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CALENDAR (Heb. לוּחַ, lu'aḥ). The present Jewish calendar is lunisolar, the months being reckoned according to the moon and the years according to the sun. A month is the period of time between one conjunction of the moon with the sun and the next. The conjunction of the moon with the sun is the point in time at which the moon is directly between the earth and the sun (but not on the same plane) and is thus invisible. This is known as the מוֹלָד, molad ("birth," from the root ילד). The mean synodic month (or lunation) is 29 days, 12 hours, 44 minutes, and 3⅓ seconds (793 parts (ḥalakim); in the Jewish system the hour is divided into 1,080 parts each of which is 3⅓ seconds). The solar year is 365 days, 48 minutes, and 46 seconds, which means that a solar year exceeds a lunar one (12 months) by about 11 days. The cycles of 12 lunar months must therefore be adjusted to the solar year, because although the Jewish festivals are fixed according to dates in months, they must also be in specific (agricultural) seasons of the year which depend on the tropical solar year. Without any adjustment the festivals would "wander" through the seasons and the "spring" festival (Passover), for example, would be celebrated eventually in winter, and later in summer. The required adjustment is realized by the addition of an extra month (Adar ii) in each of seven out of the 19 years that constitute the small (or lunar) cycle of the moon (maḥazor katan or maḥazor ha-levanah). In 19 years the solar cycle exceeds the lunar by about 209 days, which are approximately 7 months. In Temple times this intercalation was decided upon in the individual years according to agricultural conditions (Tosef., Sanh. 2:2; Sanh. 11b); later, however, it was fixed to be in the years 3, 6, 8, 11, 14, 17, and 19 of the cycle (see below).

In the calendar month only complete days are reckoned, the full (מָלֵא, male) months containing 30, and the defective (חָסֵר, ḥaser) months 29 days. The months Nisan, Sivan, Av, Tishri, Shevat and (in a leap year) Adar i are always male; Iyyar, Tammuz, Elul, Tevet, and Adar (Adar ii in a leap year) always ḥaser, while Ḥeshvan and Kislev vary. Hence, the common year contains 353, 354, or 355 days and the leap year 383, 384, or 385 days.

For ritual purposes, e.g., in reckoning the times fixed for prayers or the commencement and termination of the Sabbath, the day is deemed to begin at sunset or at the end of *twilight, and its 24 hours (12 in the day and 12 in the night) are "temporary" hours varying in length with the respective length of the periods of light and darkness. But in the reckonings of the molad the day is the equatorial day of 24 hours of unvarying length and is deemed to commence at 6 p.m., probably in terms of local Jerusalem time.

Fixing Rosh ha-Shanah (New Year's Day)

The year begins on Tishri 1, which is rarely the day of the molad, as there are four obstacles or considerations, called deḥiyyot, in fixing the first day of the month (rosh ḥodesh). Each deḥiyyah defers Rosh Ha-Shanah by a day, and combined deḥiyyot may cause a postponement of two days: (1) mainly in order to prevent the Day of Atonement (Tishri 10) from falling on Friday or Sunday, and Hoshana Rabba (the seventh day of Sukkot; Tishri 21) from falling on Saturday, but in part also serving an astronomical purpose (see below). Rosh Ha-Shanah never falls on Sunday, Wednesday, or Friday (according to the mnemonic לא אד"ו ראש known as the postponementaddu – probably first vocalized iddo; cf. Ezra 8:17). (2) Entirely for an astronomical reason, if the molad is at noon or later (מוֹלָד זָקֵן or מוֹלָד יח) Rosh Ha-Shanah is delayed by one day or, if this would cause it to fall as above, two days. These two deḥiyyot, owing to the mentioned limits on the number of days in the year, entail another two. (3) The third deḥiyyah is as follows: If the molad in an "ordinary" (not leap) year falls at ג"טר"ד, that is the third day (Tuesday), at 9 hours, 204 ḥalakim, that is, 3:11 a.m. and 20 secs. – Rosh Ha-Shanah is put off two days. A postponement to Wednesday is not permitted (as in (1)), so that it is deferred to Thursday. The object is as follows: If the molad of Tishri occurs at that hour, the outcome would be a year which is one day too long. The following table of moladot will illustrate this:

TishriTuesday3:11.20 secs. a.m.
ḤeshvanWednesday3:55.23 secs. p.m.
KislevFriday4:39.27 secs. a.m.
TevetSaturday5:23.30 secs. p.m.
ShevatMonday6:07.33 secs. a.m.
AdarTuesday6:51.37 secs. p.m.
NisanThursday7:35.40 secs. a.m.
IyyarFriday8:19.43 secs. p.m.
SivanSunday9:03.47 secs. a.m.
TammuzMonday9:47.50 secs. p.m.
AvWednesday10:31.53 secs. a.m.
ElulThursday11:15.57 secs. p.m.
TishriSaturday12:00.00 secs. (noon)

The last figure (Tishri) constitutes a molad zaken as described in (2), and this would, therefore, lead to a deferment of a day, thus making Rosh Ha-Shanah fall on Sunday, which again is not permitted, so that the festival will be moved one further day, to Monday. The interval between Rosh Ha-Shanah and the next one would then be 356 days which is a day longer than the maximum ordinary year. Rosh Ha-Shanah is therefore delayed from Tuesday to Thursday (as Wednesday is ineligible), and the result is a year of 354 days which, as distinct from the minimal year of 353 and the full one of 355 days, is called "regular" or "common." (4) This deḥiyyah is very infrequent. It is known as בט"ו תקפ"ט אחר עבור שנה, that is when the molad of Tishri, following immediately after a leap year, occurs on the second day (Monday) at 15 hours, 589 ḥalakim, which means Monday, 9:32 a.m. and 43⅓ secs. If the reckoning is made backward by subtracting 13 moladot, the Tishri of the preceding year would have had its molad on Tuesday at 12 noon. Having occurred at that time, Rosh Ha-Shanah of the previous year would have been on Thursday since Tuesday's molad was "zaken," and two days deferment must take place as Wednesday is impermissible. If Rosh Ha-Shanah then commenced on Thursday in the previous year, that year would have consisted of 382 days only which is too short for a leap year. By deferring Rosh Ha-Shanah of the current year from Monday to Tuesday, the year, retroactively, lasts for 383 days, which is a minimal leap year.

The Year

The "character" of the year, named kevi'ah (from קבע, kava; lit., "to fix"), is indicated by two or three Hebrew letters: the first, used as a numeral, gives the day of the week on which Rosh Ha-Shanah occurs; the second is the initial of the Hebrew word for defective, regular, or complete (ḥaser, ke-sidrah, or shalem); while in some calendric works a third letter, again used as a numeral, indicates the day of the week on which Passover begins. For an arithmetical reason inherent in the system, there are not 24 deḥiyyot – 4 × 3 × 2 for the four "permitted" days and the three types of both the common and the leap year – but only 14, i.e., seven for the common and seven for the leap year. For the common year, they are (זש(ג) ,זח(א) ,הש(א) ,הכ(ז) ,גכ(ה) ,בש(ה) ,בח(ג and for the leap year (זש(ה) ,זח(ג) ,הש(ג) ,הח(א) ,גכ(ז) ,בח(ה) ,בש(ז.

