Tabular Islamic calendar
Encyclopedia
The Tabular Islamic calendar (an example is the Fatimid
or Misri calendar) is a rule-based variation of the Islamic calendar
. It has the same numbering of years and months, but the months are determined by arithmetic rules rather than by observation or astronomical calculations. It was developed by early Muslim astronomers of the second hijra century (the 8th century of the Common Era
) to provide a predictable time base for calculating the positions of the moon, sun, and planets. It is now used by historians to convert an Islamic date into a Western calendar when no other information (like the day of the week) is available.
It is used by some Muslims in everyday life, particularly in the Dawoodi Bohra
Ismaili community and they believe that this calendar was developed by Ali
. It is believed by the Dawoodi Bohras that when Ali drew up this calendar, the previous events of the earlier prophets also fell into line with this calendar. It is their firm belief, that all Fatimid Imams and their Da'ees have followed this tradition.
Each year has 12 months. The odd numbered months have 30 days and the even numbered months have 29 days, except in a leap year
when the 12th and final month has 30 days.
There are 11 leap years in a 30 year cycle. Noting that the average year has 354 11/30 days and a common year has 354 days, at the end of the first year of the 30-year cycle the remainder is 11/30 day. Whenever the remainder exceeds a half day (15/30 day), then a leap day is added to that year, reducing the remainder by one day. Thus at the end of the second year the remainder would be 22/30 day which is reduced to −8/30 day by a leap day. Using this rule the leap years are
of the 30-year cycle. If leap days are added whenever the remainder equals or exceeds a half day, then all leap years are the same except 15 replaces 16.
The Ismaili Tayyebi community uses the following order of leap years in their 30-year cycle.
Apart from these, there are two more orders for the leap years which are as follows
The mean month is 29 191/360 days = 29.5305555... days. This is slightly too short and so will be a day out in about 2500 years. The Tabular Islamic calendar also deviates from the observation based calendar in the short term for various reasons.
Fatimid
The Fatimid Islamic Caliphate or al-Fāṭimiyyūn was a Berber Shia Muslim caliphate first centered in Tunisia and later in Egypt that ruled over varying areas of the Maghreb, Sudan, Sicily, the Levant, and Hijaz from 5 January 909 to 1171.The caliphate was ruled by the Fatimids, who established the...
or Misri calendar) is a rule-based variation of the Islamic calendar
Islamic calendar
The Hijri calendar , also known as the Muslim calendar or Islamic calendar , is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in many Muslim countries , and used by Muslims everywhere to determine the proper day on which to celebrate Islamic...
. It has the same numbering of years and months, but the months are determined by arithmetic rules rather than by observation or astronomical calculations. It was developed by early Muslim astronomers of the second hijra century (the 8th century of the Common Era
Common Era
Common Era ,abbreviated as CE, is an alternative designation for the calendar era originally introduced by Dionysius Exiguus in the 6th century, traditionally identified with Anno Domini .Dates before the year 1 CE are indicated by the usage of BCE, short for Before the Common Era Common Era...
) to provide a predictable time base for calculating the positions of the moon, sun, and planets. It is now used by historians to convert an Islamic date into a Western calendar when no other information (like the day of the week) is available.
It is used by some Muslims in everyday life, particularly in the Dawoodi Bohra
Dawoodi Bohra
Dawoodi Bohra is a subsect of Ismāʿīlī Shīʿa Islām. While the Dawoodi Bohra is based in India, their belief system originates in Yemen, where it evolved from the Fatimid Caliphate and where they were persecuted due to their differences from mainstream Sunni Islam...
Ismaili community and they believe that this calendar was developed by Ali
Ali
' |Ramaḍān]], 40 AH; approximately October 23, 598 or 600 or March 17, 599 – January 27, 661).His father's name was Abu Talib. Ali was also the cousin and son-in-law of the Islamic prophet Muhammad, and ruled over the Islamic Caliphate from 656 to 661, and was the first male convert to Islam...
. It is believed by the Dawoodi Bohras that when Ali drew up this calendar, the previous events of the earlier prophets also fell into line with this calendar. It is their firm belief, that all Fatimid Imams and their Da'ees have followed this tradition.
Each year has 12 months. The odd numbered months have 30 days and the even numbered months have 29 days, except in a leap year
Leap year
A leap year is a year containing one extra day in order to keep the calendar year synchronized with the astronomical or seasonal year...
when the 12th and final month has 30 days.
There are 11 leap years in a 30 year cycle. Noting that the average year has 354 11/30 days and a common year has 354 days, at the end of the first year of the 30-year cycle the remainder is 11/30 day. Whenever the remainder exceeds a half day (15/30 day), then a leap day is added to that year, reducing the remainder by one day. Thus at the end of the second year the remainder would be 22/30 day which is reduced to −8/30 day by a leap day. Using this rule the leap years are
- 2, 5, 7, 10, 13, 16, 18, 21, 24, 26 and 29
of the 30-year cycle. If leap days are added whenever the remainder equals or exceeds a half day, then all leap years are the same except 15 replaces 16.
The Ismaili Tayyebi community uses the following order of leap years in their 30-year cycle.
- 2, 5, 8, 10, 13, 16, 19, 21, 24, 27 and 29
Apart from these, there are two more orders for the leap years which are as follows
- 2, 5, 7, 10, 13, 15, 18, 21, 24, 26 and 29
- 2, 5, 8, 11, 13, 16, 19, 21, 24, 27 and 30
The mean month is 29 191/360 days = 29.5305555... days. This is slightly too short and so will be a day out in about 2500 years. The Tabular Islamic calendar also deviates from the observation based calendar in the short term for various reasons.