Kepler is the middle third of the great triumvirate of physicists that led humanity from a point where little was known about planetary motion to where nearly all was known. The first was Galileo Galilei and the last was Isaac Newton. Kepler contributed the three laws of planetary motion that are now named after him. They are:
*) The planets follow elliptical orbits about the sun.
*) The line connecting the planet to the sun sweeps out equal areas over equal times.
*) The square of the period of an orbit divided by the cube of the mean distance is a constant.
While Copernicus published the first convincing heliocentric theory, it was Kepler who gave the theory a mathematical foundation based on the years of accurate observations made by Tycho Brahe. It was his work that convinced the learned world that the planets orbited the sun.
When reading the history of Kepler, it is astonishing that he managed to be successful. He suffered from poor health, petty jealousies, lack of income, the death of some of his children, major religious persecution, plague and a war that devastated central Europe. He lived in a time of major religious conflict as the Reformation had moved strongly forward and the Counter-Reformation was responding violently. Kepler was a Protestant and remained so under the real threat of banishment and even death. Approximately one third of the people in central Europe perished during the widespread destruction of the thirty years war, which went on around Kepler. He was once trapped in a city placed under siege by Protestant forces and when told he must convert to Catholicism or be banished, he chose to leave.
Through it all, Kepler continued his intellectual pursuits, sometimes down false paths, but through perseverance and dedication, he was able to solve the puzzle of planetary motion. This story is not so much about the physicist persona of Kepler, it is a tale of triumph over tremendous obstacles where the result was of great benefit to all of humanity. This is a good, direct story of Kepler, his life and the environment he toiled in. I strongly recommend it as a textbook about Kepler, the history of his times and how modern physics was developed. Very little background in physics is needed to understand the presentation.
