Responses to Copernicus

Copernicus worked out his heliocentric system by 1514 (at the latest). He wrote up a brief description of his model of the cosmos, called it the Commentariolus (Latin for “little commentary”), and circulated it in manuscript form. A brief aside on this mode of communication: Although the printing press was invented sometime around 1450, the production and circulation of manuscripts (hand-written books) continued for at least another two hundred years. Copernicus’ decision not to have this manuscript printed may reflect the fact that he had not yet worked out all the technical details of his system in 1514. Although the Commentariolus was not printed, it circulated among astronomers all over Europe. The famous Danish astronomer Tycho Brahe reported having read it, and there are copies of this manuscript (or parts of it) in Vienna, Stockholm and Aberdeen.

Commentariolus_Wien_MS10530_Blatt_34

“Commentariolus.” Wien [Vienna] MS10530, p. 34. Wikimedia Commons.

 In the Commentariolus, Copernicus asserted that earth moves and the sun stands still. The apparent motion of the heavens results from diurnal (daily) motion of earth. The path of the sun around the ecliptic is the result of the annual motion of the earth. The apparent retrograde motions of the planets are caused by the rotation of the earth around the sun. Copernicus worked out all these ideas at much greater length and in much greater detail in his final published work, On the revolutions of the celestial spheres, published in Nuremburg in 1543.

If Copernicus was convinced in 1514 (or earlier) that the sun stands still and the earth moves, why did it take him almost thirty years to publish the final version of his work? Was he afraid that that the Catholic Church would condemn his ideas, or worse, condemn HIM for heresy? The answer to the second question is quite emphatically no. In fact, at least a few high ranking members of the Catholic hierarchy had read or were familiar with the contents of the Commentariolus and raised no objections on theological or doctrinal grounds. On this point, I quote Thony Christie’s recent blog post on the lack of religious objections to Copernicus:

In 1533 the papal secretary, Johann Albrecht Widmannstetter held a lecture on Copernicus’ theories to Pope Clemens VII and assembled company in the papal gardens. We assume this was based on Copernicus’ Commentariolus, the manuscript pamphlet of his ideas written around 1510, as De revolutionibus wasn’t published until 1543. Was he condemned to the stake for his rashness? No, Clemens found much favour in his lecture and awarded him a valuable present for his troubles. Two years later Widmannstetter became secretary to Cardinal Nikolaus von Schönberg, an archbishop and papal legate, who had been present at that lecture. In 1536 Schönberg wrote a letter to Copernicus urging him to make his theories public and even offering to pay the costs of having his manuscript copied. Not a lot of condemning to the stake going on there. Copernicus had Schönberg’s letter printed in the front of De revolutionibus.

(You can read the entire post here.)

Also note that Copernicus dedicated On the revolutions to Pope Paul III. In the sixteenth century, it was not acceptable to dedicate a book to someone without having first obtained that person’s permission. Although allowing a book to be dedicated to you did not signify that you agreed with or endorsed the contents of the book, there is absolutely no way the head of the Catholic Church would have allowed a “heretical” book to be dedicated to him.

So why did Copernicus wait so long if there was no question of religious censure? He was probably more afraid of ridicule than accusations of heresy. Recall that educated sixteenth-century people were familiar with the ideas that 1) the earth rotates on its own axis and 2) the sun is at the center of the cosmos and the earth moves around it. Of course they were familiar with these ideas – they had read all about them in Aristotle. But that meant they were also familiar with Aristotle’s very convincing refutation of these ideas.