Any particular year's sequence of the feasts and fasts and of the lectionary, in Israel and in the Diaspora, is determined by its kevi'ah. Tables of the 14 types of years, of the data necessary for the calculation of both the kevi'ah of every year and of the molad of every month, as well as tables of corresponding dates in the Jewish and in the secular calendar, are attached to a great many old and new treatises on the Jewish calendar.

the true and the mean molad

Owing to inequalities in the rate of both the solar and the lunar motion in longitude, the mean conjunction may precede or be preceded by the true conjunction. The absolute maximum interval between them, arising from the combined effect of the maximum quotas of the solar and the lunar anomaly, is approximately 14 hours. In Tishri – never far from the time of the maximum effect of the decrease in solar velocity, the solar apogee being about July 1 – approximately 14 hours is the maximum interval from the true conjunction to the mean conjunction, whereas the maximum interval from the mean conjunction to the true conjunction will not exceed six to seven hours; in Nisan – never far from the time of the maximum effect of the increase in solar velocity, the solar perigee being about December 31 – approximately 14 hours is the maximum interval from the mean conjunction to the true conjunction and only six-seven hours from the true conjunction to the mean conjunction; with varying seasonal maxima and minima in the other months of the year.

the phasis

Leaving out of account the unpredictable factor of atmospheric conditions, the length of the interval from the true conjunction to the first sighting of the new crescent, the phasis is determined by four predictable astronomical factors: the interval from the true conjunction to the ensuing sunset(s), the season of the year, the lunar latitude, and the geographical longitude and latitude of the place of observation. In the region of Jerusalem – observations at which may well be presupposed in the calculation of the astronomical basis of the Jewish calendar – shortly before the autumnal equinox the minimum interval from the true conjunction to the phasis is approximately 20 hours, while the maximum is close to 72 hours, with the minimum of approximately 18 hours shortly before the vernal equinox and the various respective maxima and minima throughout the year. The phasis necessarily occurs a short time of varying length after sunset, before or after the appearance of the stars. Hence, the day of the phasis may be the day commencing a short while before the moment of the phasis or the day ending a short while after the moment of the phasis. Rosh Ha-Shanah may commence nearly 18 hours before the moment of the molad, i.e., with the molad at 17 hours 1079 ḥalakim on one of the four "permitted" days (excepting the deḥiyyot (4) and (3) on Monday and Tuesday, respectively), or more than 38 hours after the moment of the molad, i.e., with the molad in any common year on Tuesday at 9 hours 204 ḥalakim, and Rosh Ha-Shanah postponed to Thursday (deḥiyyah (3), ג"טר"ד בִּפְשׁוּטָה), with the consequence of variations, mutatis mutandis, in the commencement of New Moons of months other than Tishri. The period of this calendric vacillation does not correspond with the periods of astronomical vacillations in the mentioned respective intervals between the true and mean conjunctions, from the true conjunction to the moment of the phasis and between the moment of the phasis and the commencement of the day of the phasis. This notwithstanding, it results from the mentioned four vacillations – one calendric and three astronomical – that in the vast majority of cases the four deḥiyyot, including deḥiyyah (1) לא אד"ו ראש, do not delay Rosh Ha-Shanah until after the day of the phasis, but merely bring the former nearer to the latter or make the two coincide, an astronomical reason underlying all the deḥiyyot noted by Maimonides. Rosh Ha-Shanah does, of course, occasionally occur before the day of the phasis begins or, in some extremely rare cases, on the day immediately after the phasis (never later), with a rather wider range of the occurrence of the New Moon before and after the day of the phasis in other months; such oscillation is inherent in a system, like the present Jewish calendar, based on mean values.

The mentioned reckoning of the lunation at 29d. 12h. 44 min. 3⅓ sec. slightly exceeds the present astronomically correct value (29d. 12h. 44 min. 2.841 secs.). The discrepancy is constantly increasing by a very small figure, owing to the secular acceleration of the mean lunar motion, but the cumulative effect of this is so small that it will remain negligible for hundreds of millennia. Nor can it be ascertained when, if ever, the moment of the molad was identical with the moment of the mean conjunction since, because of the great many inequalities in the moon's movement in longitude, it is practically impossible to fix the mean position of the moon at any time. Moreover, it is no more than an assumption (no less difficult to prove than to disprove) that the occurrences of the molad are expressed in the terms of local Jerusalem time.


As stated, the four seasons in the Jewish year are called tekufot. More accurately, it is the beginning of each of the four seasons – according to the common view, the mean beginning – that is named tekufah (literally "circuit," from קוף related to נקף, "to go round"), the tekufah of Nisan denoting the mean sun at the vernal equinoctial point, that of Tammuz denoting it at the summer solstitial point, that of Tishri, at the autumnal equinoctial point, and that of Tevet, at the winter solstitial point. The mean length of the seasons, each exactly one quarter of the year, was reckoned by Mar Samuel (c. 165–254, head of the academy at *Nehardea in Babylon) at 91d. 7½ h. Hence, with his solar year of 365d. 6h., or 52 weeks and 1¼ days – identical in length with the Julian year – the tekufot move forward in the week, year after year, by 1¼ days. Accordingly, after 28 years the tekufah of Nisan reverts to the same hour on the same day of the week (Tuesday 6 p.m.) as at the beginning: this 28-year cycle is named the great, or solar, cycle (maḥazor gadol, or maḥazor ḥammah). This length of the solar year is important in respect of two minor rituals only: (1) the date of She'elah, the commencement in the Diaspora of the petition for rain inserted in the benediction Birkat ha-Shanim in the Amidah, on December 5 or 6 in the twentieth century; (2) the Blessing of the Sun on the day of the tekufah of Nisan at the beginning of the 28-year cycle. The frequent occurrence, in the last centuries, of Passover (Nisan 15–21) prior to the day of Mar Samuel's tekufah of Nisan – whereas the purpose of intercalation is to avoid the tekufah of Tevet extending to Nisan 16 (rh 21a) – is held by some scholars to show that in the making of the present Jewish calendar Mar *Samuel's value was deliberately departed from, and the length of the solar year was more accurately calculated at 365d. 5h. 55 min. 2527/57 sec., a calculation associated with the name of Rav Adda (perhaps Rav Adda b. Ahavah, a Babylonian amora of the third century). According to other scholars, this is but the fortuitous result of dividing by 19 the 6939d. 16h. 595p. contained in 235 lunations reckoned at 29d. 12h. 793p. each, the oldest sources knowing no other value for the length of the solar year than 365¼d., arising from Mar Samuel's tekufah. Actually clues are traceable in talmudic dicta,1 as also in Abraham *Ibn Ezra's Sefer ha-Ibbur (ed. by S.J. Halberstam, 1874, 8a) and Maimonides' Code,2 for values close to the modern estimate of the length of the tropical solar year at 365d. 5h. 48 min. 46 sec. If the average length of the solar year in the present Jewish calendar exceeds this by approximately 6⅔ min., this discrepancy was left out of account as it was assumed that its cumulative effect would remain negligible over a long period at the end of which the present system was expected to be replaced again by a system based on true values more akin to the earlier Jewish calendar in which New Moons (days of the phasis) and intercalations were proclaimed on the basis of both observation and calculation.

The notable days in the present Jewish calendar are in the main the Pentateuchal festivals, with additional days in the Diaspora (see *Festivals). Earlier additions include the fasts in Zechariah 7:5 and 8:19 observed on Tammuz 17, Av 9, Tishri 3, and Tevet 10, while the observance of the festive days enjoined in Megillat Ta'anit fell into desuetude, except Purim and Ḥanukkah on Adar 14–15 (in leap years, Adar ii) and Kislev 25–Tevet 2 (or 3) respectively. Among later additions we note the Fast of *Esther on Adar 13 (or 11; or Adar ii), New Year for Trees (see *Tu bi-Shevat) on Shevat 15, and *Israel Independence Day (Yom ha-Aḥma'ut) on Iyyar 5.


