Calendar is an expression of the wish to perceive the precise time and to evaluate it in accordance with a certain plan. When calendars are examined within the historical process, it is understood that all the societies such as Mayans in the west and Egyptians in the east utilized the regular and periodic movements of the celestial bodies such as the sun and the moon for the measurement of time.
Thus, in addition to its many advantages -as stated in the Holy Quran- people also utilized the sun and moon to calculate time. The calendars which are based on the regular and periodic movements of the celestial bodies can be divided into three groups:
1- Solar Calendar: It is considered that the Egyptians were the first people to have used this calendar.
2- Lunar-Solar Calendar: The duration of the year is the same with that of the solar calendar. The months had been designed to start and end with the lunar month as much as possible. It is required to add one month to the lunar year in every three years for the new year to always coincide with the same season. As a matter of fact, the lunar year is 11 days shorter than the solar year.
3- The lunar calendar had been prepared in accordance with the different phases of the moon as seen from the earth and with the movements of the moon.
I. CALENDAR IN THE AGE OF IGNORANCE
For the people of the Age of Ignorance, the stars had been observed in order to find the route during the nights and to acquire information on meteorological incidents and climatic changes. As a result of observations and experiments in the daily life, a new kind of science was formed that drew an analogy between the movement of the stars and weather and climate occurred (ilmu al-anwa). This new knowledge came to be regarded as public astronomy and meteorology.
For Arabs the lunar year consists of 354 days and 12 months. The following names of the lunar names used in the late periods before the Islamic period and during the Islamic era had been taken from the natural states of the season with which they coincide. (1-Muharram, 2-Safar, 3- Rabi' al-awwal, 4-Rabi' al-thanni 5- Jumada al-awwal, 6- Jumada al-thani, 7- Rajab, 8- Sha'aban, 9-Ramadan, 10-Shawwal, 11-Dhu al-Quidah, 12-Dhu al-Hijjah
Although the times of the lunar months changed, the names derived from the natural states of the seasons were accepted and have been continually used up to date. For example, when the Jamad (Jamazi al-awwal and Jamazi al-thani) month first took this name, it signified the time when the water froze in the solar year. With the interchange of lunar months, the month in question coincided with the hot summer period; however its usage was continued. In the Age of Ignorance, Muharram was accepted as the first month of the year. Safar, Rabi' al-awwal, Rabi' al-thanni, Jumada al-awwal, Jumada al-thani, Sha'aban, Ramadan and Shawwal months were accepted as the "ordinary month" (asharun i'tiyadiyya); Dhu al-Quidah, Dhu al-Hijjah, Muharram and Rajab months were accepted as "illicit/peace and welfare months" (ashurun arbaatun hurum). Due to the fact they are consecutive in order, Dhu al-Quidah, Dhu al-Hijjah and Muharram months were called "serd" (consecutive) and the Rajab month was called "ferd" (solitary). The Arabs of the Age of Ignorance had derived the application of "illicit months" from the laws of Abraham and Ismael during which they abstained from all kinds of warfare and attacks as a sign of respect. They believed that this was necessary for the sacredness of the coming months. These rules were also applicable for the Bedouins who made their living by racketeering the caravans and by engaging in battles between themselves from time to time in order to find water and grazing ground. Arabs continued to respect these months until the calendar was re-organized. Due to the aforementioned reasons, the people of the Age of Ignorance had a hard time obeying the rules of the "illicit months". Moreover, due to the lunar calendar, the months shifted 11 days earlier each successive year, thus the people wished to perform the hajj (pilgrimage) ceremony - which coincided with different seasons - not on certain days of Dhu al-Hijjah, but on other days and months when the weather was mild and trade environment was suitable.
In order to ensure this, they used the nasi (adjustment) method.
The origin of the concept of a week is regarded to be related to the act of dividing the lunar month into four sections. In other words, the concept of a week must have resulted from the fact that the four phases (new moon, first quarter, full moon and last quarter) underwent by the moon while rotating around the earth continue as much as seven days each. As for the beginning of the date application during the Age of Ignorance; the beginning of a calendar would be based on significant incidents as it was true for the ancient tribes. The people of the city would not change these marking incidents which they regarded as the beginning date for a long time and they relatively had a fixed beginning date. However the nomads would choose the constant wars, illnesses and various disasters as the beginning date and annul the previous ones. As the fixing of a date, the Bedouin Arab tribes would use the wars among themselves and the significant days which they referred to as "ayyamu al-Arab"
As a consequence, the Arabs of the Age of Ignorance had an ancient tradition on the issue of observing the celestial bodies and perceived time -with a rich vocabulary- and used a lunar calendar.
II. THE AGE OF HAPPINESS
A new page had opened after the Hijrah (Emigration) of the Prophet and his companions to Medina. Islam, which was going to change the course of the history, had found a new shelter and homeland for itself. Medina transformed itself into a center that was going to influence the course of the history. Hijrah gave its name to the beginning of the Islamic Calendar and the developments related to the calendar occurred generally after this date.
