Article

Symposium on Calendars Used in Asia and Oceania

Mohammad BAGHERI*

Ancient calendars were usually based on the phases of the moon, which was the mostapparent phenomenon in the sky. However, since this calendar was not appropriate for
agricultural activities, lunisolar and later, solar calendars became popular. The same happened to Iranian calendars. In this paper, I have given an account of the early Iranian preIslamic calendars and the Iranian calendars that were used after the advent of Islam in Iran.
Since lunar and solar years do not include an integer number of days, in both types of years,
there are fractions of days which, after accumulation, result in extra days. The years withthe extra days are called leap years and the process of adding the extra day is called intercalation. Different intercalation systems have been used among different people in different
ages. I have explained methods of defining intercalary days in different Iranian calendars.
A very important source for the study of the ancient Iranian calendars is Abu Rayhan
Biruni’s Arabic treatise Chronology of Ancient Nations. This unique work was composed
around 10 centuries ago and has been translated into Persian, English and Russian. After theestablishment of Islam in Iran around 12 centuries ago, the Arabic lunar calendar became
popular in Iran. However, since it was not proper for economical purposes, several reforms
were suggested. In 1079, a solar calendar named Jalali or Maleki was devised by a group ofastronomers including Umar Khayyam. The present official calendar used in Iran isbased on the Maleki calendar.
Keywords
Iranian Calendars, Pre-Islamic Calendars, Islamic Period Calendars, Intercalation
Systems, Leap Years

Early humankind used natural phenomena to keep an

initial position, so a year was defined as twelve lunar

account of time. The consecution of day and night wasmonths. However, records over a long time showed thatthe most natural phenomenon to adjust the rhythm ofa real year or returning of nature to its initial situation

human activities. On a smaller scale, the position of thetakes longer and depends on the position of the sun in

sun in the sky, shown by the shadow of a verticalthe background of the fixed stars. This was, for example,

gnomon was used. For larger time-spans, the apparent

noticed by the heliacal rising of Sirius.

phases of the moon, from crescent to full moon and vice

Therefore, we had natural lunar months and solar

versa, were quite useful. It was noticed that after aboutyears. On the other hand, we had conventional solar

twelve full cycles of the moon, nature returns to its

months and lunar years. Agricultural activities depended* Institute for the History of Science, University of Tehran

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Ancient Iranian Calendars

Ancient Iranian Calendars号（２０２２）

Research Papers of the Anthropological Institute Vol.11 (2022)『人類学研究所 研究論集』第11on the seasons and hence, necessitated using solar years.

previous year. Besides the Iranian calendar, Biruni also

However, a solar year did not contain an integer number

imparts some valuable information about the Greek,of lunar months, so lunisolar calendars were devised.

Christian, Jewish, and Arabic calendars that has come toAgain, the pure solar calendars did not contain anus exclusively thanks to Biruni’s accurate and docu-integer number of days, so intercalation was needed tomented presentation of the data. He has also included akeep the solar calendar fixed relative to the seasons. For

short chapter on calendars in his famous book al-Tafhīm

lunar calendars, the length of a lunar month was not anli-awāʾl ṣanāʿat al-tanjīm (Introduction to astrology)

integer number of days. The combination of thesewhich is extant both in Persian and Arabic versions. It

incommensurable parameters led to different intercala-was translated into English by R. Ramsay Wrighttion systems in different ages and among different soci-(London, 1934) and a Russian version was publishedeties. Despite the extensive investigations of experts in(Tashkent, 1975). A Japanese translation by M. Yano

the history of calendars, some ambiguities remain about

and our late colleague K. Yamamoto appeared in threewhich a commonly accepted idea has not yet beenparts in the Kyoto Bulletin of Islamic Area Studies

achieved. This is due to the complexities of the interca-(2010–2013). There is also an unpublished Italianlation systems, a lack of sufficient data from past times,

version of this work translated by Claudio Cecotti, aand different interpretations of the existing texts relating

historian of astronomy from Udine in Italy.

to calendars. Computer simulation of the situation of theIn ancient Iran, the eras were defined as the year insun and the moon in the sky at any time in the past helps

which the first king of a dynasty acceded to the throne.

to solve some of these problems.

