The emergence of modern astronomy – a complex mosaic: Part VI

Copernicus first put his concept for a heliocentric cosmos in writing in a manuscript that today bears the title Nicolai Copernici de hypothesibus motuum coelestium a se constitutis commentariolus (roughly translated: Nicolas Copernicus’ short commentary on his hypothesis about the movement of the celestial bodies) of which three manuscripts are known to exist today. None of them, however, in Copernicus’ own handwriting. There is almost no direct evidence for the existence of this document in the sixteenth century and almost everything that we can say about its origin, its distribution and its impact is based on reasonable, speculative interpretation of indirect evidence.

It is disputed whether the title Commentariolus, for short, was written by Copernicus or was added at a later date; it has been speculated that it was added by Tycho Brahe, who possessed a copy, which is one of the three surviving copies and is now housed in the Viennese Court Library. In his Astronomiae Instauratae Progymnasmata (1602) Tycho wrote that his copy was given to him by Thaddaeus Hagecius (1525–1600). He also said that he had made several copies and distributed them to friends.


Title page of the Viennese Commentariolus manuscript Source: Wikimedia Commons

The Viennese manuscript was first found in 1877 but it is incomplete, missing a substantial part of Copernicus’ lunar theory. In 1881 a complete manuscript was found in the library of the Stockholm Observatory bound into a second edition of De Revolutionibus, which had been the property of Hevelius. The third manuscript was also found bound into a second edition of De revolutionibus that had belonged to Duncan Liddel (1561–1613) in the library of Saint Andrews University in Scotland. Liddel studied at various North German universities and was later a professor for mathematics at Helmstedt University before going on to qualify as a physician and becoming a professor for medicine. A fairly normal career path in the sixteenth century. He knew Tycho Brahe and visited him at least twice on the island of Hven. It should be noted that all three surviving copies of the Commentariolus were owned by people who lived after the publication of De revolutionibus and the death of its author.

The first probably mention of the Commentariolus occurred in 1514. The Cracovian physician, geographer and historian, Matthias of Miechow (1457–1523) noted in a library catalogue in the Jagiellonian Library dated 1 May 1514 the following:

Item sexternus theorice asserentis terram moveri, Solem vero quiescere

A quire of six leaves (sexternus) of a theory asserting that the Earth moves whereas the Sun is at rest.

It is assumed that this is a reference to the Commentariolus, probably a copy originally given by Copernicus to his Cracovian friend Canon Bernard Wapowski (1450–1535) a cartographer and historian.


Excerpt from the library catalogue of Matthias von Miechow (1457–1523) 1. Mai 1514 with the Commentariolus hint: „Item sexternus theorice asserentis terram moveri, Solem vero quiescere“. Source: Wikimedia Commons

There are no direct references to the Commentariolus before the publication of De Revolutionibus in 1543. However, there are various episodes in Copernicus’ life that can probably be attributed to knowledge of the Commentariolus.

Paul of Middelburg (1446–1534) sent out a general call to astronomers and rulers asking for suggestions and contributions towards a proposed calendar reform at the Lateran Council (1512–1517). Paul noted in 1516 that one of those who answered that call was Copernicus in a letter that no longer exists. Perhaps Copernicus was on Paul’s list because of the Commentariolus, he had at this point published no other astronomical works that might have motivate Paul to consult him.

In 1533 Johann Albrecht Widmannstetter (1506–1557), who was a papal secretary held a series of lectures to an audience of Pope Clement VII and some cardinals outlining Copernicus’ heliocentric theories for which he was richly rewarded by the Pope with a rare manuscript. It can be assumed that his source of knowledge of those theories was the Commentariolus.  Following the death of Pope Clement in 1534 Widmannstetter became secretary to Cardinal Nikolaus von Schönberg (1472–1537), who wrote a letter to Copernicus in 1536 concerning his theories and offering to have the manuscript of his theories (De revolutionibus) copied at his expense. This letter would be included in the published version of De revolutionibus.

