Johannes Kepler

The podcast on Johannes Kepler and Tycho Brahe:

For more on Brahe, see Tycho Brahe

  1. Horoscopes
  2. Prophecy of wallenstein
  3. “Musical Harmony”
  4. Kepler’s nova:
  5. The dream
  6. Mother witchcraft trial
  7. Kepler and Brahe in Prague

Johannes Kepler (from 1571 – to) died near Stuttgart

Studied in tübingen where it was noted that in his university years he was good at casting horoscopes


I’ll point out at this point that he had a professor named Mästlin. The university officially still taught the ptolemaic system, but Mästlin was one of the few of his time that taught that copernicus should be taken literally.

Cardinal Nicholas of Cusa came a century before copernicus, and already argued that the earth was not motionless in the center of the universe. Kepler came across his works too.

Kepler was theologically minded, and took an idea very similar to ancient pythagoreans and reinterpreted it for christianity: since the sun was the brightest object in creation, it only made sense that it signified the creator and should therefore be in the center.

“there was nothing I could state that I could also contradict” always say both sides of the coin.. which was not a positive in later political life

Protestant (Lutheran) mathematician, school master in Graz. had a reputation from using astronomy to predict crops and wars

Also district mathematician, which meant he had to compile the calendar for the next year and come up with astrological predictions: war, disease, weather, when would be good/bad times for surgery, when one should anticipate religious or political upheaval, and when the turks would attack

Now’s a good time to point out that Kepler did not believe in horoscopes.. he called it ‘feeding the fatheads superstitions’ and the ugly daughter of astronomy etc. very different than his contemporaries. He still seemed good at it. I just wanted to point this out. I get asked this. How much of this stuff did the people believe that ran horoscopes? In Kepler’s case he didn’t… he still paid attention to the stars on his wedding date. So maybe he did heed them a little.


read horoscopes for the imperial court….in fact he had written horoscopes (and was apparantly good at them) since at least his university days in Tübingen

For example for 1595 he predicted a harsh winter, an attack from Turks from the South and a peasant uprising. All came true.

planetary motion.. e.g. that they travel in elipses, not circles (like copernicus’ theory)

Prophecy of wallenstein

So wallenstein was a big cheese generalisimo in the 30 year’s war. He was more powerful militarily than the emperor. you can still see his spralling palace grounds in prime real-estate below the castle in lesser town in prague.

Well kepler forsaw his death in a horoscope.

Not entirely up to today’s snuff:

polygonal structure of the solar system (see pic.)

Kepler thought he had revealed God’s geometrical plan for the universe. Much of Kepler’s enthusiasm for the Copernican system stemmed from his theological convictions about the connection between the physical and the spiritual; the universe itself was an image of God, with the Sun corresponding to the Father, the stellar sphere to the Son, and the intervening space between to the Holy Spirit.

…platonist ideas

polyhedrons and ‘perfect solids’ (pythagorean or platonic solids): shapes that fit within spheres :

example: dodecahedron (twelve sided regular solid) fits over mars’ spere. with earth’s sphere a icosahedron (twenty sided) etc.. there are 5 perfect solids, and therefore 6 planets. BAM


So, if each solid has a shere around it (the path of the planets in 3D.. then that describes the distance apart from each other.


anyway, Kepler wanted to be a Theologian originially.. now he thought God was revealing himself through nature. So by writing about the perfection of astronomy (through math) he was saying something about God.

Galileo wrote to Kepler and Kepler replied, talking of Copernicus.

“Musical Harmony”

The planets travel at different speeds. He pointed at gravity, but called it “holy spirit force” instead :)

He noticed that the ratios of distance and speed fit, and would sound ‘harmonious’ if they were corresponding to string lenghts:

the interva; between saturn to jupier was a fourth

jupiter to mars an octave

mars to earth a major third

venus to mercury a fourth

this theory jived a bit better with copernican observations than did his polyhedral theory

math influenced:  Pascal, Leibniz, Monge and Poncelet,

point of infinity (if a straight line goes on forever they will meet, thus having the properties of a large circle)

first published description of hexagonal symetry of snowflakes

Kepler’s nova:

Astrologically, the end of 1603 marked the beginning of afiery trigon, the start of the ca. 800-year cycle of great conjunctions; astrologers associated the two previous such periods with the rise of Charlemagne (ca. 800 years earlier) and the birth of Christ (ca. 1600 years earlier), and thus expected events of great portent, especially regarding the emperor.

Now, we’ll jump ahead a bit to wrap up Kepler’s solo life and then come back to Kepler and Brahe when they are in prague together.

The dream

Around 1611, Kepler circulated a manuscript of what would eventually be published (posthumously) as Somnium (The Dream). Part of the purpose of Somnium was to describe what practicing astronomy would be like from the perspective of another planet, to show the feasibility of a non-geocentric system. The manuscript, which disappeared after changing hands several times, described a fantastic trip to the moon; it was part allegory, part autobiography, and part treatise on interplanetary travel (and is sometimes described as the first work of science fiction).

Carl Sagan and Isaac Asimov have referred to it as the first work of science fiction.

Mother witchcraft trial

Years later, a distorted version of the story may have instigated the witchcraft trial against his mother, as the mother of the narrator consults a demon to learn the means of space travel.

