observations in formulating his theory of gravitational force. Kepler was a great author by many standards. Besides his astronomical books, he is credited with having written the first science fiction novel, his Somnium, published in 1634 and describing a voyage to the Moon. He wrote extensively on geometrical optics, and was the first to correctly sort out once and for all the production of real versus virtual images by mirrors and lenses. Kepler also made contributions in the field of optics and developed a system of infinitesimals in mathematics, which was a forerunner of calculus. Kepler died on November 15, 1630, in Regensburg....