In 1539 Martin Luther (1483–1546), in his cups, reputedly launched an attack on Copernicus’ heliocentric hypothesis, as recorded by Anton Lauterbach in the Tischreden (Table Talk) first published in 1566. (More details here)

There was mention of a certain astrologer who wanted to prove that the earth moves and not the sky, the sun, and the moon. This would be as if somebody were riding on a cart or in a ship and imagined that he was standing still while the earth and the trees were moving. [Luther remarked] “So it goes now. Whoever wants to be clever must agree with nothing that others esteem. He must do something of his own. This is what that fellow does who wishes to turn the whole of astronomy upside down. Even in these things that are thrown into disorder I believe the Holy Scriptures, for Joshua commanded the sun to stand still and not the earth [Jos. 10:12].”

Copernicus was not mentioned by name in Luther’s tirade and also no great details of the hypothesis. It can be assumed that indirect knowledge of the Commentariolus had come to Luther’s ears.

Our last possible indirect knowledge of the Commentariolus can be attributed to Georg Joachim Rheticus (1514–1574), who famously persuaded Copernicus to publish De revolutionibus. Rheticus set off for Frombork in 1539 already aware of the fact that Copernicus was propagating a heliocentric hypothesis. Did this knowledge come directly or indirectly from the Commentariolus?

So what does the Commentariolus consist of? In a very brief introduction Copernicus writes:

           Our Ancestors assumed, I observe, a large number of celestial spheres for this reason especially, to explain the apparent motion of the planets by the principle of regularity. For they thought it altogether absurd that a heavenly body, which is a perfect sphere, should not always move uniformly. They saw that by connecting and combining regular motions in various ways they could make any body appear to move to any position.

Callippus and Eudoxus, who endeavoured to solve the problem by use of concentric spheres, were unable to account for all planetary movements; they had to explain not merely the apparent revolutions of the planets but also the fact that these bodies appear to us sometimes to mount higher in the heavens, sometimes to descend; and this fact is incompatible with the principle of concentricity. Therefore it seemed better to employ eccentrics and epicycles, a system which most scholars finally accepted.

Yet the planetary theories of Ptolemy and most other astronomers, although consistent with the numerical data, seemed likewise to present no small difficulty. For these theories were not adequate unless certain equants were also conceived; it then appeared that a planet moved with uniform velocity neither on its deferent nor about the center of its epicycle. Hence a system of this sort seemed neither sufficiently absolute nor sufficiently pleasing to the mind.

Having become aware of these defects, I often considered whether there could perhaps be found a more reasonable arrangement of circles, from which every apparent inequality would be derived and in which everything would move uniformly about its proper center, as the rule of absolute motion require. After I had addressed myself to this very difficult and almost insoluble problem, the suggestion at length came to me how it could be solved with fewer and much simpler constructions than were formally used, if some assumptions (which are axioms) were granted me. They follow in this order[1].

In this brief introduction, which I have given here in full, Copernicus makes very clear why he thinks that astronomy needs reforming. He is in principle quite happy with an epicycle-deferent model but not with the use of equants, which he sees as violating the fundamental principle of uniform circular motion, a philosophically founded astronomical axiom that he wholeheartedly accepts. The equant point is an abstract off-centre point inside the orbit of a planet, which when used as the viewing point gives the planet on its epicycle-deferent uniform motion.


equant: A sphere that is centered at the center of the universe, but whose motion varies irregularly as if it were centered at another spot, called the equant point. This geometrical tool allowed Ptolemaic astronomers to construct orbits with the observed variations of speed without resorting to the ugliness of a sphere that was actually off center (an eccentric). The Planet is actually on the outer circle below, centered at E, the center of the universe. The sphere, however, moves as if it were centered at the point marked equant below, so that it takes equal times for the planet to move from 1 to 2, from 2 to 3, from 3 to 4 and from 4 back to 1, even though the distances vary. This produces a variation in the observed speed of the planet. Source

What is interesting is that he gives no indication of the bombshell that he is about to lob into the astronomy-cosmology debate with the assumptions that he wishes to be granted by his readers. They follow immediately on the introduction. He merely wishes to substitute a heliocentric system for the universally accepted geocentric system. Even more interesting, and totally frustrating for historians of astronomy, he gives absolutely no indication whatsoever how or why he came to adopt this radical step in order to rescue the uniform circular motion axiom. Copernicus’ assumptions (axioms) read as follows[2]:

1: There is no one center of all the celestial circles or spheres.

