Iranian calendars
The Iranian calendar (also known as Persian calendar or the Jalaali Calendar) is a solar calendar currently used in Iran and Afghanistan. It is observation-based (specifically, of the vernal equinox), rather than rule-based.
This calendar is almost unknown in the West, although it is one of the most accurate, if not the most accurate in the world. Compared with the Gregorian calendar, which errors by one day, every 3,226 years, the Iranian calendar needs a one-day correction every 141,000 years. There are two reasons for this accuracy. The Iranian calendar uses a sophisticated intercalation system for determining the leap years. And the beginning of the year, which is a natural phenomenon (arrival of the Sun at the Vernal Equinox), is precisely determined each year by astronomical observations.
Background
Persians have always been keen on the idea and importance of calendar system throughout their recorded history. They were among the first cultures to employ a solar calendar, and have long favored a solar approach rather than lunar or lunisolar models. In general, the sun has always had an important symbolic significance in the Iranian culture.
The Iranian calendar was legally adopted by the Persian parliament on March 31, 1925, specifying the origin on the calendar (Hegira of Muhammad from Mecca to Medina in 622 CE), mentioning that the beginning of the year is the first day of spring, that the year is the "true solar" year "as it has been", and specifying the month names and the number of days in each month. The law goes further and officially deprecates the Sino-Uighur year cycles which were unofficially but commonly used.
Afghanistan legally adopted the new Iranian calendar in 1957, using the same number of days in each month but different months names. In Afghan Persian (also known as Dari), the Arabic language names of the zodiac signs for the months are used instead of the names adopted in Iran. In Afghan Pashto, native Pashto names are used.
History of calendar in Persia
The first calendars based on Zoroastrian cosmology appeared during the later Achaemenian period and though they have evolved and changed over the centuries, the names of the months have remained more or less the same till now. Before this period, old Persian inscriptions and tablets indicate that early Iranians used a 360-day calendar based on the Babylonian system modified according to their own beliefs, and their own named days. Months were divided into two or three divisions depending on the phase of the moon. Twelve months were named for various festivals or activities of the pastoral year with 30 days in each month. A thirteenth month every six years was added to keep the 360-day calendar in harmony with the seasons.
Under the unified empire of the Achaemenian it was necessary to create a distinctive Iranian calendar based on Zoroastrian beliefs. In the new calendar, following the Egyptian tradition, the twelve months and the thirty days were each dedicated to a yazata (Eyzad) with four divisions resembling the Semitic week. Four of the days in the month were dedicated to Ahura Mazda and seven days were named after the six Amesha Spentas. Thirteen days were named after Fire, the Waters, Sun, Moon, Tiri and Geush Urvan (the soul of all animals), Mithra, Sraosha (Soroush, yazata of prayer), Rashnu (the Judge), Fravashis, Verethraghna (Bahram), Raman (Ramesh meaning peace), and Vata, the wind deity. Three were dedicated to the female deities, Daena (yazata of religion and personified conscious), Ashi (yazata of fortune) and Arshtat (justice). The remaining four were dedicated to Asman (lord of sky or Heaven), Zam (Earth goddess), Manthra Spenta (the Bounteous Sacred Word, a female deity) and Anaghra Raoch (the ‘Endless Light’ of paradise).
The religious importance of the calendar dedications was very significant. Not only did it fix the pantheon of major deities, but ensured that their names were continuously uttered, since at every Zoroastrian act of worship the deities of both day and month were invoked. With the new system, the pattern of festivities became clear as well. For example, Mitrakanna or Mihregan was celebrated on Mithra day of Mithra month, and the Tiri festival (Tiragan) was celebrated on Tiri day of the Tiri month.
After the conquests of Alexander and his subsequent death, the Persian territories fell to one of his generals Seleucus (312 CE) and the Seleucid dynasty of Iran was formed. Based on the Greek tradition, they introduced the practice of dating by era rather than dating by the reign of the individual kings. Their era became known as that of Alexander. The Zoroastrian priests, having lost their function at the royal courts since the new rulers were not Zoroastrians, resented Seleucid and found it necessary to create their own era. They followed the new trend of dating by eras, and for the first time started calculating the era of Zoroaster. This was the first serious attempt to establish a historical date for the prophet.
With no Zoroastrian sources they turned to Babylonian archives famous throughout the ancient world. From these records they learned that a great event in Persian history took place 228 years before the era of Alexander. The date was 539 BCE, which was in fact the conquest of Babylon by Cyrus the Great. The Zoroastrian priests, however, misinterpreted this date to be the time the "true faith" was revealed to their prophet and since Avestan literature indicates that revelation happened when Zoroaster was thirty years old, the date of 568 BCE was taken to be his birthday. The date entered written records as the beginning of the era of Zoroaster, and indeed, the Persian Empire. This incorrect date is still mentioned in many current Encyclopedias as Zoroaster’s birth date.
Parthians adopted the same system, and dated their era from 248 BCE, the date they succeeded the Seleucids, and used the same calendar with minor modifications. Their names for the months and days are Parthian equivalencies of the Avestan ones used before and they differed slightly from the Middle Persian names used by the Sassanian. For example in Achaemenian times the modern Persian month ‘Day’ is called Dadvah (Creator), in Parthian it is Datush and Sassanian named it Dadv/Dai (Dadar in Pahlavi).
