Islamic calendar
A lunar calendar used in Islam, with twelve months in each year and an epoch marking the Hijra, Muhammad’s migration from Mecca to Medina.
Lunar month: A period measured by the Moon’s cycle of phases, usually about 29.5 days. Islamic months follow the lunar cycle and last 29 or 30 days.
Lunar phase: The changing visible shape of the Moon as it orbits Earth and reflects sunlight. Month boundaries depend on the Moon’s changing appearance.
Ramadan: The ninth month of the Islamic calendar, during which Muslims observe fasting from dawn to sunset. Its start and end depend on the calendar’s month determination.
Umar ibn al-Khattab: The second caliph, whose reign established the Hijra as the starting point for Islamic year numbering. His decision formalized the calendar’s epoch.
Hebrew calendar: A lunisolar calendar used in Judaism, with leap months that keep its months near their seasons. Its seasonal adjustment contrasts with the Islamic calendar’s unadjusted lunar year.
Crescent moon sighting: The observation of the thin crescent Moon shortly after conjunction, marking the start of a lunar month in some traditions. Traditional month beginnings depend on whether the new crescent is sighted.
Hijra: Muhammad’s migration from Mecca to Medina in 622 CE, which marks the Islamic calendar’s epoch. The calendar numbers its years from this event.
Hajj: The annual Islamic pilgrimage to Mecca, performed during Dhu al-Hijjah. Its appointed dates are fixed by the Islamic calendar.
Islamic calendar epoch: The reference point from which Islamic years are counted, conventionally corresponding to 622 CE. It anchors the calendar’s year count to the Hijra.
Chinese calendar: A lunisolar calendar used for traditional Chinese dates, combining lunar months with solar-year adjustment. Like the Hebrew calendar, it preserves seasonal alignment through intercalation.