The Babylonian Calendar

after R.A. Parker & W.H. Dubberstein, Babylonian Chronology
[Providence, Rhode Island, 1956]


The beginning of the month in the Babylonian calendar was determined by the direct observation by priests of the young cresecent moon at sunset after the astronomical New Moon. This custom is remembered in Judaism and Islâm with the principle that the new calendar day begins at sunset. In Islâm, months whose commencement is of relgious significance, like the month after the Fast of Ramadân, still depend on the actual observation of the crescent moon by a respected religious authority.
The Months of the Babylonian Calendar
1. Nisannu307. Tashritu30
2. Aiyaru298. Arakhsamna29
3. Simannu309. Kislimu30
4. Du'uzu2910. D.abitu29
5. Abu3011. Sabad.u30
6. Ululu I2912. Addaru I29
6. Ululu II2912. Addaru II30
If weather prevented the observation of the crescent, the Babylonians would begin the new month anyway after 30 days. In the Jewish and Islâmic calendars, each month is given a conventional length, alternating 30 days and 29 days. For convenience, the table at left applies that device for the Babylonian months, which will enable us to construct a working model of the Babylonian calendar without the priests of Marduk.

The Babylonian New Year was, astronomically, the first New Moon (actually the first visible cresent) after the Vernal Equinox. Modern dates on the Gregorian calendar for the Babylonian New Year may be chosen from the following table. In this table, the "uncorrected" dates use the 19 year lunar cycle, just as it was established in the 4th century BC in Babylon, continued straight down to the present. The earliest New Year is marked with "<" and the latest with ">." Note that in the "uncorrected early" column the earliest date is only 3/31 and the latest is all the way to 4/28. The 19 year cycle adjusts lunar months to the solar year; but if the Babylonian New Year was supposed to be the first New Moon after the Vernal Equinox, then the system has been running slow and the cycle is much in need of correction. There are no priests of Marduk any more to do that. The correction, however, can be accomplished simply by delaying every single intercalation a whole year. Hence the "corrected" columns, where earliest and latest dates are 3/20 & 4/17 (or 3/21 & 4/18).

Uncorrected,Uncorrected,Corrected,Corrected,
AD/AN early:late:early:late:
1990/273701- 4/2601- 4/2701* 3/2701* 3/28
1991/2738 02- 4/1502- 4/1602- 4/1502- 4/16
1992/2739 03* 4/403* 4/503- 4/403- 4/5
1993/2740 04- 4/2304- 4/2404* 3/2404* 3/25
1994/2741 05- 4/1205- 4/1305- 4/1205- 4/13
1995/2742 06* 4/106* 4/206- 4/106- 4/2
1996/2743 07- 4/2007- 4/2107* 3/2107* 3/22
1997/2744 08* 4/908* 4/1008- 4/908- 4/10
1998/2745 09- 4/28>09- 4/29>09* 3/2909* 3/30
1999/2746 10- 4/1710- 4/1810- 4/17> 10- 4/18>
2000/2747 11* 4/611* 4/711- 4/611- 4/7
2001/2748 12- 4/2512- 4/2612* 3/2612* 3/27
2002/2749 13- 4/1413- 4/1513- 4/1413- 4/15
2003/2750 14* 4/314* 4/414- 4/314- 4/4
2004/2751 15- 4/2215- 4/2315* 3/2315* 3/24
2005/2752 16- 4/1116- 4/1216- 4/1116- 4/12
2006/2753 17§ 3/31< 17§ 4/1< 17- 3/3117- 4/1
2007/2754 18- 4/1818- 4/1918§ 3/20< 18§ 3/21<
2008/2755 19* 4/719* 4/819- 4/719- 4/8
"Early" and "late" refer to the best day to see the new crescent (meaning the previous evening of the calendar date, however, since by Babylonian reckoning, as with the Jewish and Moslem calendars today, the day begins at sunset). This is the other problem that such a calendar must deal with, to adjust the length of the lunar month to whole days. This was not even attempted by the Babylonians, so the table just provides a range (early vs. late), that we can compare with other lunar and luni-solar calendars. On the Moslem calendar the first day of the month is usually the second day after the astronomical New Moon (so that the crescent can be observed). The "late" columns fit that pretty well. On the Jewish calendar, the first day of the month can be the New Moon itself, or it can be delayed as much as on the Moslem calendar. In 1992, for instance, both the Jewish and the Moslem months (Niisân & Shawwaal) corresponding to the Babylonian New Year happen to begin on 4/4, only a day after the astronomical New Moon, so the "early" date would be preferable for the 1992 Babylonian New Year, lest 1 Nisannu be lonely on 4/5.

