The Islamic Calendar, which is based purely on lunar cycles, was first introduced in 638 C.E. by the close companion of the Prophet and the second Caliph, `Umar ibn Al-KHaTTab (592-644 C.E.). He did it in an attempt to rationalize the various, at times conflicting, dating systems used during his time. `Umar consulted with his advisors on the starting date of the new Muslim chronology. It was finally agreed that the most appropriate reference point for the Islamic calendar was the _Hijrah_. The actual starting date for the Calendar was chosen (on the basis of purely lunar years, counting backwards) to be the first day of the first month (1 MuHarram) of the year of the Hijrah. The Islamic (Hijri) calendar (with dates that fall within the Muslim Era) is usually abbreviated A.H. in Western languages from the latinized _Anno Hegirae_. MuHarram 1, 1 A.H. corresponds to July 16, 622 C.E.
The Hijrah, which chronicles the migration of the Prophet Muhammad (PBUH) from Makkah to Madinah in September 622 C.E., is the central historical event of early Islam. It led to the foundation of the first Muslim city-state, a turning point in Islamic and world history.
To Muslims, the Hijri calendar is not just a sentimental system of time reckoning and dating important religious events (e.g., Siyaam (fasting) and Hajj (pilgrimage to Makkah)). It has a much deeper religious and historical significance.
Muhammad Ilyes [Ilyes84] quotes Nadvi who wrote:
  ``It (the advent of the 15th century) is indeed, a unique
  occasion to ponder that the Islamic Era did not start
  with the victories of Islamic wars, nor with the birth
  or death of the prophet (PBUH), nor with the Revelation
  itself. It starts with Hijra, or the sacrifice for the
  cause of Truth and for the preservation of the Revelation.
  It was a divinely inspired selection. God wanted to teach
  man that struggle between Truth and Evil is eternal. The
  Islamic year reminds Muslims every year not of the pomp
  and glory of Islam but of its sacrifice and prepares them
  to do the same.''
From a historical angle, Ilyes quotes Samiullah who writes:
  ``All the events of Islamic history, especially those which 
  took place during the life of the Holy Prophet and afterwards
  are quoted in the Hijra calendar era. But our calculations 
  in the Gregorian calendar keep us away from those events and 
  happenings, which are pregnant of admonitory lessons and guiding
  ...And this chronological study is possible only by adopting the
  Hijri calendar to indicate the year and the lunar month in line
  with our cherished traditions.''


The Islamic (Hijri) year consists of twelve (purely lunar) months.
They are: 

(1) MuHarram
(2) Safar
(3) Raby` al-awal
(4) Raby` al-THaany
(5) Jumaada al-awal
(6) Jumaada al-THaany
(7) Rajab
(8) SHa`baan
(9) RamaDHaan
(10) SHawwal
(11) Thw al-Qi`dah
(12) Thw al-Hijjah

The most important dates in the Islamic (Hijri) year are:
1 MuHarram (Islamic new year); 27 Rajab (Isra & Miraj); 1 RamaDHaan 
(first day of fasting); 17 RamaDHan (Nuzul Al-Qur'an); Last 10
days of RamaDHaan which include Laylatu al-Qadar; 1 SHawwal 
(`iyd al-FiTr); 8-10 Thw al-Hijjah (the Hajj to Makkah); and 
10 Thw al-Hijjah (`iyd al-'aDHHae).

It is considered a divine command to use a (Hijra) calendar with 12 (purely)
lunar months without intercalation [Ilyes84], as evident from the following
verses of the Holy Qur`an (Trans: A. Yusuf Ali):

  They ask thee
  the New Moons
  Say: They are but signs
  To mark fixed periods of time
  In (the affairs of) men
  And for Pilgrimage. (II:189)

  The number of months
  In the sight of Allah
  Is twelve (in a year)
  So ordained by Him
  The day He created
  The heavens and the earth;
  Of them four are sacred;
  That is the straight usage
  So wrong not yourselves
  Therein, and fight the Pagans. (IX: 36)

  Verily the transposing 
  (Of a prohibited month)
  Is an addition to Unbelief:
  The Unbelievers are led
  To wrong thereby: for they make
  it lawful one year,
  And forbidden another year,
  Of months forbidden by Allah
  And make such forbidden ones
  Lawful. The evil of their course
  Seems pleasing to them.
  But Allah guideth not
  Those who reject Faith. (IX: 37)

Since the Islamic calendar is purely lunar, as apposed to solar or luni-solar,
the Muslim (Hijri) year is shorter than the Gregorian year by about 11 days,
and months in the Islamic (Hijri) year are not related to seasons, which
are fundamentally related to the solar cycle. This means that important
Muslim festivals, which always fall in the same Hijri month, may occur
in different seasons. For example, the Hajj and RamDHaan can take place in
the summer as well as the winter. It is only over a 33 year cycle that lunar
months take a complete turn and fall during the same season.

For religious reasons, the beginning of a Hijri month is marked not by
the start of a new moon, but by a physical (i.e., an actual human) sighting
of the crescent moon at a given locale. From the Fiqhi standpoint, one may
begin the fast in RamDHaan, for example, based on "local" sighting (IKHTILAF
AL-MATALE') or based on sighting anywhere in the Muslim World (ITTEHAD
AL-MATALE'). Although different, both of these positions are valid Fiqhi

Astronomically, some data are definitive and conclusive (i.e. the time of the
BIRTH of a new moon). However, determining the VISIBILITY of the crescent
is not as definitive or conclusive; rather it is dependent upon several
factors, mostly optical in nature. This makes it difficult to produce
(in advance) Islamic calendars that are reliable (in the sense that they
are consistent with actual crescent visibility).

Efforts for obtaining an astronomical criterion for predicting the time of
first lunar visibility go back the the Babylonian era, with significant 
improvements and work done later by Muslim and other scientists. These 
efforts have resulted in the development in a number of criteria for 
predicting first possible sighting of a crescent. However, there remains 
a measure of uncertainty associated with all criteria developed thus far.  
Moreover, there has been little work in the area of estimating crescent 
visibility on global (as apposed to local) scale. Until this happens, no 
Hijri calendar software can be 100% reliable, and actual crescent sighting 
remains essential especially for fixing important dates such as the beginning
of RamaDHaan and the two `iyds.

The slight differences in printed Islamic calendars, worldwide, can therefore
be traced to two primary factors: (1) the absence of a global criterion for
first visibility; and (2) the use of different visibility criterion (or
method of calculation). Weather conditions and differences in the observer's
location also explain why there are sometimes differences in the 
observances of Islamic dates, worldwide.

Readers interested in further information should consult Muhammad
Ilyas' excellent book ``A Modern Guide to Astronomical Calculations of Islamic
Calendar, Times & Qibla,'' Berita Publishing, 1984, (ISBN: 967-969-009-1).
The book contains a thorough discussion of the Islamic calendrical system 
and related historical and scientific developments. It also presents a sound
proposal for a universal Islamic Calendar based on a global visibility 
criterion and the concept of a Lunar Day (or International Lunar Date Line).

Waleed Muhanna

Tuesday 13 Jumaada al-THaany 1413 A.H.