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Hebrew calendar


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The *Hebrew calendar* (Hebrew : הלוח העברי‎ /ha'luach ha'ivri/)
or *Jewish calendar* is a lunisolar calendar used by Jews , and in recent
decades, by a growing number of Christians . Today, the calendar is
predominantly used for religious observances, but is also employed by
Jewish farmers in Israel as an agricultural framework.

The calendar is used to reckon the Jewish New Year and dates for Jewish
holidays , and also to determine appropriate public reading of Torah
portions , /Yahrzeits / (dates to commemorate the death of a relative),
and daily Psalm reading, among many ceremonial uses. Originally the Hebrew
calendar was used by Jews for all daily purposes. Following the conquest
of Jerusalem by Pompey in 63 BCE (see also Iudaea province ), Jews began
additionally following the imperial civil calendar (which was decreed in
45 BCE) for civic matters such as the payment of taxes and dealings with
government officials.

The principles of the Hebrew calendar are found in the Torah , which
contains several calendar-related commandments , including God's
commandment during the Exodus from Egypt to fix the month of Aviv as the
first month of the year.^[1] The Babylonian exile in the 6th century BCE
influenced the calendar, including the adoption of Babylonian names for
the months.^[2]

During Temple times and through the Tannaitic period, the Hebrew calendar
was observational, with the beginning of each month determined by the high
court based on the testimony of witnesses who had observed a new crescent
moon . Periodically, the court ordered an extra month added to keep
Passover in the spring, again based on observation of natural events.
Through the Amoraic period and into the Geonic period, the purely
empirical calendar was displaced by calendrical rules, which finally
became systematically arranged into a computed calendar. The principles
and rules of the current calendar are fully described by Maimonides in the
/Mishneh Torah /.

Because of the roughly eleven-day difference between twelve lunar months
and one solar year , the year lengths of the Hebrew calendar vary in a
repeating 19-year Metonic cycle of 235 lunar months, with an intercalary
lunar month added according to defined rules every two or three years, for
a total of 7 times per 19 years. Seasonal references in the Hebrew
calendar reflect its development in the region east of the Mediterranean
Sea and the times and climate of the Northern Hemisphere . The Hebrew
calendar's year is longer by about 6 minutes and 25+^25 /_57 seconds than
the present-day mean solar year, so that every 224 years, the Hebrew
calendar will fall a full day behind the modern fixed solar year, and
about every 231 years it will fall a full day behind the Gregorian
calendar year.

Years in the Hebrew calendar are labeled with the era designation Anno
Mundi (Latin for "in the year of the world"), abbreviated /AM/ and /A.M./,
and are numbered from the epoch that, by Rabbinical reckoning, is a year
before the date of Creation . Early 2009 corresponds to Hebrew year 5769 ;
the Hebrew year 5770 began at sundown on the evening of 18 September 2009.


Contents

[hide ]

* 1 Structure * 2 Sources and history o 2.1 Day o 2.2 Weeks o 2.3
Importance of lunar months o 2.4 Months o 2.5 Leap months o 2.6 New year o
2.7 Epoch o 2.8 Karaite calendar * 3 Change to a calculated calendar o 3.1
Observational principles + 3.1.1 Persian period: evidence of the papyri

+ 3.1.2 Later postexilic period: evidence of the Mishnah

+ 3.1.3 Evaluation of the Mishnaic evidence

o 3.2 Epoch year o 3.3 Modern calendar o 3.4 Practice * 4 Principles o 4.1
Measurement of month o 4.2 Pattern of calendar years o 4.3 Determining
leap years o 4.4 Special holiday rules o 4.5 Measurement of hours * 5
Accuracy o 5.1 Seasonal drift o 5.2 Molad intervals o 5.3 Implications for
Jewish ritual

o 5.4 "Rectifying" the Hebrew calendar

o 5.5 Irregularities and "Missing Years"

* 6 Usage in contemporary Israel * 7 Notes * 8 References * 9 See also *
10 External links o 10.1 Date converters


[edit ] Structure

The Jewish calendar is a lunisolar calendar , or "fixed lunar year," based
on twelve lunar months of twenty-nine or thirty days, with an intercalary
lunar month added seven times every nineteen years (once every two to
three years) to synchronize the twelve lunar cycles with the slightly
longer solar year . Each Jewish lunar month starts with the new moon .
Although originally the new lunar crescent had to be observed and
certified by witnesses, the timing of the new moon is now determined
mathematically.

