Focuses on the events leading to the legal battle over plagiarism, between astronomers Tycho Brahe and Nicolaus Raimarus Ursus during the 17th century. Range of insights into the theory and practices of astronomy generated by the Tycho-Ursus controversy; Background on Johannes Kepler's contribution to the controversy through his paper "Apologia pro Tychone contra Ursum," which he composed around Christmas 1600; Information about the contemporary views on the status of astronomical hypotheses, on the duties of an astronomer, and on the origins and development of the discipline, offered in Kepler's discourse.