According to a tradition quoted in the name of *Hai Gaon (d. 1038), the present Jewish calendar was introduced by the patriarch *Hillelii in 670 Era of the Seleucids = 4119 Era of the Creation = 358/59 c.e. (500 c.e., claimed to derive from another version, seems to rest on a mistake). This possibly only refers to the present fixed order of the seven leap years in the 19-year cycle, whose introduction would have had to be more suitable at that time than earlier to achieve the main raison d'être of intercalation – to prevent the lunar Nisan 16 from occurring before the day of the tekufah of Nisan (rh 21a, see above) in the crucial 16th year in the 19-year cycle – on the presupposition that the tekufah of Nisan stands for the true, not the mean, vernal equinox. Apparent variations in the ordo intercalationis, i.e., בהז יגוח (2, 5, 7, 10, 13, 16, 18), אדוט בהז (1, 4, 6, 9, 12, 15, 17) and גבטב״ג alias גהח אדוט = גבגגגב"ג (3, 5, 8, 11, 14, 16, 19) by the side of the present order גוח אדזט (3, 6, 8, 11, 14, 17, 19), which are met with as late as the tenth century, are but variant styles of the selfsame order. These are in part also indicated by the epochal molad variously given as (דכתח = 4d. 20h. 408p.), בהרד = 2d. 5h. 204p., ויד = 6d. 14h. op. and גכבתתעו = 3d. 22h. 876p. which artificially go back to the beginning of the Era of the Creation and variously place its epoch in the autumn of 3762, −61, −60, −59 and −58 b.c.e. respectively (see *Chronology). While it is not unreasonable to attribute to Hillel ii the fixing of the regular order of intercalations, his full share in the present fixed calendar is doubtful.

Early Indications of Intercalation

Some elements in it clearly date from earlier times, others may well have been introduced much later. The present names of the 12 months are already attested in several post-exilic biblical books, the Assuan Papyri, the Apocrypha, and Megillat Ta'anit, replacing the pre-Exilic names Abib, Ziv, Bul, and Ethanim and the designation by numbers. Intercalation is claimed to be evident from the figures in Ezekiel 1:1, 3:15, 4:4–6 and 8:1, with similar indications in i Kings 12:32–3 and ii Chronicles 30:2–3; the old sectarian claim that the ancient Israelite calendar was purely solar, in vogue again because of the solar year in Enoch and Jubilees and a Qumran fragment, is militated against by the evident derivation from the moon of the terms חֹדֶשׁ (ḥodesh) and יֶרַח (yeraḥ) and by the connection between the moon and the festivals in Psalms 104:19. The New Moon (Num. 28:11, and parallels) was determined by the phasis in the preceding evening, hence the plausibility of an early biblical record (i Sam 20:18) of its prediction for "tomorrow." At a much later age, any month still consisted of either 29 or 30 days, the "sanctification" of the 30th as the New Moon being subject to witnesses' reports of the time and circumstances of their sighting of the new crescent scrutinized by a court competent to check them, and only accepted if tallying with each other and not contrary to astronomical prediction, with the further proviso of agreement by the court and formal declaration of "sanctification" before night set in. Proceedings were at times deliberately prolonged or speeded up, with the occasional choice of some observational post favorable for early sighting of the new crescent (Ein Tov), in order to avoid whenever possible a festival day, especially the Day of Atonement, falling immediately before or after the Sabbath.3 In keeping with this, the number of the full months3 varied between four and eight in the common, and between four and nine in the leap years, with 352–6 days in 12 lunar months, variations greatly in excess of those in the present calendar. Some of these variations were early eliminated. Already under the aegis of R. *Judah ha-Nasi (c. 200) and of his pupil Ray (d. 247), Elul and Adar (in a leap year Adar ii) contained invariably 29 days only. R. Yose b. Bun (c. 300) assumed the same fixed number of days in the months Adar-Elul as in the present calendar, with Rosh Ha-Shanah postponed from Wednesday and Friday but not yet from Sunday (tj Meg. 1:2, 70b). Also the mean length of the lunation in the canon of Rabban *Gamaliel (c. 100) at 29d. 12⅔h. 73p. tallies with 29d. 12h. 793p. in the present calendar. Attested in all the texts of Rosh Ha-Shanah 25a, and with a parallel in the Almagest of Ptolemy (c. 140), even though wrongly calculated, his ⅔h. 73p. is unlikely to be due to "late interpolation." As for 792p. arising from a dictum (Ar. 9b) of *Ravina (d. 420), it is an approximation only as evident from its context.

Regularization of Intervals of Intercalation

The intervals of intercalation were at first irregular, intercalation being in part due to the prevailing state of various agricultural products and to social conditions. Regularity will also have been hampered by the Romans suppressing what they considered stirrings of Jewish nationalism (Tosef., Sanh. 2:2–9, and parallels). Astronomy was, however, always a powerful factor, as the state of the crops is ultimately determined by the sun's position in its annual path. Owing to the omission of intercalation over a period of some length, R. Akiva (d. 135) once intercalated three successive years as an emergency measure (ibid). The gradual regularizing of the intervals of intercalation had to be in the terms of the seven-year sabbatical cycle as none of the styles of the 19-year Metonic Cycle would have been compatible with the rule not to intercalate in sabbatical and post-sabbatical years (ibid.). R. Abbahu4 (c. 300) reckoned, in fact, with a long cycle of 1176 y. = 24 × 49 y. (= 24 jubilee cycles) = 24 × 7 × 7 y. (= 168 sabbatical cycles)=14545 lunations (= 12 × 176 for the 1176 y., +433 intercalations)= c. 61360 weeks 4 d.5 = c. 23 × 2556 w. 3½ d. (= 23 jubilee cycles with 606 lunations each, i.e., 49 × 12, + 18 intercalations) + 2560 w. 4d. (= the 24th jubilee cycle with 607 lunations, i.e, 49 × 12, + 19 intercalations), a system in which, in the first great cycle of 1176 years at any rate, Rosh Ha-Shanah (or perhaps only its molad) was to fall on Wednesday and Sunday respectively in the alternate first years of the 49-year jubilee cycles.6 This cycle, devised by David and Samuel according to R. Abbahu's homily on i Chronicles 9:22, with a remarkably early record of a similar notion in Ben Sira 47:10, is unserviceable on account of its great length, and it is unlikely that there was ever any attempt to adhere to it in practice. It is the same with the oversimplified system, at the other end of the scale, propounded by an anonymous tannaitic authority, making the common year to consist invariably of 354d. and the leap year of 383d., exceeding the integral number of weeks by four and five days respectively (Ar. 9b and parallels). This appears never to have been accepted in practice, as it just ignores the problems entailed in the lunisolar calendar (see the bold statement by R. Hananeel of Kairouan (990–1053) to Sukkah 54b (לא הוי בקי ר׳ מאיר [האחרים] בסוד העבור). It is so a fortiori with the eight-year cycle in Enoch 74:13–16 and the often quoted observation by Sextus Julius Africanus (early third century) that both the Greeks and the Jews intercalate three extra months every eight years,7 as also with the calendric data in Pirkei de-Rabbi Eliezer, chapters 6–8, marred by interpolations, and in Baraita de-Shemu'el, bristling with calendric and astronomical absurdities. Neither of the writers concerned had access to the Jews' "secret of the calendar intercalation" (sodha-ibbur) jealously guarded by its experts from outsiders, both Jewish and gentile. Convincing illustration of palpable ignorance in matters of the calendar, on the part of people otherwise highly gifted, may be seen in the famous sixth-century mosaic floor of the ancient *Bet Alfa synagogue. It represents the 12 signs of the zodiac with the tekufah of Nisan at the beginning of Virgo, that of Tammuz at the beginning of Sagittarius, that of Tishri at the beginning of Pisces and that of Tevet at the beginning of Gemini (sic!).

Development of the Present Order of Intercalation

There is, on the other hand, unimpeachable evidence from the works of writers with expert knowledge of the calendar that the present ordo intercalationis גוח אדזט and epochal moladבהרד were not yet intrinsic parts of the calendar of Hillel ii, these being seen still side by side with other styles of the ordo intercalationis and the molad as late as the 11th century. Also the four deḥiyyot developed gradually. The deḥiyyah אד"ו as has been shown, grew out of the deḥiyyah ד"ו. The general acceptance of the deḥiyyahמולד זקן in the sense of 18h., instead of 18h. 642p., as advocated by *Saadiah Gaon's antagonist *Aaron b. Meir in their controversy, is not earlier than the tenth century. These are likely to have affected the remaining two deḥiyyot גטר"ד בפשוטה and בט"ו תקפ"ט אחר עבור since these are but corollaries of אד"ו and מולד זקן and the respective limits of 353–5 and 383–5 days in common and leap years. By the tenth century the Jewish calendar was exactly the same as today. A slight variation still prevails, between Israel and the Diaspora, in respect of the "secondary" days of the festivals, which lead in some years to fairly substantial differences in respect of the lectionary.


