Aztec calendar divisions with the Moon. 18th-century illustration of the division of an Aztec year ('xiuhpohualli') into 18 equal non-lunar periods of 20 days called veintena. Anti-clockwise from top: Atlcahualo,Tlacaxipehualiztli,Tozoztontli,Huey Tozoztli,Toxcatl,Etzalcualiztli,Tecuilhuitontli,Huey Tecuilhuitl,Miccailhuitontli,Huey Miccailhuitontli,Ochpaniztli,Teotleco,Tepeilhuitl,Quecholli,Panquetzaliztli,Atemoztli,Tititl,Izcalli. An extra 5-day nemontemi period made 365 days in total. This illustration is from a 1790 work by Mexican astronomer Antonio de Leon y Gama (1735-1802) describing the discovery of an Aztec calendar stone in Mexico City that year |