The astrolabe is an instrument designed to measure the altitude of celestial bodies in order to tell time by day or by night. An astrolabe in the Royal Ontario Museum’s collections was acquired at auction in 1988. According to the auction catalogue, it was made in Morocco, dated 1845. Years later, in preparation for a university course on the history of science, this writer’s scrutiny of the astrolabe’s inscribed features and physical condition suggested that it was a forgery. The paper (...) explains the reasoning behind the judgement of falsehood. (shrink)