calendar (or Hijri calendar) is a purely lunar calendar. It
contains 12 months that are based on the motion of the moon, and
because 12 synodic months is only 12 x 29.53=354.36 days, the
Islamic calendar is consistently shorter than a tropical year,
and therefore it shifts with respect to the Christian calendar.
The calendar is
based on the Qur'an (Sura IX, 36-37) and its proper
observance is a sacred duty for Muslims.
calendar is the official calendar in countries around the Gulf,
especially Saudi Arabia. But other Muslim countries use the
Gregorian calendar for civil purposes and only turn to the
Islamic calendar for religious purposes.
What does an
Islamic year look like?
The names of
the 12 months that comprise the Islamic year are:
al-awwal (Rabi' I)
al-thani (Rabi' II)
al-awwal (Jumada I)
al-thani (Jumada II)
(Due to different
transliterations of the Arabic alphabet, other spellings of the
months are possible.)
starts when the lunar crescent is first seen (by a human
observer's eye) after a new moon.
moons may be calculated quite precisely, the actual visibility
of the crescent is much more difficult to predict. It depends on
factors such as weather, the optical properties of the
atmosphere, and the location of the observer. It is therefore
very difficult to give accurate information in advance about
when a new month will start.
some Muslims depend on a local sighting of the moon, whereas
others depend on a sighting by authorities somewhere in the
Muslim world. Both are valid Islamic practices, but they may
lead to different starting days for the months.
So you can't
print an Islamic calendar in advance?
Not a reliable
one. However, calendars are printed for planning purposes, but
such calendars are based on estimates of the visibility of the
lunar crescent, and the actual month may start a day earlier or
later than predicted in the printed calendar.
methods for estimating the calendars are used.
mention a crude system in which all odd numbered months have 30
days and all even numbered months have 29 days with an extra day
added to the last month in 'leap years' (a concept otherwise
unknown in the calendar). Leap years could then be years in
which the number year mod 30 is one of the following:
2, 5, 7, 10, 13, 16, 18, 21, 24, 26, or 29. (This is the
algorithm used in the calendar program of the Gnu Emacs editor.)
Such a calendar
would give an average month length of 29.53056 days, which is
quite close to the synodic month of 29.53059 days, so on the
average it would be quite accurate, but in any given month
it is still just a rough estimate.
algorithms for estimating the visibility of the new moon have
How does one
counted since the Hijra, that is, Mohammed's flight to Medina,
which is assumed to have taken place 16 July C.E. 622
(Julian calendar). On that date AH 1 started (AH = Anno
Hegirae = year of the Hijra).
In the year C.E. 1998
we have witnessed the start of Islamic year AH 1419.
although only 1998 - 622 = 1376 years have passed in the
Christian calendar, 1418 years have passed in the Islamic
calendar, because its year is consistently shorter (by about 11
days) than the tropical year used by the Christian calendar.
When will the
Islamic calendar overtake the Gregorian calendar?
As the year in
the Islamic calendar is about 11 days shorter than the year in
the Christian calendar, the Islamic years are slowly gaining in
on the Christian years. But it will be many years before the two
coincide. The 1st day of the 5th month of C.E. 20874 in the
Gregorian calendar will also be (approximately) the 1st day of
the 5th month of AH 20874 of the Islamic calendar.