lunar calendar

Glossaries

Term	Definition
lunar calendar	A lunar calendar is a timekeeping system based on the phases of the Moon, historically used by many civilizations and still central to various religious traditions. A lunar calendar is structured around the synodic cycle of the Moon, approximately 29.5 days from one new moon to the next. A lunar month typically has 29 or 30 days, and a lunar year comprises 12 lunar months, totaling about 354 days. This system does not align with the solar year, which is around 365.25 days long. As a result, months in a purely lunar calendar shift each year with respect to the seasons. This is the case with the Islamic calendar (Hijri), which determines religious observances such as Ramadan and Hajj. In contrast, lunisolar calendars—like those in China or India—combine lunar months with solar years, adding intercalary months to synchronize with the seasons. Lunar calendars were used in antiquity by the Babylonians, Greeks, Hebrews, Celts, and others. They shaped the organization of sacred time, and continue to influence ritual calendars and religious architecture through orientation and festival timing.

Term

Definition

A lunar calendar is a timekeeping system based on the phases of the Moon, historically used by many civilizations and still central to various religious traditions.

A lunar calendar is structured around the synodic cycle of the Moon, approximately 29.5 days from one new moon to the next. A lunar month typically has 29 or 30 days, and a lunar year comprises 12 lunar months, totaling about 354 days.

This system does not align with the solar year, which is around 365.25 days long. As a result, months in a purely lunar calendar shift each year with respect to the seasons. This is the case with the Islamic calendar (Hijri), which determines religious observances such as Ramadan and Hajj. In contrast, lunisolar calendars—like those in China or India—combine lunar months with solar years, adding intercalary months to synchronize with the seasons.

Lunar calendars were used in antiquity by the Babylonians, Greeks, Hebrews, Celts, and others. They shaped the organization of sacred time, and continue to influence ritual calendars and religious architecture through orientation and festival timing.