Kepler’s mother supposedly had a knack for herbs and folk medicine, she had a reputation of being rude and meddlesome.. and anti social.

That’s enough in southern Germany at the time to degenerate into a witch trial.

When the charges stacked up (49 in all) they included causing pain without touching people, riding a calf to death, muttering fatal “blessings” over infants, unnatural death of animals, trying to talk a young woman into becoming a witch. And one which was true: she heard in a sermon of an archaic tradition of making goblets of deceased relatives’ skulls, she asked a grave digger for her father’s skull, so she could have it inlaid with silver for her son, the famous court mathematician.

Following her eventual acquittal, Kepler composed 223 footnotes to the story—several times longer than the actual text—which explained the allegorical aspects as well as the considerable scientific content (particularly regarding lunar geography) hidden within the text.

In his calendars—six between 1617 and 1624—Kepler forecast planetary positions and weather as well as political events; the latter were often cannily accurate, thanks to his keen grasp of contemporary political and theological tensions. By 1624, however, the escalation of those tensions and the ambiguity of the prophecies meant political trouble for Kepler himself; his final calendar was publicly burned in Graz.

Kepler and Brahe in Prague

Graz was no place for a Lutheran like Kepler… Frederik II instituted the catholic counter-reformation and made life very hard for protestants. Kepler started looking around for another place of employment not long after Brahe first read his book.

in 1600 the situation in Graz worsened regarding Lutherans and finally decided to take the risk and visit [Tycho Brahe]().

Kepler arrived in Prague, a bustling city full of new renaissance buildings surrounding the castle complex up on a hill overlooking the Vltava river. It’s hard to describe the castle if you’ve never been to Prague or seen a river. Today it is still be biggest castle complex in the world. Like a city in a city with the cathedral in the middle (plenty of pics on, including the banner if you’ve never seen it)

And now we have a great creative mathematical mind together with the astronomer with the most precise charts of the sky.

Jan Jesensky (explain who he was?) the emperor’s physician and later leader of the uprising that lead to the 30 years war came to benatky to discuss a contract of employment between kepler and brahe on kepler’s behalf… which at first did not end well, but in the end they came to an arrangement.

When the Emperor Rudolf required of tycho to be at court twice a day, he stayed at the golden griffin (on one of my old tours) within sight of the castle. His duties mainly involved advice based on horoscopes. And while Tycho did believe in this (probably more than Kepler) he thought this boring and tedious. Another thing is that Tycho believed that free will trumped the influence of the planets by a long shot.. so predicting battles was ludicrous.. but Rudolf believed in it strongly and he was paying the bills.

Eventually Kepler lived a few blocks further from the castle.. where now a statue of brahe and kepler stands.

Tycho mounted some of his instruments on the balconies of the Belvedere and used it as an observatory. (the same he had turned down on his way into Prague)

Kepler’s dabbling in optics.. ilke how the eye works. used a camera obscura to draw a solar eclipse

kepler discovered how the eye works. Before it was thought that the image was caught in the liquid in the eye, but kepler realized it was reflected upside down in the back of the eye through a lens.

he used those theories to describe how telescopes work, and his work became the foundation of 17th century optics.

According to hasner, kepler was there when he died and it was brahe’s dying wish for kepler to finsh his model (theory)

In fact there had been trust issues between Brahe and Kepler in the beginning, but Brahe soon realized that if he wanted to see his Tychonian model of the solar system finished and published he would have to trust kepler to finish it after his death.

From here on out they worked together, for which they are now famous.

See [Tycho Brahe]() for more on their time together.

After Brahe died, Kepler became Rudolf’s court mathematician. He had full use of brahe’s tools and charts and was to complete the Rudolfine Tables… and create horoscopes

when galileo’s news reached kepler that Galileo had discovered four moon around Jupiter, Kepler’s response was: surely Jupiter has inhabitants then… because why else would God create 4 moons? Just to be enjoyed by the few earth dwellers who have telescopes? surely not!

Kepler left Prague for Linz.. and moved around a few times during the 30 years war. He came to Prague once and would have seen Jesensky’s head on a pike on the charles bridge.

On the night he died there was a meteor shower. His epitaph (that he wrote himself) reads:

‘I measured the heavens, Now the earth’s shadow I measure,

Skybound, my mind, Earthbound, my body rests”

Carl Sagan described kepler as “the first astrophysicist and the last scientific astrologer.”

He made it onto an East German stamp

In 2009, NASA named the Kepler Mission for Kepler’s contributions to the field of astronomy. And with the Kepler space telescope, maybe we’ll finally find the inhabitants of Jupiter

In New Zealand’s Fiordland National Park there is also a range of Mountains Named after Kepler, called the Kepler Mountains and a Three Day Walking Trail known as the Kepler Track through the Mountains of the same name.

…and more…


The crater Tycho on the Moon is named after him, as is the crater Tycho Brahe on Mars. The Tycho Brahe Planetarium in Copenhagen is also named after him.

HEAT1X-TYCHO BRAHE is the name of a manned private spacecraft to be launched by Copenhagen Suborbitals. Other things named after him include a bar inZagreb and a ferry operating between Sweden and Denmark.


Josef Hasner: Tycho Brahe und J. Kepler in Prag – a german book printed in prague in 1873

Kitty Ferguson’s Tycho & Kepler

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