Concurrently there is a weekly cycle of seven days, mirroring the
seven-day period of the Book of Genesis in which the world is created. The
names for the days of the week, like those in the Creation story, are
simply the day number within the week, with Shabbat being the seventh day.
The Jewish day always runs from sunset to the next sunset; the formal
adjustments used to specify a standard time and time zones are not
relevant to the Jewish calendar.

The twelve regular months are: Nisan (30 days), Iyar (29 days), Sivan (30
days), Tammuz (29 days), Av (30 days), Elul (29 days), Tishrei (30 days),
Cheshvan (29 or 30 days), Kislev (29 or 30 days), Tevet (29 days), Shevat
(30 days), and Adar (29 days). In the leap years an additional month, Adar
I (30 days) is added after Shevat, and the regular Adar is referred to as
"Adar II".

The first month of the festival year is Nisan. 15 Nisan is the start of
the festival of Pesach , corresponding to the full moon of Nisan. Pesach
is a spring festival associated with the barley harvest,^[3] so the
leap-month mentioned above is intercalated periodically to keep this
festival in the northern hemisphere's spring season. Since the adoption of
a fixed calendar, intercalations in the Hebrew calendar have been at fixed
points in a 19-year cycle. Prior to this, the intercalation was determined
empirically:

The year may be intercalated on three grounds: 'aviv [i.e.the ripeness of
barley], fruits of trees, and the equinox. On two of these grounds it
should be intercalated, but not on one of them alone.^[4]

The Bible designates Nisan, which it calls /Aviv/ (Exodus 13:4 ), as the
first month of the year (Exodus 12:2 ). At the same time, the season of
the fall Festival of Booths (/Sukkoth/), is called "the end of the year"
(Exodus 23:16 ). The Sabbatical year in which the land was to lie fallow,
necessarily began at the time the winter barley and winter wheat would
have been sown, in the fall. The Gezer calendar , an Israelite or
Canaanite inscription ca. 900 BCE, also begins in the fall.

Modern practice follows the scheme described in the Mishnah: Rosh Hashanah
, which means "the head of the year", and is celebrated in the month of
Tishrei , is "the new year for years." This is when the numbered year
changes, and most Jews today view Tishrei as the /de facto/ beginning of
the year. The 15th of Shevat, the New Year of the Trees, has become a
popular minor holiday in recent decades.


[edit ] Sources and history

The Torah contains several commandments related to the keeping of the
calendar and the lunar cycle.


[edit ] Day

/For smaller units of time, see Measurement of hours below./

The Jewish day is of no fixed length. The Jewish day is modeled on the
reference to "...there was evening and there was morning..."^[5] in the
Creation story. Accordingly, it runs from sunset (start of "the evening")
to the next sunset. However, some apply special rules at very high
latitudes when the sun remains above or below the horizon for longer than
a civil day.^[6]

There is no clock in the Jewish scheme, so that a civil clock is used.
Though the civil clock incorporates local adoptions of various conventions
such as time zones , standard times and daylight saving , these have no
place in the Jewish scheme. The civil clock is used only as a reference
point - in expressions such as: "Shabbat starts at ...". The steady
progression of sunset around the world and seasonal changes results in
gradual civil time changes from one day to the next based on observable
astronomical phenomena (the sunset) and not on man-made laws and
conventions.

Instead of the international date line convention, there are varying
opinions as to where the day changes. One opinion uses the antimeridian of
Jerusalem . (Jerusalem is 35°13’ east of the prime meridian , so the
antimeridian is at 144°47' W, passing through eastern Alaska .) Other
opinions exist as well.^[/citation needed /]


[edit ] Weeks



A bronze Shabbat candlestick holder made in Israel in the 1940s.

