Johannes Kepler’s Somnium and Katharina Kepler’s Trial for Witchcraft: The emergence of a myth.

At the beginning of the month physicist and popular science writer, Paul Halpern posted the following tweet:

Kepler’s remarkable Somnium, one of the 1st sci-fi stories, later used as evidence in his mother’s witchcraft trial:

Now knowing a thing or two about Kepler’s Johannes and his more than bizarre life, I’ve even written a post on the witchcraft trial, I tweeted back:

It wasn’t used as evidence in his mother’s trial

Now Paul is a conscientious historian of science who likes to check his facts and so he tweeted back, in turn:

Here’s my source:  ‪@APSphysics

The American Physical Society is an honourable organisation and one would expect them to get their facts right and here is what they have to say about Somnium:

Kepler also tried his hand at more fanciful writing, penning an allegory called Somnium (The Dream) in 1611 — arguably the earliest work of science fiction, since it centered on a trip to the moon and speculated about what astronomy would be like if conducted on another planet.

Many years later, Somnium would be used as evidence in his mother’s 14-month imprisonment and trial for witchcraft; it described a woman who summons a demon for help in mixing potions. (He revised the work after her acquittal to make the allegorical aspects crystal clear for the too-literal minded.)

The records of Katharina Kepler’s trial for witchcraft are still extant and I can state with confidence that Somnium was not only not used as evidence in the trial but was in fact never even mentioned, so it would appear that the APS is in the business of creating history of science myths. To make matters worse it would appear, at least superficially, that such a use would have been impossible as the trial took place in 1620-1621 and Somnium was first published in 1634!


To be fair to the APS the myth that they are peddling on their website wasn’t entirely their own creation and has its origins in a somewhat cryptic remark made by Kepler himself in the Somnium and first brought to notice by the historian of science, Marjorie Hope Nicolson.

Before we proceed to uncovering the story of this myth and few words about Somnium and how it relates to Frau Kepler and her alleged witchcraft. The origins of Somnium are somewhat convoluted. Whilst still a student in the 1590s Kepler wrote a disputation arguing in favour of Copernican heliocentricity based on the science-fiction device of viewing a heliocentric earth from the Moon. Vitus Müller, a professor of theology, refused to allow the theme to be disputed because of the subject matter. Kepler was, however, obviously pleased with his invention as he reworked the idea into a science-fiction short story in 1609, Somnium, which he mentions for the first time as “a geography of the moon” in his letter congratulating Galileo on the Sidereus Nuncius in 1610. The background story, which introduces the tale, concerns a youth called Duracotus who lives on the island of Iceland with his mother Fiolxhilde, a ‘wise woman’, who sold herbal charms to sailors. Out of curiosity the fourteen-year-old Duracotus opens and thereby destroys one of the charms that his mother has sold to a sea captain. Enraged his mother gives him to the captain as a servant to replace the, already paid for, charm. The youth ends up in Denmark on the island of Hven with Tycho Brahe where he stays for five years studying astronomy. Returning home he and his penitent mother are reunited and she reveals some of her magical powers to her son. Through her rapport with a daemon of the moon she is able to assist her son in travelling there, at which point this frame story is dropped. I won’t go into the main part of the story as everything we need in contained in this brief opening sequence. Aspects of the opening are very obviously autobiographical if only in a very loose way. Kepler did work together with Brahe but in Prague and not on Hven and as a mature mathematician and astronomer and not as a youthful apprentice. Katharina Kepler did in fact deal in charms and herbal cures and so can be identified with Fiolxhilde the mother in the story. It would appear that Kepler is accusing his own mother of being a witch in 1609. However, if Somnium was first published in 1634 how could this fictional accusation be involved in the real life accusations against Katharina Kepler, which started around 1615 and would play a major role in the lives of both mother and son. Somnium lay dormant amongst Kepler’s papers until the 1620s when over the entire decade Kepler added a total of 223 often very extensive explanatory footnotes to the text, in volume significantly greater than the story itself. Kepler uses the eighth of these footnotes to explain why he thinks that he and his story are to blame for his mother’s misfortune.