The "AN" years are the Era of Nabonassar, Anno Nabonassari, dating from the reign of the Babylonian King Nabûnâs.iru in 747 BC. Any AN year can be obtained simply by adding 747 to the year of the AD era. Note that 747 BC is equivalent to -746 AD (1 BC=0 AD). The appropriate Seleucid year (Anno Seleucidarum), named after Seleucus I, one of Alexander the Great's generals, who obtained the eastern part of Alexander's Empire, can be calculated by adding 311 to the AD era -- e.g. 1992 AD = 2739 AN = 2303 Anno Seleucidarum -- but the Greek reckoning of 2303 begins the previous fall. The Era of Nabonassar works excellently for the Babylonian calendar, since dividing any AN year by 19 gives the year of the 19 year cycle as the remainder; e.g. 2739/19 = 144 rem 3. Although the 19 year cycle was not regularized until the 4th century, the astronomical records handed down from the Babylonian Priests Kidunnu and Berossos through the Greco-Roman astronomer Claudius Ptolemy begin with Nabonassar. It was Ptolemy who thus formulated the Era of Nabonassar for his astronomical reckoning. The Era was never used by the Babylonians themselves.

A further complication was that the Era of Nabonassar was only used by Ptolemy in conjunction with the Egyptian calendar, which had a year that was exactly 365 days long (no leap years) and so ran fast: That "Era of Nabonassar" was already up to 2741 in 1992. The Seleucid Era was used with the Babylonian calendar, but division by 19 inconveniently does not work with it. The Era of Nabonassar doesn't cover much of Mesopotamian history, but it does cover the history of the calendar that we know about; and Ptolemy's "Canon of Kings," a list of rulers from Nabonassar to the Roman Emperor Antoninus Pius, was absolutely fundamental for ancient chronology -- as recounted in E.J. Bickerman's Chronology of the Ancient World [Cornell, 1982].

The tables above are not constructed from astronomical data (except indirectly) but are schematically determined using a trick borrowed from the construction of the Gregorian Easter tables: the corresponding New Moon for the following year is determined simply by subtracting 11 from the given year's date; e.g. a 4/26 New Year one year means that the next year it will be 4/15. In an intercalary year (marked with "*"), 30 days are added; e.g. 4/4 -11 +30 = 4/23. This works out quite well, except that it comes out a day off after 19 years. The Gregorian Easter reckoning simply ignores that extra day. With the Babylonian calendar, something else is possible: once every 19 years a second month of Ululu is added as the intercalary month instead of a second Addaru. Originally that was in the 17th year (marked "§"). If Ululu II is added as 29 days instead of 30, that makes the whole cycle come out even, which is what is done in the table. Year 17 also happens to be the one with the earliest New Year, so we could adopt the rule that the year with the earliest New Year, which will always be an intercalary year, is also the one with an extra Ululu instead of an extra Addaru. Hopefully, the priests of Marduk would have approved. In the "corrected" calendar, the year with Ululu II turns out to be year 18 anyway, which isn't very different from the traditional year.

Using Gregorian dates as above, we end up off by a day against the moon about every 235 years. Thus, as time goes on, a day must occasionally be added to the given dates. Right now we happen to be in a bit of a cusp: the "late" tables above will become increasingly accurate and will remain so for a couple of centuries, longer than we now need to worry about. Or we can simply construct a complete modern system for the Babylonian calendar, as follows.