The Hebrew calendar follows a seven-day weekly cycle, which runs
concurrently but independently of the monthly and annual cycles. The names
for the days of the week are simply the day number within the week. In
Hebrew, these names may be abbreviated using the numerical value of the
Hebrew letters, for example יום א׳ (/Day 1/, or Yom Rishon (Hebrew :
יום ראשון‎):

Yom Rishon (יום ראשון), abbreviated יום א׳ = "first day" =
Sunday Yom Sheni (יום שני), abbr. יום ב׳ = "second day" =
Monday Yom Shlishi (יום שלישי), abbr. יום ג׳ = "third day" =
Tuesday Yom Reviʻi (יום רבעי), abbr. יום ד׳ = "fourth day" =
Wednesday Yom Chamishi (יום חמישי), abbr. יום ה׳ = "fifth
day" = Thursday Yom Shishi (יום ששי), abbr. יום ו׳ = "sixth
day" = Friday Yom Shabbat (יום שבת or more usually שבת -
Shabbat), abbr. יום ש׳ = "Sabbath day (Rest day)" = Saturday

The names of the days of the week are modeled on the seven days mentioned
in the Creation story. For example, Genesis 1:5 "... And there was evening
and there was morning, one day". "One day" also translates to "first day"
or "day one". Similarly, see Genesis 1:8 , 1:13 , 1:19 , 1:23 , 1:31 and
2.2 .

The Jewish Shabbat has a special place in the Jewish weekly cycle. There
are many special rules which relate to the Shabbat, discussed more fully
in the Talmudic tractate "Shabbat ".

In Hebrew, the word "Shabbat" (שַׁבָּת) can also mean "(Talmudic)
week",^[7] so that in ritual liturgy a phrase like "Yom Reviʻi
bəShabbat" means "the fourth day in the week".^[8]


[edit ] Importance of lunar months

Num 10:10 stresses the importance of the new moon and consequently lunar
months, "... in your new moons, ye shall blow with the trumpets over your
burnt-offerings,"^[9] . Similarly in Num 28:11 .

In his work /Mishneh Torah /, of 1178, Maimonides included a chapter
"Sanctification of the New Moon," in which he discusses the calendrical
rules and their scriptural basis. He notes,

"By how much does the solar year exceed the lunar year? By approximately
11 days. Therefore, whenever this excess accumulates to about 30 days, or
a little more or less, one month is added and the particular year is made
to consist of 13 months, and this is the so-called embolismic
(intercalated) year. For the year could not consist of twelve months plus
so-and-so many days, since it is said: throughout the months of the year
(Num 28:14 ), which implies that we should count the year by months and
not by days."^[10]


[edit ] Months



Mosaic pavement of a zodiac in the 6th century synagogue at Beit Alpha,
Israel.

Biblical references to the pre-Jewish calendar include ten months
identified by number rather than by name. In parts of the Torah portion
/Noach / (Noah) (specifically, Gen 7:11 , Gen 8:4-5 , Gen 8:13-14 ) it is
implied that the months are thirty days long.^[11] There is no indication
as to the total number of months in the annual cycle.

In the parts of the Tanakh (the Hebrew Bible ) prior to the Babylonian
exile, only four months are named: /Aviv / (Exodus 13:4 , 23:15 , 34:18 ,
Deut. 16:1 ) (first; literally "spring", which originally probably meant
"the ripening of barley"); /Ziv / (1 Kings 6:1 , 6:37 ) (second; literally
"light"); /Ethanim / (1 Kings 8:2 ) (seventh; literally "strong" in
plural, perhaps referring to strong rains); and /Bul / (1 Kings 6:38 )
(eighth). All of these are Canaanite names, and at least two are
Phoenician (Northern Canaanite).^[/citation needed /]

According to the Book of Exodus , the first commandment the Jewish people
received as a nation was to determine the new moon : Exodus 12:2 states,
"This month [Nisan] is for you the first of months." Deut 16:1 refers to a
specific month: "Observe the month of Aviv (HE: spring), and keep the
passover unto the LORD thy God; for in the month of Aviv the LORD thy God
brought thee forth out of Egypt by night."

