Solar, lunar, lunisolar

A solar calendar (like the Gregorian) follows the Sun and keeps the seasons fixed but lets the months drift from the Moon; a lunar calendar (like the Islamic) follows the Moon and lets the year drift through the seasons; a lunisolar calendar (like the Hebrew, Chinese and Hindu) follows the Moon but adds a leap month periodically to stay in step with the Sun. Each choice shapes a tradition's festivals and life.

The atlas describes each calendar's rule, its months and eras, and its religious use. The individual months and units of particular calendars (Hebrew, Islamic, Maya and others), are treated in their own categories under Calendars & Time.