Somnium was published posthumously by Kepler’s son having been prepared for publication by his son in law in the hopes of generating some income for his family who had been left in a dire financial position by Kepler’s death and although it very obviously influenced other proto-science-fiction stories in the following centuries it was largely ignored both by scientists and by the historian of science who were apparently too busy analysing his real science publications to bother with this strange little tale. The first scholar to take a serious look at Somnium was the historian of science and literature Marjorie Nicolson in a paper from 1940, Kepler, The Somnium, and John Donne[1]. Nicolson draws our attention to Kepler’s footnote eight, which I will now quote in full

If I am not mistaken the author of that insolent satire called Ignatius, His Conclave [John Donne], got hold of a copy of this little work of mine, he stings me by name at the very beginning. As he goes along he brings poor Copernicus before the tribunal of Pluto, to which, if I am not mistaken, there is access through the abysses of Hekla. You, my friends, who have some knowledge of my affairs, and know the cause of my last trip to Swabia, especially those of you who have previously seen this manuscript, will judge that this writing and those affairs were ominous for me and mine. Nor do I disagree. Ominous indeed is the infliction of a deadly wound or the drinking of poison; and the spreading abroad of this writing seems to have been equally ominous for my domestic affairs. You would think a spark had fallen on dry wood; that is, that my words had been taken up by dark minds which suspect everything else of being dark. The first copy went from Prague to Leipzig, thence was taken to Tübingen in 1611 by Baron von Volckelsdorff and his tutor in morals and studies. Would you believe in the barbershops (as if the name Fiolxhilde is particularly ominous to people there by reason of their occupation) my little tale became the subject of conversation? Certainly in the years immediately following, from that city and that house, there issued slanderous talk about me, which, taken up by foolish minds, became blazing rumor, fanned by ignorance and superstition. Unless I am mistaken, you will agree that my home might have been without that plague of six years, and I without my recent year-long trip abroad, had I obeyed the instructions I dreamed Fiolxhilde had given. It has pleased me, therefore, to avenge the trouble my dream has caused me by publishing this work, which will be another punishment for my adversaries.[2]

Before considering the content of this fascinating footnote it pays to ask the question, “was Kepler a reliable witness”? In any court case where an accusation is carried by the unsubstantiated testimony of a single witness, as is often the case with rape for example, it is customary to question the general reliability of the witness, so how reliable should we consider Kepler to be in this case. Based on a survey of his voluminous autobiographical writings not very reliable at all. When writing about himself and his family Kepler displays clear evidence of paranoia and a very powerful persecution complex so all statements made by him concerning his personal circumstances should be treated with a healthy dose of scepticism; he has a strong tendency to pessimistic exaggerations.

This tendency can be very clearly seen in the opening sentences of the footnote. Because Donne’s Ignatius, His Conclave takes place in hell and mentions Kepler and because Kepler mentions the volcano Hekla on Iceland a supposed portal to hell in Somnium then it follows that Donne must have read Somnium, a rather thin justification, don’t you think? In fact if we look at Donne’s actually reference to Kepler then the accusation looks even stranger. In the opening paragraphs to Ignatius, His Conclave Donne writes the following:

“… [I] had liberty to wander through all places [… … …] the Planets, and of all those which are fixed in the firmament. Of which, I thinke it an honest part as yet to be silent, then to do Galileo wrong by speaking of it, who of late hath summoned the other worlds, the Stars, to come neerer to him, and give him account of themselves. Or to Keppler [sic], who (as himselfe testifies of himselfe) ever since Tycho Brahes death, hath received it into his care, that no new thing should be done in heaven without his knowledge” [3][emphases in original]

The reference to Galileo is, of course, to the Sidereus Nuncius and the quip about Kepler is a direct translation from Kepler’s De stella in Cygno, published in 1606, so there is no need to invoke an imaginary contact with the Somnium, although Nicolson erroneously tries just that. As Edward Rosen, in his authoritative translation of the Somnium[4], points out Donne’s Ignatius was written and published before Kepler claims to have misplaced a copy of the Somnium, so the facts don’t stack up. Rosen also points out that Donne deliberately leaves words out of his Kepler translation, making Kepler look more pompous than he is was in reality.

