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I chose to do a term paper on Johannes Kepler. The existing literature on Kepler includes books on his personal and professional life. Most of these books are not very new, but since Kepler died in 1630, it is not horribly necessary that new books be studied.
I will be looking into several things in the life of Johannes Kepler. I will be, of course, looking at some of Kepler’s discoveries and calculations. I will also be examining his personal life and how he became the scientist he was. Because Kepler was Tycho Brahe’s assistant, and then successor, a small fraction of this paper will be discussing him, also.
Johannes Kepler was born in Germany in 1571. Although his grandfather was mayor of his village, his family was middle-class. Kepler had bad eyesight and many illnesses as a child. This bad eyesight will influence the type of astronomer he becomes and will also influence Tycho Brahe’s opinion of him. Kepler was raised a Lutheran. Scholarship money was to be awarded to him if he was adept at education and if he was seen as extraordinary. He got the scholarship and was sent to study theology with the hope that he would become a member of the clergy. Fortunately for the future of science, he was more interested in math and astronomy. There was a teacher there, who was secretly a Copernican, who taught Kepler.
Just before Kepler graduated, the school needed a new math teacher. His teachers were so impressed by him that he got the job. Kepler’s career was quite a disaster. He was a poor teacher and his students did not seem to want to learn, which had to be discouraging. The school had him try teaching outside of mathematics. He was much better at that, even thought he wasn’t passionate about it.
During this time, he also did astrological charts, although he questioned their validity, to make more money. He continued to do this throughout his life. This was quite a common thing for astronomers to do at this time. Few astronomers thought astrology held any real value, but there was a demand for it and it was hard to make enough money pursuing astronomy.
Tycho Brahe now enters the picture. Tycho, who thinks that the Copernican and Aristotelian universes are both wrong, finds a book by Kepler. Although Brahe doesn’t like the book, we must give him credit for seeing the possible genius behind it. Kepler is invited to study with Brahe. The extraordinary observations of Brahe are now teamed up with the exceptional computing of Kepler. In the beginning, Brahe, who was born into an aristocratic family and still acted like a demanding aristocrat, treated Kepler like a servant. Brahe was probably the greatest naked eye astronomer ever; he therefore expected the same abilities from Kepler. Unfortunately, Kepler had very bad eyesight and was unable to perform well with naked eye astronomy. Because of this, Kepler was a disappointment to Brahe, which probably contributed to him treating Kepler like a servant.
When Kepler can no longer take the shabby treatment from Brahe, he demands to be treated like a partner. Thankfully, although grudgingly, Brahe agrees. By the time Brahe dies in 1601, he begs Kepler not to become a Copernican and to remember his works. He even wants Kepler to have his scientific notes and papers, which he is extremely protective of. Unfortunately, Brahe’s son takes over his estate and doesn’t want to give Kepler the notes or papers. Years of negotiations pass before the son finally gives the papers to Kepler.
Kepler studied the motion of the planet Mars, which led him to discover the first two fundamental laws of planetary motion. In 1609, his book, Astronomia Nova, was published. His first two fundamental laws were published in this. The first states that the planets orbit, not in a circle, but in an ellipse, where the sun is the focal point. The second law, the law of area, states that a straight line from the sun to a planet will cover the same amount of area in the same amount of time. It is important to note that Kepler’s discovery of elliptical orbits was made possible by the remarkable accuracy of Brahe’s observations. The difference between the assumed circular orbit and the elliptical orbit was only eight minutes of arc in longitude. As Kepler said, “These eight minutes in themselves alone have led to a complete renovation of astronomy.”
Kepler always considered the action of the sun on the motion of the planets. He knew that there was a relationship between distance from the sun and time of orbit: that if you increase the distance, you increase the time it takes to complete one orbit. Kepler theorized that there were rays, which he called “anima motrix,” extending from the sun in the way spokes extend from the center of a bicycle wheel. He thought that these rays propelled the planets around the sun, but that the rays became weaker as distance from the sun increased. Isaac Newton took up his mathematical laws about this 75 years later.
Kepler’s third law was published in 1619 in his book, Harmonics Mundi, the Harmonies of the World. This law states that “the squares of the periods of revolution of the planets are related to one another as the cubes of the major axis of their orbits.” (Vancouleurs, p52,53)
When a scientist tells the scientific community that they have discovered a new way of thinking and that previously accepted things are obsolete, there is usually a bit of an uproar while many people live in denial. In this case, Kepler’s three fundamental laws of planetary motion did such a better job of maintaining accuracy then the previous thoughts related to circular orbits, the scientific community quickly embraced them. These laws paved the way for Newton to establish the principle of universal attraction.
Kepler made many other important hypotheses and observations in the coming years. He published Treatise on Comets in 1619. In this, he pointed out that a comet’s tail always points away from the sun. He theorized that this was due to matter being repelled by solar rays, preceding the discovery of radiation pressure by two and a half centuries. Kepler was the first to be convinced that the atmosphere has weight. He was also the first to explain that the reddish color of the moon during lunar eclipses was due to sunlight passing through the Earth’s atmosphere.
Johannes Kepler was a mystic throughout his life. He did however believe that God was a master geomatrician, combining mysticism and a scientific mind. He believed that there was harmony to be found in numbers and that the sun had almost God-like powers. This may very well explain why he concentrated on mathematics, the Sun, and its revolving planets. His mysticism probably also explains how, in his 40’s, he was creative and imaginative enough to write a book about traveling to the moon.
Kepler was still doing the astrological forecasts he hardly believed in when he died. He died in 1630 on his way to the Emperor to collect the stipend that the ruler always tried to put off paying him for doing the forecasts. Despite the many discoveries made by Kepler, he died in utter destitution.
Kepler was an amazing scientist and mathematician. He made many amazing discoveries and had many accurate theories that had not been examined before that point. We owe much gratitude to Kepler for what we know of our solar system. If not for Kepler, how much longer would it have been before man realized that orbits around the sun were elliptical? Would someone else have come up with the three fundamental laws of planetary motion in time for Newton to use them? Science is amazing in how each new scientist builds on the discoveries of yesterday’s scientists. Brahe, Kepler, and Newton are unmistakable linked in their accomplishments. Who knows where we would be if any of them had not been able to build on each other’s genius? Kepler’s aptitude amazes me, not simply because of his obvious intelligence, but because he was able to combine that intelligence with such creativity. Had he not been so creative, he might never have even considered some of the things that made his genius truly come to light.
1. Casper, Max, 1954. Kepler. United States of America: Collier Publishing.
2. Christiansen, Gale, 1997. Lecture notes: Science and Society, Indiana State University.
3. Small, Robert, 1963. An Account of the Astronomical Discoveries of Kepler. Ann Arbor, Michigan: Cushing-Malloy, Inc.
4. Vancouleurs, Gerard De. 1957. Discovery of the Universe: An Outline of the History of Astronomy from the Origins to 1956. New York: Macmillian Company.
© 1997 norrickv@coral.indstate.edu
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