Later, they chose the first year of the kingdom of each

For all these reasons, in the chronological texts, theking as the beginning of their calendar. The last Iranianinterval between different epochs are given in terms of

pre-Islamic king Yazdigird acceded to the throne in thedays to avoid the ambiguities due to different intercala-year 632 AD. After the advent of Islam in Iran, the year

tion systems. These intervals in terms of days arein which the prophet Mohammad emigrated fromusually very large numbers and sometimes we have

Madina to Mecca (622 AD) was adopted as the Hejira

difficulty with the wrong numbers found in the manu-era. I will return to Hejira calendars at the end of myscripts written by the scribes. The beginning of a lunartalk.

month is not always a certain observation, because it

Before the Achaemenian dynasty, which emerged independs on the astronomical parameters, the eyesightthe sixth century BC, the intercalation system for adjust-power of the observer and the clearness of the sky in theing the year with the seasonal changes was as follows.

locality of observation. To avoid this uncertainty, theIn eastern Iran, each year had 360 days (12 months, eachcorrectness of conversions of dates between differenthaving 30 days). Then at the end of each period of six

calendar systems is controlled by checking the weekday

years, they inserted one intercalary month to compen-of the given day.

sate the extra 5 days of the solar year (6 x 5 = 30), and at
the end of each period of 120 years, an extra month

A very informative and reliable text about the ancient(actually two months, because 120 is a multiple of 6)

Iranian calendars was composed by Abu Rayhan Biruni,

was intercalated to compensate for the extra one-quarter

the Iranian polymath scholar who lived in Khwarazmof a day (120 x ¼ = 30). In western Iran, there was a(Central Asia) about ten centuries ago, and has beenlunisolar calendar influenced by the Babylonian calen-recognized as the greatest scholar in the whole ofdar. This calendar had a regular lunar year of 354 or 355

Islamic civilization. His book al-Āthār al-bāqiya ʿandays (12 lunar months) and a leap year of 383 or 384

al-qurūn al-khāliya has been translated into Englishdays. The intercalation system involved inserting 7with the title Chronology of Ancient Nations (London,months every 19 years (19 x 11= 209 days ≈ 7 months)

1879) by the German scholar Edward Sachau. He had

and, in some cases, 3 months every 8 years (8 x 11= 88

also edited the original Arabic text in London in thedays ≈ 3 months). This is in accordance with the factor

742.7 which Prof. Ram mentions in his paper (7 x 2.7 =Therefore, in these two centuries, cultural activities

18.9 ≈ 19 and 3 x 2.7 = 8.1 ≈ 8).

decreased or stopped due to the resistance wars throughout Iran. Either no treatise was composed, or no com-by the Iranians, the simple and regular Egyptian calen-

posed treatise was preserved in this period. Even thedar was introduced in Iran. It was used in Egypt for 3000

existing manuscripts were burned either by Arabs or by

years and was purely solar, because it was based on thethe Iranians themselves to save their lives. So we know

heliacal rising of Sirius at the time when the Nile over-very little about this two-century period in Iran.

flowed. This calendar had 12 month, each with 30 daysFortunately, an Armenian scholar named Anania ofand 5 extra days at the end of the year.

Shirak, who lived in the seventh century, and is known

In the first century AD, a group of knowledgeable

as the greatest scholar of Medieval Armenia, imparted

Zoroastrian priests from Sistan, the southeastern prov-

precious information about the calendars of 14 nations

ince of Iran, immigrated to India. They were called

including Jews, Arabs, Macedonians, Romans, Syrians,

Sun-worshipper Sistanis or Mugh-Brahmans. They took

Greeks, Egyptians, Ethiopians, Athenians, Bithynians,

their beliefs, rituals, and knowledge to India where they

Cappadocians, Georgians, Albanians and Persians.

exchanged and mixed them with Indian traditions. InThese unique data are preserved in the Armenian manu-Sanskrit they were called Shak-Dipy, which refers toscripts extant in the Mesrop Mashtots Matenadarantheir ethnicity (Shaka or Saka) and the fact of being alibrary in Yerevan (Armenia). According to Anania, theminority. Their calendar system became recognized as

first month of the Iranian calendar (Farvardin) started on

Shaka calendar, which is still in use, and its radix is

August 6th. In present comparative tables, Farvardin

March 3rd of 78 AD. The same calendar system with astarts on March 21st. This shows that due to the cessa-shift starting from February 23rd of 57 BC was known

tion of intercalations, the beginning of the Iranian year

as the Vikrami calendar and became the formal Indian

had moved in the seasons by more than four months.

calendar after the independence of India in 1950.

