In a discussion of optical effects of the atmosphere, Aristotle here addresses the formation of a halo around the Moon. This is one of the most interesting uses of mathematics in all of Aristotle’s writings. Aristotle defined the subject of meteorology as everything that takes place beneath the Moon, including earthquakes, comets, rainbows and topics that now fall under other disciplines including astronomy and geology. Because Aristotle regarded sublunar matter as imperfect, beset by chance, he taught that in these things one could only hope for probable rather than certain knowledge.