Copernicus and Kepler: Towards a Heliocentric Theory


Copernicus and Kepler: Towards a Heliocentric Theory



This paper will compare and contrast the approaches that Copernicus and Kepler took toward establishing the heliocentric theory and the mobility of the earth. Attention will be given to their evaluation of ancient and current astronomical thought.


Copernicus’ approach


Copernicus took pains to read everything he could find from the ancient Greek and Roman astronomers and philosophers. He was well read in Aristotle, the Pythagoreans, Ptolemy and the Scholastics. In 1474, Regiomontanus (1436 – 1376), the first astronomer-printer, published an advanced list of important works soon to come from his press in Nuremberg – among them, many mathematical and astronomical works, with which Copernicus was surely familiar.1 Regiomontanus’ own Epitome of the Almagest (printed in 1496) was used by Copernicus in his studies. However, the confusion of the competing astronomical theories of his day led Copernicus to think that there must be an alternative explanation. As Copernicus himself confesses to Pope Paul III in the preface to De Revolutionibus,

“For a long time, then, I reflected on this confusion in the astronomical traditions…I began to be annoyed…For this reason I undertook the task of rereading the works of all the philosophers which I could obtain to learn whether anyone had ever proposed other motions of the universe’s spheres than those expounded by the teachers of astronomy in the schools.”2


His “rereading” did not disappoint him. He found that in one of Cicero’s works a certain Hicetas had believed the earth moved. Later on he discovered that Plutarch mentioned at least three Pythagoreans who believed the same: Philolaus, Ecphantus and Heraclides of Pontus. In addition, during his time there were some novel ideas circulating about the nature of the universe. For example, Nicholas of Cusa (c. 1401 – 1464) had proposed an infinite and centerless universe 100 years before the publication of De Revolutionibus. Nicole Oresme (c. 1323 – 1392) theorized, but ultimately rejected, the possibility that the earth rotated on its axis in a commentary on Aristotle’s in his non-published tract entitled, Traité du ciel et du monde, written in 1377 at the request of King Charles V. Such views were the grand exceptions, however, and the accepted and majority view held that Ptolemy had gotten it right, with only some corrections needed to his theory. Copernicus came at the problem from this point of view.

Rheticus in his Narratio Prima relates to us Copernicus’ thinking in rejecting the main features of the Ptolemaic system.3 Firstly, the indisputable precession of the equinoxes and the change in the obliquity of the ecliptic was most satisfactorily explained by the motion of the earth. Secondly, the diminution of the eccentricity of the sun is explained more readily by the same reason. Thirdly, the planets have the centers of their deferents in the sun, as the center of the universe, and not the earth as the center of the universe. This is so because of the observed motion of Mars. Mars sometimes shows a parallax greater than the sun’s, an observation inconsistent with the earth at the center of the universe. Fourthly, to preserve the principle of uniform circular motion, only with the sun at the center could all the circles in the universe be made to revolve uniformly about their own centers and not about other centers (epicycles). Fifthly, the simple motion of the earth satisfies an innumerable number of appearances, and this is consistent with the principle of simplicity where one cause can satisfy the many. Sixthly, and lastly, Rheticus says that we should regard the rule that “the order and motions of the heavenly spheres agree in an absolute system.” This, according to Copernicus, is true only when the sun is placed in its rightful place in the center of the universe.

In spite of the novelty of Copernicus’ new vision, he still retained many features of the old Ptolemaic system. Indeed, it is Kuhn’s judgment that Copernicus’ De Revolutionibus

“…is a relatively staid, sober and unrevolutionary work. Most of the essential elements by which we know the Copernican Revolution – easy and accurate computations of planetary position, the abolition of epicycles and eccentrics, the dissolution of the spheres, the sun a star, the infinite expansion of the universe – these and many others are not to be found anywhere in Copernicus’ work.”4


What was
bold on Copernicus’ part was his notion of putting the sun in the center of the universe with our earth and the rest of the planets revolving around it. It is true as Kuhn and others have pointed out that he did retain some key Ptolemaic ideas such as epicycles and uniform circular motion. However, I think that on balance, given the conventional wisdom supporting the Ptolemaic theory and the culture of a tradition-driven Church not fond of novelty, his heliocentric and mobile earth ideas were certainly innovative and bold when evaluated in his own setting.

Cohen concludes that Copernicus’ significance

“…lay not so much in the system he propounded as in the fact that the system he did propound would ignite the great revolution in physics that we associate with the names of Galileo, Johannes Kepler and Isaac Newton.”5


Kepler’s approach


We must start by noting that Kepler was an early convert to the Copernican theory and remained an unabashed Copernican throughout his life. His teacher and mentor, Michael Maestlin, favorably reviewed Copernicus in his lectures at the University of Tubingen, where Kepler attended, beginning in 1589.