The rest of the footnote is more interesting and Kepler sketches a path of how a copy of his manuscript might have (did) arrived in Swabia and there have caused all of his mother’s subsequent troubles. There are however major problems with this thesis. Firstly the court records allow a very clear reconstruction of all the events leading up to and during Katharina Kepler’s witchcraft trial and it was very clearly the typical sort of dispute amongst neighbours and ex friends that characterise the majority of witchcraft trials in the period, no need to invoke a Somnium influence at all to explain what happened. More important if the Somnium had played a role, as Kepler suggests, wouldn’t it have been presented as evidence at the trial? “See, even her son thinks she’s a witch!” Nothing of the kind took place so I very much doubt that there is any truth what so ever to Kepler’s claims and insinuations. Not so Nicolson, who is convinced Kepler’s claims are correct. In her paper she writes:

Clearly, then, some work of Kepler’s, written about 1610, was circulated in manuscript, and carried into the “tonstrinae[barber’s shop, emphasis in original] – those early predecessors of the coffee-house – fanned a spark already burning, which then blazed up into a fire which almost consumed Kepler and his mother[5].

Even if we follow Nicolson in accepting Kepler’s footnote as gospel truth what we have here is the Somnium as a spark that started the rumours of witchcraft against Katharina Kepler and not a piece of evidence submitted at her trial.

It had taken more than three hundred years before somebody, Nicolson, took serious notice of Kepler’s footnote but it would only be twenty years before it was referenced again, also by Nicolson, in her monograph, Voyages to the Moon. In this book, which is justifiably regarded as a classic Nicolson very much features the Somnium devoting a substantial number of pages to it and its influence on later lunar voyage literature. In this account after a brief sketch of the witchcraft troubles of Katharina Nicolson write the following:

It was in 1615 – after the first version of the tale had circulated for some time in manuscript – that Kepler’s mother was charged with sorcery and came near to condemnation.

[ … … … ]

If Kepler had intended to publish the Somnium, any such idea was now out of the question. One of his most cryptic notes, in which long bitterness may be read into every line, implies the reason[6]. …

[There now follows the footnote quoted above interspersed with quote from her earlier paper]

Voyages to the Moon was, within academic circles, very widely read and so the claim that Somnium was responsible for Katharina’s troubles was now in the Keplerian public forum.

The next to pick up on this theme was the science writer John Lear who commissioned and annotated, what he thought was, the first English translation of the Somnium[7] in 1965. (As Lear himself admits, during the writing of his book he discovered there had been two earlier English translations one published and one unpublished) Unlike Nicolson, Lear rejects the possibility of Donne having read the Somnium, however he also accepts Kepler’s paranoid suspicions that his little tale was responsible for his mother’s woes devoting several pages of his introduction to the theme adding a great deal of detail of his own invention to the story in a way that makes it difficult to separate the known facts from his speculations. Lear even goes as far as accusing Max Casper, whose biography of Kepler he uses extensively in his book, of failing to correctly join up the dots and nail the lost manuscript of the Somnium as the tinder that started the flames that consumed Katharina.

In his definitive scholarly translation of the Somnium historian of science Edward Rosen, as stated above, demolishes the accusations against Donne but accepts the other accusation without a great deal of comment.

In 1976 popular science writer, Gale E. Christianson, repeated the story in a paper published in the journal Science Fiction Studies, Kepler’s Somnium: Science Fiction and the Renaissance Scientist.