A. HOLY QURAN AND THE CALENDAR
The Holy Quran commands that the skies become a matter of contemplation and be researched. It contains the necessary information so that its addressees acquire and develop a consciousness of time and the Holy Quran frequently employs terms that express time in order to draw attention to it.
The Holy Quran ensured the formation of a strong perception of time for its audience. Indeed, the Islamic preference of lunar calendar over the solar calendar is related to the lunar calendar being more fit for the religious purposes, and it brought justice. Seyyid Hossein Nasr explains this condition as follows: "Islam embraced the Arabic lunar calendar. It was this calendar which determined the rhythm of the religious worshipping of the Muslims so far. With this verse, the Holy Quran foresaw a problem that may occur later, and by prohibiting additions to this calendar, it established the sole solution to settle the justice among the Muslims. The basic means of worshipping such as the salah (ritual prayer) and fasting are determined in accordance with the sunrise and sunset times. Moreover, Islam is a worldwide religion the members of which live in various geographical regions. The duration of days and climatic conditions differ to a large extent in these regions. If the lunar year-as it is asserted by some modernized Muslims without realizing its results-was left fixed in the solar year, there would be a great injustice. For instance, some Muslims would always fast in long days and they would worship in more difficult conditions throughout their lives than other Muslims. Prohibiting such a practice alone would bring the divine justice among all the believers. Thus, with this verse, the Holy Quran took into account the future condition of the Islamic ummah (community) and foresaw that its borders would stretch far beyond Arabia where the revelation was sent."
B. THE CALENDAR IN THE PERIOD OF THE PROPHET
In the 2nd year of the Hijrah, there emerged a necessity to use the lunar year without nasi practice with the obligation of fasting and sacrifice worships. The time viewpoint which was suggested by the Holy Quran and its regulations on the calendar must also be regarded as a part of the developments achieved in calendar practices of the period of the Holy Prophet.
The formation of the Islamic calendar, which gained formality by taking its final form and which found a general field of use in the period of Umar, occurred in the course of time. After the Hijrah of the Holy Prophet, the Muslims-whether with the guidance of the Holy Prophet or at their own discretion-started to use the time of the Holy Prophet's Hijrah to Medina (Rabi' al-awwal) as the beginning of the history in an unofficial way and without a generalization. The first month of this calendar is Rabi' al-awwal, and the last month is Safar. We can call this the "unofficial Islamic calendar" or the "original Islamic calendar." Umar revived this calendar, finalized it, and made it formal. The most important development related to the calendar in the period of the Holy Prophet is the fact that nasi practice was actually ended with the Farewell Hajj which was read in the 10th year of Hijrah on the month of Dhu al-Hijjah. The Holy Prophet removed the problem that break the course of the lunar year by annulling the nasi practice in His Farewell Khutba. Therefore, a calendar that was independent of the calendars based on the solar year, and that was based on the movements of the moon was thereby established.
C. THE OFFICIAL ESTABLISHMENT OF THE ISLAMIC CALENDAR
As it is mentioned before, despite many developments related to the calendar, it could not be finalized during the time of the Prophet. It was only in the time of Umar that the borders of the Islamic State expanded in a short time; Muslims started to interact with various religious, political views and civilizations more intensely; other nations started to accept Islam in masses; official procedures and official relations increased; military operations overspread in a wide range; and state revenue increased. In parallel with these developments, in the period of Umar, the bodies of the government started to settle; courts were established; and there emerged a necessity to write the date on the written documents.
The requirement in question was stated by some companions and this was reported to Umar. Umar called in the leading figures of the companions who constituted a state council, and he discussed the issue of a calendar with them. While some foreign calendars were proposed, they were rejected. As a result of these negotiations, the unofficial Islamic lunar calendar which took the Holy Prophet's Hijrah as the beginning of the history and which started with the month of Rabi' al-awwal was revived, formalized, and generalized by Umar on Rabi' al-awwal 15 in the 16th or 17th year of the Hijrah. It can be named as the "official Islamic calendar." As it is pointed out by Ibn al-Khutayba, in the "official Islamic calendar", Muharram was accepted as the first month of the year in accordance with the former tradition, whereas in the "unofficial lunar Islamic calendar" without nasi, Rabi' al-awwal was accepted to be the first month of the year. Another reason for this is the fact that this month is the first work month in the Arabian Peninsula after the Hajj season.
The companions asserted four alternatives when they determined the beginning of the Islamic history:
The birth of the Holy Prophet,
The prophethood of the Holy Prophet,
The Hijrah of the Holy Prophet,
The decease of the Holy Prophet.
Although it was possible to accept each of the four alternatives as a beginning, the companions decided to use the time of Hijrah as the beginning of history. There are several reasons for this choice: the companions did not know the exact dates of the birth and prophethood of the Holy Prophet and the decease date of the Holy Prophet saddened them too much. Thus they accepted the Hijrah as the beginning of the Islamic history.
In conclusion, the Islamic lunar calendar, which was the successor of the Meccan nasi lunar calendar with some alterations and improvements, was established in this process; was finalized, formalized, and found a general field of usage in the period of Umar.