Adding 7 months every 19 years approximates the solar year with 235 lunar months. That is mathematically (by continued fractions) the most accurate convenient cycle for a luni-solar calendar and would give, using the mean value of the synodic month (29.530588 days), a year of 365.2467463 days long. This may be called the "Metonic" year, after the Greek astronomer who described the cycle, although the Babylonians discovered it first. The mean solar (tropical) year is 365.24219878 days long. The calendar thus has two problems: (1) This is more accurate than the Julian Calendar (365.25) but less accurate than the Gregorian (365.2425) and must in the long run make provision for correction -- it is off a day every 219 years against the sun. (2) The calendar cannot be corrected for the sun by subtracting a day every 219 years or so, because this would then put it out of synchronization with the moon. A luni-solar calendar must regulate its lunar side with days and its solar side by its addition of months. The solar side thus must be corrected by modifying the 19 year cycle, most conveniently by delaying an intercalation every 342 years (18 cycles). By such delays, the calendar would lose an entire month after 6498 years, which reduces the Metonic year to 365.2422018 days, accurate to a day in 336,700 years.

For the moon, days may be added just as days are added to the Julian, Gregorian, and Moslem calendars. The Julian pattern, a day every four years, is conveniently accurate, more accurate than in the Julian calendar itself: 365.25 days is off a day in 307 years against the Metonic year but off a day in only 128 years against the solar year [note that the Gregorian year, 365.2525, is less accurate against the Metonic year, off a day in 235 years]. A Gregorian-like correction on the Julian year may thus be imposed against the Metonic year: skipping a day every 300 years; 365 + 1/4 - 1/300 = 365.2466666. That approximates the Metonic year to within a day every 12,555 years. Quite accurate enough for the moon. With the 6498 year cycle of intercalations, 365 +1/4 - 1/300 - 29/6498, this produces a solar year of 365.2422038 days. That is not quite as accurate as the pure intercalation cycle: it is now off a day in 201,005 years. That is practically perfect, however; the orbits of the earth and the moon are liable to vary enough in that period of time, and the rotation of the earth to slow down enough, to render greater "accuracy" meaningless.


The Jewish and Moslem Calendars with the Era of Nabonassar

Philosophy of Religion

Home Page

Copyright (c) 1996, 1997, 1998, 1999 Kelley L. Ross, Ph.D. All Rights Reserved


The Jewish and Moslem Calendars and the Era of Nabonassar

Jewish MonthsChristian Months in Arabic
1. Tishrii3010. Tishriinu l'awwaalOctober
2. Xeshwân29/3011. Tishriinu ttaaniiNovember
3. Kislêw30/2912. Kaanuunu l'awwaalDecember
4. T.êbêt291. Kaanuunu ttaaniiJanuary
5. Shebât.302. Shubaat.February
6. 'Adâr293. 'AadaarMarch
6. 'Adâr Shênii30
7. Niisân304. NiisaanApril
8. 'Iyyâr295. 'AyyaarMay
9. Siiwân306. H.aziiraanJune
10. Tammuuz297. TammuuzJuly
11. 'Âb308. 'AabAugust
12. 'Eluul299. 'AyluulSeptember


The Jewish calendar (described below) retains not only the Babylonian Month names (e.g. Nisan for Nisannu) but also the Babylonian 19 year cycle. The adoption of the cycle is evidently the reform effected by the Patriarch Hillel II in the 4th century, but the cycle as presently consituted dates from the 9th or 10th centuries, when the complete calendar system was apparently formulated. The 19 year cycle is the only true cycle in the Jewish calendar, since the method of adding days depends on the mean value of the synodic month and does not produce a repetition of dates within any significant length of time. The dates of Rô'sh Hashshânâh, however, roughly repeat after 247 years (13 cycles).

The Months of the Moslem Calendar
1. alMuh.arram307. Rajab30
2. Shafar298. Sha'baan29
3. Rabii'u l'awwal309. Ramad.aan30
4. Rabii'u ttaanii2910. Shawwaal29
5. Jumaadaa l'uulaa3011. Duu lQa'dah30
6. Jumaadaa l'aaxirah2912. Duu lH.ijjah29/30
The Moslem calendar consists of years of 12 lunar months. A reform effected by the Prophet Muh.ammad dispenses with attempts at intercalation. The Moslem year is therefore short, only 354 or 355 days, and the calendar runs fast. The Era for the calendar begins on the evening of the Prophet's Flight from Mecca to Medina. That occurred at the time of the first visible crescent of the New Moon, on the first day of the month of Muh.arram, or 16 July 622 AD (Julian reckoning). The "Flight" in Arabic is the H.ijrah, so the Era of the Moslem calendar is called that of the H.ijrah or, in English, the Hegira -- "AH," the Anno Hegirae.