The lunar geography was probably read privately in manuscript form for the last time in 1610. Through a rather complicated and unfortunate series of events, Kepler lost control of a copy in 1611 and a number of individuals—many of them unknown to Kepler personally—gained access to it, including some that the author would not have approved of. The Somnium was written for scientists and was little understood, except on the most superficial level, by those lacking a scientific background. Kepler suggests that it became the subject of gossip in the tonstrinae, the forerunner to the modern coffeehouse.19 Some of those who knew Kepler and his family, or at least thought they did, discovered sufficient autobiographical material in the manuscript to feed the fires of ignorance and superstition then engulfing Germany. They equated Johannes with Duracotus and made particular note of the similarities between Katherine Kepler, the astronomer’s mother, and Fiolxhilde, the fictional peddler of magic charms and herbs. Especially damning was the description of Fiolxhilde as a “wise woman” in league with celestial spirits, nor did Kepler’s joke about the Daemon’s preference for old witches as traveling companions help. To make matters worse, Katherine Kepler was well known for her vile temper and generally cantankerous disposition, not to mention the fact that the aunt who had cared for her as a child was burned at the stake as a witch. The stage was set, charges were leveled, and in 1615 Katherine Kepler was arrested on suspicion of practicing witchcraft. In his attempt to evade the scorn of the Aristotelians by concealing his pro-Copernican work in the guise of classical mythology, Kepler had inadvertently set a trap for himself and his mother, for they had become the unwitting victims of the seventeenth-century European witch-craze.

Johannes Kepler’s reputation as a noted mathematician-astronomer by no means served as a guarantee that Katherine Kepler would escape the fate of thousands of others who had already died at the stake for their alleged complicity in what authorities envisioned as a mass satanic conspiracy. Kepler was well aware of the seriousness of the charges and he put all else aside to work for Katherine’s exoneration. A long, tedious, and taxing legal battle resulted: only after five years, part of which his mother spent in prison, was the old woman released; but the damage had been done. Katherine Kepler died in April of 1622 from causes directly attributable to the rigors of her imprisonment; her son had been able to do little significant work while trying to obtain his mother’s release; and the publication of the Somnium, at least for the present, was out of the question. Historical circumstances, as during his student days at Tübingen in 1593, had again deprived Kepler of the opportunity to publicly air his views. Under these conditions, could it have truly mattered to Kepler whether or not his desire to speak out had been thwarted by a narrow-minded faculty senate impervious to all scientific inquiry deemed anti-Aristotelian, or a group of superstitious and half-crazed witch-hunters who had mistaken fantasy for reality?

Here, although according to her own footnotes her account is based on Nicolson’s Voyages to the Moon, there are no ifs, buts or maybes, Christianson lays the blame for Katharina’s troubles clearly on the “lost” Somnium manuscript.

Kepler’s original footnote is clearly highly speculative and although she hardens it up Nicolson still only sees it, to quote Kepler, as “a spark” that started the rumours against his mother and not an item of evidence at the trial. Although both Lear and Christianson add layers of speculative detail to Nicolson’s account neither of them takes the step of introducing the Somnium into the actual court proceedings. This leaves the question open as to whether the anonymous author of the APS piece consulted another text, as yet unknown to me, which took the fatal misstep from the Somnium as a spark that started rumours to the Somnium as substantive evidence at Katharina Kepler’s trial for witchcraft or whether this anonymous author consulting one or more of the texts that I have quoted put two and two together and made five and in the process set another myth of science free to muddy the waters of science history.


The Somnium is by the way an interesting document in the history of science of the Early Modern Period and well worth reading.

[1] Nicolson, Marjorie Hope, Kepler, the Somnium and John Donne, Journal of the History of Ideas, 1940, Vol. 1 pp. 259-80. Reprinted in Roots of Scientific Thought, eds. Philip P. Wiener and Aaron Noland, New York, Basic Books 1957, pp. 306-27.

