Galileo wrote these letters as a refutation to sunspot theories put forth by a Jesuit scientist and astronomer, Christoph Scheiner (1575-1650). In his willingness to draw conclusions based on his own observations of physical events, even when those conclusions contradicted scientific dogma, Galileo laid the foundation for modern scientific method and for his later rejection of the Ptolemaic system, which assumed that the sun and planets revolved around the earth.