In order to illustrate some of the main criticisms of the Copernican system, I shall quote from an English astronomy textbook published in 1599. The book is Thomas Hill’s The Schoole of Skil. Although this book was published over fifty years after Copernicus’ On the revolutions, the criticisms of Copernicus’s heliocentric model of the cosmos date back to 1549, just six years after the publication of On the revolutions. The prominent Lutheran scholar and educator Philip Melanchthon (1497 – 1560) discussed Copernicus’ book, and offered a refutation of heliocentrism, in his physics textbook Initia doctrinae physicae (1549). A later Lutheran astronomer, Caspar Peucer (1525 – 1602), “borrowed” (and by borrowed I mean plagiarized) large sections of Melanchthon’s book, including the critique of heliocentrism, for his book on astronomy, Elementa doctrinae de circulis coelestibus et primo motu (1551). Thomas Hill in turn, translated large sections of Peucer’s book, including the passages on heliocentrism, and passed them off as his own in The Schoole of Skil. As you may gather from this, there were no effective copyright laws in place in the sixteenth century! But for our purposes, the following passages from Hill’s Schoole of Skil represent the first responses of highly educated and knowledgeable readers of Copernicus.  (I have modernized Hill’s spelling, and occasionally his punctuation, but otherwise left his Elizabethan English intact._

Hill’s section on heliocentrism begins as follows:

Aristarchus Samius [Aristarchus of Samos], which was 261 years before the birth of Christ, took the earth from the middle of the world, and . . . [put it in motion] about the sun, which he feigned to stand in the middle of the world as immoveable, after the manner of the fixed stars. The like argument doth that learned Copernicus apply unto his demonstrations. (p. 42)

Hill alludes to the fact that the IDEA of heliocentrism was ancient and familiar. Medieval and early modern scholars all knew about Aristarchus, but they believed they had very convincing arguments (drawn from Aristotle) that the earth was in the center of the cosmos and was stationary. Although Hill is about to launch into a number of arguments against Copernicus’ heliocentric model of the cosmos, he nonetheless accords him a certain respect, referring to him as “that learned Copernicus.” And indeed, if you read the entire book, you find numerous positive references to Copernicus. Hill often uses Copernicus’ calculations for various astronomical values like the length of the solar year. Many early readers of Copernicus used the mathematical models in On the revolutions for calculating planetary positions. Although very few sixteenth-century readers accepted the physical reality of heliocentrism, they still saw considerable value in Copernicus’ work.

Let’s look at some of the objections Hill raises to Copernicus’ sun-centered system. First, he cites astronomical observations:

 If the earth were not as the center of the world, then of necessity should these ensue, that the earth should approach, either nearer to the east, or west, or south part. And when any of the stars (as well the fixed as planets) shall come unto that part, they shall appear nearer to us, then being in any other part of heaven. And by that above said, they shall also appear greater, which is altogether untrue, and we also see the contrary in that (as above written) they always appear of one greatness, either being in the east, or in the west. (p. 44)

Nicolaus Copernicus, De revolutionibus (1543)

Nicolaus Copernicus, De revolutionibus (1543). Courtesy of OU History of Science collections.

Copernicus’ cosmos, like the Aristotelian earth-centered centered cosmos, is spherical and finite. The fixed stars are all embedded on a giant sphere that forms the boundary of the world. But in Copernicus’ cosmos, the earth is moving around the sun. As it moves around the sun, some of the fixed stars should appear larger, because the earth is closer to them, and others should appear smaller, because the earth is farther away from them. As the earth moves, the sizes of the fixed stars ought to change, getting bigger and smaller. But obviously this does not happen. And when I say “obviously,” I means after literally THOUSANDS OF YEARS of observations, it was quite clear to sixteenth-century people that the fixed stars are always the same size and brightness to observers on earth.

Ecliptic_path

“Ecliptic path” by Tauʻolunga. Wikimedia Commons.

Another problem (not raised by Hill, but noted by other critics of Copernicus) is that if the earth is in motion, the fixed stars should appear to change in position relative to each other. This is a phenomenon known as stellar parallax, and it is not observed. Consider the following diagram, which depicts the earth at two positions, six months apart. If an observer on earth looks at a planet against the background of the fixed stars, that planet should appear to be in a different position relative to the stars after six months. Again, this phenomenon is NOT observed.  For more on stellar parallax and the problems it posed for the acceptance of heliocentrism, see here.