Kepler’s major works, Mysterium Cosmographicum (1596), Astronomia Nova (1609) and Harmonices Mundi (1619) display an interesting curiosity in numbers and geometrical and mathematical relationships. Why are there only 6 planets and no more or less? Why are the distances between the planets as they are and not another? Kepler even once penned an essay on why the snowflake had six sides and not five or seven.6 He went to great lengths in explaining various geometrical reasons for its appearance. This same curiosity drove his astronomical thinking.

In Mysterium Cosmographicum Kepler presented the first published defense of the Copernican system and posited that Euclid’s five platonic solids serve to explain the distance relationships among the six planets. Kepler has the same issue as Copernicus regarding the Ptolemaic theory: it simply does not account for a number of observed phenomena.

“I reply first that the old hypotheses simply do not account at all for a number of outstanding features. For instance, they do not give the reasons for the number, extent, and time of the retrogressions, and why they agree precisely, as they do, with the positions and mean motion of the Sun.”7

And so in the same way Kepler accepts the presumption that nature should be explained by simpler explanations, not more difficult ones.

“…these hypotheses of Copernicus not only do not offend against the Nature of things, but do much more to assist her. She loves simplicity, she loves unity. Nothing ever exists in her which is useless or superfluous, but more often she uses one cause for many effects…And although all these motions, eleven in number, are banished from the universe by the substitution of this single motion of the Earth, nevertheless reasons are supplied for a great many other matters for which Ptolemy for all his many motions could give no reason.”8

Kepler also makes an argument from common sense regarding the speed of the supposed revolutions of the bodies in the universe (an argument Copernicus also used). He explains that it is easier to suppose that the earth rotates in one direction in a twenty-four-hour period than to believe that the rest of the universe move at incredible speed about the motionless earth.

“Consequently there disappears that incredibly lofty and swift tenth and starless sphere, the swiftness of which and of the whole universe would be so great according to Ptolemy that it would traverse several thousand miles in the blinking of an eye…finally decide whether it is easier for it to happen and to be believed that that small point within the little circle A, and hence the Earth, rotate in one direction, or that the complete universe goes with ten distinct motions (as there are ten mutually independent circles) with inconceivable rapidity, and is subject to nothing but that small point, which along is motionless, because there is nothing outside.” 9

Here we have two thinkers, pushing forward our understanding of our place in the universe. Copernicus provided the sun-centered, mobile earth and Kepler agrees, adding the elliptical paths for planetary orbits. Once this new paradigm was in place, it needed an answer to the question: How to the planets move? On their own or from another source? A new physics was born from these questions.

Although Kepler, which Gilbert’s assistance, moved toward the notion of action at a distance, it was not until Newton that the answer was finally explained. Nonetheless, both Copernicus and Kepler were able to establish the heliocentric theory and mobility of the earth, with both observational and mathematical evidence. By questioning the reasoning of the ancients and working from fresh perspectives, which so many were unable or unwilling to try, a revolution was in the making, thanks to them both.



1 Elizabeth L. Eisenstein, The Printing Revolution in Early Modern Europe, Cambridge University Press, Cambridge, 1993, p.210.


2 Nicholas Copernicus, On the Revolution of the Heavenly Spheres, translated by Charles Glenn Wallis, Prometheus Books, Amherst, NY, 1995, Preface.


3 Joachim Rheticus, Narratio Prima, as found in Edward Rosen, Three Copernican Treatises, 2nd edition, Dover Publications, Mineola, NY, 1959, p.131.


4 Thomas S. Kuhn, The Copernican Revolution, Random House, New York, 1959, p. 135.


5 I. Bernard Cohen, The Birth of a New Physics, W.W. Norton & Company, New York, 1985, p.52.


6 Johannes Kepler, The Six Cornered Snowflake, translated by Colin Hardie, Oxford University Press, Oxford, 1996.


7 Johannes Kepler, Mysterium Cosmographicum, translated by A. M. Duncan, Abaris Books, New York, 1981.


8 Ibid.


9 Ibid.

Nine New Testament Facts about Jesus Corroborated by Josephus and Tacitus

Tacitus_portraitJosephusbustSome question what evidence for a historical Jesus exists outside the writings of the New Testament. This is a fair question, and one that continues to be asked from time to time. I firmly believe that the documents contained in the New Testament are completely sufficient entirely on their own to establish the historicity of Jesus of Nazareth. Some have charged that it is inadmissible to use the New Testament as a historical source for the life of Jesus because it is a biased account. I must agree that it is a biased account, but all historical documentation is biased in one way or another. It must be evaluated on its own merits. Well over a hundred years of scholarly research has confirmed its viability as a valid source for our knowledge of Jesus of Nazareth. A summary of early extra-Biblical evidence has recently been provided by Lawrence Mykytiuk in the January/February 2015 bulletin of the Biblical Archaeology Society. The end notes alone in his piece are worth their weight in gold. I recap his findings in this post, and add a few of my own. (see reference at the end).