During the Babylonian exile , which started in 586 BCE, Jews adopted
Babylonian names for the months, which are still in use. The Babylonian
calendar also used a lunisolar calendar, derived from the Sumerian
calendar , which was not dissimilar in structure from the Hebrew one.

Hebrew names and romanized transliteration may somewhat differ, as they do
for חשוון / /Mar/heshvan or כסלו / Kislev: the Hebrew words shown
here are those commonly indicated /e.g./ in newspapers. The Syrian
calendar

used in the Levant countries shares many of the same names for months as
the Hebrew calendar, such as Nisan, Iyyar, Tammuz, Ab, Elul, Tishri, and
Adar.

*Hebrew names of the months with their Babylonian analogs* Number
Hebrew 	Tiberian  	Academy
	Common/
Other 	Length 	Babylonian analog 	Holidays/
Notable days 	Notes

1 נִיסָן Nīsān Nisan Nissan 30 days /Nisanu/ Passover
	Called /Abib/ (Exodus 13:4 , 23:15 , 34:18 , Deut. 16:1 ) and
Nisan (Esther 3:7 ) in the Tanakh . 2 אִיָּר / אייר ʼIyyār
Iyyar Iyar 29 days /Ayaru/ Pesach Sheni Lag B'Omer Called /Ziv/ in 1 Kings
6:1 , 6:37 . 3 סִיוָן / סיוון Sīwān Siwan Sivan 30 days
/Simanu/ Shavuot 4 תַּמּוּז Tammūz Tammuz Tamuz 29 days /Du'uzu/
Seventeenth of Tammuz 5 אָב ʼĀḇ Av Ab 30 days /Abu/ Tisha B'Av

Tu B'Av 6 אֱלוּל ʼĔlūl Elul Elul 29 days /Ululu/ 7
תִּשׁרִי Tišrī Tishri Tishrei 30 days /Tashritu/ Rosh Hashanah
Yom Kippur Sukkot Shmini Atzeret Simchat Torah Called /Ethanim/ in 1 Kings
8:2 . First month of civil year. 8 מַרְחֶשְׁוָן /
מרחשוון Marḥešwān Marẖeshwan Marcheshvan Cheshvan 29 or 30
days /Arakhsamna/ Called /Bul/ in 1 Kings 6:38 . 9 כִּסְלֵו /
כסלוו Kislēw Kislew Kislev Chisleu Chislev 29 or 30 days /Kislimu/
Hanukkah 10 טֵבֵת Ṭēḇēṯ Tebeth Tevet 29 days /Tebetu/ Tenth
of Tevet 11 שְׁבָט Šəḇāṭ Shevat Shvat Shebat 30 days
/Shabatu/ Tu B'Shevat 12^* אֲדָר א׳ Adar I ^* 30 days ^* Only in
leap years. 12 / 13^* אֲדָר / אֲדָר ב׳ ʼĂḏār Adar / Adar
II ^* 29 days /Adaru/ Purim

In a short (/chaser/) year, both Cheshvan and Kislev have 29 days. In a
regular (/kesidran/) year, Cheshvan has 29 days and Kislev has 30 days. In
a full (/maleh/) year, both Cheshvan and Kislev have 30 days.

The calendar rules have been designed to ensure that Rosh Hashanah does
not fall on a Sunday, Wednesday or Friday. This is to ensure that Yom
Kippur does not directly precede or follow Shabbat , which would create
practical difficulties, and that Hoshana Rabbah is not on a Shabbat, in
which case certain ceremonies would be lost for a year.


[edit ] Leap months

The solar year is about eleven days longer than twelve lunar months. The
Bible does not directly mention the addition of "embolismic" or
intercalary months . However, without the insertion of embolismic months,
Jewish festivals would gradually shift outside of the seasons required by
the Torah. This has been ruled as implying a requirement for the insertion
of embolismic months to reconcile the lunar cycles to the seasons, which
are integral to solar yearly cycles.

