Islamic calendar (Hijri) — the lunar calendar for Muslim religious observances

The Ancient Arabian calendar as background of the Islamic calendar

The Islamic calendar with its month names goes back to the ancient Arabian calendar, which was a lunisolar calendar and was common in large parts of the Arabian Peninsula. The year began in autumn, probably in mid to late September. It consisted of twelve lunar months, counted from new moon to new moon as in the modern Islamic calendar; however, every two or three years a thirteenth month was added so that the beginning of the year in autumn could be maintained. This leap month was called nasīʾ, "shift," because it shifted the first month of the new year. With this system, the ancient Arabian calendar resembled the Jewish calendar.

Some of the names of the months in the ancient Arabic calendar referred to the seasons. For example, the Arabic word Rabīʿ, which occurs in the names of the third and fourth months, means "spring. Al-Biruni, who wrote a work on the different time calculations, explains this by the fact that during this time in ancient Arabia much rain fell and flowers bloomed.

The calendar served primarily to calculate the dates of pilgrimages and markets. Four months of the year were considered holy: the month of Rajab because of the ʿUmrah that took place at that time, the month of Dhū l-Hijjah, and the two months before and after because of the Hajj that took place at that time. During these four months there was a general obligation of peace (cf. Sura 9:36). The markets of ʿUkāz and Dhū l-Majjāz were also calculated according to this calendar.

According to al-Azraqī, in early times the responsibility for calculation lay with members of the Kinda tribe because they "usually provided the kings of the Arabs". Then this prerogative passed to the Kināna tribe. In the period immediately preceding Islam it rested with the clan of Banū Fuqaim, who belonged to the Kināna. The man in charge of intercalation would stand in the square in front of the Kaaba at the end of Hajj and deliver a speech in rhyming prose announcing whether or not a leap month would be inserted before the beginning of the new year.

The Islamic calendar reform

After the Muslim conquest of Mecca in 630, the ancient Arabian calendar was reformed: The leap month nasīʾ was abolished and in this way a pure lunar calendar was created. The exact date of the abolition is not clear. Ibn Ishāq mentions it both for the pilgrimage led by Abū Bakr in 631 and for Muhammad's farewell pilgrimage in 632.

As is evident from the Qur'anic verse (Sura 9:37) that refers to this event, the intercalation of the Nasīʾ was judged to be pagan conduct and human interference with the divine world order. Among the results of the calendar reform was that the Kināna, who had previously had the right to set the intercalary months and thus also decided on the movement of goods and military activity in the Arabian Peninsula, lost much of their power, and furthermore, the traditional cycle of markets in the Arabian Peninsula disappeared. More importantly, however, in this way the pure lunar year with its 354 days became the basis for the Islamic calendar and henceforth served to determine religious festivals.

The Islamic calendar adopted the ancient Arabic names of the months unchanged. However, the names lost their original seasonal meaning, because from now on they moved through the year.

The continuation of solar calendars in Islamic countries

Advantages of the Islamic lunar calendar were the simple determination of the beginning of the month and the uniform duration of months and years. However, the lunar year is not practical for an economic system based on seasonal agriculture. In particular, it is difficult to fix dates at which annual dues were to be paid. Therefore, in almost all countries where Islam took root, a solar calendar continued alongside it:

• in the Maghreb, the Julian calendar, later the Gregorian calendar, with Roman month names (yanayir, fibrayir, maris, abril, etc.),
• likewise in the Mashreq, but with ancient Near Eastern month names (kanun ath-thani, shubat, adhar, nisan, ayar, haziran, tammuz, ab, aylul, tischrin al-awwal, tischrin ath-thani, kanun al-awwal),
• in Egypt the Coptic calendar,
• in the Iranian area the old Iranian solar calendar, which took however the year of the Hidschra as starting point,
• In the Ottoman Empire, the Rumi calendar was used for a time, a variant of the Julian calendar with Hijra year counting and the beginning of the year first in September, later in March.

