Date: December 27, 2009

Title: The Protestant Galileo


Podcaster: Ted Haulley

Contact: E-Mail

Description: Johannes Kepler was a contemporary of Galileo who also supported heliocentrism. His three laws of planetary motion are so fundamental that they still the basis for studies in planetary motion. He made his discoveries among personal and religious turmoil surrounding him. Today’s episode will look at the complicated life of Johannes Kepler, born on this date in 1571.

Bio: This will be Ted’s fifth contribution to the 365 Days of Astronomy. He still lives in Waldorf, Maryland with his wife Tammie, and two daughters; Tanda and Trillian. A long time amateur astronomer, you can sometimes find Ted volunteering as a docent at the Smithsonian National Air and Space Museum in Washington, D.C.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by The National Radio Astronomy Observatory (NRAO), celebrating five decades of training young scientists through summer programs. Explore the hidden Universe at in radio


Hello again! This is Ted Haulley talking to you from Maryland, so it must be another anniversary. The same year Galileo first turned his telescope skyward, Johannes Kepler published Astronomia Nova, or ‘New Astronomy,’ that contained his first two laws of planetary motion. These laws expanded on the idea of Copernicus that the Sun, not the Earth was the center of the solar system. Copernicus and Galileo had conflicts with the Catholic Church. Kepler was a Lutheran and did not have the same troubles. He did, however, have his share of strife, religious and otherwise. Today’s episode will look at the life of the Protestant Galileo, Johannes Kepler, born on December 27, 1571.

Most modern sources state that Kepler was born prematurely, but the only evidence of that comes from writings of Kepler himself from his 20s, when he was making astrological charts for himself. Johannes was born seven months after his parents got married, so he assumed that he was born prematurely. That is the only possible explanation, right? He concluded that he spent 224 days, 9 hours and 53 minutes in the womb. He was also a weak and sickly child, just like his chart said he would be. More on Kepler’s astrology later.

Kepler’s family was fairly well-to-do once upon a time, but by Kepler’s birth the family fortune had almost disappeared. They were never poor, but the family was reduced to living in a small home on the fringes of society, with the kids working in their grandfather’s inn.

His father Heinrich was a mercenary who left his family several times to fight wars. Johannes did not have many kind words for him, calling him ‘vicious’,’ quarrelsome’,’ immoral’, and ‘rough.’ He twice went to the Netherlands to fight against a Protestant uprising. Since his family was Lutheran, this caused a lot of family strife. He was last heard from in 1588, and it is assumed that he died in the Netherlands.

His mother Katherina also had a bit of a temper. Her father was a politician, but her mother died young and Katherina was raised mainly by her aunt. Her aunt would eventually be convicted of witchcraft and burned at the stake. In her later years Katherina herself would be accused of witchcraft. Though uneducated, she was intelligent, headstrong, and deeply religious. She would pass on many of these traits to Johannes, along with being the first to expose him to the wonders of the universe. When Johannes was six his mother took him to see the Great Comet of 1577. That experience would have a lasting impact on his life.

Johannes had two brothers and a sister that survived into adulthood. Johannes was the oldest. Heinrich, a year or two younger, was also sickly and accident-prone. He was often beaten by his father who also threatened to sell him into servitude. He frequently ran away, only to return penniless. He died at the age of 42, unmarried and penniless. Sister Margaretha was gentle, married a clergyman, and remained close to Johannes and her mother her whole life. Youngest son Christophe grew up proper and honorable, and eventually became a craftsman.

After a difficult childhood Kepler entered the University of Tübingen in 1588. Deeply religious, he studied theology and planned to enter the ministry. As part of the curriculum he learned math and astronomy. He was taught both the model of Ptolemy, with the Earth being the center of the universe, called geocentric, and the model of Copernicus, with the Sun being in the center, called heliocentric. He enthusiastically embraced the heliocentric model and often publically defended this position.

Despite his desire to enter the ministry, in 1594 Kepler accepted a job as teacher of astronomy and mathematics at a Protestant school in Graz, Austria. It was here that he came up with his first theory about the workings of the universe. He theorized that there were six planets because the five gaps between the planets would perfectly fit the five platonic solids. Platonic solids are symmetrical, congruent geometric shapes. Many of you may probably seen platonic solids as the various sided dice used in many role playing games. It said the solar system had a perfect mathematical, geometric order. He lectured on this often, and even wrote a book about his discovery.

I’m sure you realize that this theory is, as they say in internet circles, “an epic fail.” In the light of modern science it is complete nonsense. No matter. It did show Kepler was determined to prove that planetary motions can be described mathematically without extraneous motions like epicycles that were required to match observations with geocentrism. This would eventually lead to his three laws of planetary motion.