Some preliminary observations:

First, it is not to be expected that Rome would have paid any attention to an obscure cult leader in the remote province of Judea. It is therefore surprising that any reference has survived from such an early period – just mere decades after the death of Jesus.

Second, as F.F. Bruce noted, few classical writings survive from the period of about the first 50 years of the Christian church (c. 29 to 80 C.E.). Again, that we have any first century material outside the New Testament is itself remarkable. (see F.F. Bruce, Jesus and Christian Origins, p. 17.)

Third, Josephus and Tacitus are excellent witnesses to the historicity of Jesus as they are both non-Christian sources and have no interest in pushing a Christian agenda. Indeed, Tacitus could be classified as a hostile witness. Their references to Jesus in a completely neutral context in the course of discussing other issues. The mention of Jesus is tangential to the immediate story.

Josephus (37-100 AD) was a first-century Jewish priest turned military commander who initially fought for the Jews during the first Jewish War with Rome (66-70 AD). He soon saw the futility of fighting against Rome and turned against his people, sided with the Romans and provided them valuable intelligence during the course of the war. For his efforts he was rewarded with a comfortable living in Rome and was charged with writing the official account of the war. His two greatest works were The Jewish War and Jewish Antiquities. It was in the Antiquities, Book 20, that his shorter reference to Jesus occurs. An earlier and longer reference is found in Book 18. Here are both references (the second with Christian additions italicized):

“Being therefore this kind of person [i.e., a heartless Sadducee], Ananus, thinking that he had a favorable opportunity because Festus had died and Albinus was still on his way, called a meeting [literally, “sanhedrin”] of judges and brought into it the brother of Jesus-who-is-called-Messiah … James by name, and some others. He made the accusation that they had transgressed the law, and he handed them over to be stoned.”

“Around this time there lived Jesus, a wise man, if indeed one ought to call him a man. For he was one who did surprising deeds, and a teacher of such people as accept the truth gladly. He won over many Jews and many of the Greeks. He was the Messiah. When Pilate, upon hearing him accused by men of the highest standing among us, had condemned him to be crucified, those who in the first place came to love him did not give up their affection for him, for on the third day, he appeared to them restored to life. The prophets of God had prophesied this and countless other marvelous things about him. And the tribe of Christians, so called after him, have still to this day not died out.”

Tacitus, or more formally, Gaius Cornelius Tacitus (55/56–c. 118)—was a Roman senator, orator and ethnographer, and perhaps one of the best of Roman historians. An interesting fact about his personal career is that Tacitus likely had access to some official archives by virtue of his status, either as Proconsul of Asia, as a Senator – or, as has been often overlooked, from his position as a high-ranking priest of Roman religion. Robert Van Voorst notes that in 88 AD Tacitus became “a member of the Quindecimviri Sacris Faciundis [“The Board of Fifteen for Performing Sacrifices”], the priestly organization charged, among other things, with … supervising the practice of officially tolerated foreign cults in the city … [and facing] the growing necessity to distinguish illicit Christianity from licit Judaism” (Van Voorst, Jesus Outside the New Testament, p. 52). Membership in this priestly group very likely gave him access to at least some of the accurate knowledge he possessed about Christus.

Tacitus’s last major work, titled Annals, written c. 116–117, includes a biography of Nero. In 64, Nero was suspected of secretly ordering the burning of a part of town where he wanted to carry out a building project, so he tried to shift the blame to Christians. This was the occasion for Tacitus to mention Christians, whom he despised. This is what he wrote—the following excerpt is translated from Latin by Robert Van Voorst:

“[N]either human effort nor the emperor’s generosity nor the placating of the gods ended the scandalous belief that the fire had been ordered [by Nero]. Therefore, to put down the rumor, Nero substituted as culprits and punished in the most unusual ways those hated for their shameful acts … whom the crowd called “Chrestians.” The founder of this name, Christ [Christus in Latin], had been executed in the reign of Tiberius by the procurator Pontius Pilate … Suppressed for a time, the deadly superstition erupted again not only in Judea, the origin of this evil, but also in the city [Rome], where all things horrible and shameful from everywhere come together and become popular.”