  1. TJ, Yoma 4:5, 41d; TJ, Suk. 5:8, 55d = Ta'an 4:2, 68a; see The Code of Maimonides, The Book of Seasons (1961), 581.
  2. Maim., Yad; interpretation of the figures there by E. Baneth (in Siebzehnter Bericht ueber die Lehranstalt fuer die Wissenschaft des Judenthums (1899), 31–42, and in Moses Ben Maimon, sein Leben, seine Werke und sein Einfluss, 2 (1914), 259) is correct; contra the strictures by O. Neugebauer, in The Code of Maimonides, Sanctification of the Moon (1956), 148; see also The Book of Seasons (1961), 581.
  3. RH 2:6–8 and 3:1; Shab. 15:3; Suk. 4:2–3; Ar. 2:2, with related passages in Tosefta and the Jerusalem and Babylonian Talmuds.
  4. For references see above, notes 1–2. A garbled version of this cycle is given in Kallir's piyyut for Parshat Shekalim (Baer, S., Seder, 654) where be-esrim ushenayim and u-shetei yadayim need correction and the specification of the tekufah as 911/3d. is rounded off from less than 91d. 7½ h.
  5. 1176 solar years at 365d. 5h. 48m. 48s. exceed this value by 18h. 43m. 12s. and 14545 lunations at 29d. 12h. 44m. 2.8s. by 2d. 9h. 4m. 26s. This discrepancy, if considered at all, may have been thought to be partly eliminated by 434 intercalations (instead of 433) in every alternate 12th and 13th great cycle of 1176 years, reducing the discrepancy to less than 16h. in 29,400 years. Its complete elimination is, of course, impossible; the length of the day and its parts, in the terms of mean solar time, being incommensurable with either the solar year or the lunation. Kallir's obscure ששת אלפים עושים חמשה ושתי ידים מחזורות appears to be an attempt to eliminate the discrepancy by limiting the applicability of the series to the interval from the institution of the 24 priestly courses some time in David's reign (I Chron. 24:3), between 2887 and 2927 Era of the Creation (calculable from I Kings 6:1 and the traditional talmudic dating of the Exodus in c. 2450 E.C.) to 6000 E.C.
  6. See below for the affinity with the Qumran calendar.
  7. Transmitted in the Chronography of Georgius Synkellus (8th century).

[Ephraim Jehudah Wiesenberg]

Sectarian Calendars

A calendric deviation from the approved norm (see above) by Jeroboam, ruler of the Kingdom of Israel, is implied in i Kings 12:32–33, according to many modern scholars. The talmudic interpretation of ii Chronicles 30:2, 13–15 also infers such a divergence (tj, Pes. 9:1, 36c). The *Samaritans seem to have followed the northern calendar as distinct from that of the other Jews. In Hasmonean and Herodian times the *Sadducees and *Boethusians each had their own calendar as did – subsequently in talmudic and post-talmudic periods – the Karaites and other less well-known sects.

the 364-day solar calendar

These calendars differed in a number of respects from the normative Jewish calendar, but the most radical departure appears to have been made in the solar calendar advocated in the pseudepigraphic works, Enoch and Jubilees. The "astrological" section of the (Ethiopian) Book of Enoch (chs. 72–78) describes in detail the apparent yearly movement of the sun through several points ("12 gates") of sunrise and sunset. The (basically correct) description leads to the (wrong) calculation of 364 days for the solar year – 30 days for each month and four additional days for "the signs" ("in which the sun lingers"), i.e., the solstices and equinoxes. There is also a discussion of the lunar year, with a calculation of the difference in length between it and the solar year. The tenor of these observations is that nature obeys the solar calendar, whose four quarters are the four seasons of change in climate and vegetation; that the universe moves in perfect numerical harmony; and that any other reckoning of the year is wrong. Likewise the Book of Jubilees (6:29–30) stresses that there are exactly 52 (4 × 13) weeks in the year, and condemns vehemently the sinners who use a lunar calendar, thus observing the festivals on the wrong dates.

in the dead sea sect

In the writings of the Dead Sea sect, there are several indications that the sect adopted the 364-day calendar. The Book of the Covenant of Damascus (p. 16), for instance, states that the Book of Jubilees should be followed in all matters of calendar reckoning. Again, according to the *War Scroll (column 2), in the future Temple there shall be 26 "courses" (i.e., "divisions") of priests and levites, i.e., a neat allocation of two weeks of service per solar year to each "course" (in direct contradiction to the biblical division into 24 courses, which does not attempt an exact division of the year (i Chron. 24:1–18)). A fragment of a sectarian schedule for service in the future Temple has also been found; its evidence is, however, inconclusive (though deemed important by several scholars).

the fixing of the omer

The 364-day calendar – obviously opposed to the lunisolar calendar of normative Judaism – must (like any Jewish calendar) somehow solve the problem of finding a fixed date for the Omer ceremony and for Shavuot, which follows seven weeks later. The Bible, fixing no date, commands that the Omer be offered on the "morrow of the Sabbath" (Lev. 23:11). According to the tannaim (Men. 65b) this means "on the second day of Passover" – an obviously forced interpretation, which was rejected by some sects (the Beothusians, Men. 10:3), according to tannaitic sources. It can be safely assumed that the advocates of the 364-day calendar insisted that "the morrow of the Sabbath" means "Sunday." To the problem of which Sunday was meant, a convincing solution has been suggested by A. Jaubert (in vt, 3 (1953), 250–64) as follows: The Book of Jubilees indicates that the correct date of Shavuot is the 15th of the third month. This is always a Sunday (for the obvious advantage of a 364-day calendar is that all dates fall on the same days of the week in all years). By counting back 49 days, the 26th of the first month (Nisan) is reached, i.e., the first Sunday after the week of Passover. This means that the last and first days of Passover, and the first days of Nisan and of Tishri (Rosh Ha-Shanah) are all Wednesdays, which is very logical, for the luminaries were created on Wednesday (the fourth day of the creation).

inconclusive evidence for use of calendar

As long as the sectarian calendar was known only from the Books of Enoch and Jubilees, there was no need to assume that anybody actually tried to put it into practice. The discovery of the writings of the Dead Sea sect introduces a thoroughly organized social body, with its own blatantly separatist way of life, which was quite capable of practicing what it preached. There is some force to S. Talmon's argument (in Scripta Hierosolymitana, 4 (1958), 162–99) that the sect's adoption of the 364-day calendar was the single most decisive factor of its separatism, for practical symbiosis of two groups using different calendars is impossible.

On the other hand, the assumption that the sect actually used this calendar – despite the rather convincing evidence in its favor – remains somewhat problematical. Because the true solar year has 365¼ days, whoever uses the 364-day calendar must discover within some 30 years that it is not in accord with nature. Passover, for instance, will fall in the middle of the (Palestinian) winter. Moreover, there is reason to suppose that the sect existed for more than 30 years. An intercalary device of some kind can be conjectured, although none is indicated by our sources. It is also possible that the sect actually followed its calendar for a short period, or that it persisted with it regardless of the consequences. The evidence on the actual use of the calendar remains contradictory and inconclusive.

[Jacob Licht]


E. Mahler, Handbuch der juedischen Chronologie (1916); A.A. Akavya, Ha-Lu'aḥ ve-Shimmusho ba-Kronologyah (1956); S. Poznański, in: J. Hasting, Encyclopedia of Religion and Ethics, 3 (1910), 123, incl. bibl.; U. Cassuto, in: ej, 9 (1932), incl. bibl.; Wiesenberg, in: huca, 33 (1962), 153–96; Z. Ankori, Karaites in Byzantium (1959), index; E. Kutsch, in: vt, 11 (1961), 39–47; J. Morgenstern, in: huca, 1 (1924), 13–78; 3 (1926), 77–107; 10 (1935), 1–148; 20 (1947), 1–136; 21 (1948), 365–496; idem, in: vt Supplement (1955), 34–76; A. Jaubert, ibid., 3 (1953), 250–64; 7 (1957), 35–61; S. Talmon, in: Scripta Hierosolymitana, 4 (1958), 162–99.