That there is, is one of the fundamental axioms of Aristotelian cosmology

2: The center of the earth is not the center of the universe, but only of gravity and the lunar sphere

That the earth is the centre of the universe is another of the Aristotelian axioms

3: All the spheres revolve about the sun as their mid-point, and therefore the sun is the center of the universe.

Bombshell lobed without comment!

4: The ratio of the earth’s distance from the sun to the height of the firmament is so much smaller than the ratio of the earth’s radius to its distance from the sun that the distance from the earth to the sun is imperceptible in comparison with the height of the firmament.

Copernicus needs this assumption to explain the lack of observable stellar parallax. Much is made of Copernicus’ vast increase in the size of the cosmos in comparison to Ptolemaeus. However in the Almagest Ptolemaeus states, “Moreover, the earth has, to the senses, the ratio of a point to the distance of the sphere of the so-called fixed stars[3].” Even Ptolemaeus’ cosmos is in principle unimaginably large.

5: Whatever motion appears in the firmament arises not from any motion of the firmament, but from the earth’s motion. The earth together with its circumjacent elements performs a complete rotation on its fixed poles in a daily motion, while the firmament and highest heaven abide unchanged.

The concept of diurnal rotation, the earth’s daily rotation about its own axis, had been hypothesised on many occasions throughout the history of astronomy as I explained in an earlier blog post. Copernicus would call upon some of those earlier examples as support for his own views in De revolutionibus. More interesting is the phrase “together with its circumjacent elements”, where Copernicus is basically saying that the earth carries its atmosphere with it when it rotates. This counters some of the arguments already listed by Ptolemaeus against diurnal rotation. The problem for Early Modern supporters of heliocentricity or simply diurnal rotation is they lacked the physics to explain how the earth could carry its atmosphere with in on its daily spin. We will return to this topic in a later episode.

6: What appear to us as motions of the sun arise not from its motion but from the motion of the earth and our sphere, with which we revolve around the sun like any other planet. The earth has, then, more than one motion.

The first sentence merely confirms the consequences of a heliocentric model. The second states another break with the Aristotelian axioms. According to Aristotle celestial bodies have just one type of natural motion, uniform circular motion and the earth also has just one type of natural motion upward or downward perpendicular to the earth’s surface.

7: The apparent retrograde and direct motion of the planets arises not from their motion but from the earth’s. The motion of the earth alone, therefore, suffices to explain so many apparent inequalities in the heavens.

This last assumption is, of course, the biggest selling point for the adoption of a heliocentric system but in the debates following the publication of De revolutionibus, the other arguments against heliocentricity weighed so heavily that this explanation for retrograde planetary motion got largely ignored.


Second page of the Stockholm manuscript with the assumptions Source: Wikimedia Commons

Copernicus now begins to fill in the details:

            Having set forth these assumptions, I shall endeavor briefly to show how uniformity of the motions can be saved in a systematic way. However I have thought it well, for the sake of brevity, to omit from this sketch mathematical demonstrations…[4]

Once again we have a confirmation that Copernicus’ main interest, as he sees it, is to restore the uniform circular motion axiom. I shall not into detail about the rest but the section headings are:

The Order of the Spheres

The Apparent Motion of the Sun

Equal Motion Should Be Measured Not by the Equinoxes but by the Fixed Stars

The Moon

The Three Superior Planets Saturn–Jupiter–Mars



Of interest here is that some of the epicycle-deferent models he outlines here differ from those that he would later develop for De revolutionibus indicating that this is an initial concept that would undergo development in the following thirty plus years, although he announces his intention to produce a larger more detailed work in the sentence I broke off above:

However I have thought it well, for the sake of brevity, to omit from this sketch mathematical demonstration, reserving these for my larger work[6].

We have no idea how many copies of the Commentariolus Copernicus made and distributed or how many further copies were made by others. As I have indicated above there is circumstantial evidence that it was read but the lack of any direct mentions before the publication of De revolutionibus, plus the fact that there seems to have been no heliocentricity debate triggered by it, as opposed to the debate triggered by Fracastoro’s Homocentrica (1538),and a couple of other contemporary published texts on the homocentric spheres model, indicate that the Commentariolus had very little impact on the sixteenth-century astronomical community.

