[2] Lear, pp. 90-91

[3] John Donne, Ignatius His Conclave, An edition of the Latin and English texts with introduction and commentary by T. S. Healy S.J., Oxford at the Clarendon Press, 1969, p. 7

[4] Kepler’s Somnium: The Dream or Posthumous Work on Lunar Astronomy, Translated with a commentary, by Edward Rosen, University of Wisconsin Press, Madison, Milwaukee, and London, 1967, Appendix E, Kepler and Donne, pp. 212-13

[5] Nicolson 1957 pp. 312-13

[6] Marjorie Hope Nicolson, Voyages to the Moon, The Macmillan Company, New York, 1960, p. 44

[7] John Lear, Kepler’s Dream: With the full text and notes of Somnium, Sive Astronomia Lunaris, Joannis Kepleri Translated by Patricia Frueh Kirkwood, University of California Press, Berkeley ans Los Angeles, 1965.


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27 responses to “Johannes Kepler’s Somnium and Katharina Kepler’s Trial for Witchcraft: The emergence of a myth.

  1. You patrol the popular press to arrest myths about the history of science—this post is an excellent example of that—but there are also myths about the history of literature that are more down my line. The American Physical Society claim that Keplers Somnium was “arguably the earliest work of science fiction.” In Halpern’s tweet, the Somnium becomes “one of the 1st sci-fi stories.” Both claims are pretty peculiar. They assume (apparently) that the Somnium was the first of its kind because it’s the oldest example they happen to know about. In fact, there are umpteen earlier versions of the voyage to the moon theme. Ariosto’s Orlando Furioso, written in the century before Kepler, features an episode in which the paladin Astolfo flies on a hippogryph to the moon in search of Orlando’s lost wits—the moon is where everything lost winds up, including combs and lost socks. A moon trip also shows up in Folengo’s comic epic Baldo, one of the funniest books every written IMHO, though its commercial possibilities are somewhat limited by the fact that it was written in a mix of classical Latin and dirty Italian. It would be easy to give many other examples of moon trips from Renaissance-era writings. The vogue for the theme is easily explained. It goes back to the True Story, a prose work by Lucian, a second century Greek author who got translated into Latin in the middle of the 15th Century and was read by everybody. Of course, Lucian didn’t invent the idea of going to moon. He just popularized it. I’ll be merciful, however, and let the earlier part of the story of the story disappear in the mists of pedantry.

  2. edaviesmeuk

    Have you any comments on Arthur Koestler’s _The Sleepwalkers_ which, as I recall, contains an account of Katharina Kepler’s trial? Could it possibly be the source the APS writer used? I haven’t read it for quite a few years so my memory of the details is vague and my copy is in storage so I can’t look it up easily.

    • Naturally, I checked both Casper’s Kepler biography and Koestler’s The Sleepwalkers, the first biography of Kepler I ever read, researching this post but both of them give conventional accounts of the Somnium and the witchcraft trial completely separate from each other.

  3. Having been blissfully unaware of Katharina Kepler’s trial, Somnium or any of the other material, I found this post just fascinating. Thanks so much Thony.

  4. laura

    I’m a huge obsessive fan of Kepler and I love Somnium but it’s hard to beat this (from the linked article) for hagiographic nonsense:

    Kepler was too good a scientist not to understand that the dual effects of the lunar climate and the irregular, hostile terrain would produce plants and animals far different from those that inhabit the earth. He rejected the temptation, which others had not, of simply recreating a terrestrial civilization on the moon; for in Kepler’s Lavania there are no men and women, no civilization as he knew it. Thus nearly two centuries before Buffon, Lyell, and Darwin, Kepler had grasped the close interrelationship between life forms and their natural environment.

    What’s funny to me is that modern geocentrists (who exist!) use this argument as evidence that Kepler was “Darwinian” and thus evidence that the acceptance of heliocentrism necessitates the acceptance of evolution by natural selection.

  5. This is a fascinating history and thank you so for organizing it.

  6. Will Thomas

    Thony, was this myth ever called out by a historian (i.e., who sorted through the records of Kepler’s mother’s trial), or is it something that simply doesn’t appear in careful biographies?

    • The APS website is the only instance that I’ve come across of somebody claiming that Somnium was actually used as evidence in the witchcraft trial of Katharina Kepler. However this website is almost certainly, in our Internet age, highly influential as a quick history source for physicists, which is why I decided to call it out.

