This contribution examines the Jesuit adaptation of astronomy as a tool for proselytization in Japan, focusing on the first known work of Western science authored in the country: Pedro Gomez's De Sphaera (1593). Said work offers a snapshot of Western cosmology as part of a compendium, coupled with the Aristotelian theory of the soul and an exposition of Christian theology. Taken together, the trilogy served as a textbook for Japanese students preparing for priesthood. The utilization of astronomy for a theological education in Japan stands in stark contrast to the discomfort this science caused to the Catholic Church in 16th century Europe - here, cosmological discourse was routinely censored by ecclesiastic authorities seeking to defend theological dogma. This study discusses this apparent paradox: How a science considered subversive to the Catholic faith at home could be used to corroborate Church doctrine abroad. The argument first explores how the Jesuits were involved in the defence of traditional cosmology in 16th century Europe. A textual comparison between Gomez's textbook and other prominent exponents of Jesuit astronomy in Europe then specifies what kind of knowledge he brought to Japan in order to illustrate the purpose it served in the missionary context.