When the observational form of the calendar was in use, whether or not an
embolismic month was announced after the "last month" (Adar ) depended on
whether "the barley was ripe".^[/citation needed /] It may be noted that
in the Bible the name of the first month, /Aviv /, literally means
"spring" but originally it probably meant "the ripening of barley". Thus,
if Adar was over and the barley was not yet ripe, an additional month was
observed. However, according to some traditions, the announcement of the
month of /Aviv / could also be postponed depending on the condition of
roads used by families to come to Jerusalem for Passover , adequate
numbers of lambs to be sacrificed at the Temple, and on the ripeness of
the barley that was needed for the first fruits ceremony.^[/citation
needed /]

Under the codified rules, the Jewish calendar is based on the Metonic
cycle of 19 years, of which 12 are common years (12 months) and 7 leap
years (13 months). The leap years are years 3, 6, 8, 11, 14, 17, and 19 of
the Metonic cycle. Year 19 (there is no year 0) of the Metonic cycle is a
year exactly divisible by 19 (when the Jewish year number, when divided by
19, has no remainder). In the same manner, the remainder of the division
indicates the year in the Metonic cycle (years 1 to 18) the year is in.

During leap years, a month, Adar II is added before Nisan. During leap
years Adar I (or Adar Aleph — "first Adar") is actually considered to be
the extra month, and has 30 days. Adar II (or Adar Bet — "second Adar")
is the "real" Adar, and has the usual 29 days. For this reason, during a
leap year, holidays such as Purim are observed in Adar II, not Adar I.


[edit ] New year



A /shofar / made from a ram's horn is traditionally blown in observance of
Rosh Hashanah , the beginning of the Jewish civic year.

The Jewish year has four distinct starting points, according to the
Mishnah , Rosh Hashanah 1:1 :

The day most commonly referred to as the "New Year" is 1 Tishrei, when the
formal New Year festival, Rosh Hashanah ("head of the year") is observed.
(see Ezekiel 40:1 , which uses the phrase "beginning of the year".) This
is the *civil new year*, and the point at which the year number advances.
Certain agricultural practices are also marked from this date.^[12]

However, the /first month/ of the year referred to in Exodus 12:2 is Aviv
(now called Nisan ): "This month shall be to you the beginning of months".
This is referred to as the *ecclesiastical new year*, which means that the
civil new year, Rosh Hashanah, actually begins in the seventh month of the
ecclesiastical year.

Josephus , in the first century CE, states that while -

Moses...appointed Nisan...as the first month for the festivals...the
commencement of the year for everything relating to divine worship, but
for selling and buying and other ordinary affairs he preserved the ancient
order [i. e. the year beginning with Tishrei]."^[13]


In ancient Israel, the start of the ecclesiastical new year (ie. Nisan)
was determined by reference to Passover . Passover begins on the 14th day
of the month of Nisan, (Leviticus 23:4-6 ) which corresponds to the full
moon of Nisan. As Passover is a spring festival, the 14th of Nisan begins
on the night of a full moon after the vernal equinox . To ensure that
Passover did not start before spring, the tradition in ancient Israel held
that the 1st of Nisan would not start until the barley is ripe, being the
test for the onset of spring.^[14] If the barley was not ripe an
intercalary month (Adar II ) would be added.

Edwin Thiele has concluded that ancient Kingdom of Israel counted years
using the ecclesiastical new year (which was the practice of Babylon , as
well as other countries of the region), while the Kingdom of Judah counted
years using the civil new year,^[15] a practice followed to this day.

The month of Elul is the new year for counting animal tithes (ma'aser ).
/Tu Bishvat / ("the 15th of Shevat ") marks the new year for trees (and
agricultural tithes).

There may be an echo here of a controversy in the Talmud about whether the
world was created in Tishrei or Nisan; it was determined that the answer
is Tishrei, and this is now reflected in the prayers on Rosh
Hashanah.^[16]

The use of multiple starting dates for a year is comparable to different
starting dates for civil "calendar years", "tax or fiscal years ",
"academic years ", "religious cycles", etc.

