Maggie and Me (a philosophical dialogue): On Johannes Kepler

IMG_3744John:  Let’s slow our walk down just a bit.  I am getting older and I will never be able to talk about Johannes Kepler if we continue at this speed.

Maggie:  No worries (slowing her pace).  Is that better?

John:  Yes, thanks. 

Maggie:  So on to Kepler. 

John:  I know these are just boring facts, but he was born in 1571 and died in 1630.  So he lived the latter part of his life during the Thirty Years War (1618-1648), when he was doing most of his important work.


Maggie:  That had to make doing his work even harder.

John:  Yes, I am sure it was extremely challenging at times.   

I saw you doing some reading yesterday.  Why don’t you tell me one thing that interested you about Kepler?

Maggie:  I like the fact that he wasn’t afraid to be wrong, like so many people today.  He wanted to make advancements in astronomy, so he wrote his books based on the knowledge that he had at the time.  These books had errors in them, and when he learned more, he acknowledged the errors and corrected them.  But he wasn’t embarrassed or ashamed at all.  As long as astronomy was moving forward, he wasn’t afraid to throw out his thoughts for all to consider.  I wish I had that kind of courage.

John:  Me too. 

Maggie:  What is your favorite thing about Kepler?

John:  He had a normal background to which most of us can relate.  His family had money at one point, to be sure.  But by the time he was entered school, it appears that they were no longer part of the upper-crust society.  He didn’t have the advantages that come with being raised in wealth, like Tycho Brahe.  He was just super smart and super motivated, and he worked hard to accomplish what he accomplished.  I like that.

Maggie:  I find people like him motivating.  Did he study astronomy in school?

John:  Only indirectly. He came to astronomy in a weird way.  

He entered the University of Tubingen with the intention of becoming a Lutheran minister.  As part of his training, however, his classes included mathematics and astronomy.  He turned out to be a mathematical genius, and so much so that, during his third year of studies, the authorities in Tubingen nominated him to take over for a math teacher in the city of Graz who had recently died.  Although he was worried about it, he accepted the position and began his mathematical and astronomical career. 

Maggie:  That’s a beautiful-mind story. 

John:  Yes! And it just gets better.  Remember what you liked about him?

Maggie:  That he wasn’t afraid to be wrong.

John:  Well keep that thought in mind.

When Kepler was just 25, not long after starting his teaching position, he wrote a book entitled Mysterium Cosmographicum. He agreed with Copernicus that the sun was at the center of the universe, but he suggested that the sun was larger than the rest of the planets.  Much, much larger.  And due to its size, it exerted a physical (also called a dynamical) influence on the other planets.

Maggie:  Like gravity?

John:  Yes, good, something like that.  He explained that this force pushed the planets around the sun in their orbits.  He further explained that this force was more effective on the planets closest to the sun, and that it grew less powerful as it moved out towards the furthest planets.  This is why, he concluded, the planets furthest from the sun moved more slowly than those closer to the sun.

Maggie:  The theory seems kind of reasonable.

John:  It does have a reasonable ring to it. 

He threw these ideas out to the scientific world at an early age, but he continued to modify and change these theories—and their supporting mathematical formulas—throughout the rest of his life. 

And do you want to hear something funny?

Maggie:  Sure.

John:  Do you remember Tycho Brahe’s theory about the universe?

Maggie:  Sure, we just talked about that last month.  He thought that all the planets revolved around the sun, except the earth, which was at the center of the universe.  The sun and the other planets, while still in their own motion, then revolved around the earth. 

John:  Right.  Well Kepler was not shy about sharing his ideas, so he sent a copy of his book to Brahe, whom he knew would disagree with his theories.

Maggie:  What happened?

John:  A complete surprise.  Brahe was so impressed with the math and formulas in the book that he invited Kepler to come visit him, which Kepler eventually did in February of 1600.

Kepler’s first visit lasted just three months, and he studied Mars during that time, trying to understand and predict its orbit.  But after he returned to Graz, things got politically and religiously dicey for him, as it did for all Protestants in Graz at that time.  So he packed up and returned to Brahe’s observatory in October.

Maggie:  How long did he study with Brahe?

John:  Not long at all.  Do you remember when Brahe died?

Maggie:  That’s right, he died in 1601.

John:  Correct, just a year after Kepler arrived. After Brahe died, it only took 48 hours before Kepler was appointed as Brahe’s successor, which was very fortunate for Kepler.  He now had at his disposal all of Tycho Brahe’s meticulous observation tools and records.

Maggie:  That’s right.  Brahe carefully observed and tracked the planets and stars, writing down his observations. 

John:  And using these records, along with his theory about the heliocentric universe and his incredible math skills, Kepler went on to further developed his astronomy. 

In 1609, he published a book entitled Astronomia Nova, or the New Astronomy. This book presented ideas that were completely radical for his day.  Let me explain the two most important ones. 

First, Kepler showed that the planets revolved around the sun in elliptical orbits.  This is known as Kepler’s first law, and it broke with the long-standing belief held since the time of Aristotle that the planets followed perfectly circular patterns.     


Kepler's Universe


Second, building off his previous work, he postulated that the sun’s physical force had two parts: it attracted the planets in one part of their elliptical orbits and repulsed them (pushed away) on the other part. 

Maggie:  Oh oh oh, I have an idea.  He thought the sun’s force was like a magnet.  One side of a magnet pulls metal to it, but the other side pushes metal away.  Is that right?

John:  I love your imagination.  That analogy is perfect. 

So those are the two most important ideas in the New Astronomy.

Maggie:  Did he do anything else interesting?

John:  Well, we should mention the Rudolphine Tables.  When Kepler joined Tycho Brahe, they were both commissioned by Emperor Rudolf II to create new planetary tables predicting the movement of the planets. The old tables had proven to be wildly inaccurate.  Kepler didn’t complete the project until several years after Brahe’s death. But again using his math skills and Brahe’s observations, he created extremely accurate tables that were used for many years. 

Maggie:  What do you think is the most important thing to remember about Kepler?

John:  Good question.  When we look back on his contributions from our current vantage point, we can see that Kepler radically changed astronomy as a science.  If you recall, the Greeks changed astronomy from a pure observational science to one that relied upon geometry. Kepler then changed the science once again.  It became less focused on geometry and more focused on complex mathematical formulas and the science of physics, and it never looked back from there.  The mathematical-physics model is still the model used today. 

Kepler's First LawMaggie: Cool!  So who are we talking about next?

John:  Let’s explore Galileo.

Maggie:  I will do a little reading before then.

John:  Great.  See you next month.

One thought on “Maggie and Me (a philosophical dialogue): On Johannes Kepler

  1. Interesting blog. Your topics are not only interesting, this old auntie is relearning things I have long ago forgotten. Thanks Maggie and John.


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