Patterns of Moon, Patterns of Sun
by Paul Lunde
In AD 638, six years after the death of the Prophet Muhammad,
Islam's second caliph 'Umar recognized the necessity of a calendar to govern the affairs of the Muslims. This was first of all a practical
matter. Correspondence with military and civilian officials in the newly conquered lands had to be dated. But Persia used a different
calendar from Syria, where the caliphate was based; Egypt used yet another. Each of these calendars had a different starting point, or
epoch. The Sasanids, the ruling dynasty of Persia, used June 16, AD 632, the date of the accession of the last Sasanid monarch, Yazdagird
III. Syria, which until the Muslim conquest was part of the Byzantine Empire, used a form of the Roman "Julian" calendar, with an epoch of
October 1, 312 BC. Egypt used the Coptic calendar with an epoch of August 39, AD 284. Although all were solar, and hence geared to the
seasons and containing 365 days, each also had a different system for periodically adding days to compensate for the fact that the true
length of the solar year is not 365 but 365.2422 days.
In pre-Islamic Arabia, various other systems of measuring time had
been used. In South Arabia, some calendars apparently were lunar, while others were lunisolar, using months based on the phases of the
moon but intercalating days outside the lunar cycle to synchronize the calendar with the seasons. On the eve of Islam, the Himyarites appear
to have used a calendar based on the Julian form, but with an epoch of 110 BC. In central Arabia, the course of the year was charted by the
position of the stars relative to the horizon at sunset or sunrise, dividing the ecliptic into 28 equal parts corresponding to the location
of the moon on each successive night of the month. The names of the months in that calendar have continued in the Islamic calendar to this
day and would seem to indicate that, before Islam, some sort of lunisolar calendar was in use, though it is not known to have had an
epoch other than memorable local events.
There were two other reasons 'Umar rejected existing solar
calendars. The Qur'an, in Chapter 10 Verse 5, states that time should be reckoned by the moon. Not only that, calendars used by the
Persians, Syrians and Egyptians were identified with other religions and cultures. He therefore decided to create a calendar specifically
for the Muslim community. It would be lunar, and it would have 12 months, each with 29 or 30 days.
This gives the lunar year 354 days, 11 days fewer than the solar
year. 'Umar chose as the epoch for the new Muslim calendar the hijrah, the emigration of the Prophet Muhammad and 70 Muslims from Makkah to
Madinah, where Muslims first attained religious and political autonomy. The hijrah thus occurred on 1 Muharram 1 according
to the Islamic calendar, which was named "hijri" after its epoch. (This date corresponds to July 16, AD 622 on the Gregorian
calendar.) Today in the West, it is customary, when writing hijri dates, to use the abbreviation AH, which stands for the Latin anno
hegirae, "year of the hijrah."
Because the Islamic lunar calendar is 11 days shorter than the
solar, it is therefore not synchronized to the seasons. Its festivals, which fall on the same days of the same lunar months each year, make
the round of the seasons every 33 solar years. This 11-day difference between the lunar and the solar year accounts for the difficulty of
converting dates from one system to the other.
The early calendar of the Roman Empire was lunisolar,
containing 355 days divided into 12 months beginning on January 1. To keep it more or less in accord with the actual solar year, a month was
added every two years. The system for doing so was complex, and cumulative errors gradually misaligned it with the seasons. By 46 BC,
it was some three months out of alignment, and Julius Caesar oversaw its reform. Consulting Greek astronomers in Alexandria, he created a
solar calendar in which one day was added to February every fourth year, effectively compensating for the solar year's length of 365.2422
days. This Julian calendar was used throughout Europe until AD 1582.
In the Middle Ages, the Christian liturgical calendar was grafted
onto the Julian one, and the computation of lunar festivals like Easter, which falls on the first Sunday after the first full moon after
the spring equinox, exercised some of the best minds in Christendom.
The use of the epoch AD 1 dates from the sixth century, but did not become common until the 10th. Because the zero had not yet reached the
West from Islamic lands, a year was lost between 1 BC and AD 1.
The Julian year was nonetheless 11 minutes and 14 seconds too
long. By the early 16th century, due to the accumulated error, the spring equinox was falling on March 11 rather than where it should, on
March 21. Copernicus, Christophorus Clavius and the physician Aloysius Lilius provided the calculations, and in 1582 Pope Gregory XIII ordered
that Thursday, October 4, 1582 would be followed by Friday, October 15, 1582. Most Catholic countries accepted the new "Gregorian" calendar,
but it was not adopted in England and the Americas until the 18th century. Its use is now almost universal worldwide. The Gregorian
year is nonetheless 25.96 seconds ahead of the solar year, which by the 4909 will add up to an extra day.
This article was taken from the 2005 Saudi Aramco World Calendar.
It was written by historian Paul Lunde, who specializes in Islamic history and literature.
His most recent book is Islam: Culture, Faith and History
(2001, Dorling Kindersley), a beautifully illustrated and concise introduction to the Muslim world. To find out more or to purchase
this book, click