This, however, resulted in synchronization problems. In the Ottoman Empire, for example, revenues, mostly from agriculture and often in kind, were collected on dates according to the sun-based Rumi calendar. Expenditure, such as the salaries of civil servants, soldiers, etc., on the other hand, was due according to the Islamic calendar. In order to synchronize the year of revenue and the year of expenditure, the Hijrah year count was also extended to the years of the Rumi calendar. However, because the solar years were longer than the lunar years, there were discontinuities in the counting of years in the Rumi calendar, i.e., there were years of expenditure to which no year of revenue could be assigned. The Ottoman administration's efforts to avoid the accounting inconveniences associated with such discontinuities also resulted in the aforementioned bringing forward of the beginning of the year of the Rumi calendar from September to March.

In everyday and economic life, however, the Gregorian calendar has been used in almost all Islamic countries since the early 20th century. In the territory of the Ottoman Empire, the lunar calendar was officially replaced by the Gregorian calendar on March 1, 1917.

For the months of the Gregorian or Julian calendar, the familiar European month names are used in some parts of the Arab world, and oriental month names in the rest. In Iran, the French names are in use. In addition, the Iranian solar calendar is officially in use.

The Islamic calendar is a lunar calendar. The months are lunar months with a duration of 30 or 29 days. The calendar is strictly based on astronomical observation: a new month begins at new light, which is the moment after the new moon when the waxing crescent moon can be observed again for the first time in the evening after sunset.

Twelve months form a lunar year. This is with 354 or 355 days 10 to 12 days shorter than a solar year. Unlike lunisolar calendars such as the Jewish calendar or the Chinese calendar, there is no compensation in the Islamic calendar through leap months. Therefore the beginning of the year shifts annually by 10 to 12 days backward in relation to the Gregorian calendar. 33 lunar years correspond to about 32 solar years.

How the calendar works

Since the onset of the new light is fluctuating and difficult to predict, a calendar with alternating 30 and 29 day months and the resulting 354 day common year is used. This includes an occasional intercalary day to adjust the calendar lunar year to the astronomical period of 12 synodic months of about 29.53059 days each.

In a 30-year calendar cycle, a day is added to the last calendar month eleven times. If the year divided by 30 has a remainder of 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, or 29, it is a leap year. The last cycle began in the year 1411 AH, the next cycle begins in the year 1441 AH.

The calendar cycle length is 30 × 354 + 11 = 10631 days. The astronomical cycle length is 360 × 29.53059 = 10631.0124 days. The deviation of 0.0124 days in 30 years only adds up to one day in about 2500 years.

Calculation of the beginnings of the month

The following table gives the lengths of the individual months and the beginnings of the months calculated according to this cyclical calendar for the Islamic years 1436 to 1438. The date is highlighted in bold if the month Dhū l-Hiddscha has 30 days as a leap month.

Islamic feast days

Of the Islamic holidays, the fasting month of Ramadan and the month of pilgrimage, Dhū l-ḥiddshah, have particularly great religious significance. The Feast of Sacrifice (ʿĪdal-aḍḥā) on the 10th of Dhū l-hiddscha is the highest holiday of the Muslims, the second highest being the Feast of Breaking the Fast (ʿĪd al-fitr) at the end of Ramadān. In the first ten days of the month of Muḥarram, the Shiites celebrate their highest mourning festival, the Ashura rites, in which they commemorate the death of Imam Husain ibn Ali in the battle of Karbala with processions, passion plays, and flagellations.

For religious purposes in most Islamic countries it is not astronomical calculation but the observation of the moon that is decisive. The new month begins when the crescent moon (hilāl) is visible again after a new moon (new light). If a sighting is not possible due to weather conditions, then it ends after the 30th day. This form of observation is particularly important for determining the beginning and end of the month of Ramadan.

However, this means that the calculated beginning of the month can deviate from the actual beginning of the month. Therefore, in printed calendars, the dates of Islamic festivals often state: "The actual date may deviate by 1 to 2 days". Corresponding shifts of festivals can have unpleasant consequences, as the following newspaper notice proves: