Shin Nomoto: The Islamic World and Various Calendars

A traveler visiting an Islamic country is greeted by the call to prayer (Adhan) echoing from the minaret of a nearby mosque. The profound impression of the dawn call ("Prayer is better than sleep, God is great...") has often been written about. Let us take a brief look at the calendars used in the Islamic world, starting from the day in terms of Islamic religious practice, and then in the order of week, month, and year. We will also look at the issue of calendars from the periphery, unrelated to religion.

Muslim prayers are performed five times a day—dawn, noon, afternoon, sunset, and night—but in the Middle East, there is a custom that a "day" begins at sunset and ends at sunset. In other words, "Friday" of a certain week begins at sunset on Thursday and ends at sunset the following Friday. Because the length of daylight changes every day, the times for prayer must be precisely determined daily. Before the modern era, major mosques in a region had timekeepers who determined prayer times by observing the movement of the sun. Following Babylonian and Egyptian traditions, a week consists of seven days, the same as in Judaism and Christianity. While Saturday is the day of communal prayer for Judaism and Sunday for Christianity, Friday was designated in Islam, and many countries still officially recognize it as the weekly day of rest today.

Regarding months and years, the Islamic religious calendar is a lunar calendar (approx. 354.37 days per year) based on the cycle of the moon's phases (approx. 29.53 days). It begins on the first day of the first month (Muharram) of the year (July 15, 622 AD) when the Prophet Muhammad (c. 570–632) performed the "Hijra" (migration) from his hometown of Mecca to the new land of Yathrib (later Medina [City of the Prophet]). This is known as the Hijri lunar calendar, where each month consists of 29 days for even-numbered months and 30 days for odd-numbered months, with one day added to the last month in 11 years out of every 30. Naturally, this calendar creates a discrepancy with the solar calendar (approx. 365.25 days per year) based on the Earth's revolution around the sun. Therefore, during the famous month of Ramadan, the "month of fasting," people abstain from food and drink from dawn to sunset, but this may fall in winter when days are short, or in summer when days are long and the heat is taxing on the body. Incidentally, the beginning of a month is defined as the time when the new crescent moon is confirmed by the naked eye in the evening sky after sunset, so the end and beginning of a month may shift by one day from the date determined by calculation. It is tough if Ramadan does not end and fasting is required for one more day, but the sense of accomplishment upon completing it must be all the greater.

However, a lunar calendar is very difficult to use for farming and for collecting taxes based on those harvests. Therefore, in Japan and China, lunisolar calendars were used, incorporating devices such as inserting a leap month every two or three years so that the calendar and the seasons did not drift significantly. In the Arabian Peninsula, there was also a lunisolar calendar with leap months before Islam, but it had already fallen into disuse by the time of the Prophet. There is a theory that attributes the reason for this to a revelation in the Quran (Chapter 9, Verses 36–37) condemning the alteration of the twelve months ordained by God, but there are other theories, and a definitive conclusion is hard to reach.

Eventually, the Hijri lunar calendar came to be used alongside solar calendars that were dominant in the regions conquered by Arab Muslims from the mid-7th century onwards, such as the Julian calendar of the former Roman Empire and the Iranian calendar centered on the spring and autumn equinoxes since the Sasanian Empire (224–651), in order to coordinate agriculture and tax collection periods. The financial calendar of the Ottoman Empire was also based on the Julian calendar. In Egypt, there is an agricultural calendar called the Coptic calendar, which improved upon the ancient local calendar (consisting of 12 months of 30 days each for a 365-day year, with 5 days added at the end), adding an extra day every four years so that the beginning of the year coincides with the flooding of the Nile on August 29 of the Julian calendar.

The first day of the year in the Iranian calendar is called Nowruz ("New Day" in Persian) and is linked to the spring equinox. However, common theory suggests that after the fall of the Sasanian Empire, the year was fixed at 365 days or became inconsistent due to tax collection timing issues. It was the Jalali calendar, created during the era of Malik-Shah I (r. 1072–92) of the Seljuk Empire, that fixed it to the spring equinox; this calendar has 365 days in a year with a leap year every four or five years. In these Iranian calendars, the names of beautiful indigenous Iranian angels and holy beings are used for the names of each month. Finally, the Hijri solar calendar, which is one of the current official calendars of Iran, was established in 1925, and a similar Hijri solar calendar is used in Afghanistan.

Another interesting aspect is the twelve zodiac signs (the Twelve Deities) adopted by Turkic and Mongol peoples from China. This was brought to Iran and its surroundings along with the great Mongol conquests of the 13th century; the twelve animals were adopted in the same order, and even today, Iranian folk calendars include descriptions and fortunes for each year.

Many calendars have been omitted here, and the diversity of calendars in the Islamic world increases even further if those of the Indian subcontinent and Southeast Asia are included. Since the 19th century, the Gregorian calendar (the current Western calendar) has been added and is officially adopted in many countries. In this way, the Islamic world maintained a pure lunar calendar as its religious calendar, but on the other hand, many pre-Islamic calendars remained for agriculture and finance, and these were further improved, with the calendars of foreign peoples also being added, resulting in a wide variety of calendars being used. This fact speaks to the cultural diversity of the Islamic world and the flexibility of people's thinking.