ParallaxeV2

Copernicus was well aware of these problems with his system. He posited that the universe was much larger than Ptolemy had calculated. In a much larger cosmos, the distance of the fixed stars from the earth would be so great that they would not appear to change in size as the earth moved, and no stellar parallax would be observed.  In Book I, chapter 5 of On the revolutions, he writes, “Anyone who denies that the earth occupies the middle or center of the universe may nevertheless assert that its distance (therefrom) is insignificant in comparison with (the distance of) the sphere of the fixed stars, but perceptible and noteworthy in relation to the spheres of the sun and the other planets.”  In other words, in Copernicus’ model, the fixed stars are MUCH farther away from the earth than are the planets.

In addition to citing the evidence of astronomical observations, Hill raises physical objections to the Copernican cosmos.

[E]very grave or heavy matter by nature is through his weight carried after a most straight line unto the center, and both settleth, stayeth, and resteth at the same, where it neither falleth, or is carried any further. So that all grave matters, as the parts of the earth, and those which consist of the earth, are sent or carried by a most straight leading unto the earth, and at his upper face shall stay and rest. And were it not that they are stayed through the fastness of the earth, they should so long be carried downwards, until they came unto the center. Also the earth through his fastness, receiveth and beareth all things falling on it. Therefore doth the earth much more (being within the center) stay and rest fixed and immoveable, bearing all other heavy things falling on it, seeing the earth is heaviest of all others. (p. 50)

This argument should be very familiar to you, as you recently read it in Aristotle. Aristotle argued that the terrestrial realm was made of four elements, earth, water, air and fire. Each of these elements had a natural place, and the natural place of the element earth was in the center of the cosmos. Hence the earth as a whole was stationary in the center of the cosmos. Because we no longer accept Aristotle’s physics as an accurate description of the natural world, this may not seem like it should have been a serious objection. But remember, this physics explained not just why the earth was central and stationary, but why it was spherical. And it explained why heavy bodies (like rocks) fall and light bodies (like bubbles in water) rise. It explained natural phenomena like thunderstorms, earthquakes, volcanoes and comets. To convince people to jettison this physics, you would have to be able to replace it with a physics that could explain all of these natural phenomena – the everyday things like rocks falling and the more extraordinary ones like earthquakes – in a coherent and convincing way that was consistent with observation and experience. That’s a tall order, and Copernicus couldn’t fill it. Not until Isaac Newton was there an entirely new physics that could adequately replace Aristotelian physics. (Although, as we shall see, Galileo and Descartes did crucial work in this area.)

Copernicus was aware that this would be an objection to heliocentrism, and he suggests a possible solution.

I believe that gravity is nothing but a certain natural desire, which the divine providence of the Creator of all things has implanted in parts, to gather as a unity and a whole by combining in the form of a globe. This impulse is present, we may suppose, also in the sun, the moon, and the other brilliant planets, so that through its operation they remain in that spherical shape which they display. Nevertheless, they swing round their circuits in divers ways. (Copernicus, On the revolutions, Book I, chapter 9)

In other words, there could be multiple natural centers in the universe. The natural place of the element earth is the center of the earth we live on, not the center of the entire cosmos. This too should be familiar to you, as Nicole Oresme proposed a similar explanation for how it could be possible that there was more than one cosmos with more than one center. (Review his arguments about the possibility of a plurality of worlds.)

Oresme

Nicole Oresme. Wikimedia Commons.

