Johannes Kepler's work transformed both our knowledge of the heavens and the enterprise of astronomy itself. Kepler adopted Copernican's sun-centered universe as a young man, before using Tycho Brahe's extremely accurate observations to overthrow a tradition of astronomical theorising that extended back to Ptolemy. His argument that the planets followed paths that were not circular but elliptical challenged a millenium of consensus among astronomers. His insistence on trying to trace the real motions of the planets, and their causes, challenged their practices no less radically. Both were the result of years of tedious calculation and relentless determination. Kepler's willingness to endure this drudgery grew from his conviction that the harmony of Creation was essentially geometrical, and sprang from the mind of God. His efforts to articulate that harmony occupied the bulk of his life and produced his most interesting work.
During the Renaissance, a professor of mathematics or astronomy occupied what was considered a lowly position. The main foci of universities were law, theology, and medicine, because these were the reckoned most useful branches of knowledge. Even when mathematics began to become more popular in the mid-1500's, it was viewed largely as a tool to improve medicine and astrology. Astronomers and mathematicians were not supposed to formulate ideas about the physical nature of the world, but only to "save the phenomena" by numerical techniques. They studied the motions of the heavens for practical purposes, such as improving navigation techniques, making crucial changes in the calendar, or providing better observation instruments. Kepler transformed both the social status of the astronomer and the kind of knowledge an astronomer created.
Kepler was born on December 27th, 1571 in the little town of Weil located in
southwest Germany. His mother and father, Katharina and Heinrich Kepler, were
reputedly dubious characters. Katharina was rumored to practice witchcraft,
and Heinrich was something of a mercenary. Johannes inherited from them an adventurous
and rebellious spirit. Fortunately, though, that spirit would be exercised in
scholarly battles. As for many Europeans living through the early years of the
Thirty Years' War, Kepler's life was filled with twists and turns. He moved
frequently, was married twice, and had a total of 6 children who survived past
infancy. His first marriage occurred in 1597 when he married one Barbara von
Muhleck, who was already twice widowed at the tender age of 23. After she died
in 1611, he soon remarried, this time to a woman named Susanna Reuttinger who
was 17 years younger than Kepler. The great astronomer seemed content in both
marriages, but he suffered from incessant health problems. He fitted well the
persevering cliché that great minds inhabit fragile bodies.
Kepler received an excellent education. As a result of the desire to win the
religious controversy that was raging during this time period, Germany had set
up a superb school system in order to produce bright young Lutheran clergymen.
And being a priest was exactly what Kepler desired. By the time he entered the
University of T¸bingen, he was already educated in mathematics, music,
and languages such as Latin and Greek. Fate intervened, however, before Kepler
could become a priest. He was offered a position in Graz, Austria where he would
teach mathematics and astronomy. Kepler initially wanted to reject the offer
because he knew so little about astronomy. But soon he was moving to another
country.
He arrived in Graz at the age of 22. In the beginning, his classes had very
poor attendance. His major real responsibility was to provide the annual calendar
of astrological forecasts. This was by no means unusual. The pay of the mathematics
or astronomy professor was quite poor. In order to make a better living these
men had two major options. The first was to continue studying until one could
become a professor of medicine - a position that paid almost double that of
a mathematician. The second was to get a second job creating astrological calendars
for the wealthy or for royal families. For much this reason, astrology continued
to be a major part of Kepler's life until the day he died. Indeed, although
Kepler was very critical of traditional astrology, he firmly believed that he
could discover a new and true astrological science.
Kepler's own account of his principal discovery presents it as something resembling a revelation. One day, while teaching a small class, about a year after his arrival in Graz, he hit upon the idea that would change his life forever. He conceived of a model for the universe that included the five regular solids. Based on this inspiration, Kepler wrote his first major work, which he entitled Mysterium Cosmographicum. The book was meant to answer such questions as why there were exactly 6 planets (Neptune, Uranus, and Pluto had not yet been discovered), why they were arranged in such a manner, and why they moved as they did. He finished this remarkable piece of work in about a year, at the age of 24; the book was published in the spring of 1597. Throughout his life, publishing problems would continue to plague Kepler, as well as most other astronomers of his time. The printing industry was growing, but could not effectively satisfy the needs of technical works such as the Mysterium Cosmographicum. Nor could the instrument-making trade: Kepler repeatedly tried to get a model of his cosmological scheme made, but with no success.