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CALENDAR. It was widely recognized in the early sixteenth century that the calendar was inaccurate, but the question of how it should be reformed and who had the authority to do so raised fundamental issues. It was some two hundred and fifty years before all of Europe had changed.

The Christian Church had adopted the Julian calendar from the Roman Empire at the Council of Nicaea in 325 c.e.: the first general council of the church, its authority acknowledged thereafter by East and West, Protestants and Catholics. A slight error in the original Roman calculations had by 1500 accumulated to ten days, leaving the real spring equinox on 11 March instead of 21 March. What really bothered the Roman Catholic Church (though not, apparently, the Orthodox Church) was the error this produced in the date of Easter. This was supposed to fall on the Sunday on or after the full moon after 21 March, but it now often fell a month late relative to the real equinox. Nicolaus Copernicus's De Revolutionibus Orbium Caelestium (1543; On the revolutions of the celestial orbs) had originally been commissioned as a basis upon which to reform the calendar, but the intervening Reformation and Copernicus's heretical views about the solar system overlaid the issue.

One of the last acts of the Counter-Reformation Council of Trent was to order a reform of the calendar, which it was hoped would provide a basic measure of agreement between Protestants and Catholics on at least one fundamental issue. The observations and calculations were undertaken by the Jesuit astronomer Christoph Clavius (15371612), and the results embodied in Pope Gregory XIII's bull of 1582. Ten days were to be removed from October 1582 to bring the calendar back in line with the seasons, and the system of leap years was modified to keep it on track; from then on there was to be a leap year only at the end of every fourth century, and not of every century as before. The old formula for calculating the date of Easter was modified but retained. The Gregorian reform was fundamentally religious rather than astronomical, and the Roman Catholic Church continued to reject Copernicus.

Only a handful of countries (Spain, Portugal, Poland, and parts of Italy) adopted the new Gregorian calendar on time, not least because the bull was promulgated so late. By 1585 most Roman Catholic countries had followed. Most Protestant statesincluding large parts of Switzerland, Germany, the Protestant Low Countries, Great Britain, and Scandinaviaretained the Julian calendar for another century or more, creating a patchwork of calendrical practice throughout Europe, particularly complex in the Holy Roman Empire. The key issue was not astronomical accuracy but papal authority. By accepting a papal bull, states would appear to be recognizing the authority of the pope not only to interfere in civil affairs but also to alter decisions of the early church; indeed, most Roman Catholic countries took care to adopt the new calendar by their own civil acts. In England, the mathematician and astrologer John Dee (15271608) argued that the time of Christ, rather than that of the early church, was the appropriate "radix of time" for Protestants, and proposed his own Elizabethan imperial calendar one day ahead of Rome, but his views were unwelcome to the authorities and in the end England did nothing.

In 1700, with the gap between the two calendars set to widen to eleven days, most Protestant states followed a resolution of the imperial Diet of Regensburg and adopted a modified version of the Gregorian calendar. They did so using their own calculations, following the German astronomer Johannes Kepler (15711630), and substituting an astronomical Easter for the traditional version, to the same practical effect. In Britain, where antipopery remained strong, the new calendar was not adopted until September 1752, when eleven days were omitted and a third Easter calculation adopted, also to identical effect. Sweden pursued its own course, coming fully into line in 1753. The churches of the East remained unmoved, standing fast by the decisions of early Christendom; the fast-secularizing states of eastern Europe generally went Gregorian for civil purposes around the time of World War I.


Did the calendar change create practical, as opposed to political, problems? Undoubtedly it did, especially in international communications and where Protestant and Catholic jurisdictions were interspersed, as in much of central Europe and the Low Countries. The modest disruption of the familiar relationship between the feasts of the church and the seasons was quite quickly overcome, but the actual details varied according to how the reform was implemented. In Britain in 1752, for example, the eleven days September 313 inclusive were omitted from the calendar, bringing human events eleven days forward in the natural year. Fairs however were left at the same place in the natural year, putting their calendar dates back by eleven days (although many fairs in practice moved forward). Financial payments too kept their full natural term, leaving the financial year ending on 5 April rather than the traditional 25 March. At the same time, the start of the legal year was altered from 25 March to 1 January. The arrival of the new Christmas Day eleven days early took many by surprise in a society that still reckoned by feasts and fairs as much as by dates and diaries. There was widespread resistance and resentment, although the tale that people rioted for their eleven lost days is a myth. In Bohemia and in Augsburg, though, there were several years of strife between Catholics and Protestants over the issue in the 1580s, known as the "Kalenderstreit."

In navigating between old-style and new-style calendars, it is necessary to remember that in general Roman Catholic states were ten days ahead of Protestant and Orthodox states from 1583 until 1700. Care must be taken in the 1580s, and with Britain, Sweden, the Netherlands, and Switzerland. Catholic minorities in Protestant states may have adopted either calendar for religious purposes. For clarity, historians often note "O.S." or "N.S." after Julian and Gregorian dates respectively.

The issue of the calendar is a reminder that the reference points for the calculation of time express the most basic assumptions of society. The disputes it engendered were symptomatic of religious and political divisions in a world where nothing could be taken for granted.

See also Copernicus, Nicolaus ; Dee, John ; Kepler, Johannes ; Time, Measurement of ; Trent, Council of .


Cheney, C. R. A Handbook of Dates for Students of British History. Rev. ed. London, 2000.

Coyne, G. V., M. A. Hoskin, and O. Pedersen, eds. Gregorian Reform of the Calendar: Proceedings of the Vatican Conference to Commemorate its Four Hundredth Anniversary, 15821982. Vatican City, 1983.

Poole, Robert. Time's Alteration: Calendar Reform in Early Modern England. London, 1998.

Richards, E. G. Mapping Time: The Calendar and Its History. Oxford and New York, 1998.

Whitrow, G. J. Time in History: The Evolution of Our General Awareness of Time and Temporal Perspective. Oxford, 1988.

Robert Poole


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The Jewish calendar is fixed according to the number of years since the creation of the world (traditionally 3761 BCE. Thus the year 5000 began on 1 Sept. 1239 CE. When using the secular calendar, Jews use the terms BCE (before common era) and CE (common era) rather than BC and AD. The year follows a 354 day year of twelve lunar months. To harmonize this with the solar year of 365 1/4 days, an extra month, Adar II, is added into seven of every nineteen years. The months received Babylonian names during the Exile: Tishri (Sept./Oct.), Heshvan (Oct./Nov.), Kislev (Nov./Dec.), Tevet (Dec./Jan.), Shevat (Jan./Feb.), Adar (Feb./Mar.), Adar II (see above), Nisan (Mar./Apr.), Iyyar (Apr./May), Sivan (May/June), Tammuz (June/July), Av (July/Aug.), Elul (Aug./Sept.). The year begins with 1 Tishri, Rosh ha-Shanah.

A day begins and ends at sunset. Rosh ha-Shanah (the new year) is kept on 1 Tishri. It is followed by the days of repentance and Yom Kippur on 10 Tishri. The season of Sukkot (tabernacles) begins on 15 Tishri and concludes with Shemini Azeret (the Closing Festival) and Simḥat Torah (the rejoicing in the law) on 22/23 Tishri. Ḥanukkah (Lights) begins on 25 Kislev and ends on 2 Tevet. 10 Tevet is a fast day and 15 Shevat is the new year for trees. Purim (Lots, the Feast of Esther) is celebrated on 14 Adar. It is preceded by the Fast of Esther (13 Adar) and succeeded by Shushan Purim (15 Adar). Pesaḥ (Passover) begins on 15 Nisan and ends on 21/22 Nisan. 27 Nisan is Yom ha-Shoʾah (Day of the Holocaust) and 5 Iyyar is Israel Independence Day. Lag ba-Omer (the thirty-third day of the counting of the omer) is celebrated on 18 Iyyar and Shavuot (Pentecost) takes place on 6/7 Sivan. There are fast days on 17 Tammuz and 9 Av, and 15 Av is a minor holiday.