Another physical objection that Hill raises is that if the earth is in motion, we should feel this motion. After all, if we stand on a moving ship we can feel the wind against our faces. If the earth was moving, shouldn’t we feel wind? And if the earth is moving, it must be moving much much faster than any ship. So the wind we should feel if the earth were rotating would be incredibly violent. Aristotle and later Ptolemy had certainly taken the fact that we don’t feel any such wind as experiential evidence that the earth is stationary. Hill refers to such arguments:

If the earth should be drawn about by a circular motion, and should in a day’s turn (at the least) be carried about the axis, from the west into the east, as either alone or with the first orb; then every day should many most disordered things, and contrary to experience happen. For it should be a most speedy motion, and swiftness inseparable, which should draw circularly all the whole earthly body round about in 24 hours. And therefore that the earth is carried with so swift motion, should not only overthrow buildings, but high hills, and greatly shake and harm all things fastened and growing on the earth. Yea, all living beasts, and other creatures dwelling on the face of the earth, should be likewise shaken and harmed. Also the clouds, fowls, and whatsoever liveth and hangeth in the air should be carried and left behind at the setting in the west. (p. 51)

Again, Copernicus is quite familiar with these arguments and aware that they pose a problem for his system. He writes:

Therefore, remarks Ptolemy of Alexandria (Syntaxis, 1, 7), if the earth were to move, merely in a daily rotation, the opposite of what was said above would have to occur, since a motion would have to be exceedingly violent and its speed unsurpassable to carry the entire circumference of the earth around in twenty-four hours. But things which undergo an abrupt rotation seem utterly unsuited to gather (bodies to themselves), and seem more likely, if they have been produced by combination, to fly apart unless they are held together by some bond. The earth would long ago have burst asunder, he says, and dropped out of the skies (a quite preposterous notion); and, what is more, living creatures and any other loose weights would by no means remain unshaken. Nor would objects falling in a straight line descend perpendicularly to their appointed place, which would meantime have been withdrawn by so rapid a movement. Moreover, clouds and anything else floating in the air would be seen drifting always westward. (Copernicus, On the revolutions, Book I, chapter 7)

Notice how close this is to the passage from Hill! Both are drawing on a common and well-known set of arguments. However, Copernicus answer is rather weak:

Yet if anyone believes that the earth rotates, surely he will hold that its motion is natural, not violent. But what is in accordance with nature produces effects contrary to those resulting from violence, since things to which force or violence is applied must disintegrate and cannot long endure. On the other hand, that which is brought into existence by nature is well-ordered and preserved in its best state. Ptolemy has no cause, then, to fear that the earth and everything earthly will be disrupted by a rotation created through natures handiwork, which is quite different from what art or human intelligence can accomplish. (Copernicus, On the revolutions, Book I, chapter 8)

So, if rotation of the earth were natural (i.e. if God had made the earth rotate), then its motion would be natural and not violent, and no violent disturbances would result. The logic here is circular and unsatisfying. Recall that Nicole Oresme actually had a much more satisfactory explanation of why we would not feel a violent wind if the earth were rotating about its own axis. He says simply that the entire terrestrial realm – the earth and its surrounding “atmosphere” – could rotate. Since everything in the terrestrial realm partakes in the rotation of the earth, we don’t feel this rotation. We can only detect motion, according to Oresme, “if we can see that one body assumes a different position relative to another body.”

In addition to scientific objections – that is objections based on the observed appearances of the heavens and physical reasoning – Hill also points to passages of scripture that describe the earth as stationary. (I have added the complete references to the biblical chapters and verses, and full quotes from the King James Version in brackets.)

That neither the earth, in right [rectilinear] nor circular motion is drawn about the axis of the world, nor about any other axis, but to rest and stay in the middle of the world, both holy scriptures confirm, and physic[al] reasons prove. For the Psalm saith, which established the earth upon his foundation, that it shall never be moved. [Psalm 104:5 “Who laid the foundations of the earth, that it should not be removed for ever.”] And Ecclesiastes in the first chapter saith: that the earth standeth for ever, and the sun both riseth, setteth, and goeth about unto the place where he arose. [Ecclesiastes 1:4-5 “. . . the earth abideth for ever. The sun also ariseth, and the sun goeth down, and hasteth to his place where he arose.”] Also that the sun is drawn about, the Psalm doth manifestly witness, where it is said: that for the sun, he hath placed a tabernacle in them, and He, as a bridegroom going forth of His chamber, doth rejoice as a giant to run his course, which goeth forth from the uttermost bound of heaven, and returneth about unto the end of I again. [Psalm 19:4-6 “In them hath he set a tabernacle for the sun, which is as a bridegroom coming out of his chamber, and rejoiceth as a strong man to run a race. His going forth is from the end of the heaven, and his circuit unto the ends of it: and there is nothing hid from the heat thereof.”] (p. 49)