The multiplicity of new years for different purposes has long been in use.
By the time of the redaction of the /Mishnah/ , Rosh Hashanah 1:1

(ca. 200 CE), jurists had identified four new-year dates:

The 1st of Nisan is the new year for kings and feasts; the 1st of Elul is
the new year for the tithe of cattle... the 1st of Tishri is the new year
for years, of the years of release and jubilee years, for the planting and
for vegetables; and the 1st of Shevat is the new year for trees-so the
school of Shammai; and the school of Hillel say: On the 15th thereof.^[17]


[edit ] Epoch



The Jewish calendar's reference point is traditionally held to be about
one year /before/ the Creation of the world.

Since about the third century CE, the Jewish calendar has used a calendar
era /anno mundi / ("in the year of the world"), abbreviated AM. The
beginning of "year 1" is /not/ Creation , but about one year before
Creation. This caused the new moon of its first month (Tishrei) to be
called /molad tohu/ (the mean new moon of chaos or nothing).

The Jewish calendar's epoch (reference date), 1 Tishrei 1 AM, is
equivalent to Monday, 7 October 3761 BCE in the proleptic Julian calendar
, the equivalent tabular date (same daylight period) and is about one year
/before/ the traditional Jewish date of Creation on 25 Elul AM 1, based
upon the /Seder Olam Rabbah / of Rabbi Yossi ben Halafta , a second
century CE sage.^[18] Thus, adding 3760 before Rosh Hashanah or 3761 after
to a Julian or Gregorian year number after 1 CE will yield the Hebrew
year. For earlier years there may be a discrepancy (see: "Missing Years"
in the Hebrew Calendar ).

The Jewish year starting on Rosh Hashanah , 1 Tishrei 5769 AM is
equivalent to 29 September 2008.

Before the adoption of the current year numbering system, other systems
were in use. For example, during the Greek period Seleucid era counting
was used: eg. 1 Maccabees 1:54 . During the Baylonian captivity Ezekiel
counted the years from the first deportation, that of Jehoiachin , who was
not the last king of Judah: eg. Ezekiel 1:1-2 .


[edit ] Karaite calendar

For several centuries, many Karaites , especially those outside Israel,
followed the calculated Rabbinical calendar used by Jews for the sake of
convenience. However, in recent years most Karaites have chosen to again
follow the observational method.

Karaites use the lunar month and the solar year, but the Karaite calendar
differs from the Rabbinical calendar in a number of ways.

For Karaites, the beginning of each month, the Rosh Chodesh , can be
calculated, but is confirmed by the observation in Israel of the first
sightings of the new moon.^[19] This may result in an occasional variation
of a maximum of one day, depending on the inability to observe the new
moon. The day is usually "picked up" in the next month.

The addition of the leap month (Adar II) is determined by observing in
Israel the ripening of barley (called aviv ),^[20] rather than using the
calculated and fixed calendar of Rabbinic Judaism . Occasionally this
results in Karaites being one month ahead of Jews using the calculated
Rabbinic calendar. The "lost" month would be "picked up" in the next cycle
when Karaites would observe a leap month while other Jews would not.

Furthermore, the seasonal drift of the Rabbinical calendar is avoided,
resulting in the years affected by the drift starting one month earlier in
the Karaite calendar.

Also, the four rules of postponement of the Rabbinical calendar are not
applied, as they are not found in the Tanakh . This affects the dates
observed for all the Jewish holidays by one day.


[edit ] Change to a calculated calendar


[edit ] Observational principles



A stone (2.43x1 m ) with Hebrew inscription "To the Trumpeting Place" is
believed to be a part of the Second Temple.


