How Traditions Count Time

A calendar is a system for organising and counting days into larger units (weeks, months, years and eras), and this category holds the calendars of the world's traditions: solar, lunar and lunisolar, with their months, intercalations and reckonings of the year. Each entry records a system's structure, where and by whom it is used, and how it relates to the common civil calendar.

The fundamental problem every calendar solves is that the natural cycles do not divide evenly: the year is not a whole number of days or of lunar months, so any calendar must choose which cycle to follow and how to reconcile it with the others.