Titian_-_Pope_Paul_III_-_WGA22962

Titian, Pope Paul III (1545-46). Wikimedia Commons.

These will become standard passages used in critiques of Copernicanism in the late sixteenth and seventeenth centuries. However, they are not given pride of place in this section on heliocentrism. They add to the scientific objections; they don’t dominate the discussion. Copernicus briefly notes that some readers might claim his model of the cosmos was incompatible with the Bible. In his dedication to Pope Paul III, he writes

Perhaps there will be babblers who claim to be judges of astronomy although completely ignorant of the subject and, badly distorting some passage of Scripture to their purpose, will dare to find fault with my undertaking and censure it. I disregard them even to the extent of despising their criticism as unfounded. For it is not unknown that Lactantius, otherwise an illustrious writer but hardly an astronomer, speaks quite childishly about the earth’s shape, when he mocks those who declared that the earth has the form of a globe.

Note that he’s not afraid – when addressing the pope no less! – to mock those who would raise scriptural objections as “babblers” and refuse to take them seriously. In this passage Copernicus refers to the early Christian writer Lactantius (240 – ca. 320), who argued that the earth was flat because this was consistent with a literal reading of certain scriptural passages. Although Lactantius was an important and influential theologian, this particular idea was almost universally rejected. Copernicus does not include any more explanation of how a sun-centered cosmos is compatible with scripture, but recall, Nicole Oresme had already argued that a moving earth was not opposed to the Bible (and he addressed many of the same passages that Hill uses).

In conclusion, the major reasons for not accepting Copernicus’ heliocentric model of the cosmos were that 1) it did not fit observational evidence as well as the Aristotelian/Ptolemaic geocentric model of the cosmos, and 2) the geocentric model was supported by Aristotelian physics (and the heliocentric system had no comparable physics). Since all the scientific evidence and arguments were against the physical reality of the Copernican system, religious objections were not particularly salient in the decades immediately following the publication of On the revolutions.

References:

Thomas Hill, The schoole of skil containing two bookes: the first, of the sphere, of heauen, of the starres, of their orbes, and of the earth, &c. The second, of the sphericall elements, of the celestiall circles, and of their vses, &c. Orderly set forth according to art, with apt figures and proportions in their proper places, by Tho. Hill (London: Printed by T. Iudson, for W. Iaggard, 1599.) This is available in Early English Books Online. There is also a facsimile edition: Thomas Hill, The Schoole of Skil, London, 1599 (Amsterdam and New York: Da Capo Press, 1973).

Katherine Tredwell traced the connections between Hill’s Schoole of Skil, Caspar Peucer’s Elementa doctrinae de circulis coelestibus et primo motu (1551), and Philipp Melanchthon’s Initia doctrinae physicae (1549) in her dissertation.  Katherine Anne Tredwell, “The Exact Sciences in Lutheran Germany and Tudor England” (Ph.D. dissertation, University of Oklahoma, 2005); on Peucer’s book see pp. 131-135; on Hill’s book see pp. 225-230.

[1] Katherine Anne Tredwell, “The Exact Sciences in Lutheran Germany and Tudor England” (Ph.D. dissertation, University of Oklahoma, 2005); on Peucer’s book see pp. 131-135; on Hill’s book see pp. 225-230.

Nicholas Copernicus, On the revolutions (1543), trans. Edward Rosen

Useful resources:

“Copernican System” from the Galileo Project

Owen Gingerich on readers of On the revolutions

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