Johannes Kepler was born in Germany in 1571, in the middle of the Scientific Revolution. The weak and sickly child was abandoned by his father Heinrich in early childhood. Because his family moved around so much, it took Kepler twice as long as usual to get through elementary school. He eventually graduated, moving on to a theological seminary and then to the University of Tuebingen.
At the university, Kepler decided to pursue a graduate degree in theology, but he was soon distracted from that goal. A Protestant school in the Austrian town of Gratz offered him a job as a professor of math and astronomy. Although Kepler believed he had no special skills in those subjects, he took the job. Once there, he turned his attention toward deciphering the mysteries of the universe. Kepler was convinced that God had created a universe with some discernable pattern or structure, and he devoted himself to figuring out what it might be.
In 1595 Kepler decided that the planets were spaced as they were because the planetary orbits were arranged around geometric figures: the perfect solids. Perfect solids are three-dimensional figures whose sides are all identical, and Kepler was convinced that God had used these forms to build the universe. He elaborated on this view in his first book, the Mysterium Cosmographicum, or the Cosmic Mystery. Kepler's theory was incorrect, but the book was the first major work in support of the Copernican system since Copernicus's death fifty years before. The book was also significant because Kepler was the first major astronomer in centuries to address physical reality, rather than being content with a mere mathematical description of the universe.
Kepler could not quite get his data to fit his theory; he needed a source of more accurate data. He found this in Tycho de Brahe, a wealthy Danish astronomer. Tycho was the best observational astronomer of his age, and Kepler decided that only Tycho's observations would do. So Kepler traveled to Prague to work in Tycho's lab. Tycho, an arrogant, demanding, and unpleasant employer, died after only a year. But Kepler worked for seven more years on the problem he had started on while there: constructing the orbit of Mars.
Kepler's work on Mars led him to discover his first two planetary laws: that the planets travel in elliptical orbits and that they sweep out equal areas of their orbits in equal times. He published his results in 1609 in the Astronomia Nova, or the New Astronomy, revolutionizing astronomy and greatly simplifying the Copernican system.
Kepler was considered one of the top astronomers in Europe–although not because of his published work. Few of his peers recognized the importance of his planetary laws, and few even accepted that they were true. It was difficult for his colleagues to recognize him as a scientist of the modern age, when his work remained mired in the mysticism of the past.
The years just before and after the Astronomia Nova were a professional triumph for Kepler – he was well known and well respected. He spent these years researching lenses, as well as astronomy, adding several major contributions to the field of optics. At the same time, his personal life was taking a turn for the worse. In quick succession, Kepler's wife and favorite son died, and his patron went insane and abdicated the throne. His new home, Prague, was torn apart by civil war, and his mother was accused of being a witch.
Through it all, Kepler continued to work toward his greatest goal: finding a way to explain the structure of the universe. He had been forced to abandon most of his theory of the perfect solids, and needed something new to replace it. After years of thought, he came up with a new idea: the theory of universal harmonies. Kepler decided that the planets were spaced around the harmonic ration of another set of geometrical figures. Once again, he believed he had looked directly into the mind of God. Once again, his theory was completely wrong. Butthe pursuit of an incorrect theory led him to a stroke of scientific genius.
In 1618, Kepler published the Harmonice Mundi, or the Harmony of the World, in which he explained his new harmonic theory. Kepler's third law offered a specific mathematical relationship between the distance of a planet's orbit from the sun and the time it took a planet to circle the sun. Kepler thought little of this law, as did his peers, because it made little sense to him at the time. It was only later, when Sir Isaac Newton created the theory of universal gravitation, that the fundamental importance of this law became clear.
Kepler continued to publish important works. In 1619, he published Epitome Astronomiae Copernicanae, a summary of the Copernican system, adjusted to accommodate Kepler's laws. The Copernican system as we now know it is basically the one offered in the Epitome. Then, in 1627, Kepler published the Tabulae Rudolphine, or the Rudolphine Tables, a comprehensive list of astronomical observations, predictions, and explanations, all based on Tycho's data and Kepler's discoveries.
Kepler's final publication came a few years after his death. Though filled with scientific explanations, it is not actually a scientific work – instead, it is a science fiction story. Somnium, or Dream, tells the story of a young boy's trip to the moon. Much of the story seems to be a thinly veiled autobiography. However, the Somnium was also packed with notes on the scientific ramifications of Kepler's discoveries. The accuracy of his prediction of what a lunar journey would be like reveals what remarkable physical intuition he had.
Kepler is perhaps the least known of the major figures of the Scientific Revolution. His lack of fame may be due to the fact that he is difficult to classify – he seems less modern than the other scientists of the time, and he relies on mysticism and religion. His scientific contributions are themselves harder to simplify than those of Copernicus or Newton. But while he may be less known than his peers, Kepler is no less important. Physics and astronomy had been separated for two thousand years before Kepler's birth. It was an incredible leap for him to put the two together – and in doing so, he paved the way for the Newtonian revolution that was to come.