The Julian calendar was reformed by Pope Gregory XIII in 1582 when it was realized that the Christian calendar was ten days in advance of the solar year. The reformed calendar is known as the Gregorian (or New) Style, the unreformed as the Julian (or Old) Style. The difference between the two calendars is now thirteen days, so that some Orthodox observe Christmas, 25 Dec. (Old Style), on 7 Jan. The Christian calendar follows each year the preparation for the coming of Christ, his life, death, and resurrection, and the being of God (see FESTIVALS AND FASTS). Thus, it begins with Advent, which has four Sundays, and then either one or two Sundays after Christmas bridge the gap to the Epiphany (6 Jan.). Thereafter ‘Sundays after Epiphany’ are reckoned until what used to be known as Septuagisma, Sexagesima, and Quinquagesima (Sundays before Lent); Ash Wednesday introduces the forty days of Lent, with its six Sundays; and five Sundays after Easter lead up to Ascension day with its following Sunday and Pentecost (Whitsunday). The remaining Sundays until Advent are numbered ‘after Trinity’ or ‘after Pentecost’. The Sundays of the Orthodox year fall into three segments: triodion (the ten weeks before Easter), pentecostarion (the paschal season), and octoechos (the rest of the year). See also FESTIVALS AND FASTS.

The system of dating years AD (Lat., Anno Domini, ‘in the year of the Lord’) goes back to Dionysius Exiguus (‘the Small’; c.500–50). The abbreviations CE (Common Era) and BCE to replace AD and BC began with Jewish historians in the 19th cent., in order to avoid a religious confession within the words abbreviated.


The Muslim calendar is lunar, with twelve months of twenty-nine or thirty days. Because this is not adjusted to the solar calendar (contrast the Jewish system), the religious festivals and holidays advance around the seasons: thus the month of fasting, Ramaḍān, moves around the entire solar year, occurring sometimes in summer and sometimes in winter (intercalation is forbidden in the Qurān 9. 37). The months are: Muḥarram; Ṣafr, Rabīʿ al-Awwal, Rabī al-Thāni, Jumādā al-Ūlā, Jumādā al-Thāniyya, Rajab, Shaʿbān, Ramadhān, Shawwal, Dhū al-Qadah, Dhū al-Ḥijjah. The years are numbered from the Hijra, the move of the Prophet Muḥammad from Mecca to Madīna in 622 CE. 1 Muḥarram of that year was 16 July 622, which begins the first year of the Muslim era. The years are referred to as AH, i.e. ‘after the Hijra’.


The Hindu religious calendar is lunar, with the months divided into a bright (śulapakṣa) and a dark (kṛṣṇapakṣa) half, with fifteen tithis (days) in each. The correlation of human activity with the whole cosmic process (made evident in the movement of heavenly bodies) is of paramount importance. The religious calendar is then a proliferation of special observances, for some of which see FESTIVALS AND FASTS. There are six seasons (ṛtu): (i) Vasanta (spring); (ii) Grīṣma (hot season); (iii) Varṣa (rainy season); (iv) Śarad (autumn); (v) Hemanta (winter); (vi) Śiśira (cold). To each of these is allocated two months (Caitra, Vaiśākha; Jyaiṣtha, Aṣāḍha; Śrāvana, Bhādarapada; Aśvinā, Āśvayuja; Mārgaśīrṣa, Pauṣa; Māgha, Phālguna. Every two or three years a thirteenth month was added to adjust the lunar year to the solar year.


The spread of Buddhism did not take with it a calendar which it then imposed on other countries; rather, it adapted to local calendars, and worked its own festivals into the local scene. Buddhist calendars thus vary from culture to culture.


The Sikhs' religious calendar is a modified form of the Bikramī calendar. The year is solar (23 minutes 44 seconds shorter than the Christian year) and the months are lunar. Lunar month dates, varying within fifteen days, are used for gurpurbs. So in 1984 Gurū Gobind Siṅgh's birthday fell on both 10 Jan. and 29 Dec. Solar months, based on the twelve zodiac signs, are also used, e.g. for saṅgrānds, Baisākhī, and Lohṛī. The anniversaries of the battle of Chamkaur, martyrdom of the younger sāhibzāde, and battle of Muktsar are solar dates. Because of the discrepancy between the Bikramī and Christian solar year these dates advance one day in sixty-seven years.


The Chinese have traditionally followed both a solar and a lunar calendar. These run concurrently and coincide every nineteen years. The solar calendar divides the year into twenty-four periods, named (mainly) according to the weather expected in that period in the N. China plain. The only festival fixed by the solar calendar is at the beginning of the fifth period, Chʾing Ming. The lunar calendar is used to record public and private events. The New Year begins with the second new moon after the winter solstice, between 21 Jan. and 20 Feb. The months have no names and are known by numbers; but they are associated with the five elements of the cosmos, wood, fire, earth, metal, and water; and also with animals; hence each year is known as ‘the year of’. Thus 2000 is the year of the dragon; 2001 the snake; 2002 the horse; 2003 the sheep; 2004 the monkey; 2005 the chicken; 2006 the dog; 2007 the pig; 2008 the rat; 2009 the ox; 2010 the tiger. The traditional starting-point for chronological reckoning is the year in which the minister of the emperor, Huang-ti, worked out the sixty-year cycle, i.e. 2637 BCE.




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A calendar is a system of reckoning and ordering time beyond the period of a day in a repetitive, usually annual, cycle. A calendar's primary function is regulating and organizing human activities; the word derives from the Latin calendarium or calendra, "account book," and kalendae or "calends," the new moon and first day of the Roman month, when Romans paid their debts. Calendars may have derived from the human penchant for imposing order; however, the most efficient exploitation of natural resources implies synchronizing productive efforts with nature's cycles. Sensitivity to such cycles is biologically programmed into humans as circadian rhythms, including the twenty-four-hour cycle of sleep and wakefulness and fluctuating body temperature; and in the female menstrual cycle, which approximates a lunar period.

Calendric periodicities are traced ultimately to the Sun and the Moon. The daily apparent rising and setting of the Sun is due to the rotation of the Earth, while the annual cycle of the seasons is related to the revolution of the Earth around the Sun, and the tilt of the Earth relevant to its plane of revolution. The most commonly reckoned calendrical period beyond day and night is the synodical lunar month (the cycle of lunar phases) of 29.5 days. Incommensurability between this period and the seasonal cycle based on the solar year of 365.24 days and the need to process fractions of days in the astronomical cycles with whole-day counts have been among the most difficult challenges for calendar specialists.

Early, Nonliterate, and Folk Calendars

Alexander Marshack sees in the scorings and tally marks on Paleolithic fossils and artifacts the beginnings of time recording. With Neolithic domestication, systematic time reckoning allowed farming practices to fit local moisture and temperature patterns. Such concerns and efforts are suggested at Stonehenge in England, where, beginning about five thousand years ago, massive stones were arranged in geometric patterns. While interpretations of the site vary, its main axis includes an alignment to the June solstice sunrise, the day of longest sunlight.

Small-scale and nonliterate societies such as the Nuer of Africa emphasize a sensitivity and responsiveness to seasonal cycles that E. E. Evans-Pritchard calls "ecological time." Such calendars are characterized by:

  1. space-time (the fusing of concepts of time with the space accessed and occupied in that time);
  2. fuzzy-bordered seasons (increasing rains gradually transform dry season to wet);
  3. "layered" observations of synchronous events at different ecological levels (for example, the bloom of plant species coincident with the movement of fish or game); and
  4. diachronic sequences, such as episodic faunal or floral changes or consecutive astronomical observations (for example, advancing stellar positions, changes in the Moon's position and shape, or the movement of the Sun on the horizon).