[edit ] Persian period: evidence of the papyri

Calendrical evidence for the postexilic Persian period is found in papyri
from the Jewish colony at Elephantine, in Egypt. These documents show that
the Jewish community of Elephantine used the Egyptian and Babylonian
calendars.^[21] ^[22]


[edit ] Later postexilic period: evidence of the Mishnah

In the Maccabean, Herodian, and Mishnaic periods, according to the
evidence of the /Mishnah/ and Tosefta , the Hebrew calendar operated on an
observational basis. The beginning of each lunar month was decided on the
basis of two eye witnesses testifying to the Sanhedrin to having seen the
new lunar crescent at sunset.^[23] Patriarch Gamaliel II (c. 100) would
ask the witnesses to select the appearance of the moon from a collection
of drawings that depicted the crescent in a variety of orientations, only
a few of which could be valid in any given month.^[24] These observations
were compared against calculations.^[25] When thirty days elapsed since
the last new moon, the witnesses were readily believed.^[/citation needed
/]

At first the beginning of each Jewish month was signaled to the
communities of Israel and beyond by fires lit on mountaintops, but after
the Samaritans began to light false fires, messengers were sent.^[26] The
inability of the messengers to reach communities outside Israel before
mid-month High Holy Days (Succot and Passover ) led outlying communities
to celebrate scriptural festivals for two days rather than one, observing
the second feast-day of the Jewish diaspora because of uncertainty of
whether the previous month ended after 29 or 30 days.^[27]


[edit ] Evaluation of the Mishnaic evidence

It has been noted^[28] that the procedures described in the Mishnah and
Tosefta are all plausible procedures for regulating an empirical lunar
calendar. Fire-signals, for example, or smoke-signals, are known from the
pre-exilic Lachish ostraca.^[29] Furthermore, the Mishnah contains laws
that reflect the uncertainties of an empirical calendar. Mishnah
Sanhedrin, for example, holds that when one witness holds that an event
took place on a certain day of the month, and another that the same event
took place on the following day, their testimony can be held to agree,
since the length of the preceding month was uncertain.^[30] Another
Mishnah takes it for granted that it cannot be known in advance whether a
year's lease is for twelve of thirteen months.^[31] Hence it is a
reasonable conclusion that the Mishnaic calendar was actually used in the
Mishnaic period.

The accuracy of the Mishnah's claim that the Mishnaic calendar was also
used in the late 2nd temple period is less certain. One scholar has
noted^[32] that there are no laws from Second Temple period sources that
indicate any doubts about the length of a month or of a year. This led him
to propose that the priests must have had some form of computed calendar
or calendrical rules that allowed them to know in advance whether a month
would have 30 or 29 days, and whether a year would have 12 or 13 months.


[edit ] Epoch year

One notable difference between the calendar of that era and the modern
form was the date of the epoch (the fixed reference point at the beginning
of year 1), which at that time was one year later than the epoch of the
modern calendar.

Most of the present rules of the calendar were in place by 823, according
to a treatise by the Muslim astronomer al-Khwarizmi (c. 780–850 CE).
Al-Khwarizmi's study of the Jewish calendar, /Risāla fi istikhrāj
taʾrīkh al-yahūd/ "Extraction of the Jewish Era" describes the 19-year
intercalation cycle , the rules for determining on what day of the week
the first day of the month Tishrī shall fall, the interval between the
Jewish era (creation of Adam) and the Seleucid era , and the rules for
determining the mean longitude of the sun and the moon using the Jewish
calendar.^[33] ^[34]

In 921, Aaron ben Meir proposed changes to the calendar. Though the
proposals were rejected, it indicates that all of the rules of the modern
calendar (except for the epoch) were in place before that date. In 1000,
the Muslim chronologist al-Biruni described all of the modern rules of the
Hebrew calendar, except that he specified three different epochs used by
various Jewish communities being one, two, or three years later than the
modern epoch.^[35]


[edit ] Modern calendar



The Arch of Titus depicting the objects from the Temple being carried
through Rome.

