<Christopher Clavius>(1) was a German Jesuit mathematician and astronomer who modified the proposal of the modern Gregorian calendar after the death of its primary author, <Aloysius Lilius>(2). <Clavius>(1) would later write defences and an explanation of the reformed calendar, including an emphatic acknowledgement of <Lilio>(2)'s work. In his last years he was probably the most respected astronomer in Europe and his textbooks were used for astronomical education for over fifty years in and even out of <Europe>(3). ___ (1) owl:sameAs dbr:Christopher_Clavius (1) foaf:isPrimaryTopicOf wiki:Christopher_Clavius (2) owl:sameAs dbr:Aloysius_Lilius (3) foaf:isPrimaryTopicOf wiki:Europe