Calendar Codification and Civilization

Awareness of the astronomical significance behind seasonal phenomena allowed human communities to coordinate their activities seasonally for strategic and productive ends. Once a reliable system of recording such information was devised, calendar refinement and codification were possible. Calendar codification and the enhanced utilization of energy and other resources that this enabled are a significant factor in the process of civilizationa topic deserving additional study. The earliest centers of civilization in Mesopotamia, the Indus and Nile valleys, eastern China, Mesoamerica, and the Andes all have information recording systems and codified calendars, which were probably overseen by high-ranking astronomer-priests who also likely oversaw timely rituals relating human endeavors to cosmic powers.

Varieties of Calendars

The prominence of the Moon in premodern societies with limited lighting and the regularity of its phases resulted in the synodical lunar month being basic to many traditional calendars. In the Muslim calendar, twelve lunar months of twenty-nine or thirty days are reckoned in a year of 354 days, or a leap year of 355, in a thirty-year cycle. The approximately eleven-day difference between such a synodical lunar calendar and the solar year, however, results in a slippage of months through the seasons. In order to maintain synchrony between lunar months and the seasons, an intercalated month is necessary, a strategy employed in the Jewish calendar with influence from Babylonia: seven leap years intersperse with twelve common years in a nineteen-year cycle.

Ancient Egyptians used the annual heliacal rise (predawn reappearance) of Sirius to help coordinate their lunar months with the seasons and solar year. While maintaining this system for religious observance, they later developed a civil year of 365 days comprising twelve fixed months of thirty days with five additional days. The ancient Maya had a similar five-day end-of-year, but divided the other 360 days into eighteen named periods of twenty days. This yearly calendar intermeshed every fifty-two years with a divinatory cycle of 260 days. Maintaining separate calendars for civic and religious (and/or regional and ethnic) functions is a common practice, useful in the twenty-first century for the retention of local traditions amidst the spread of the Gregorian calendar.

The Gregorian Calendar and Globalization

The Gregorian calendar spread through European colonialism and later through international relations, exchange, and commerce. It developed from the first-century b.c.e. Julian calendar, named after Julius Caesar, who commissioned its development and approved the reckoning of months no longer determined by lunar observations in a year that averaged 365.25 days. The Gregorian gets its name from Pope Gregory XIII, by whose election in the year 1572 c.e. the day marking the vernal equinox had strayed ten days from its occurrence. His papal bull in 1582 set out the mechanisms by which:

  1. the spring equinox would occur on its actual date;
  2. Easterwhich depends on calculations from the vernal equinoxwould be determined; and
  3. a leap year system would be implemented, allowing for prolonged congruency between the calendar and its astronomical underpinnings.

Since the sixteenth century, countries around the world have adopted the Gregorian calendar, including its twelve fixed months, seven-day weeks, and beginning date. However, day and month names usually occur in the vernacular, and traditional reckonings may be kept for local, ethnic, and religious observances.

Through calendars, humans impose culturally significant rhythms on the perception of time. Across human cultures two primary perceptions of the character of time predominate:

  1. time as recursive or cyclic, observed in the recurrence of day and night, lunar waxing and waning, and the return of the seasons; and
  2. time as linear, an ongoing process, observed in the maturation of vegetation, decay, and the transition of a human life from birth to death.

Specially marked dates and periodicities are the human, cultural cadence in the infinitude of time. While unable to control the passage of time, humans with calendars have increasingly ordered their relationship to and utilization of it.

See also Astronomy, Pre-Columbian and Latin American ; Time .


Aveni, Anthony. Empires of Time: Calendars, Clocks, and Cultures. Boulder: University Press of Colorado, 2002.

Evans-Pritchard, E. E. The Nuer: A Description of the Modes of Livelihood and Political Institutions of a Nilotic People. Oxford: Oxford University Press, 1940. Reprint, 1969.

Fabian, Stephen Michael. Space-Time of the Bororo of Brazil. Gainesville: University Press of Florida, 1992.

Marshack, Alexander. The Roots of Civilization: The Cognitive Beginnings of Man's First Art, Symbol and Notation. London: Weidenfeld and Nicolson, 1972.

Richards, Edward G. Mapping Time: The Calendar and Its History. Oxford: Oxford University Press, 1998.

Westrheim, Margo. Calendars of the World: A Look at Calendars and the Ways We Celebrate. Oxford: Oneworld Publications, 1994.

Stephen M. Fabian


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A calendar is a system of measuring the passage of time for the purpose of recording historic events and arranging future plans. Units of time are defined by three different types of motion: a day is one rotation of Earth around its axis; a month is one revolution of the Moon around Earth; and a year is one revolution of Earth around the Sun. The year is the most important time unit in most calendars, since the cycle of seasons repeat in a yearly cycle as Earth revolves around the Sun.

Making a yearly calendar, however, is no simple task because these periods of time do not divide evenly into one another. For instance, the Moon completes its orbit around Earth (a lunar month) in 29.5 days. A lunar year (12 lunar months) equals 365 days, 8 hours, and 48 minutes. A solar year (time it takes Earth to complete its orbit around the Sun) is 365.242199 days, or 365 days, 5 hours, 48 minutes, and 46 seconds. The calendar we currently use is adjusted to account for the extra fraction of a day in each year.

Development of the present-day calendar

The official calendar currently used worldwide is the Gregorian calendar. The ancient Egyptians adopted a 365-day calendar sometime between 4000 and 3000 b.c. The first major improvement to that 365-day calendar was made by Roman dictator Julius Caesar (10044 b.c.) in 46 b.c. With the help of Greek astronomer Sosigenes, Caesar developed a calendar divided into 12 months of 30 and 31 days, with the exception of 29 days in February. In this new Julian calendar (named after Caesar), an extra day, or leap day, was added to every fourth year to account for the 365.25-day solar year.

The Julian calendar, however, was still off by 11 minutes and 14 seconds each year. Over 300 years, this difference added up to just over 3 days. By the mid-1500s, the Julian calendar was another 10 days ahead of Earth's natural yearly cycle.

To adjust this calendar to line up with the seasons, Pope Gregory XIII (15021585) introduced another change in 1582. He first ordered that 10 days be cut from the current year, so that October 4, 1582, was followed by October 15, 1582. He then devised a system whereby three days are dropped every four centuries. Under the original Julian calendar, every century year (200, 300, 400, etc.) was a leap year. In the new calendar, named the Gregorian calendar, only those century years divisible by 400 (800, 1200, 1600, etc.) are leap years.

Although not perfect, the Gregorian calendar is accurate to within 0.000301 days (26 seconds) per year. At this rate, it will be off one day by about the year 5000.

The Jewish and Muslim calendars

The Jewish calendar is a lunisolar calendar, a combination of lunar and solar years. The calendar is 12 lunar months long, with an additional month added every few years to keep the calendar in line with the seasons. The months (with corresponding days) are Tishri (30), Marheshvan (29 or 30), Kislev (29 or 30), Tebet (29), Sebat or Shebat (30), Adar (29), Nisan (30), Iyar (29), Sivan (30), Tammuz (29), Ab (30), and Elul (29). Adar II, the extra month, is added periodically after Adar. Calendar years vary from 353 to 355 days; leap years may have 383 to 385 days. Rosh ha-Shanah, the Jewish New Year, is observed on the first day of Tishri.

The Muslim calendar is a strict lunar calendar. Calendar years vary from 354 to 355 days, with the months and seasons having no connection. The months are Muharram (30), Safar (29), First Rabia (30), Second Rabia (29), First Jumada (30), Second Jumada (29), Rajab (30), Shaban (29), Ramadan (30), Shawwal (29), Dhu-I-Kada (30), and Dhu-I-Hijja

(29 or 30). The first day of the first year of the Muslim calendar corresponds to July 16, 622, of the Gregorian calendar.