The reception of the Mysterium was mixed. Some astronomers liked the work, approving of Kepler's a priori deduction of the heavenly arrangement. Other contemporaries, such as Galileo, rejected the book because of its apparent speculations. Neither group saw the brilliance and potential of Kepler. Only one man saw its potential, and that man was Tycho Brahe. Tycho, the wonderful astronomer who revolutionized the field of observations and recordings of the planets's positions throughout their paths, could see that Kepler had new and unique ideas about the universe. But the two were forced to wait three years before they would finally meet. In the meantime Kepler studied further mathematics to improve his previously shaky knowledge of the subject. He also investigated fields such as optics, magnetism, and meteorology. During this time Kepler also contemplated further his theory of the heavens, incoporating musical harmonies with the five perfect solids. But he desperately needed Tycho's observations to make any further advancements or improvements.
At this point in Kepler's life, fate once again intervened. He was chased out of Austria by the new archduke, who was determined to rid his lands of the Lutheran religion. As a result, Kepler was forced to seek a new home. Tycho Brahe, by now the Imperial Mathematician of Emperor Rudolph II, invited Kepler to Prague to become an assistant. Their relationship proved rocky, but it lasted. Tycho wanted the young Kepler to use his observations data to perfect his own model of the heavens (in which the earth was stationary and the other planets orbited around the sun, which traveled around the earth). But he also valued wanted his skills for his propaganda campaign against mathematical rivals. But Tycho was not very forthcoming with his many years' worth of observations, and would only give Kepler the desired information periodically.
Only eighteen months after Kepler arrived in Prague, Tycho Brahe died. Soon afterward Kepler was appointed to take over the position of Imperial Mathematician. Finally, with all of Tycho's data in hand, Kepler was able to make serious strides. He began to study the orbit of Mars. This problem, which he initially thought he could solve in eight days, eventually led him to the discovery of his first two so called "planetary laws" approximately eight years later. It was a long and difficult road for sure, but Kepler's determination won out and he finally solved the problem of Mars' orbit. He published his results in his second great work, the Astronomia Nova (1609).
The Astronomia Nova was a unique and revolutionary book. It was in part a retrospective account of the path Kepler had followed in search of his truth. Many times he believed to have solved the problem, he recalled, but dismissed his hypotheses because they did not fit Tycho's observations closely enough. His insistence that his theory match the observations so closely, while still remaining physically consistent, was what brought him success. Moreover, this conviction about the physicality of theories carried over into their reasons. The Astronomia Nova was also the first astronomer's work to concentrate on the causes - material, geometrical, and physical - of the planets' motions.
Two years after Astronomia Nova was published, Kepler was forced to leave Prague. A civil war had erupted, and his patron and provider Rudolph II was forced from power. Kepler accepted a position as Provincial Mathematician in Linz, Austria. Here he continued to work with his model of the universe, and finally published his third major work, Harmonices Mundi, in 1619. This work, in which he claimed to explain the harmony of the world, was a series of five books and contained what is known today as his third law. The work was founded on geometry, from which Kepler derived first a theory of musical harmony and then a cosmology of the heavens and the earth. His hypothesis fit the observed data surprisingly well, and Kepler was overjoyed by his success. He believed that he had finally discovered God's reasoning in the heavens.
After the Harmonices Mundi, Kepler continued to write books and pamphlets. He completed two more major works before he passed away: the Epitome Astronomiae Copernicanae and the Tabulae Rudolphinae. The Epitome was a summary of the Keplerian system that extended his three laws to all of the planets and moons in the form of questions and answers. The Tabulae Rudolphinae was a compilation of the tables that contained all of Tycho Brahe's observations that he had recorded for over 30 years, but accompanied by Keplerian glosses. Along with these two major works and a number of small pamphlets, Kepler also wrote a fantasy entitled the Somnium seu Astronomia Lunari, which concerned a dream of a journey to the moon. It was not published until after his death. He died on November 15th, 1630 while on a journey to obtain money owed to him. He succumbed to a fever in the town of Regensburg and was buried in a local Protestant cemetery.