Young German mathematician, Johannes Kepler, decided to prove the heliocentric theory of Copernicus.  After publishing his first book, "The Cosmic Mystery" he was offered a position as an assistant at the astronomy laboratory of Tycho Brahe. It was Tycho's analytical data of the position and movements of the planets that led Kepler to formulate his mathematical description of the heavens.  Kepler's three laws described the elliptical movement of planets around the sun; these laws were a foundation for modern astronomy. Kepler earned his living as an astrologer, while following his scientific passion, astronomy.  His last manuscript, Somnium, written in 1611, described an imaginary trip to the moon, and is sometimes called the first science fiction novel ever published.