The Gregorian calendar and the third millennium

Technically, the year 2000 on the Gregorian calendar was not the beginning of the third millennium (a 1,000-year span). In actuality, it was the last year of the second millennium. When the Gregorian calendar was adopted, the transition of the years b.c. to a.d.marking the birth of Jesus of Nazarethdid not include the year 0. The sequence runs 2 b.c., 1 b.c., a.d. 1, a.d. 2, etc. According to this sequence, since there is no year zero, the first year of the first millennium was a.d. 1. Thus, the first day of the third millennium was January 1, 2001.

Possible future calendar reform

Although the Gregorian calendar allows for the oddity of Earth's orbit and for the dates when Earth is closest and farthest from the Sun, the shortness of February introduces slight problems into daily life. For example, a person usually pays the same amount of rent for the 28 days of February as is paid for the 31 days of March. Also, the same date falls on different days of the week in different years. These and other examples have led to several suggestions for calendar reform.

Perhaps the best suggestion for a new calendar is the World Calendar, recommended by the Association for World Calendar Reform. This calendar is divided into four equal quarters that are 91 days (13 weeks) long. Each quarter begins on a Sunday on January 1, April 1, July 1, and October 1. These 4 months are each 31 days long; the remaining 8 months all have 30 days. The last day of the year, a World Holiday (W-Day), comes after December 30 (Saturday) and before January 1 (Sunday) of the new year. W-Day is the 365th day of ordinary years and the 366th day of leap years. The extra day in leap years would appear as a second World Holiday (Leap year or L-Day) between June 30 (Saturday) and July 1 (Sunday). The Gregorian calendar rules for ordinary, leap, century, and non-century years would remain unchanged for the foreseeable future.


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In Russia, the calendar has been used not only to mark the passage of time, but also to reinforce ideological and theological positions. Until January 31, 1918, Russia used the Julian calendar, while Europe used the Gregorian calendar. As a result, Russian dates lagged behind those associated with contemporary events. In the nineteenth century, Russia was twelve days behind, or later than, the West; in the twentieth century it was thirteen days behind. Because of the difference in calendars, the Revolution of October 25, 1917, was commemorated on November 7. To minimize confusion, Russian writers would indicate their dating system by adding the abbreviation "O.S." (Old Style) or "N.S." (New Style) to their letters, documents, and diary entries.

The Julian Calendar has its origins with Julius Caesar and came into use in 45 b.c.e. The Julian Calendar, however, rounded the number of days in a year (365 days, 6 hours), an arithmetic convenience that eventually accumulated a significant discrepancy with astronomical readings (365 days, 5 hours, 48 minutes, 46 seconds). To remedy this difference, Pope Gregory XIII introduced a more accurate system, the Gregorian Calendar, in 1582.

During these years Russia had used the Byzantine calendar, which numbered the years from the creation of the world, not the birth of Christ, and began each new year on September 1. (According to this system, the year 7208 began on September 1, 1699.) As part of his Westernization plan, Peter the Great studied alternative systems. Although the Gregorian Calendar was becoming predominant in Catholic Europe at the time, Peter chose to retain the Julian system of counting days and months, not wanting Orthodox Russia to be tainted by the "Catholic" Gregorian system. But he introduced the numbering of years from the birth of Christ. Russia's new calendar started on January 1, 1700, not September 1. Opponents protested that Peter had changed "God's Time" by beginning another new century, for Russians had celebrated the year 7000 eight years earlier.

Russians also used calendars to select names for their children. The Russian Orthodox Church assigned each saint its own specific feast day, and calendars were routinely printed with that information, along with other appropriate names. During the imperial era, parents would often choose their child's name based on the saints designated for the birth date.

Russia continued to use the Julian calendar until 1918, when the Bolshevik government made the switch to the Gregorian system. The Russian Orthodox Church, however, continued to use the Julian system, making Russian Christmas fall on January 7. The Bolsheviks eliminated some confusion by making New Year's Day, January 1, a major secular holiday, complete with Christmas-like traditions such as decorated evergreen trees and a kindly Grandfather Frost who gives presents to children. Christmas was again celebrated in the post-communist era, in both December and January, but New Year's remained a popular holiday.

See also: old style


Hughes, Lindsey. (1998). Russia in the Age of Peter the Great. New Haven, CT: Yale University Press.

Ann E. Robertson

Chinese calendar

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Chinese calendar


Years (19012008)

Although officially banned in 1930 the ancient Chinese calendar is still widely used in China, and the New Year (the second new moon after the beginning of winter) is a national holiday. It also remains in use in Tibet, Malaysia and other parts of Southeast Asia. Based on the lunar year, it comprises 12 months of 29 or 30 days, each starting with a new moon. A month is repeated seven times during each 19-year cycle.

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65. Calendar

See also 11. ALMANACS ; 396. TIME

a flgure-of-eight-shaped scale, for showing the declination of the sun and the equation of time for every day of the year. analemmatic, adj.
the twenty-ninth day of February, added to the calendar every four years, except in centenary years evenly divisible by 400, to compensate for the discrepancy between the arbitrary 365-day calendar year and the actual time of the solar year. bissextile, adj.
Rare. a person who makes calendars.
1. an intercalation of a day or days in the calendar to correct error.
2. the day or days intercalated. embolic, embolismic, embolismical, adj.
the study of the origin, growth, meaning, and history of Christian religious feasts. heortological, adj.
in the Roman Empire, the cyclical, fifteen-year fiscal period, used for dating ordinary events. Also called cycle of indiction. indictional. adj.
inserted into the calendar, as the twenty-ninth day of February in a leap year. intercalation, n. intercalative, adj.
the period of the moons synodic revolution, from the time of the new moon to the next new moon; one lunar month or approximately 29 1/2 days.
lustrum, luster, lustre
a period of five years.
1. a list or calendar of months.
2. Eastern Orthodoxy. a calendar of all festivals for martyrs and saints, with brief accounts of their lives. Also Menologion.
2. a church calendar, listing festivals for saints.
the practice of eliminating the bissextile day every 134 years to adjust the date of the new moon. Cf. proemptosis.
1. the time of the new moon or the beginning of the month.
2. a heathen festival at the time of the new moon.
the adding of a day every 300 and again every 2400 years to adjust the date of the new moon. Cf. metemptosis.


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calendar Way of reckoning time for regulating religious, commercial and civil life, and for dating events in the past and future. Ancient Egyptians had a system based on the movement of the star Sirius and on the seasons. Calendars are based on natural and astronomical regularities: tides and seasons, movements of the Sun and Earth, and phases of the Moon. The basic units are day, month and year. The main difficulty in compiling a calendar is that the month is not an exact number of days and the year not an exact number of months. For convenience, months and days are assigned a whole number of days, and extra days (intercalations) are added at intervals to compensate. In the modern Gregorian, or New Style, calendar, an extra day (February 29) is added every four years (leap year). The Gregorian calendar was based on the Julian, or Old Style, solar calendar. This was introduced by Julius Caesar in the 1st century bc and was developed from an earlier Moon-based calendar. The Jewish calendar is semilunar, made up of 12 common years and 7 leap years. The leap years have an additional month (Adar II). The Muslim calendar is wholly lunar, the year always consisting of 12 months without intercalations. The months have alternately 30 and 29 days, except for the twelfth month (Dulhajj) which has one intercalary day in 11 years out of a cycle of 30 calendar years.


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cal·en·dar / ˈkaləndər/ (abbr.: cal or cal.) • n. a chart or series of pages showing the days, weeks, and months of a particular year, or giving particular seasonal information. ∎  a datebook. ∎  a system by which the beginning, length, and subdivisions of the year are fixed. ∎  a timetable of special days or events of a specified kind or involving a specified group: the college calendar. ∎  a list of people or events connected with particular dates, esp. canonized saints and cases for trial.• v. [tr.] enter (something) in a calendar or timetable.DERIVATIVES: ca·len·dric / kəˈlendrik/·len·dri·cal / kəˈlendrikəl/ adj.