The University of Oklahoma History of Science Collections recently acquired a 1623 manuscript which has been attributed to the Jesuit mathematician Orazio Grassi. The first section of the manuscript, entitled “Tractatus de sphaera” or “Treatise on the sphere,” is a fair copy of student notes on spherical astronomy. As such, it is a significant new primary source for understanding the teaching of astronomy at the Collegio Romano in the seventeenth century. Through a physical examination of the manuscript, critical discussion of its subject matter and comparison with other Jesuit writings, this thesis argues that Orazio Grassi was teaching physico-mathematics in his astronomy course at the Jesuit Roman College in 1623 as part of a concerted effort started by Christopher Clavius and institutionalized in Jesuit education. Jesuit educators such as Orazio Grassi were actively introducing novel observations and contemporary discoveries to astronomy students in the early seventeenth century.