Johannes Kepler

Johannes Kepler, the son of a mercenary soldier and an innkeeper's daughter, was born prematurely just 2 days after Christmas 1571, in Weil der Stadt in Wurttemburg (now part of Germany). He attended the University of Tubingen, where he studied theology and the classics. There, he met mathematics professor, Michael Maestlin, who became his mentor.

Maestlin was a proponent of the heliocentric model of the solar system and planets introduced by astronomer Nicolaus Copernicus. Johannes Kepler, too, accepted this theory immediately, seeing the hand of God in its simplicity and becoming interested in astronomy.

Giving up his plan of becoming a clergyman, Johannes Kepler departed the University of Tubingen in 1594 to accept a chair in mathematics and astronomy at the university in Graz, Austria. After taking this position, he developed a complex hypothesis to explain the distance between the orbits of planets. (He, like so many before him, mistakenly believed these orbits were circular. Still, his early calculations matched the observational evidence within 5%. In his later work, he altered his thinking to believe that planetary orbits are elliptical.)

Johannes Kepler next theorized that the sun emitted a constant force across the planes of a planet's orbit, which diminished with distance. He believed this force pushed the planets around their orbits. In 1596, he published these theories in a treatise called Mysterium Cosmographicum (Cosmographic Mystery). This was the first written defense of the Copernican model, which used geometric calculations as evidence.

Although Danish astronomer Tycho Brahe did not subscribe to the Copernican theory, himself, he was so impressed with the work of Johannes Kepler that in 1600, he invited Kepler to become his assistant. Brahe, the mathematician at the court of Emperor Rudolph II at Prague, was one of the most prolific observers of the cosmos. At the time of his death, one year after Johannes Kepler became his assistant, the data he collected during his lifetime was far superior to any others made prior to the invention of the telescope.

After Tycho Brahe's death, Johannes Kepler stepped into his role of imperial mathematician and court astronomer. He remained in this position until he became mathematician to the states of Oberosterreich (upper Austria) in 1612.

During his working years, Johannes Kepler was a brilliant astronomer and mathematician and a prolific writer. His first major contribution came in the form of a treatise on the theory of optics, just two years after he stepped into Brahe's shoes.

His next major work was entitled Astronomia Nova (New Astronomy), which was published in 1609. Using the observations of his predecessor along with his own, he was able to calculate the orbit of the planet Mars. Forgetting all previous notions of circular planetary orbits, he theorized that the planets move in elliptic orbits with the sun at one focus. This was the first of Kepler's so-called Laws of Planetary Motion. The second, which also appeared in this work is called the area rule, which says that a hypothetical line from the sun to a planet sweeps out equal areas of an ellipse during equal intervals of time, meaning that the closer a planet comes to a sun, the faster it moves.

Some of the other work Johannes Kepler accomplished during his stint in Prague included a book enthusiastically accepting and expanding on Galileo's observations using a telescope. He also completed a treatise on optics as telescope lenses the year before his departure to Linz.

After moving to northern Austria to accept his new position, Johannes Kepler continued his observations and writing. In 1619, he published Harmonice Mundi (Harmony of the World), which contained the third of his Laws of Planetary Motion. The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes. (Basically, the ratio of a planet's distance from the sun cubed to the planet's orbital period squared is a constant and is the same for all planets.)

During this same period, Johannes Kepler was laboring on his greatest work, Epitome Astronomiae Copernicanae (Epitome of Copernican Astronomy), which was finally published in 1621. This publication tied together all of his previous work. This book, the first astronomy textbook based on the Copernican model, became the primary astronomical text for many years to follow.

The last major tome published during Johannes Kepler's life was Tabulae Rudolfinae (Rudolfine Tables), which appeared in 1625. This work was based on observations and calculations of Tycho Brahe. With these new tables of planet motion the mean errors of a planet's actual position were reduced from 5° to within 10'. Later, Sir Isaac Newton utilized Kepler's theories and observations in formulating his theory of gravitational force.

Johannes Kepler died on November 15, 1630, in Regensburg (now part of Germany).

Four years after his death, Somnium (Dream), was published. In this work, he described a journey to the Moon and spoke of lunar inhabitants. So, besides his voluminous contributions to astronomy and mathematics, Johannes Kepler was also one of the first science fiction writers.