At sundown on November 19,1979, a new century will begin - a new Muslim century.
For Muslims, who do not use the Gregorian, or Western calendar, that date will be the first day of the year 1400 "A. H." - the abbreviation for Anno Hegirae. The Latin term means "the year of the Hijra," and refers to the Prophet Muhammad's migration from Mecca to Medina, taken as the starting point of the Islamic calendar.
The Hijra occurred in the year 622 A.D. - as the Western world measures it - a year of great importance, for it marked the beginning of the first organized Muslim community, predecessor of today’s world-wide community.
To most laymen today the organization of calendars is a total mystery. And even experts are hard pressed to give lucid explanations of why 1979, in China, is the year 4676, why "leap years" are vital, why February, in the Gregorian calendar, usually has only 28 days and why, to quote the schoolday mnemonic rhyme, "thirty days hath September, April, June and November."
Calendars always were confusing. The confusion, in fact, was one of the elements that persuaded 'Umar, the second caliph, to establish a purely Islamic calendar.
Until the time of 'Umar, exact calendars in the Arab World were of minimal importance to the Muslims. But as the Islamic empire grew, so did the problems of administration. 'Umar, for example, found himself faced with an extensive correspondence with his generals and regional governors, as well as with the daily tasks of regulating the financial affairs of the community. And one man, Abu Musa al-Ashari, later the governor of Kufa, finally wrote to 'Umar tactfully pointing out a problem. "You are sending us undated letters," he said.
Pondering this, 'Umar saw how undated correspondence might lead to confusion, and consulted with his advisors. What he found was that the various systems of dating then used in the empire were bewildering in their variety.
The Christian and Jewish communities, for example, used calendars calculated from the date of the creation of the world, a date about which there was, understandably, a good deal of doubt. The Coptic community in Egypt used a calendar based on the date of the accession to the throne of the Emperor Diocletian; other communities used the "Era of Alexander" and there were two calendars in use in Iran: one based on the date of the accession to the throne of Yazdegird III, the other based on the date of his death. Because of this confusion - and the fact that the various calendars in use were intimately linked to other religions or to rival states - 'Umar decided to establish an Islamic dating system.
The first step, of course, was to choose a starting date, and immediately there were suggestions that the year of the Prophet's birth be the first year of the proposed new era. As this was not known with certainty, however, it was suggested - and agreed - that the Muslims adopt the year of the Hijra as the base year, because of the journey's importance to Islam.
But the Muslims did not take the exact day of Muhammad's arrival in Medina as the first day of the new year. Instead they took the first day of the first month - Muharram - of the year in which this crucial event took place. Thus the Muslim calendar started on 1 Muharram, 1 AH. - which corresponds with 16 July, 622 AD. (Some reference books give 15 July instead of 16 July; this discrepancy arises from the fact that Muslims reckoned their days from sunset to sunset, while the West reckons them from midnight to midnight.)
Because the Koran (Sura 10:5) establishes the use of lunar months for Muslims - that is, a calendar based on the phases of the moon - the Islamic year does not correspond with the Gregorian calendar, which is based on a solar year; as an astronomical lunar month contains 29 days, 12 hours, 44 minutes and 3 seconds, a year composed of 12 such lunar months contains 354 days, 8 hours, 48 minutes and 36 seconds - which is approximately 11 days shorter than the solar year.
The months of the Muslim year, by convention, have 29 and 30 days alternately. This means that the Hijra - or, more exactly, the Hizri-year contains exactly 354 days. The 8 hours, 48 minutes and 36 seconds difference (11/30 of a day) between this figure and the astronomical lunar year adds up to 11 days in every cycle of 30 years. These 11 days are inserted into the calendar by establishing leap years. Every period of 30 years, therefore, has 11 leap years of 355 days instead of 354. These are normally the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th, and 29th years of the 30-year cycle. The "leap day" which is added to these years is always assigned to the end of the month of Dhu al-Hijja, the month of the Hajj - the Muslim pilgrimage to Mecca - and last month of the year. In just the same way, the Gregorian calendar adds an extra day to February every four years.
Since the Hijri year is 11 days shorter than the Gregorian year, the beginning of each Hijri year falls 11 days earlier in the Gregorian calendar each year. Thus the Hijri year moves backward in relation to the Western calendar. This retrograde motion has an important consequence: Muslim festivals fall at different times each year, according to the Western calendar, although always, of course, in the same month of the Hijri year. Every 33 years, the months of the Muslim calendar make a complete backwards circuit of the seasons. This explains why the Hajj, for example, sometimes falls in midwinter and sometimes in summer. The months of the Hijri year, unlike the Gregorian year, bear no relation to the seasons.
The conversion of Gregorian to Hijri dates and vice-versa is no easy matter, particularly if one is trying to find the exact day. The matter is further complicated by the fact that the Gregorian calendar used now did not come into use until 1582 in Europe, and not until the early 18th century in England. Dates before then, therefore, must be calculated according to still another system: the Julian calendar. Given this final complication, the easiest way to find the correspondence between a Gregorian and a Hijri date is to refer to a table.
Converting years is much easier. A simple rule of thumb is that each Gregorian century equals approximately 103 Hijri years, and that, conversely, each 100 years of the Hijri calendar equals 97 years of the Gregorian. A useful benchmark is that the year 1300 A.D. corresponded with 700 A. H.
A more exact calculation can be made by using the following formulae, where G = Gregorian year and H = Hijri year:
G = H + 622 – (H/33)
H = G – 622 + {(G-622)/32}
Applying the second formula, therefore, and consulting the tables, November 19, 1979 is 1 Muharram, 1400, the first day of the first month of the first year of the 15th century - A. H.
Paul Lunde is a staff writer for Aramco World Magazine.