The problem of the Moslem clalendar is then simply to add days to keep it accurate with the moon. This is accomplished with a calendar cycle that adds 11 days every 30 years -- in years 2, 5, 7, 10, 13, 16, 18, 21, 24, 26, and 29. The extra days comes at the end of the calendar year, making the month of Dhuu lH.ijjah 30 days long instead of 29. There are 360 months in the cycle, and 354 days in a common year. The gives 10620 + 11 = 10631 days for the cycle, or an average of 29.53055556 days for the month. That will be off a day against the mean synodic month (29.530588) every 2568.5 (Moslem) years, or just slightly less accurate for the moon than the Gregorian calendar is for the sun (off a day in 3320 years).

Since the Jewish calendar adds a month every two or three years, the correspondence between Jewish and Moslem months shifts at those times. Muh.arram of year 1 of the Hegira Era corresponded to Abh in the Jewish calendar. Muh.arram move entirely around through the seasons and returns to being Abh in 32 or 33 years. If we ask how long it would take for the 19 year Jewish cycle and the 30 year Moslem cycle to commensurate, this turns out to be 1368 solar (Jewish) or 1410 Moslem years. The following table shows how these numbers break down into prime (or small multiples of prime) factors.

235 m72
47 x5 x 6 x 4 x 3 = 16920 m
3012 m
1410 y
The number of months in a 19 year cycle is 235, which is simply 47 times 5. 47 is then the smallest number of Moslem 30 year cycles (360 months) that is commensurate with an integer number of 19 year cycles (72). 47 30-year cycles is 16920 months, or 1410 Moslem years. 16920 months is 72 19-year cycles, or 1368 (72 times 19) Jewish years. In Iran a "solar" Hegira Era is also used, so 1410 lunar Moslem years would equal 1368 solar Iranian Moslem years (at least on the approximation of the 19 year cycle).

1368 is a number that turns out to have a curious property. 1368 years before 622 AD puts us in 747 BC, the first year of the Era of Nabonassar. An interesting coincidence. The year 1 AH is thus the year 1369 AN. The full Jewish/Moslem cycle brings us from 622 AD down into our own time: 622 plus 1368 is 1990. The year 1990 thus corresponds to 1411 AH and to 2737 (1368 x 2 + 1) AN. This may be of no practical importance, but it is a curiosity of history that the Era of a Babylonian King, as used by a Greco-Roman astronomer with the Egyptian calendar, fits in with the Era of the Moslem calendar on the basis of a cycle generated by the interaction of the Moslem calendar 30 year cycle and the Babylonian 19 year cycle as used by the Jewish calendar. Since the chronology of ancient history is based on the Era of Nabonassar in Ptolemy's Canon of Kings anyway, it makes one wonder if the Era of Nabonassar should be used as the proper, neutral Common Era between the religions of Judaism, Christianity, and Islam.


The Babylonian Calendar

The Jewish Calendar

Islâmic Dates with Julian Day Numbers

Philosophy of Religion

Home Page

Copyright (c) 1996, 1997, 1998, 1999 Kelley L. Ross, Ph.D. All Rights Reserved


The Jewish Calendar


The following technique for analyzing the Jewish calendar is based on that of Charles Kluepfel, known from personal correspondence, with definitions paraphrased from Arthur Spier, The Comprehensive Hebrew Calendar (Feldheim Publishers, 1986).

The date of Rô'sh Hashshânâh is determined by the occurrence of the actual mean New Moon, the Môlâd, associated with the first month of the year, Tishrii. Calculated to an accuracy of 3/10 of a minute, the length of the synodic month is expressed in special units (at 18/minute or 1080/hour) called "parts" (p). The synodic month (m) is thus 765433p long. The day is considered to begin at mean sunset or 6 PM. Noon is therefore reckoned to occur at 18h, not 12h. The Môlâd Tishrii is calculated by an absolute counting of months from a Benchmark of 5h 204p on Monday 7 October 3761 BC/BCE (the Môlâd Tishrii of year 1 Anno Mundi).

