The Islamic Hijri Calendar
The Hijri calendar is the principal calendar used throughout the Islamic world for religious observances. Based on the lunar cycle rather than the solar year, it has been in continuous use since it was established during the caliphate of Umar ibn al-Khattab in 638 CE.
Historical Origin
The Hijri calendar counts from the Hijra — the migration of Prophet Muhammad ﷺ from Mecca to Medina in 622 CE. This event was chosen as the starting point because it marked the establishment of the first organized Muslim polity in Medina. The calendar was formally adopted about 17 years later to standardize date-keeping across the growing Muslim world. Year 1 AH (After Hijra) corresponds to 622 CE.
Calendar Structure
The Hijri calendar consists of 12 lunar months alternating between 29 and 30 days, totaling 354 or 355 days per year. This makes it about 11 days shorter than the Gregorian solar calendar. As a result, Islamic dates cycle through the Gregorian calendar over approximately 33 years, meaning Ramadan, Hajj, and other observances pass through every season over time.
The Twelve Months
The twelve Hijri months are: Muharram, Safar, Rabi al-Awwal, Rabi al-Thani, Jumada al-Ula, Jumada al-Thani, Rajab, Sha'ban, Ramadan, Shawwal, Dhul Qa'dah, and Dhul Hijjah. Four months are considered sacred: Muharram, Rajab, Dhul Qa'dah, and Dhul Hijjah. Ramadan is the month of fasting, and Dhul Hijjah is the month of the Hajj pilgrimage.
New Moon Sighting
Traditionally, a new Hijri month begins when the crescent moon (hilal) is sighted by reliable witnesses after sunset following a new moon. Different regions and authorities use different criteria: some require physical sighting with the naked eye, others accept astronomical calculations, and some use a combination. This can lead to different communities starting the month on different days — which is why Eid dates sometimes vary between countries.
Visibility Criteria
Modern astronomical criteria attempt to predict crescent visibility scientifically. The Umm al-Qura calendar uses calculations for Mecca as a reference. MABIMS (used in Southeast Asia) requires minimum altitude and elongation angles. ISNA uses astronomical calculations for North America. The South African and Turkish criteria each have their own parameters. The tabular method uses a fixed 30-year arithmetic cycle as a simpler alternative.
Religious Significance
The lunar nature of the Hijri calendar carries deep religious significance. It ensures that religious obligations like fasting in Ramadan are experienced in all seasons over time, sharing the varying difficulty across climates. The reliance on moon sighting connects Muslims to celestial observation and the natural rhythms of creation.
This content is based on astronomical calculations and scholarly traditions. For religious rulings, please consult your local Islamic authority.
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