[1]3 Copernican Treatises: The Commentariolus of Copernicus, The Letter Against Werner, The Narratio Prima of Rheticus, Translated with Introduction, Notes and Bibliography by Edward Rosen, Dover Publications, Inc., New York, 1959 pp. 57-58

[2]Copernicus/Rosen pp. 58-59

[3]Ptolemy’s AlmagestTranslated and Annotated by G. J. Toomer, Princeton University Press, Princeton New Jersey, ppb. 1998 p. 43

[4]Copernicus/Rosen p. 59

[5]Copernicus/Rosen pp. 59-90

[6]Copernicus/Rosen p. 59


Filed under Early Scientific Publishing, History of Astronomy, Renaissance Science, Uncategorized

12 responses to “The emergence of modern astronomy – a complex mosaic: Part VI

  1. Gavin Moodie

    Might this series on the emergence of modern astronomy be the core of a monograph on the subject?

  2. Ray

    One of the Aristotelian assumptions rejected by Copernicus seems kind of remarkable to me — that a celestial body may have no more than one natural motion. It’s my understanding that the Copernicans didn’t have a good counterexample until sunspots showed the rotation of the sun in 1613. But, it seems pretty easy to throw a thing in the air and see it rotates as it goes up and down. This also seems like something someone would need to know if he was, to give an example I’m quite sure is old enough, in the business of juggling short swords. I suspect an Aristotelian, if asked, might say this was violent rather than natural motion (although I’m not aware of any philosopher considering rotating projectiles at all before the late 17th century. Are there any?) Even then, I’m not sure natural motion should be what’s relevant, since everyone was apparently ok with the planets being simultaneously moved by the very different motion of an epicycle, a deferent, and the diurnally rotating primum mobile. Also didn’t Buridan seek to explain both projectile motion, and the motions of heavenly bodies by the same impetus theory? What ever happened to that idea?

    A couple more more quick questions:

    Even more interesting, and totally frustrating for historians of astronomy, he gives absolutely no indication whatsoever how or why he came to adopt this radical step in order to rescue the uniform circular motion axiom.

    Does he not give a small indication in the second to last sentence of his introduction?

    After I had addressed myself to this difficult and almost insoluble problem, the suggestion at length came to me how it could be solved with fewer and much simpler constructions than were formerly used, if some assumptions (which are axioms) are granted to me.

    Is he not saying that heliocentrism while not strictly required to restore uniform motion, allows it to be done with “fewer and simpler constructions?” In fact, might the phrase “than were formerly used” refer to an earlier geocentric system Copernicus himself had developed to solve the problem of uniform motion but subsequently rejected as too complicated?

    Also, would it be possible to get and compare the number of sold copies at various times for De Revolutionibus and Homocentrica?

    • By assigning both a solar orbit and diurnal rotation to the Earth, Copernicus is definitely attributing two natural motion to the same body. At that point there was no evidence that any of the celestial bodies rotated on its axis. Defenders of the homocentric sphere theory were not happy with the deferent-epicycle model!

      Copernicus’ claim that a heliocentric model would require fewer and much simpler constructions (which turned out to be false when he worked out the full system in De revolutionibus) is a consequence of his choosing a heliocentric system not the reason for doing so. We have no idea why he chose to investigate a heliocentric model in the first place.

      What the fuck does the comparison of the sales figure of De revolutionibus and Homocentrica have to do with the fact that the Commentariolus was almost totally ignored?

      And no, it is almost impossible to find out what the print runs or sales figures were for any books published in the sixteenth century. BTW sales figures say nothing about the discussions that a publication generates.

      • Ray

        What the fuck does the comparison of the sales figure of De revolutionibus and Homocentrica have to do with the fact that the Commentariolus was almost totally ignored?

        Nothing. I didn’t mean to deny that Commentariolus was almost totally ignored. But the relative influence of heliocentrism and homocentrism in the late 16th century came up previously in the series and your point about Commentariolus in this post also speaks to that. I was interested in more context to better understand when the influence of homocentrism was overtaken by the influence of heliocentrism and didn’t see the harm in throwing in a quick question among the others, while I was thinking about it. I can’t say I’m not disappointed by the negative response, but thanks for answering the question.

