Johannes Kepler, His Mother Katharina, and Witchcraft!

Johannes Kepler… German mathmatician, astronomer, astrologer… he wrote the laws of planetary motion, was appointed mathematician to the Holy Roman Emperor, and he is considered the father of modern optics. But also….the son of a WITCH? It’s hard to believe, but Johannes Kepler put his career on hold, and spent 6 years defending his widowed mother against charges of witchcraft.


I came across the story by chance. While my daughter and I were stocking up at the local bookstore, a title caught her eye, she looked over her shoulder and said, “this book totally sounds like you”. Naturally, I grabbed it. The book, “Everyone Knows Your Mother Is a Witch” by Rivka Galchen views Katharina Kepler’s life, and the charges against her, through her eyes. And wouldn’t you know it, my daughter was right. The book falls right into my reading taste…. Historical, a little funny,, and both interesting and engaging.

So… let me tell you a little more about the accused Katharina Kepler, her very important son Johannes, witchcraft, and this intriguing book.

Who was Johannes Kepler?

As a child, the Keplers were of modest means, but luckily their son Johannes showed real promise in school, and was granted a scholarship to the Lutheran Stift (Seminary) in Tübingen. While his gift was for mathematics, Johannes felt his calling was religion. At Tübingen he studied under famous German mathematician Michael Mästlin, who believed Copernicus’s theory that the sun was at the center of our solar system. Kepler wanted to prove that Copernicus was right, but in a way that followed religious doctrine.

“Nature is a book that the divine plan is written on”

His first book, Mysterium Cosmographicum in 1596 laid out some of the ideas he had about the Universe. He developed calculations about the rotations of planets and distances between them.  But he wanted to go further. He wanted to prove that God’s hand was in the heavens. He worked in Prague under the Danish Astronomer Tycho. And when Tycho died, he inherited the notes, and began working with them as imperial Mathematician to the Holy Roman Emperor Rudolph II.

Portrait Confused With Johannes Kepler 1610
Unidentified painter, Public domain, via Wikimedia Commons
In 1611 Kepler’s wife and 3 of his children died from Smallpox, and right around that time that Rudolph II abdicated. Kepler found himself out of a job. He looked in Tübingen, but his religion was becoming a problem. (Look at the timeline on this… remember the Thirty Years War begins in 1618). Although Kepler’s family was Lutheran, he refused to sign the Formula of Concord (basically the Lutheran articles of faith and belief) so he wasn’t allowed to receive sacraments in the Lutheran church, therefore wasn’t able work in a Lutheran institution. When he married to a woman named Susanna Reuttinger, he converted to Catholicism.  He found work in Linz under the new Holy Roman Emperor, and he got to work with Tycho’s Tables and notes.

Harmonicae Mundi or Harmonies of the World, the Laws of Harmonics was a result of  decades of work, combining principles of geometrical, musical, metaphysical, astrological, astronomical, and even the soul. Everything was related… and everything could be described in geometric terms with ratios. (Galileo and Descartes were influenced by this work, and Newton used it as well, leaving out the theology.) He also published the Epitome Astronomiae, which describes astronomy in a systematic way,  and the Rudolphine Tables based on Tycho’s observations that predicted the location of the planets at any time.

Kepler Mysterium Platonic SolidsKepler, Mysterium Cosmographicum, Tübingen, 1596

Kepler saw the Christian Trinity as a sphere,  interconnected and equal, in balance with nature. (The importance of the Trinity, and the various disputes of exactly how it works are well documented by the book 381 AD by Charles Freeman. It really was a bigger deal than we imagine today).

But we mostly remember Kepler for discovering the 3 laws of Planetary Motion
1. The planets move in an elliptical orbit, with the sun as the focus.
2. The time necessary to traverse any arc of a planetary orb is proportional to the area of the sector between the central body and that arc (area law)
3. Harmonic Law-  There is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits.
(I copied this verbatim from Britannica Johannes Kepler because I didn’t want to mess it up, and honestly, it’s above my physics education level to explain.)

(Note– he didn’t call them laws at the time, he just wrote them up as ideas. And while we look at this and say… yes, the planet thing is obvious… and I vaguely remember the arc measurement thing from a wildly difficult geometry class, remember, he came up with these formulas and ideas without the help of your geometry teacher or the internet.)