With these texts before us, let us now consider the Nine Facts of the New Testament Corroborated by Josephus and Tacitus:

1. He existed as a man. The New Testament presents Jesus as a real historical person, not a mythical figure. The gospels tell us of his physical genealogy, his parents, brothers and sisters, his cousin (John the Baptist), his birthplace, his deeds and sayings. They name his friends, his enemies, the names of cities to which he travels and ultimately, describe in detail his death in Jerusalem. They record the names of the Roman and Jewish rulers who reigned during his lifetime. They set him in a completely historical home in the Judeo-Greco-Roman world of the first century. Indeed, the gospels reek of real history. (Matthew chapters 1 and 2, Mark 3:31-32, Matthew 5, Luke 1-2, John 18-19).

The historian Josephus grew up in a priestly family in first-century Palestine and wrote only decades after Jesus’ death. Jesus’ known associates, such as Jesus’ brother James, were his contemporaries. The historical and cultural context was second nature to Josephus. “If any Jewish writer were ever in a position to know about the non-existence of Jesus, it would have been Josephus. His implicit affirmation of the existence of Jesus has been, and still is, the most significant obstacle for those who argue that the extra-Biblical evidence is not probative on this point,” Robert Van Voorst observes. And Tacitus was careful enough not to report real executions of nonexistent people.

2. His personal name was Jesus, as Josephus informs us. (Matthew 1:21, Luke 1:30)

3. He was called Christos in Greek, which is a translation of the Hebrew word Messiah, both of which mean “anointed” or “(the) anointed one,” as Josephus states and Tacitus implies, unaware, by reporting, as Romans thought, that his name was Christus. (John 1:41, 17:3)

4. He had a brother named James (Jacob), as Josephus reports. (Matthew 13:55, Galatians 1:19)

5. He won over both Jews and “Greeks” (i.e., Gentiles of Hellenistic culture), according to Josephus, although it is anachronistic to say that they were “many” at the end of his life. Large growth
in the number of Jesus’ actual followers came only after his death. (John 12:20-21, Acts 8, 10, et. al., Romans 16, etc.)

6. Jewish leaders of the day expressed unfavorable opinions about him, at least according to some versions of the Testimonium Flavianum (the longer text in Josephus, Antiquities, Book 18). In the New Testament, see the various encounters of Jesus with the Scribes and Pharisees, and especially the account of Jesus’ trial before the Sanhedrin – John 18).

7. Pilate rendered the decision that he should be executed, as both Tacitus and Josephus state. (Matthew 27, Mark 15, Luke 23, John 18)

8. His execution was specifically by crucifixion, according to Josephus. (Matthew 27, Mark 15, Luke 23, John 19)

9. He was executed during Pontius Pilate’s governorship over Judea (26–36 C.E.), as Josephus implies and Tacitus states, adding that it was during Tiberius’s reign. (Luke 3:1)


I am most grateful to Lawrence Mykytiuk’s feature article from the January/February 2015 issue of BAR with voluminous endnotes:

Profiles in Atheism: Bertrand Russell

I’ll be teaching a class on “The History of Atheism” at the NY Divinity School next Spring 2015 and thought it a good idea to publish some of my material here for your review. So, in the next coming weeks we’ll be taking a look at the life and thought of some of the most prominent and not-so-prominent atheists. I will present them in no particular order. We will begin with Bertrand Russell, certainly among the most famous unbelievers of the twentieth century. Stay tuned to this channel.

Neil deGrasse Tyson denigrates Philosophy. Great response from Massimo Pigliucci

Neil deGrasse Tyson denigrates Philosophy. A response from Massimo Pigliucci via @mpigliucci

Next NYC Reasonable Faith Meeting Sunday 2PM April 13th 2014 – How Jesus Became God: A Closer Look

Good evening, everyone.

Next Sunday we will take a look at Bart Ehrman’s latest book, How Jesus Became God. It was released late last month and is already making waves. I was reading it on the bus and a fellow and I started a conversation about it. Bart has put together his case and it is important to know what he says as many will be echoing his thoughts after him. We will discuss his case, its methods and merits. It will be a journey through theology, New Testament Source Criticism and the philosophy of history. We look forward to a great discussion as this meeting will primarily focus on you as questioner and responder.Come ready to learn and then to be able to share with others what you discover. Hope to see you there! Same place, same time. Location details below to the Everyday Church (our venue for RF meetings): Jesus Became God

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