        Could you also elaborate a bit more on your response to this question from my previous comment:

        Also didn’t Buridan seek to explain both projectile motion, and the motions of heavenly bodies by the same impetus theory? What ever happened to that idea?

        That is to say, it seems to me that the evidence for multiple simultaneous inertial (I know, not the same as natural) motions of terrestrial objects was, or at least should have been, overwhelming in the 16th century, and the framework for relating inertial motions on Earth to the motions of heavenly bodies already existed in the work of Buridan from what I can tell. But, this doesn’t seem to play a role in defenses of heliocentrism for the first 100 years or so. Do you have any insight into why not?

        Also, why did Aristotelians consider Copernicus’s triple motion of the Earth more problematic than the geocentric motions the planets inherited from primum mobile, deferent, and epicycle in Ptolemy’s system?

      • Also didn’t Buridan seek to explain both projectile motion, and the motions of heavenly bodies by the same impetus theory? Whatever happened to that idea?

        It slowly morphed into Descartes’ Law of Inertia, aka Newton’s First Law. Just how long the road was and how much intermediate figures contributed to the transformation was and is a topic for much discussion. For example, Wootton’s and Heilbron’s biographies of Galileo each devote a chapter to this. The position that Buridan and other medieval figures deserve almost all the credit is sometimes called Duhem’s thesis.

        But, this doesn’t seem to play a role in defenses of heliocentrism for the first 100 years or so.

        I don’t think that’s accurate. The thought experiments and arguments most famously presented in Galileo’s Dialogs belong to a long tradition, stretching back to Buridan and even earlier. Now, if you’re specifically referring only to the “multiple natural motions” argument, I don’t think you can isolate that one thread from the general project of disentangling astronomy from Aristotelian physics.

    • One more thought: the “multiple motions” of the earth (rotation and revolution) was the basis for Galileo’s infamous theory of the tides. (Possibly taken from Sarpi.)

      • Buridan did indeed seek to explain both unnatural motion on the Earth and the cause of uniform circular motion in the heavens with his version of the impetus theory. His motivation for applying impetus theory to celestial motion was however motivated by religion and not by science. Because neither Aristotle nor Plato were in the Bible, Buridan rejected Aristotle’s unmoved mover, the accepted Church explanation for the unending celestial motion and suggested instead the God set the heavenly spheres in motion with impetus and because there was no resistance in the heavens the impetus never ran down. Like many, many other theories over the centuries in the history of science Buridan’s theory of celestial impetus was not taken up by other scholars, as opposed to his terrestrial theory of impetus.

  3. Carl Vehse

    Your posting a quip about a heliocentric astronomer attributed to Martin Luther in the Table Talk collection brings to mind an event involving Luther that serendipitously provided the spark igniting the fuse leading to the “emergence of modern astronomy”… or at least the publication of Copernicus’ De Revolutionibus.

    And that spark was the major brouhaha that broke out during the summer of 1538 between Martin Luther and a Wittenberg poet named Simon Lemnius over his controversial poems dedicated to Luther’s archenemy, Archbishop Albrecht of Mainz. As things quickly reached the boiling point, caused by satirical poems aimed at Luther and his wife Kate, Lemnius, perhaps warned by colleagues that his life was at risk, decided it was time to get out of Wittenberg, and did.

    However, Lemnius was a former fellow student and drinking companion of Joachim Rheticus, who now felt some “guilt by association” heat. Because of this Rheticus requested and received approval from Philipp Melanchthon to take a sabbatical to Nuremberg and other cities in October, 1538. And the rest is history.

    The conflict between Luther and Lemnius is discussed in Dennis Danielson’s book, “The First Copernican” (pp. 26-30, with “poetry” examples from Lemnius and Luther on pp. 234-5).

    • Dennis Danielson’s theory about Rheticus leaving Wittenberg because of Lemnius’ dispute with Luther is just that, a theory. A plausible one but not a proven one.
      BTW The First Copernican is a great book.

  4. Callippus and Eudoxus, who endeavoured to solve the problem by use of concentric spheres, were able…

    Shouldn’t that be “unable”? (The Edward Rosen translation says, “…could not thereby account…)

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