun could function as the centre of the world” is simply bizarre. As I have pointed out in a number of different posts, in Galileo’s time the scientific evidence actually favoured a geocentric system. This also applies to the comment about the theologians, whose belief in a geocentric system was strongly supported by the available scientific evidence and was not just based on Sacred Scripture. It is also interesting to note how a chronology of the geocentric/heliocentric astronomical systems suddenly veers off into an account of Galileo’s troubles with the Catholic Church, which in real terms in the history of astronomy and cosmology is just a small side show.



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