The Jalali calendar, also referred to as ''Malikshahi'' and ''Maliki'', is a

solar calendar A solar calendar is a calendar whose dates indicates the season or almost equivalently the apparent position of the Sun relative to the stars. The Gregorian calendar, widely accepted as a standard in the world, is an example of a solar calendar ...

compiled during the reign of Jalaluddin Malik-Shah I, the

Sultan Sultan (; ', ) is a position with several historical meanings. Originally, it was an Arabic abstract noun meaning "strength", "authority", "rulership", derived from the verbal noun ', meaning "authority" or "power". Later, it came to be use ...

of the

Seljuk Empire The Seljuk Empire, or the Great Seljuk Empire, was a High Middle Ages, high medieval, culturally Turco-Persian tradition, Turco-Persian, Sunni Islam, Sunni Muslim empire, established and ruled by the Qiniq (tribe), Qïnïq branch of Oghuz Turks. ...

(1072–1092 CE), by the order of

Grand Vizier Grand vizier (; ; ) was the title of the effective head of government of many sovereign states in the Islamic world. It was first held by officials in the later Abbasid Caliphate. It was then held in the Ottoman Empire, the Mughal Empire, the Soko ...

Nizam al-Mulk Abū ʿAlī Ḥasan ibn ʿAlī Ṭūsī () (1018 – 1092), better known by his honorific title of Niẓām al-Mulk (), was a Persian Sunni scholar, jurist, political philosopher and vizier of the Seljuk Empire. Rising from a low position w ...

, using observations made in the cities of

Isfahan Isfahan or Esfahan ( ) is a city in the Central District (Isfahan County), Central District of Isfahan County, Isfahan province, Iran. It is the capital of the province, the county, and the district. It is located south of Tehran. The city ...

(the capital of the Seljuks), Rey, and

Nishapur Nishapur or Neyshabur (, also ) is a city in the Central District (Nishapur County), Central District of Nishapur County, Razavi Khorasan province, Razavi Khorasan province, Iran, serving as capital of both the county and the district. Ni ...

. Variants of the Jalali calendar are still in use today in

Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...

and

Afghanistan Afghanistan, officially the Islamic Emirate of Afghanistan, is a landlocked country located at the crossroads of Central Asia and South Asia. It is bordered by Pakistan to the Durand Line, east and south, Iran to the Afghanistan–Iran borde ...

. In Iran, the Persian names of the

zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north and south celestial latitude of the ecliptic – the apparent path of the Sun across the celestial sphere over the course of the year. Within this zodiac ...

are used, while in

the original Arabic names are used. The Jalali calendar gains approximately 1 day on the

Julian calendar The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year (without exception). The Julian calendar is still used as a religious calendar in parts of the Eastern Orthodox Church and in parts ...

every 128 years. The tropical Jalali calendar (), which inherited some aspects from the Yazdgerdi calendar, was adopted on 15 March 1079 by the Sultan, based on the recommendations of a committee of astronomers, including

Omar Khayyam Ghiyāth al-Dīn Abū al-Fatḥ ʿUmar ibn Ibrāhīm Nīshābūrī (18 May 1048 – 4 December 1131) (Persian language, Persian: غیاث الدین ابوالفتح عمر بن ابراهیم خیام نیشابورﻯ), commonly known as Omar ...

, at the imperial observatory in the capital city of

. It was Khayyam who positioned Isfahan as the prime meridian, otherwise known as the nasf. Month computations were based on solar transits through the zodiac, and it remained in use for eight centuries. The need for a revised calendar arose from the inconsistencies and seasonal drift in the prior Islamic calendar due to the use of lunar cycles instead of solar; a lunar year consisted of 354 days. While acceptable to a desert nomadic people, this proved to be unworkable for settled, agricultural peoples. The Iranian calendar is one of several non-lunar calendars adopted by settled Muslims for agricultural purposes (others include the

Coptic calendar The Coptic calendar, also called the Alexandrian calendar, is a liturgical calendar used by the farming populace in Egypt and used by the Coptic Orthodox and Coptic Catholic churches. It was used for fiscal purposes in Egypt until the adoptio ...

, the

, and the Semitic calendars of the Near East). The adoption, however, of the Persian year would not have brought complete stability into the calendar because the Persian year's beginning was aligned with the collection of taxes and payment of pensions. Sultan Jalal commissioned the task in 1073. Its work was completed well before the Sultan's death in 1092, after which the observatory would be abandoned. The year was computed from the

March equinox The March equinox or northward equinox is the equinox on the Earth when the subsolar point appears to leave the Southern Hemisphere and cross the celestial equator, heading northward as seen from Earth. The March equinox is known as the ver ...

(

Nowruz Nowruz (, , () , () , () , () , Kurdish language, Kurdish: () , () , () , () , , , , () , , ) is the Iranian or Persian New Year. Historically, it has been observed by Iranian peoples, but is now celebrated by many ...

), and each month was determined by the transit of the sun into the corresponding zodiac region, a system that incorporated improvements on the fourth-century-CE Indian system of the Surya Siddhanta (''Surya''=solar, ''Siddhanta''=analysis), also the basis of most

Hindu calendar The Hindu calendar, also called Panchangam, Panchanga (), is one of various lunisolar calendars that are traditionally used in the Indian subcontinent and Southeast Asia, with further regional variations for social and Hindu religious purposes ...

s. Though there is little information about the social and cultural details of the solar calendars which were used in the Persian territory in later centuries up to the invention of the Jalālī Calendar, we know that the Persian solar calendars suffered a degree of disorganization due to the lack of official supervision. Since the solar transit times can have 24-hour variations, the length of the months vary slightly in different years (each month can be between 29 and 32 days). For example, the months in the two last years of the Jalali calendar had: * 1303 AP: 30, 31, 32, 31, 32, 30, 31, 30, 29, 30, 29, and 30 days, * 1302 AP: 30, 31, 32, 31, 31, 31, 31, 29, 30, 29, 30, and 30 days. Because months were computed based on precise times of solar transit between zodiacal regions, seasonal drift never exceeded one day, and also there was no need for a leap year in the Jalali calendar. However, this calendar was very difficult to compute; it required full ephemeris computations and actual observations to determine the apparent movement of the Sun. Some claim that simplifications introduced in the intervening years may have introduced a system with eight leap days in every cycle of 33 years. (Different rules, such as the 2820-year cycle, have also been attributed to Khayyam.) However, the original Jalali calendar based on observations (or predictions) of solar transit would not have needed either leap years or seasonal adjustments. Owing to the variations in month lengths, and also the difficulty in computing the calendar itself, the Iranian calendar was modified to simplify these aspects in 1925 (1304 AP), resulting in the

Solar Hijri calendar The Solar Hijri calendar is the official calendar of Iran. It is a solar calendar, based on the Earth's orbit around the Sun. Each year begins on the day of the March equinox and has years of 365 or 366 days. It is sometimes also called the S ...

References

See also