I'm going to talk about calendars again.
Web pages and popualr books often state that calendars can be solar or lunar, and lunisolar calendars combine both types. This is exactly backwards. Every polity with any sort of state-like organisation starts off with a lunisolar calendar, which may drop the lunar correlation to become purley solar. (There is only one purely lunar calendar, and it too is descended from a lunisolar ancestor).
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In the remotest, most archaic days of Egyptian civilisation, the lunisolar year was tied to the heliacal rising of Sirius, which signalled that the Nile ws about to flood. This day was called Wepet-Renpet, or Head of the Year. Months began with the observation of the new moon, but we don't know exactly how they related to Wepet-Renpet. Perhaps the year began with the first new moon after the rising of Sirius, or perhaps the first month containing the rising.
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In any case, Egyptians at some point introduced a purely solar calendar of exactly 365 days. We actually have a pretty good idea that this was introduced on 12 August 2973 BC, as that is the closest date to the unification of Egypt on which the 1st of Thoth falls on the same day as the haliacal rising of Sirius.
This calendar consisted of 12 months of 30 days each plus five extra days, and there was no leap year mechanism.
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For most of Egyptian history, the 12-month calendar was just used to coördinate religious observance, and even that was mostly just for the pharaoh and the priesthood. Workers and peasants continued to use the heliacal rising of Sirius to determine the start of the year; this date is referred to in inscriptions at the Esna Temple as "the Wepet-Renpet of the ancestors". Peasants also divided the year into three seasons: Flood (when they built the pyramids), Sowing, and Harvest.
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Anthony Spalinger manages to interpret the Esna inscriptions as meaning that the first solar year began on the ninth day of the lunisolar year, ina rambling and confusing paper which uses half a page on a simple diagram to illustrate an *analogy* he makes about looking at things from different angles.
Leo Depuydt inteprets it as simpley referring to the difference between the civil and astronomical new year, which is far more reasonable.
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Meanwhile, Iranians were using the Babylonian calendar, which the Persians might have learned from the Elamites. Iran conquered Egypt early in the Achaemenid Dynasty. The Zoroastrian priesthood were quite impressed with the Egyptian priests incredibly sensible and straightforward calendar and adopted it for religious purposes during the reign of Xerxes I, but the Iranian year began a few months later than the Egyptian.
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The common people of Iran kept using the Babylonian calendar well into the Seleukid era. The ruling Seleukids used the Makedonain calendar, which is basically the Babylonian calendar but the year beginsi in autumn rather than spring. Contemporary writings refer to the common people celebrating new year six months after the rulers.
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But back to the Achaemenid dynasty! The modified Egyptian calendar spread throughout the empire, and was adopted for at least some official purposes in Sogdia, Khwarezm, and Armenia; it subsequently became the state calendar when Armenia gained independence from Iran.
Both the Egyptian and Zoroastrian priests were well aware that 365 days was slightly shorter than a calendar year, but they weren't willing to intercalate, as only the gods can make new days.
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Sogdians, Khwarezmians, and Armenians gave the months names in their own languages, some derived from Persian. Sogdians jsut identified years by how long the current king had been in power, while Khwarezmians and Armenians went with the legendary origins of their kingdoms.
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Among other things, the set of inscriptions inclusing the Rosetta Stone give dates in the Egyptian and Greek calendars, allowing us to calibrate exactly when the Egyptian solar calendar, and hence the Iranian solar calendars, start.
One of the inscriptions on the Canopus Stone orders the Egyptian priests to add one extra day every four years, but the priests refused.
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They only relented much later, when Sosigenes fixed the Roman calendar for Julius Caesar. Since the Roman calendar finally made something resembling sense, the Egyptians added an extra day in sync with the Julian calendar so that their years would not drift apart.
This calendar is still the liturgical calendar of Coptic Christians, who date from the reign of Emperor Diocletian. It is also the state calendar of Ethiopia and Eritrea, dating from the birth of Christ.
