Johannes Kepler, born in Weil in Würtemberg (now southwestern Germany) in 1571, seemed destined for a life in the church. He obtained a B.A. degree in theology in 1588 and entered the University of Tübingen, one of the great centers of Protestant learning, in 1589. He graduated with an M.A. in 1591.

While at Tübingen, Kepler had learned mathematics, and when the high school in Graz, Austria, needed a mathematics teacher, he got the job. He turned out to be very poor at teaching; during his first year only a handful of students attended his lectures, and the following year he had no students at all. That gave him considerable free time to further his interest in astronomy and produce annual almanacs, which were often heavy on astrological content. He also raised additional income by casting horoscopes.

Kepler, always the mystic, published a book...