365-day calendar 365-day calendar A 365-day calendar consists of exactly 365 days per year (no leap days), and is primarily used in computer models and as an assumption in every-day calculations. For example, a calculation of a daily rate may use an annual total divided by exactly 365. Interest rates in some banks are calculated using a 365-day calendar. Some Mesoamerican calendars used a 365-day year with no leap year, resulting in a gradual shift of the seasons relative to the calendar. This includes the Maya Haab' and the Aztec Xiuhpohualli calendars. Some versions of the Zoroastrian calendar also use a fixed
Mesoamerican calendars (year count) and "tonalpohualli" (day count) respectively. The Veintena was called "metztli" (moon), and the five unlucky days at the end of the solar year were called "nemontemi". Other calendar cycles were also recorded, such as a lunar calendar, as well as the cycles of other astronomical objects, most importantly Venus. Mesoamerican calendars Mesoamerican calendars are the calendrical systems devised and used by the pre-Columbian cultures of Mesoamerica. Besides keeping time, Mesoamerican calendars were also used in religious observances and social rituals, such as for divination. The existence of Mesoamerican calendars is known as early as ca. 500 BCE, with