Understanding the Hijri Calendar

By W.A.O. Akewusola, Esq.

“Verily, the number of months with Allah is twelve months (in a year), so was it ordained by Allah on the Day when He created the heavens and the earth…” (Qur’an 9:36)

A calendar can simply be described as a system of measuring time for human activities—religious or secular—by dividing time into days, weeks, months, and years. It is based on the movements of the earth and the regular appearances of the sun and the moon.

A day is the average time required for one rotation of the earth on its axis. The measurement of a year is based on one revolution of the earth around the sun and is called a seasonal, tropical, or solar year. A solar year contains 365 days, 5 hours, 48 minutes, and 45.5 seconds. On the other hand, the moon completes its orbit around the earth in approximately 29.5 days. This measurement, called a synodic or lunar month, results in a lunar year of 354 days—about 11 days shorter than a solar year. This is where the Hijri calendar of the Muslims falls.

Long before the Islamic calendar was instituted, several other systems existed:

• The Jewish Calendar is lunisolar, based on lunar months of 29 and 30 days alternating, with an extra month intercalated every three years in a 19-year cycle. Derived from the ancient Hebrew calendar, it has remained largely unchanged since about AD 900 and is still in use in modern Israel.

• The Roman Calendar, introduced around the 7th century BC, originally had 10 months and 304 days in a year beginning with March. Two more months, January and February, were later added.

• The Gregorian Calendar, also called the Christian calendar, uses the birth of Jesus Christ as its starting date. It replaced the Julian calendar (implemented by Julius Caesar) and remains the global standard today. The British eventually adopted January 1 as the start of the new year. The Gregorian system is based on the solar cycle, adjusting the lengths of the 12 months to fit into a solar year of 365 days.

Out of all these systems, only the Gregorian calendar is now used worldwide. In this system, the relative movement of the sun and the earth defines the year as 365.25 days. By contrast, the Hijri calendar uses the relative movement of the moon and the earth, with a year defined as 12 × 29.53 days, approximately 354.36 days.

The Islamic calendar is a lunar-based system reckoned from AD 622, the year of the Hijrah(emigration of Prophet Muhammad (pbuh) from Makkah to Madinah). It consists of 12 lunar months.

Thirty years form a cycle in which the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years are leap years of 355 days; the others are common years of 354 days. The Hijri calendar was first adopted during the caliphate of Umar ibn al-Khattab (RA), the second caliph, in 17 AH (Anno Hegirae—“in the year of the Hijrah”).

The number of days in Hijri months is not fixed. It relies on the moon’s movement around the earth. Traditionally, the crescent moon is physically sighted to determine the start and end of each month especially important for spiritual months such as Ramadan (fasting) and Dhul-Hijjah (Hajj). However, scientific calculations and astronomical predictions are increasingly used today.

In Islam, the sighting of the new moon (hilal) is crucial for determining the start of Islamic months, particularly Ramadan and Shawwal (the month of Eid al-Fitr). Hadith narrated by Prophet Muhammad (pbuh) emphasized this practice, saying:

“Fast when you see the crescent (of Ramadan), and break your fast when you see the crescent (of Shawwal). If the sky is cloudy and you are unable to see it, then complete thirty days of Shaʿbān.”(Sahih Muslim 1081b)

The 12 months of the Hijri year are:

Muḥarram, Ṣafar, Rabīʿ al-Awwal, Rabīʿ al-Thānī, Jumādā al-Awwal, Jumādā al-Thānī, Rajab, Shaʿbān, Ramaḍān (month of fasting), Shawwāl, Dhū al-Qaʿdah, and Dhū al-Ḥijjah (month of Hajj).

In lunar calendars, a lunar month is the time between two identical syzygies (new moons or full moons). Since the Hijri year is approximately 10.88 days shorter than the Gregorian year, Islamic festival dates shift earlier each year on the Gregorian calendar.

Culled from Islam, Science and the Production of an Enduring Islamic Calendar by W.A.O. Akewusola, Esq.

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