While he worked on all of these things, Kepler also calculated the birth year of Jesus Christ, worked out that the mood and tides were closely related, explained HOW the telescope worked… which directly related to how human optics work. He explained the EYE. He coined the term “satellite”. And he formed the base of Integral Calculus (yup, his fault you had to suffer). 

But… then his mother was arrested for Witchcraft.

Katharina Kepler

Widowed Katharina raised three children, lost a husband to war, and now lives alone with her cow and her herbs. In 1615 her abrasive nature makes her a target for local baker’s wife, Ursula Reinbold who claimed that Katharina poisoned her after an argument, and accuses her of Witchcraft. At first, Katharina brushes this off. And countersues Ursula for making false accusations. But more and more witnesses come forward…altogether 24! (including one from her other son, Johannes’s brother!), with strange claims about the old widow. Suspicious behaviors like how she walked around alone at night, how she caused intense pain in the Butcher’s knee, marked a young woman with her touch, and that she asked the gravedigger if it were possible to put silver over a skull to make it a drinking vessel. (FYI. You can, but it isn’t dishwasher safe) Included also is a story her younger son Hans told of her riding a cow backwards, then roasting it. Rivka Galchen introduces chapters with reworked depositions from the original documents so you can see just how flimsy the accusations were.

Katharina Kepler Eltingen

Katharina Kepler Eltingen Harke, CC BY-SA 3.0  via Wikimedia Commons

Between 1560 and 1700 over 70,000 people were accused of witchcraft, and around 50,000 were executed. Half of them were in Germany… and ¾ of them were women. Katharina faced a very real danger of being put to death for her “crimes”.

When the accusations became serious, her son Johannes put aside his work, and came to her defense.

It seems that Katharina got the same sort of judgement as the witch in the the scene from the film Monty Python film “The Quest for the Holy Grail” . The villagers bring Lord Bedevere a woman they’ve accused of being a witch. “Well, how do you know she is a witch”, Bedevere asks. “SHE LOOKS LIKE ONE!” they shout. Then one villager says “She turned me into a newt!” looks around  “I got better”….

The non-fiction book, The Astronomer and the Witch: Johannes Kepler’s Fight for his Mother, by German historian Ulinka Rublack covers the trial in a more scholarly tone, but Galchen’s “Everyone Knows Your Mother is a Witch”,  uses the original source materials and declarations to weave a page-turning tale. In the book, Katharina’s a strongly independent woman, having lost her husband early. She also says exactly what she thinks, and gives advice where perhaps it’s unwelcome. This nature makes her unpopular with some of the local villagers. (Honestly, I think it’s a trait among many German women of a certain age). I found it interesting that she refers to her son as many mothers would… not with “awe” at his prestigious title… but as her son who should help his mama.

And she wasn’t merely locked up, she was chained to a dungeon wall and guarded by two men (all of which was financed by the sale of her home). Katharina’s troubles go on for years. An old woman chained to a wall with guards. Madness. During that entire time Johannes Kepler acts as her lawyer, traveling across the country to use his influence to have her freed. The time and trial bankrupt Katharina, and Kepler’s work suffers. After 6 years she is finally freed to live with her daughter in 1622.

Kepler spends the rest of his life trying to pick up pieces. He’s unable to find work. In 1627 he manages to get a new patron, Albrecht von Wallenstein. Kepler is sent to Sagen in Silesia where Wallenstein had a printing press built for him to get his papers printed. In exchange, Kepler wrote Wallenstien horoscopes (oddly, he was fairly close at predicting Wallenstiein’s death). Johannes Kepler never managed to collect all the money owed to him for his work before his death a few years later in 1630.

Shortly before his death, Kepler wrote the epitaph for his own grave…

“I used to measure the skies, now I measure the shadows of Earth.
Although my mind was sky-bound, the shadow of my body lies here.”

Read more about Kepler and his Mother here

The Astronomer and the Witch: Johannes Kepler's Fight for his MotherThe Astronomer and the Witch: Johannes Kepler’s Fight for his MotherThe Astronomer and the Witch: Johannes Kepler's Fight for his MotherEveryone Knows Your Mother Is a WitchEveryone Knows Your Mother Is a WitchEveryone Knows Your Mother Is a Witch



Everyone Knows Your Mother is a Witch by Rivka Galchen

Kepler and K2- NASA website

Britannica- Johannes Kepler


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