By Gerd Michalek

The famous astronomer Johannes Kepler was born in 1571 in a discreet half-timbered house in Weil der Stadt. (imago / Arnulf Hettrich)

There would be no modern space travel without Johannes Kepler: the astronomer discovered the elliptical orbits of the planets and revolutionized modern thought. Kepler was born in 1571 in the small town of Weil – what traces of him can be found there today?

The Württemberg community of Weil der Stadt – almost 30 kilometers west of Stuttgart – still has a picturesque city center today. Some of the half-timbered houses around the market square are over 400 years old. One of them, quite compact and only 80 square meters, is a little hidden on the edge of the square: Keplegasse 2.

Germany’s most famous astronomer was born on December 27, 1571, on the first floor of the brownish half-timbered house, whose parquet cracks violently.

Born in difficult circumstances

It’s hard to believe, says Wolfgang Pleithner, director of the Kepler Museum located here: “It’s quite fascinating, a little half-timbered house around the corner and a very great spirit emanates here. There was once a nice competition for the ‘Kepler Prize’. There was a girl there Prague wrote: “They say: Such geniuses were not born on earth, they fall from stars. And such a star fell on Weil der Stadt in 1571. ‘ How did this happen? I don’t know! “

There are a lot of confusing things in the life of the great astronomer. Kepler comes into the world as a weak seven month old child.

From a family perspective, the chances of leaving for the thinker of world harmony are anything but good: his parents are quarrelsome and resentful people.

On the other hand, the very intelligent Johannes grew up in a progressive education system for the time, underlines Hermann Faber, former director of the Johannes-Kepler-Gymnasium: “With Duke Christoph, the great school reform was introduced in 1559. And this allowed a basic education for all children, at the time it was called the German school, where children learned arithmetic and writing. It was certainly a great privilege here in Württemberg that there had an education. And the Latin school built on the German school. “

Kepler founded modern thought

Kepler attended school in the nearby town of Leonberg. The family house and the school building are still on the market square today. After Kepler finally studied in Tübingen in his mid-twenties, he raises questions that leave traditional medieval thought far behind.

“This is what is really fascinating about Kepler, that he comes from a world which until then knew only two sources: what does the Bible say or what does Aristotle say about this or the problem?”, Says Wolfgang. Pleitner. “Then he did science for the first time in the sense that we do today, which is that we make observations and then correct our hypotheses. It was new.”

Fictional trip to the moon

In the year of Kepler’s birth, the Reformation was only 54 years old. According to the rulers, the faith in Central Europe is interpreted in a Catholic or Protestant way. The idea that the sun – and not, as it is traditionally thought, the earth – is the center of the world is still frowned upon by Catholics and Protestants. Kepler is clearly attached to the new Copernican worldview.

Johannes Kepler impresses by the combination of a strict empiricism and a speculative vision of the whole. (photo alliance / Bildagentur-online / Sunny Celeste)

With a literary trick he tries to radically challenge the traditional view of people, says Hermann Faber: “He wrote a novel for it, ‘Somnium’, which was published posthumously in 1634. Moon and educates people : What does it actually look like when we are on the moon and look at the earth and the planetary system, what do the inhabitants of the moon say? “We rest, we stand in the center and everything revolves around us. ‘ So it was a very smart and ingenious way of getting people to understand the subjectivity of seeing the universe. “

No space travel without Kepler

Another fascination for Kepler, who is about to leave his home in Württemberg to write world history in Prague, is the mixture of strict empiricism and a speculative view of the whole. Finally – thanks to the observation data of his professor at the imperial court in Prague, Tycho Brahe – he discovers the elliptical shape of planetary orbits, and he becomes a pioneer of what Newton will later call the gravitational force.

This made Kepler one of the first modern researchers, on whose shoulders all NASA projects rest today, says Wolfgang Pleitner: “In space, Kepler is still driving! When the engine is not running everything obeys Kepler’s laws, everything travels through space. The International Space Station, which orbits the earth in 92 minutes, is in Kepler orbit. All satellite orbits are now described with Kepler’s orbit elements, he brought that to the world. “

The fate of the Kepler family shows how central Europe still clung to superstition 400 years ago. When Kepler was already established as an Imperial astronomer, his mother was caught in the sights of the Leonberger witch hunt. Even after 14 months in prison, Katharina Kepler remains steadfast in the face of the instruments of torture. Because her son Johannes defended her patiently, the trial ended in October 1621 – exactly 400 years ago – with an acquittal.