The next major calendar change happened during the reign of Ardashir I the founder of the Sassanid dynasty in 224 CE. In 46 CE, Julius Caesar the Roman Emperor, adopted the Egyptian solar calendar system of 365 days with some modifications. Iranians had known about the Egyptian system for centuries but never used it. Ardashir, however, changed the system to 365 days by adding five extra days at the end and named these ‘Gatha’ or ‘Gah’ days, after the ancient Zoroastrian hymns of the same name. The new system created confusion and was met with resistance, and many Zoroastrian feasts and celebrations have two dates, to this day. Many rites were practiced over many days instead of one day and duplication of observances was continued to make sure no holy days were missed.
The situation got so complicated that another calendar reform had to be implemented by Ardeshir’s grandson Hormizd I. The new and old holy days were linked together to form continual six-day feasts. No Ruz was an exception. The first and the sixth day of the month were celebrated as different occasions and sixth became more significant as Zoroasters’ birthday rather than a continuation of No Ruz itself. The reform however did not solve all the problems and Yazdegird III, the last ruler, introduced the last changes. Year 631 CE was chosen as the beginning of a new era and the last calendar is known as the Yazdegirdi calendar. However, before work on the new calendar was completed, Muslim Arabs overthrew the dynasty in the 7th century and with their victory, a new lunar calendar based on Islamic principles replaced the old solar calendar of the Sassanid period.
This calendar was proposed earlier by the Prophet himself but was first systematically introduced around 638 CE, by the close companion of the Prophet, and the second Caliph, Umar ibn Al-Khatab (592-644 CE). This was done to end the conflicting dating systems used at the time. The Prophet’s flight from Mecca to Medina (Hijrat) in 622 was chosen as the beginning of the Islamic calendar. The actual starting date for the calendar was chosen based on lunar years, counting backwards to be the first day of the first month (Muharram) of the first year of the Hijrat. The Islamic (Hijri) calendar is usually abbreviated A.H. in Western languages from the Latin Anno Hegirae.
The Iranian calendar was revised in the 11th century by a panel of scientists, allegedly including Omar Khayyám. The recalibration was completed during the reign of Jalaal ad-Din Malik Shah Seljuki, one of the Seljuk sultans, and named in his honor.
The Islamic lunar calendar was widely used till the end of the 19th century. During Pahlavi era, in 1925, the lunar calendar was officially replaced by the modern Iranian calendar. The ancient Persian names, which are still in use today, were also revived.
Details
The Iranian calendar year begins on the midnight between the two consecutive solar noons which include the instant of the Northern spring equinox, when the sun enters the northern hemisphere; in other words, the start of Spring in the northern hemisphere. The calendar consists of twelve months with Persian names. The first six months are 31 days each, the next five 30 days, and the last month has 29 days but 30 days in leap years. The reason the first six months have 31 days and the rest 30, was not a random decision of the designers – it has to do with the fact that the sun moves slightly more slowly along ecliptic in the northern spring and summer than in the northern autumn and winter.
In other words, the Persian new year is determined by noon-time observation of the Northern spring equinox. If between two consecutive noons the sun's altitude rises through its equinoctial altitude then the first noon is on the last day of one calendar year and the second noon is on the first day (Norouz) of the next calendar year.
Typically leap years are devised and used by various solar calendar systems, usually every four years. Four-year leap years add 0.25 day to each year in the period, but that is a slight overcompensation compared to the actual behaviour of the sun. To remedy this overcompensation, after every six or seven four-year leap years, the Persian solar calendar produces a five-year leap year. It usually follows a thirty-three year cycle with occasional interruptions by single twenty-nine year subcycles.
This general picture of the Persian calendar's leap-year behaviour contrasts with less accurate predictive algorithms which are based on confusion between the astronomers average tropical year (365.2422 days, approximated with near 128-year cycles or 2820-year great cycles) and the mean interval between spring equinoxes (365.2424 days, approximated with a near 33-year cycle).
Month Names
| Order | Days | (Iranian) Persian name | |
| Latin | Perso-Arabic | ||
| 1 | 31 | Farvardin | فروردین |
| 2 | 31 | Ordibehesht | اردیبهشت |
| 3 | 31 | Khordad | خرداد |
| 4 | 31 | Tir | تیر |
| 5 | 31 | Mordad | مرداد |
| 6 | 31 | Shahrivar | شهریور |
| 7 | 30 | Mehr | مهر |
| 8 | 30 | Aban | آبان |
| 9 | 30 | Azar | آذر |
| 10 | 30 | Dey | دی |
| 11 | 30 | Bahman | بهمن |
| 12 | 29/30 | Esfahnd | اسفند |
The first day of this calendar year is also the day of the greatest festival of the year in Iran called Norouz (a single word made up of two parts, no and rouz, meaning "new day").
Calendar seasonal error
This image shows the difference between the Iranian Solar calendar (using the 33-year arithmatic approximation) and the seasons. The Y axis is "days error" and the X axis is Gregorian calendar years.
Each point represents a single date on a given year. The error shifts by about 1/4 day per year, and is corrected by a leap year every 4th year regularly, and one 5 year leap period to complete a 33-year cycle. One can notice a gradual shift upwards over the 500 years shown.
By comparison, the Gregorian calendar, introduced in 1582, is almost as accurate in the long term, but has larger swings of seasonal errors over the centuries.