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Now let's get back to Iran. By the Sasanid dynasty, Nowruz had drifted from the northward equinox to summer. Since every day of a Zoroastrian month has a specific name and rituals associated with it, so just add ing an extra day wouldn't do. This is something that was debated quite a bit by Zoroastrians, and the best solution they could agree upon was that the extra days should be moved forward a month every 120 years so they would always come right before the month containing the equinox.
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So, towards the end of the 28th year of Khoswrow I, the extra days were moved from after Esfand to after Aban, and Nowruz would now fall in Azar (but they year would still begin on 1 Farvardin). This mean that Khosrow's 29th year started five days earlier than it would have had he not done an intercalation.
This, however, led to a trifurcation of calendars within Iran.
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Armenia, Sogdia, and Khwarezm entirely rejected the new calendar and stuck with the old one; some Persians did the same, celebrating Nowruz on the day they always had. Other accepted teh new calendar but insisted on still celebrating Nowruz on 1 Farvardin.
The result was three Nowruzes in Persia. Lesser Nowruz on 1 Farvardin, Greater Nowruz on 6 Farvardin (which is 1 Farvardin in the old calendar), and New Nowruz on 1 Azar.
At some point, the extra days were moved back to after Esfand.
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So it remained until the Arab conquest. Muslim Arabs were averse to intercalation besed on Qu'ranic injunctions, but Zoroastrian intercalation was at best ad hoc, so no real issues there. The Zoroastrians who fled to India did intercalate a month at some point, which resulted in the Indian Zoroastrian calendar being a month ahead of the Iranian.
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Under Muslim rule, Iranian Zoroastrians were permitted to pay their taxes on Nowruz, as per ancient custom. This caused problems when Nowruz regressed to before the spring grain was ripe, forcing them to borrow money to pay. They appealed ot Caliph al-Mutawakkil; whether motivated by compassion or pragmatism, he consulted with Zoroastrian sages to come up with an acceptable solution.
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Al-Mutawakkil's proposal would have moved Nowruz forward by two months and thereafter added one extra day every four years, so that 1 Farvardin would always coïncide with 17 June by Julian calendar. However, he died before he could introduce his reform.
His successor, al-Mu'tadid, did reform the Persian calendar, but because he didn't get around to it for decades, the new calendar now began ion Julian 11 June. Intercalation was justified on the basis this was just for secular purposes.
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The Iranian calendar was next reformed by a committee of astronomers led by the great Omar Khayyam at the behest of Nizam al-Mulk, Grand Vizier to Jalal-ud'din, better known as Sultan Malik-Shah (which translates as King King-King). This reform fixes Nowruz on the date of the northward equinox (Iran time).
Omar Khayyam also came up with al algorithm whereby there are 8 leap years in 33 years. This is more accurate than the Gregorian calendar, designed 500 years later.
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The Jalali calendar has the same year structure as the Ethiopian. Wikipedia's description is incorrect: Months are actually 30 days long and are NOT determined by how long it takes for the sun to cross 30° of the ecliptic. Khayyam's astronomers did come up with such a scheme, but it was neither intended nor used for governmetn purposes; it was only ever a tool for astronomers.
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The Jalali calendar was the official calendar of Iran until 1303 AH, when the months were rejigged. Now, the frist six months have 31 days, the next five have 30, and Esfand has 29 days in normal years and 30 in leap years.
Kurdish nationalists also use the Solar Hijri calendar, but instead of dating from the Hijra, they date from the Battle of Nineveh, which marked the beginning of Iranic hegemony over Western Asia.
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A few Zoroastrians, mostly in India, continue to use the non-inttercalated calendar. Most, however, accept leap days as being consistent with the Denkard.
American Zoroastrians celebrate Nowruz every year on 21 March, while in Iran, they celebrate on equinox day; this means Nowruz is a a holiday shared by everybody.
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Infrapink (he/his/him)