Johannes Kepler and the Joy of Science

Johannes Kepler and the Joy of Science

            The German astronomer Johannes Kepler is counted among the greatest scientists in history. He is best known for his three laws of planetary motion, which shaped our modern understanding of the solar system.

            His achievements expanded beyond astronomy to cover optics and mathematics. But his brilliance didn’t shelter him from a host of financial, personal, and religious challenges.

Youth and First Works

            In 1571, when Kepler first opened his eyes to the world in the small town of Weil der Stadt, the Holy Roman Empire was still divided in matters of religion. While the 1555 Peace of Augsburg had created some stability by maintaining that each ruler could determine which religion was practiced in his state (cuius regio, eius religio), it had not provided a permanent settlement.

            Württemberg, the region where Kepler was born, was Lutheran, and he was raised in that faith, mostly by her mother (his father was a mercenary soldier). Kepler hoped to become a pastor. At age 18, he entered the University of Tübingen with that goal in mind.

            Kepler was near the end of his theological studies, when his astronomy teacher, Michael Mästlin, convinced him to pursue science instead. Kepler agreed for several reasons.

            Besides his love for science, he had a feeling he was not cut out to be a pastor. For one thing, he thought he didn’t have the physical built and stamina that pastoral work required. He was, like his mother, thin and frail – a constitution which, in his eyes, was more fit for a scholar.

            Besides, he was not comfortable with the Lutheran teaching on the real presence of Christ in the Lord’s Supper (consubstantiation). To him, the Reformed objection that Christ’s body could not be present in substance both in heaven and with the elements had strong merits. But he was not ready to leave the Lutheran church. Because of this, he continued to be seen as a fish out of water.

            An invitation to teach mathematics in Graz, in today’s Austria, came as a confirmation of his new vocation, although initially he had few students and spent most of his time making astrological calendars.

            He also had time to write his first astronomical publication, Mysterium cosmographicum (1596), where he claimed to have discovered God’s mathematical structure in the creation of the universe. As the author of beauty and order, God created a world which is both beautiful and orderly (which, to Kepler, meant mathematical).

            Since both beauty and order are expressions of God’s love toward mankind, Kepler kept this love foremost in his observations. “For I think that very many causes of what we find in the world can be deduced from the love God bears to Man.”[1]

            His ability to study God’s creation gave a purpose to his life. “I wanted to become a theologian,” he wrote to Mästlin; “for a long time I was restless. But now I see how by my pains God is celebrated in astronomy also.”[2]

            It was in Graz that Kepler met a woman who became his wife, Barbara Müleck, a 23-year-old widow with a young daughter. Initially, her father, a successful mill owner, opposed the marriage because Kepler was not wealthy. He softened his opinion after Mysterium was published. The couple married in 1597. Their first two children died in infancy.

Kepler’s Battle With Mars

            Around the same time, Tycho Brahe, imperial mathematician to Emperor Rudolf II in Prague, asked Mästlin to recommend an assistant. After a few letters back and forth, they agreed that Kepler was the best choice. In 1600, Kepler moved to Prague with his family. This move was providential, because the Catholic archduke Ferdinand had banished all Protestants from his region (including Graz).

            Prague provided an excellent environment for Kepler’s work, even if working with Brahe was not easy and the two had strong disagreements. Brahe asked Kepler to determine the path and distance of a planet he had found most puzzling – Mars.

            In October 1601, Brahe died unexpectedly, and Kepler succeeded him as imperial mathematician. He also continued Brahe’s work by studying his observations. It was only in 1605 that Kepler announced his victory in his “battle with Mars,” as he called it. It was truly a battle, because the previous astronomical systems didn’t help. His breakthrough came in part by determining that Mars’s orbit was elliptical and not circular. Further work with Tycho's observations showed that the other planets moved in the same way.

Troubles and Trials

            In the meantime, the Keplers had three children: Susanna, Friedrich, and Ludwig, who – to their joy – stayed healthy through infancy. Their peace, however, didn’t last long. In 1611, Barbara contracted Hungarian spotted fever, followed by seizures. She was barely recovering when their children became infected with smallpox, which claimed the life of six-year old Friedrich. Eventually, Barbara relapsed and died too.

            The following year marked the death of Emperor Rudolph, who had already been stripped of every effective power. As Rudolph’s successor, Matthias confirmed Kepler's title as imperial mathematician. At the same time, he allowed him to move to Linz, where Kepler had obtained a position as teacher.

            In Linz, Kepler married a younger woman named Susanna Reutlinger, who bore him seven children, though only one seems to have survived to adulthood.

            Kepler’s new marriage was harmonious, but in 1615 Kepler’s joy was interrupted by a new, serious trial: his mother had been accused of witchcraft – a serious accusation in those days.

            He moved back to his home town in order to defend his mother. He faced this challenge as he did scientific problems – by collecting and studying the documents and examining the evidence. The negotiations lasted a year. In the end, he was able to prove that the accusations were inconsistent.

             He returned to Linz but had to move to Ulm in 1626, when Linz became besieged in the course of the Thirty Years War. In Ulm, he finished his best-known work: the Rudolphine Tables, based on the observation of Tycho Brahe.

            Impressed by this work, the emperor offered to take care of Kepler and his family for the rest of their lives if they could convert to Catholicism. Kepler refused. He died on November 15th, 1630 at age 59, after traveling to a nearby city to collect money to pay some debts.

Kepler’s God

            Biographers are often surprised at Kepler’s optimism in spite of the troubles that marked his life, but his studies had done nothing but confirm the biblical teaching of a loving God who has a perfect and beautiful plan for his creation. To him, science was a delightful discovery of this exciting truth, to be pursued for the joy of it, and not necessarily for utilitarian reasons.

            Just as birds sing for pleasure, following their natural impulses, Kepler thought that human beings should follow their natural curiosity about nature. That’s why Kepler asked questions no one had asked before: Why are snowflakes symmetrical? Why are cannon balls best stacked in a face-centered-cubic lattice? Why aren’t pomegranate seeds spherical? He didn’t know if his inquiries would generate useful answers, but he knew they would open a new window on God’s orderly creation.

            For those of us who can barely grasp a basic explanation of astronomy or calculus, Kepler has a comforting advice. If you just can’t get it, stop trying. “He should stay away from our wanderings through the world, return home, and there cultivate his little field. But he should raise his eyes, with which he alone can see, to the visible heaven, and give himself up with a full heart entirely to the thanks and praise of God the Creator, convinced that he shows no less reverence to God than does the astronomer.”[3]



[1] Johannes Kepler, Mysterium Cosmographicum, quoted in J. V. Field, Kepler's Geometrical Cosmology, Bloomsbury Academic, 1988, p. 56.

[2] Max Caspar, Kepler, Dover Books, 1993, p. 375.

[3] Caspar, Kepler, p. 373.