If the reckoning of days is always kept to whole weeks following an original Shabbât, the remaining excess of parts places the Môlâd Tishrii in a clear relation to the week. In the following tables, only the excess of parts need be stated. For the determination of an absolute date in relation to other calendars, a count of whole weeks and excess parts may be made for convenience from a 0 year benchmark of Julian Date 347,610d, with an excess of 60,095p. Since there are 181,440p in a week (w), any excess of parts that exceeds that amount may be reduced by it, with 7d added to the count of days. A number for the day of the week must be added for the proper Julian Date. The four dehiyyôt or postponements modify the way in which the Môlâd Tishrii determines Rô'sh Hashshânâh.

BeforedpAfterdp
Sunday100
Monday225,920Monday2
Tuesday351,840Tuesday351,840
Wednesday477,76077,760
Thursday5103,680Thursday5
Friday6129,600129,600
Shabbât7155,520Shabbât7
Sunday8181,440181,440
Monday9Monday9

The First Dehiyyâh

When the Môlâd Tishrii occurs on a Sunday, Wednesday, or Friday, Râ'sh Hashshânâh is postponed to the following day. This is done to prevent Y&ocric;m Kippûr from occurring on the day before or the day after the Shabbât or Hôshanâ Rabbâ from occurring on the Shabbât. Add 25,920p (1080px24h) for each day; strike out disallowed days and irrelevant thresholds. Sunday and Monday of the following week are included in this table for reasons that will be apparent in the second dehiyyâh.

Closed Updp
Monday20
Tuesday351,840
Thursday577,760
Shabbât7129,600
Monday9181,440

BeforedpAfterdp
Monday20Monday20
Tuesday351,840Tuesday345,360
Thursday577,760Thursday571,280
Shabbât7129,600Shabbât7123,120
Monday9181,440Monday9174,960

The Second Dehiyyâh

When the Môlâd Tishrii occurs at noon (18h) or later, Rô'sh Hashshânâh is postponed to the next day -- or if this day is a Sunday, Wednesday, or Friday, to Monday, Thursday, or the Shabbât, respectively, because of the first dehiyyâh. This is done to prevent Rô'sh Hashshânâh from occurring before the New Moon, since the reckoning of the Môlâd is based on the mean New Moon, which may occur several hours before the apparent New Moon. Subtract 6480p (=6h) from each threshold.

Format: In the tables below, on the left is found a notation such as "2/353/5," wherein "2" signifies the day upon which the year begins, i.e. a Monday, "353" the length of the year, and "5" the day upon which the following year begins, i.e. a Thursday. The equation to its right demonstrates how the length of the year and the day upon which the following year begins are calculated. A common year (C=12m) contains exactly 50w 113,196p, and a leap year (L=13m) exactly 54w 152,869p, with common and leap years arranged in the 19 year lunar cycle thus: 1 C, 2 C, 3 L, 4 C, 5 C, 6 L, 7 C, 8 L, 9 C, 10 C, 11 L, 12 C, 13 C, 14 L, 15 C, 16 C, 17 L, 18 C, 19 L. (This cycle, like the month names of the Jewish calendar, is adopted from the Babylonian calendar, and the position of an AM year in the cycle may be determined by finding the remainder after the year has been divided by 19 -- but the cycle has become inaccurate over the centuries so that at least the 8th and 19th year leap years should be delayed one year.) The excess of parts for each kind of year need only be added to the excess of parts for the current year to determine the placement of the Môlâd Tishrii for the following year and, as a consequence and with the addition of the weeks, the length of the current year. Determining the threshold for a change in the length of years starting on the same day simply involves reckoning backwards from the thresholds of the following years, as is shown by the use of subtraction rather than addition in the equations on the right. The thresholds calculated in the second dehiyyâh are always underlined below.

The Third Dehiyyâh

When the Môlâd Tishrii of a common year falls on Tuesday, 204 parts after 3 A.M. (3d 9h 204p or 61,764p) or later, Rô'sh Hashshânâh is postponed to Wednesday, and, because of the first dehiyyâh, further postponed to Thursday. This is done to eliminate the 356d long common year, making for only seven kinds of common year. Drop the year 3/356/2 and the irrelevant old threshold for Thursday. Now there is a single threshold for the change from Tuesday to Thursday for the current year and from Saturday to Monday for the following year.