The trace of such displacements remains in local IranianDuring the Sassanid dynasty (gov. 226–651 AD), thecalendars. For example, in the mountains of Gilansame Egyptian calendar system was used. In this Iranianprovince in the south of the Caspian Sea, the New Yearversion of the Egyptian calendar system, each day of thefestivities (Nowruz) falls around the August 5th (insteadmonth had a name taken from the angels of theof the formal date March 21st).

Zoroastrian religion. Whenever the name of the day was

After the establishment of the Islamic government in

the same as the name of the month, it was celebrated asIran, the Arabic lunar calendar with the Hejira epocha festivity. At the end of the year, five extra days werebecame popular. However, the solar Iranian calendar

named after the titles of five sections of Avesta, thewas still necessary for agricultural activities. The slow

sacred book of Zoroastrians.

shift in the solar calendar due to curtailment of theIn this calendar, to compensate for the extra fraction

intercalations created problems for tax affairs, so someof the day in a true solar year, they inserted an interca-calendar reforms were suggested to solve this inconsis-

lary month at the end of each period of 120 years (120 xtency. The most important reform was implemented at¼ = 30). However, this rule was not implemented regu-

the request of Malekshah king of the Saljuk dynasty inlarly because of the long period between intercalations.

the year 1079 AD by a group of astronomers including

Moreover, since this intercalation was established by theUmar Khayyam (who was also a famous poet). Thisroyal authorities, after the conquest of Iran by the Arabs,

calendar was based on solar years starting from thethe intercalation was not implemented.

vernal equinox. It was called the Maleki or Jalali calen-

The seventh and eighth centuries AD are called “thedar after the name of the king. In this ingenious calendar,

two centuries of silence” in Iranian history, because,the six months of spring and summer had 31 days. The

during these two centuries, Iranians were defending

next five months had 30 days and the last month had 29

their land and religion against the Arab invaders.

days or, in leap years, 30 days. This arrangement was75

Ancient Iranian Calendars

Around the year 500 BC, after the conquest of Egypt

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Research Papers of the Anthropological Institute Vol.11 (2022)『人類学研究所 研究論集』第11defined based on the astronomical calculation regarding

cally defined system, the beginning of the year will

the mean motion of the sun on the ecliptic. They had

always remain near the vernal equinox. In other systems

noticed that when the sun is close to its apogee (from the(Julian or Grigorian) there will be a discrepancy of

geocentric point of view) it moves slower, so it traverses

about three days every 10,000 years. Moreover, in thethe 30 degrees of a zodiacal sign over a slightly longer

Jalali calendar, the variations of the years’ length, whichtime. Another important aspect of this calendar was its

amounts to 20 minutes, will not affect the intercalation

system of defining leap years. For solar years of 365

process.

days, we should have a leap year of 366 days every four

In 1925 the Iranian parliament approved a new calen-years and sometimes after 5 years. In all other intercala-dar that was based on the Jalali calendar but its radixtion systems of the years with 365 days, special cycles

was the emigration of the prophet Mohammad to Mecca

are defined for deciding which years have the extra

in 622 AD. In this solar calendar, the names of theintercalary day. For the Jalali calendar, there is a rulemonth are taken from pre-Islamic Persian months’

based on astronomical calculation: The first day of thenames. This one is now the formal Iranian calendar,

Jalali New Year is the day in which the sun enters Aries

however, the lunar Hejira calendar and the Christian(first zodiacal sign, vernal equinox) between the noon of

calendar are used in parallel for religious and interna-

the previous day and the given day. With this astronomi-tional affairs, respectively.

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