Johannes Kepler was a German astronomer, mathematician and astrologer, who discovered laws of planetary motion. Kepler was a key figure in the Scientific Revolution of the 17th Century – confirming the theories of Copernicus and laying the foundation for Issac Newton to discover the laws of gravity. He also worked on optics, inventing an improved version of the refracting telescope. Kepler sought to show that scientific reason was compatible with religion and belief in an intelligent God – he described his astronomy as “celestial physics.”
“I feel carried away and possessed by an unutterable rapture over the divine spectacle of heavenly harmony… I write a book for the present time, or for posterity. It is all the same to me. It may wait a hundred years for its readers, as God has also waited six thousand years for an onlooker.”
– Kepler, Harmonices Mundi (1618)
Kepler was born on 27 December 1571 in Weil der Stadt, (close to Stuttgart) in Germany. From an early age, he displayed prodigious mathematical talent and a love of astronomy. He studied at the University of Tubingen, where he studied philosophy and theology and also astrology and astronomy. He learned about the geocentric Ptolemaic system and the innovative, yet unproven Copernicus system of planetary motion. Kepler inclined to the Heliocentric view of Copernicus and defended it from both a scientific and religious perspective.
In 1894, at the age of 23, he accepted a position in Graz to teach mathematics. Here in Graz, he published his first major work Mysterium Cosmographicum (The Cosmographic Mystery, 1596) which promoted a Copernicus viewpoint, he later rejected some of the main thesis in his own work, but its brilliant mathematics and clear reasoning helped establish his reputation.
In 1597, he married Barbara Müller – they had five children, two of whom died in infancy. The marriage was often rocky.
In 1600, Kepler met Tycho Brahe who was an influential scientist – serving as the imperial mathematician to the Holy Roman Emperor Rudolph II. Tycho Brahe was impressed with the mathematical ability of Kepler and allowed him access to his meticulous records of astrological data. For Kepler, this was very important for his future work. Also, on the recommendation of Tycho and the favourable impressions he created on the Royal Court, he was appointed to succeed Tycho as Imperial Mathematician. When Tycho died shortly after, Kepler gained this post for the rest of his life. He brought his family to Prague, which was also convenient timing because his family had been banished from Graz for refusing to convert to Catholicism. At the imperial court in Prague, the only official religion was Catholicism, but with his imperial position, Kepler’s family were able to follow their Lutheran beliefs without
Kepler made use of Tycho’ astronomical observations and sought to test the theories of Plotomy, Copernicus and a third proposed by Tycho. After painstaking calculations, Kepler came to the conclusion that all three theories were inaccurate. However, Kepler believed his calculations showed that the planets did rotate around the sun; however, they did so in an elliptical pattern. With the speed of planetary motion dependent on their closeness to the sun.
“I was almost driven to madness in considering and calculating this matter. I could not find out why the planet would rather go on an elliptical orbit. Oh, ridiculous me!.. there is no figure left for the orbit of the planet but a perfect ellipse.”
– Kepler, Astronomia nova (1609)
In 1609, he was able to publish his classic Astronomia nova. This laid out his first two laws of planetary motion. Many years later he was able to publish a third law, which was that the further planets are away from the sun, the slower their orbit. With a combination of empirical data and excellent mathematical proofs, Kepler had managed to explain and prove the essence of planetary motion – something that had eluded Copernicus and Galileo.
There was no immediate recognition and acceptance of Kepler’s ideas, but over time, they became accepted as the correct view of planetary motion. Kepler’s work was particularly important for Isaac Newton’s laws of gravity. Newton made use of Kepler’s data, observations and calculations to develop his theory of gravity. Kepler’s planetary laws all point to the laws of gravity. Indeed Kepler referred to some force emanating from the sun, which enabled planetary orbits.
“Gravity is a mutual affection between cognate bodies towards union or conjunction (similar in kind to the magnetic virtue), so that the earth attracts a stone much rather than the stone seeks the earth.”
Astronomia nova (1609)
Newton later said “If I have seen further than other men, it is because I stood on the shoulders of giants” The work of Kepler is a prime example of this.
As well as his work in astronomy, Kepler served as an adviser to the Holy Roman Emperor, Rudolph II. Rudolph retained an active interest in the work of his court scientists and especially astronomy. He also had Kepler draw up astrological charts and sought the advice of Kepler on matters of state. At the time there was considerable interest in the stars and astrology bridging a gap between religion and science. In 1604, a bright new star appeared in the night sky. Changes in the night-sky were considered to be of great significance. This was combined with the cycle of 800 years for great conjugations of planets, which had occurred at the birth of Christ 0AD, 800 AD (rule of Charlemagne) and 1600.
In 1604, he published Astronomiae Pars Optica (The Optical Part of Astronomy). This is generally regarded as a foundation of modern optics, with an awareness images are inverted by the eye’s lens onto the retina.
In 1610, Kepler entered into correspondence with Galileo after Galileo had observed satellites orbiting Jupiter with his new telescope. Kepler responded enthusiastically, appreciating Galileo’s work and suggesting the importance for astronomy. Kepler also took Galileo’s development of optics and telescopes to build an improved telescope which became known as the astronomical or Keplerian telescope.
Kepler was not just a great scientist, but also good imagination and intellectual freedom. In 1611, he published a manuscript Somnium (Dream) which described an imaginary trip to the moon. It was a combination of autobiographical, allegory and explanation of astronomical laws.
Around 1611, King Rudolph abdicated in favour of his brother Matthias. Matthias was less enthusiastic about employing Kepler and in 1612, Kepler moved to Linz.
In Linz, his mother was accused and imprisoned on charges of witchcraft. It was alleged her mother had made a woman sick with an evil brew. The accuser had a financial dispute with Kepler’s brother. The witchcraft trial may also have been motivated by Kepler’s work in astrology and the family’s unorthodox Lutheran views which meant they were excluded from the Eucharist. Witchcraft trials were common at the time, and those found guilty could be tortured to death. However, Kepler was successful in defending his mother through getting the best legal advice which proved there was only rumour and no hard evidence. After her release, he released his manuscript Somnium with many footnotes to explain his allegories.
In 1613, after the death of his first wife, he also married a second time to Susanna Reuttinger. He retained the employ of Emperor Matthias but with the religious wars taking a financial strain on the Empire, Kepler was often not paid, and he began to struggle financially. In 1615, he published Epitome astronomiae Copernicanae (Epitome of Copernican Astronomy) which was a summation of his elliptical view of heliocentrism. It became an important textbook in astronomy and science.
In his later year, Kepler continued his intellectual curiosity investigating harmony in the natural world.
“The diversity of the phenomena of nature is so great and the treasures hidden in the heavens so rich precisely in order that the human mind shall never be lacking in fresh enrichment.”
As quoted in Cosmos (1980)
This included musical harmony and also the evidence of harmony in meteorology and astrology. It was a consequence of Kepler’s view to use scientific reason to strengthen and prove his own religious view of the world.
“Those laws [of nature] are within the grasp of the human mind; God wanted us to recognize them by creating us after his own image so that we could share in his own thoughts.”
In 1626, he published another major work his Rudolphine Tables, which was a comprehensive index of stars and planetary tables.
On 15 November 1630, he died in Regensburg. His own poetic epitaph was
I measured the skies, now the shadows I measure
Skybound was the mind, earthbound the body rests
Kepler’s work in time became enormously influential and was often held up as a turning point in the use of empirical data and scientific reason. Despite Kepler’s quasi-spiritual perspective on the invisible forces of the world and belief in God’s harmony, later scholars put Kepler as an important figure in the transition from classical to modern scientific methods.
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