Common Years (C) (see below for common years following leap years)

BeforeAfter (C)
2/353/50 + 113,196 = 113,1962/353/50 + 113,196 = 113,196
2/355/79,924 = 123,120 - 113,1962/355/79,924 = 123,120 - 113,196
3/354/745,360 + 113,196 = 158,5563/354/745,360 + 113,196 = 158,556
3/356/261,764 = 174,960 - 113,19661,764 = 174,960 - 113,196
5/354/271,280 + 113,196 = 3,0365/354/2
5/355/3113,604 = 45,360 - 113,1965/355/3113,604 = 45,360 - 113,196
7/353/3123,120 + 113,196 = 54,8767/353/3123,120 + 113,196 = 54,876
7/355/5139,524 = 71,280 - 113,1967/355/5139,524 = 71,280 - 113,196
9/353/5174,960 + 113,196 = 106,4469/353/5174,960 + 113,196 = 106,446

The Fourth Dehiyyâh

When, in a common year succeeding a leap year, the Môlâd Tishrii occurs on Monday, 589 parts after 9 A.M. (2d 15h 589p or 42,709p) or later, Rô'sh Hashshânâh is postponed to Tuesday. This is done to eliminate the 382d long leap year, making for only seven kinds of leap year. Drop the year 5/382/2 and the irrelevant old threshold for Tuesday of the following year. Now there is a single threshold for the change from Tuesday to Thursday for the current year and from Monday to Tuesday for the following year. Note new following year Thursday threshold from the third dehiyyâh. The fourth dehiyyâh results in three different tables for common years, with the original C table holding only for common years that follow common years.

Leap Years (L)

BeforeAfter (L)
2/383/70 + 152,869 = 152,8692/383/70 + 152,869 = 152,869
2/385/222,091 = 174,960 - 152,8692/385/222,091 = 174,960 - 152,869
3/384/245,360 + 152,869 = 16,7893/384/245,360 + 152,869 = 16,789
5/382/271,280 + 152,869 = 42,70971,280 + 152,869 = 42,709
5/383/373,931 = 45,360 - 152,8695/383/3
5/385/590,335 = 61,764 - 152,8695/385/590,335 = 61,764 - 152,869
7/383/5123,120 + 152,869 = 94,5497/383/5123,120 + 152,869 = 94,549
7/385/7151,691 = 123,120 - 152,8697/385/7151,691 = 123,120 - 152,869
9/383/7174,960 + 152,869 = 146,3899/383/7174,960 + 152,869 = 146,389

Common Years between leap years

Before (C)After (CB)
2/353/50 + 113,196 = 113,1962/353/50 + 113,196 = 113,196
2/355/79,924 = 123,120 - 113,1962/355/79,924 = 123,120 - 113,196
3/354/745,360 + 113,196 = 158,5563/354/742,709 + 113,196 = 155,905
5/354/261,764 + 113,196 = 174,9605/354/261,764 + 113,196 = 174,960
5/355/3113,604 = 45,360 - 113,1965/355/3113,604 = 45,360 - 113,196
7/353/3123,120 + 113,196 = 54,8767/353/3123,120 + 113,196 = 54,876
7/355/5139,524 = 71,280 - 113,1967/355/5139,524 = 71,280 - 113,196
9/353/5174,960 + 113,196 = 106,4469/353/5174,960 + 113,196 = 106,446

Common Years following but not between leap years
Note new following year Thursday threshold from the third dehiyyâh.

Before (C)After (CF)
2/353/50 + 113,196 = 113,1962/353/50 + 113,196 = 113,196
2/355/79,924 = 123,120 - 113,1962/355/79,924 = 123,120 - 113,196
3/354/745,360 + 113,196 = 158,5563/354/742,709 + 113,196 = 155,905
5/354/261,764 + 113,196 = 174,9605/354/261,764 + 113,196 = 174,960
5/355/3113,604 = 45,360 - 113,1965/355/3113,604 = 45,360 - 113,196
7/353/3123,120 + 113,196 = 54,8767/353/3123,120 + 113,196 = 54,876
7/355/5139,524 = 71,280 - 113,1967/355/5130,008 = 61,764 - 113,196
9/353/5174,960 + 113,196 = 106,4469/353/5174,960 + 113,196 = 106,446