After a few years of teaching he began working for another well-known astronomer: Tycho Brahe. The professional relationship these two had was so influential that even today you rarely hear of one without mention of the other. Brahe wanted Kepler’s theoretical knowledge, and Kepler wanted Brahe’s observational data. The two only worked together for 18 months before Brahe died, but their names would be forever linked. Brahe promoted an odd hybrid of heliocentrism and geocentrism now known as the Tychonic system where the Earth was in the center, the Sun and the Moon revolved around the Earth, but the other planets revolved around the Sun. However, Kepler never swayed from the heliocentric system and was convinced that he would be able to take Brahe’s planetary observations and mathematically prove the Sun was in the center.

The problem Kepler had was that even in the heliocentric system it was always thought the planetary orbits were perfect circles. The observations were not making sense mathematically. Then he finally figured it out. Orbits were not circular, but ellipses. Once he discovered that he established his first two laws of planetary motion and published them in New Astronomy in 1609. He added the third law ten years later.

Law 1: Each Planet follows an elliptical orbit that has the Sun at one of the focal points.

Law 2: The vector drawn from the Sun to a planet will sweep out an equal area over an equal period of time.

Law 3: The orbital period of a planet is directly proportional to the distance of the planet from the sun. Orbital period squared equals the distance cubed.

These laws are true for all bodies orbiting the Sun, no matter how elliptical the orbit, and can be tested today. About seventy years later Isaac Newton would expand on these laws to develop the laws of universal gravitation. Kepler showed how the planets moved, Newton showed why they moved that way.

After the death of Brahe, Kepler became imperial mathematician under Emperor Rudolph II of the Holy Roman Empire. Under his patronage and using Brahe’s data, Kepler developed planetary movement charts that would prove to be many times more accurate than the ones that previously existed. He called them the Rudolphine Tables in honor of his patron because even back then scientists knew how to suck up to the person giving the grants. They took decades to complete, finally being published in 1627, long after Emperor Rudolph had died. Their accuracy was proven by a transit of the Sun by Mercury in 1631, one year after Kepler died.

The laws of planetary motion may be Kepler’s best known discovery, but he also did work to improve telescope optics. He corresponded with Galileo about topics in astronomy and telescopes, but Galileo never revealed his thoughts about Kepler’s laws of planetary motion. He also wrote what many consider the first work of science fiction. The Dream contained descriptions of what a resident of the moon might see when observing the Earth and was published by his son five years after he died.

Kepler was a deeply religious person. He held the opinion that the fact that planetary movements can be explained mathematically, and that there was an observable geometric order to the solar system were all evidence of God’s work. Kepler thought the harmony displayed by the planets was an example of the geometry and architecture that God used to create and rule the universe.

Like many astronomers at the time, Kepler was also involved in astrology. Some modern sources say he didn’t put much faith in it and only used it as a source of income, but others say he fully embraced it as a science. Either way, Kepler was deeply involved in astrology. Part of his job as Imperial Mathematician was to make astrological charts with predictions for the upcoming year. Some of his predictions were accurate enough for him to be held in high regard as an astrologer, and he was sought after by many rulers and nobles for astrological readings.

All of Kepler’s accomplishments came in spite of a troubled personal life. He entered a loveless marriage with twice-widowed Barbara Müller in 1597. Their first two children died in infancy. They had three more children, Susanna, Friedrich, and Ludwig. In 1611 Barbara became seriously ill with Hungarian Spotted Fever, and when she was recovering, all three kids contracted smallpox and Friedrich died. Barbara then had a relapse and died in July, 1611. His second marriage to Susanna Reuttinger was happier, but still had a share of sorrow. They had six children, but only three of them lived to adulthood.

Then there was his mother. She stubbornly refused to change her ways, despite the accusations of witchcraft. In 1619 she even returned to the town that ordered her arrest for witchcraft, concluding that staying away would make her look guilty. She was promptly arrested and jailed. The charges against her stemmed from a dispute between families that is too complicated to outline here. She was held for about 14 months, never confessing, despite being threatened with torture. She was probably saved by her famous son, who was active in her defense. It was eventually judged that she was ‘cleansed’ and released. The ordeal put a strain on an already old woman, and she died shortly after her release.

Kepler did not have to deal with the Catholic Church, as Galileo had to, but religious turmoil surrounded him as well. Kepler lived in Germany during the Counter-Reformation, and religious conflict between Protestants and Catholics was almost constant as the Catholic Church attempted to re-establish its dominance in Central Europe. There was even conflict between different sects of Protestantism. Kepler and his family were constantly forced to move to avoid persecution by Catholics. He was exiled from Graz in 1600, and it influenced his decision to work for Brahe that same year. War and persecution by both Catholics and Protestants forced Kepler to move at least three other times. There were attempts to convert him to Catholicism, but he refused, remaining a Lutheran his whole life. Kepler himself displayed a religious tolerance to Christians of all sects that was very uncommon for the time. He believed that all baptized Christians were children of God, and he was very disturbed by the idea of Christians killing each other.

Johannes Kepler died on November 15, 1630, three years before Galileo was put on his famous trial. He was buried at a cemetery in Regensburg, Bavaria. The cemetery was destroyed a few years later, and there is no trace of Kepler’s burial site.

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