      I do however find it interesting that the major Kepler biographies ignore Kepler’s own suspicion that he, or better the Somnium, was responsible for the original rumours that his mother was a witch.

  7. It is always highly amusing to see claims about the beginnings of “science fiction” like the one that appears in this article. Perhaps the historians of “science” would do well to become acquainted with the history of “literature.” For example, in Dante’s Paradiso written some 300 years (!) earlier than Kepler’s Somnium, Dante describes a fanciful trip to the moon he took with Beatrice.

  8. In my defense, I saw the APS “This Month in Physics History,” thought “wow, I didn’t know that about Somnium,” assumed from the source that it was factually correct (but little known), and wrote the tweet.

    Thanks to Thony for his careful research! I’ve learned much about Kepler from the post. I’m only relieved that the “HistSci Hulk” didn’t come after me🙂

  9. Jeb

    John lane, The Forgotten Voyage of 1609, The Saturday Review May 4th 1963.pp 39. in particular with regard to relationship with witchcraft trail.

    • Thank you Jeb, that is indeed an interesting earlier source for this false claim.

      • Jeb

        I would love to read a credible account of the witchcraft trial and the legal documents. It appears to be seriously needed. Alongside a critical examination of Kepler’s text on the moon.

        A fascinating and rich slice of history.

        “Circulation of the Somnium manuscript had, after all, caused the prosecution of Kepler’s mother on the charge of witchcraft”

        In the introduction to a recent edition of Francis Godwin’s the Man on the Moon edited by William Poole.

        The introduction suggests that the source for this historical claim are Kepler’s notes in the dream and gives no further references.

        Claim seems to be rather wide spread.

      • That version is OK because that is Kepler’s own claim but it doesn’t claim that the Somnium was used as evidence in the trial itself.

        The trial documents are included in Vol. 12 of the complete works of Kepler. There is a good account in German of the whole sad story based on the court records published by the Kepler Society in Weil der Stadt in 1979, Bertoldt Sutter, Der Hexenprozeß gegen Katharina Kepler.

  10. Jeb

    p.s Carl Sagan’s Cosmos, on the persecution of Johannes Kepler. Seriously sloppy piece of script writing in regard to the witchcraft accusation and the Somnium.

    • Jeb

      “That version is OK”
      Its somewhat terse given the confusion. From the little I have read the accusations look rather standard and typical; matter of local dispute coupled with local elites with too much control over the judicial mechanisms (an issue in Scotland at least that looks to be the case here as well).

      The standard social mix and differing belief systems of a range of social classes, which is such a feature of this form of activity in this period in many parts of Europe. Legal issue of over-enthusiastic local elites with to much judicial power also standard.

      If their is any politics in regard to Kepler I would suspect its opportunistic and post dates accusation and initial legal issues.

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  16. I think it’s interesting that a fallback position seems to be psychoanalysis of Kepler, a stance that most historians of science now reject. What seems to me to be shown by your careful investigations is in fact not that the claim the leaked ms of Somnium led to Katharina Kepler’s arrest for witchcraft is false, only that it can’t be proven: since historians cannot penetrate barber-shop conversations. As such we can only note that Kepler himself said this, but while necessarily suspending judgement about its veracity. I don’t think that looking at the court proceedings would help, since Somnium was unlikely to have been invoked as evidence. But knowing that witchcraft accusations were much more likely to be upheld in court with the backing of learned folk, one might suspect some link to a written source here.

  17. Interesting and informative post, as always.
    For me, the big surprise the story that Kepler’s mother was suspected of witchcraft is not a myth. An unusual background story for a scientist surely – but it would be interesting to know what percentage of women in her region were tried for witchcraft at the time!

    • You can find the numbers for witch trails in the area at the time in Ulinka Rublacks excellent The Astronomer and the Witch: Johannes Kepler’s Fight For His Mother (OUP 2015), which I shall be reviewing soon here.

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