Philosophy of Religion

Home Page

Copyright (c) 1996, 1997, 1998, 1999 Kelley L. Ross, Ph.D. All Rights Reserved


The Calendar in India


There is a completely separate Indian calendrical tradition. In the "Book of the Cattle Raid," in the Book of Virât.a, in the Mahâbhârata, Duryodhana claims that the Pân.d.avas have failed to keep their agreement to stay in exile for twelve years and in hiding for one. Bhis.ma reckons (47.1-5) that they have kept the agreement, and he mentions that the calendar adds an extra month every five years. A.L. Basham, in The Wonder that was India, gives the same rule (p. 494), though he states it as adding an extra month every thirty months. Sixty months is five years (5x12). That means two months in five years. Basham also says that this was done "as in Babylonia." But that is not true. The Babylonians added seven months every nineteen years, which is often called the "Metonic" cycle (after the Greek astronomer Meton) and is still used by the Jewish calendar.

The best approximations (by continued fractions) to the difference between twelve synodic months and the solar year would be to add one month every three years, three every eight, four every eleven, seven every nineteen, or 123 every 334. The last is not very practical. Some Greek cities used three every eight. That already is a lot more accurate than two every five. Three months in every eight years results in an error of a month in 149 years, while two in every five results in an error of a month in only 32 years. That is better than one in every three, which is off a month in 29 years, but otherwise looks pretty miserable. Four months every eleven years results in an error of a month in 216 years; and seven every nineteen results in an error of a month in 6494 years. For all practical purposes, of course, 6494 years is eternity. That does not mean that the Babylonian (or Jewish) calendar is just fine for that long. Those calendars can be adjusted before an error of an entire month builds up. But Indian calendars using the 2/5 rule are going to be wildly inaccurate before the passage of much time at all.


Philosophy of Religion

Home Page

Copyright (c) 1996, 1997, 1998, 1999 Kelley L. Ross, Ph.D. All Rights Reserved


Iranian Calendars


While modern Îrân has become a fiercely Islâmic country, it retains some elements to remind us of its previous religion, Zoroastrianism. Thus, a very common male given name is Mehrdâd, which actually means "given by Mithra," Mithra being a god even of pre-Zoroastrian Îrân (Mitra in the Vedas). There are even versions of the same name in Greek and Latin: Mithradates

Of great interest is the continuation in modern Îrân of the ancient Zoroastrian calendar. While the religious Islâmic calendar is of course used in Îrân, the ancient solar calendar also continues to be used as a civil calendar.
AvestanMiddle Persian,
Pahlavi
Modern Persiandays
FravashinâmFravardînoFarvardin31
Ashahê VahistahêArdavahistOrdi Behesht31
HaurvatâtoHorvadadKhordâd31
TistryêheTîrTir31
AmerotâtoAmerôdadMordâd31
Khshathrahê VairyêheShatvaîrôShahrivar31
MitrahêMitrôMehr30
ApâmÂvânÂbân30
ÂthrôÂtarôÂzar30
DathushôDînôDei30
Vanheus MananhoVohumânBahman30
Spentayâo ArmatôisSpendarmadEsfand29/30
The table contains the names of the Zoroastrian months as they occur in Avestan, the ancient sacred language of Zoroastrianism, in Middle Persian, or Pahlavi ("Parthian"), the language of the Sassanid Empire, and in Modern Persian (Fârsi), as used today. Many of the Avestan names are identifiable as relating to what have been called the Zoroastrian Archangels, and to some familar, pre-Zoroastrian gods (Mithra again). The spelling for Modern Persian indicates the Persian vowel quality, not, as is common, the vowels as they would be read in Arabic.

The Îrânian year begins with the Vernal Equinox, March 20 or 21. This Persian New Year, Noruz (literally, "New Day"), is often celebrated by Îrânian expatriots as their distincitvely national holiday. The assignment of the lengths of the months reflects the fact that spring and summer in the northern hemisphere are longer than fall and winter. The Persian months are thus actually zodiacal months, comparable to the Chinese Solar Terms. The twelfth month is 29 days in common years, 30 days in leap years. My source (A.K.S. Lambton, Persian Grammar, Cambridge University Press, 1967, p.255-256) does not specify in what year the extra day is added or whether the intercalation scheme is merely Julian or if the Gregorian or some other correction is now applied.

The Era used with this solar calendar is still the Islâmic H.ijrah Era, but it is counted in full solar (365 day) rather than in the short lunar (354 day) years of the Islâmic calendar proper. This means that the Persian year beginning on March 21 can be determined just by subtracting 621 from the AD Era year. Thus, the Persian New Year in 1999 began the solar Hegira year 1378. As discussed elsewhere, this solar Hegira era is equivalent to the year of the Era of Nabonassar (747 BC) minus 1368. Since, astronomically, the Babylonian year also began at the Vernal Equinox, the Babylonian year of the Era of Nabonassar can always be obtained just by adding 1368 to the Îrânian solar Hegira year -- 1999 is 1378 + 1368 = 2746 Anno Nabonassari.

Another Îrânian calendar also begins with the Vernal Equinox. That is the sacred calendar for the Bahâ'i Faith. The founder of the Faith, the prophet Bahâ'ullâh, was exiled from Îrân and imprisoned by Turkey in Haifa.
MonthLengthDate
Bahâ19March 21
Jalâl19April 9
Jamâl19April 28
'Az.amat19May 17
Nûr19June 5
Rah.mat19June 24
Kalimât19July 13
Kamâl19August 1
Asmâ'19August 20
'Izzat19September 8
Mashîyyat19September 27
'Ilm19October 16
Qudrat19November 4
Qawl19November 23
Masâ'il19December 12
Sharaf19December 31
Sult.ân19January 19
Mulk19February 7
[intercalation]4/5February 26
'Alâ'19March 2
There he was buried after his death in 1892, and there the international headquarters of the Faith is located, while the city itself has passed from Turkey to British Palestine and now to the State of Israel.

The Bahâ'i calendar has the unique structure of being divided into 19 months of 19 days each. This only falls 4 days short of a 365 day year, which is filled in with intercalary days. The names of the months are given with their Arabic vowel quality, since they are all Arabic words. The intercalary period has been located so that, if the dates given in the table are observed, an intercalation by the Gregorian calendar on February 29 will automatically produce a Bahâ'i intercalary period of 5 rather than 4 days.

The Bahâ'i Faith, although owing much to Islâm, and especially to Îrânian Islâm, sees itself as a separate religion that is the successor to Islâm, as Christianity saw itself as the successor to Judaism -- without, however, rejecting the legitimacy of the earlier religions. Unfortunately, to the Îrânian authorities, especially after the advent of the "Revolutionary" Îrânian theocracy, this meant that Bahâ'is were actually apostates from Islâm, a crime punishable by death under Islâmic Law. Thus, after 1979, all the Bahâ'i holy places in Îrân were systematically destroyed and an intense persecution of members of the Faith begun. Many, consequently, fled the country as quickly as possible.

The Faith had long seen itself, however, as an international religion, and communities had long been established all over the world. A local Bahâ'i community had been founded in Hawai'i, for instance, while it was still an independent country. Persecution in Îrân, therefore, is liable to be of little significance for the growth of the religion. Indeed, air travelers approaching O'Hare International Airport, in Chicago, are often curious what the unusual large building is on the shore of Lake Michigan. It is the Bahâ'i Temple, in Wilmette, Illinois, which has existed since the early days of the century.

Îrânian calendars thus present us with intriguing combinations of pre-Islâmic, Islâmic, and post-Islâmic features, even as Îrânian nationalism struggles violently with its own identity and its own religious heritage. In the Persian national epic, the Shâh Nâmah of the poet Firdawsî (c.940-c.1020), one of the first books written in New (i.e. Islâmic) Persian, there is a striking image from a dream:  Four men pulling hard on the corners of a square white cloth, but the cloth does not tear. The men are interpreted to be Moses, Jesus, Muh.ammad, and Zoroaster (Zarathushtra in Avestan; Zardasht, Zardosht, Zarâdosht, etc. in Modern Persian), and the cloth the Religion of God. The inclusion of Zoroaster with the other principal Founders of Monotheism is the distinctively Îrânian touch, as Îrân itself could be the cloth, pulled fiercely by both internal and external religious influences -- though ironically the word for "religion" in Arabic itself, dîn, appears to be borrowed from Middle Persian (dên).


Philosophy of Religion

Home Page

Copyright (c) 1999 Kelley L. Ross, Ph.D. All Rights Reserved