Between 70 CE and 1178 CE, the observation based calendar was gradually
replaced by a mathematically calculated one.^[36] Except for the epoch
year number, the calendar rules reached their current form by the
beginning of the 9th century, as described by al-Khwarizmi in 823.^[33]
^[34]

There is a tradition, first mentioned by Hai Gaon (d.1038 CE), that Hillel
b. R. Yehuda "in the year 670 of the Seleucid era" (i.e. 358–359 CE) was
responsible for the new calculated calendar with a fixed intercalation
cycle. Later writers, such as Nachmanides, explained Hai Gaon's words to
mean that the entire computed calendar was due to Hillel b. Yehuda.
Maimonides, in the 12th century, stated that the Mishnaic calendar was
used "until the days of Abaye and Rava", who flourished ca. 320–350 CE,
and that the change came when "the land of Israel was destroyed, and no
permanent court was left." Taken together, these two traditions suggest
that Hillel b. Yehuda (whom they identify with the mid-4th century Jewish
patriarch Ioulos, attested in a letter of the Emperor Julian^[37] , and
the Jewish patriarch Ellel, mentioned by Epiphanius^[38] ) instituted the
computed Hebrew Calendar because of persecution. H. Graetz attempted^[39]
to link the introduction of the computed calendar to a sharp repression
following a failed Jewish insurrection that occurred during the rule of
Constantius and Gallus . A later writer, S. Lieberman, argued^[40] instead
that the introduction of the fixed calendar was due to measures taken by
Roman authorities to prevent the Jewish patriarch from sending calendrical
messengers.

Both the tradition that Hillel b. Yehuda instituted the complete computed
calendar, and the theory that the computed calendar was introduced due to
repression or persecution, have been questioned.^[41] ^[42] ^[43]
Furthermore, two Jewish dates during post-Talmudic times (specifically in
506 and 776) are impossible under the rules of the modern calendar,
indicating that its arithmetic rules were developed in Babylonia during
the times of the Geonim (seventh to eighth centuries).^[44] The Babylonian
rules required the delay of the first day of Tishrei when the new moon
occurred after noon .^[/citation needed /]

The Talmuds do, however, indicate at least the beginnings of a transition
from a purely empirical to a computed calendar. According to a statement
attributed to Yose, an Amora who lived during the second half of the third
century, the feast of Purim , 14 Adar, could not fall on a Sabbath nor a
Monday, lest 10 Tishrei (Yom Kippur ) fall on a Friday or a Sunday.^[45]
This indicates that, by the time of the redaction of the Jerusalem Talmud
(ca. 400 CE), there were a fixed number of days in all months from Adar to
Elul, also implying that the extra month was already a second Adar added
before the regular Adar. In another passage, a sage is reported to have
counseled "those who make the computations" not to set the first day of
Tishrei or the Day of the Willow on the sabbath.^[46] This indicates that
there was a group which "made computations" and was in a position to
control, to some extent, the weekday on which Rosh Hashanah would fall.


[edit ] Practice

Outside of Rabbinic circles, the evidence shows a diversity of Jewish
practice. The Sardica paschal table shows that the Jewish community of
some eastern city, possibly Antioch , used a calendrical scheme that kept
Nisan 14 within the limits of the Julian month of March^[47] . Some of the
dates in the document are clearly corrupt, but they can be emended to make
the sixteen years in the table consistent with a regular intercalation
scheme. Peter, the bishop of Alexandria (early 4th century CE), mentions
that the Jews of his city "hold their Passover according to the course of
the moon in the month of Phamenoth , or according to the intercalary month
every third year in the month of Pharmuthi "^[48] , suggesting a fairly
consistent intercalation scheme that kept Nisan 14 approximately between
the Phamenoth 10 (March 6 in the 4th century CE) and Pharmuthi 10 (April
5). Jewish funerary inscriptions from Zoar, south of the Dead Sea, dated
from the 3rd to the 5th century CE, indicate that when years were
intercalated, the intercalary month was at least sometimes a repeated
month of Adar. But the inscriptions reveal no clear pattern of regular
intercalations, nor do they indicate any consistent rule for determining
the start of the lunar month.^[49]

In 1178, Maimonides included all the rules for the calculated calendar and
their scriptural basis, including the modern epochal year in his work,
/Mishneh Torah /. The rules detailed in Maimonides' code are those used
throughout the Jewish world today.


[edit ] Principles


[edit ] Measurement of month

Synodic month

A synodic month is the period between two lunar conjunctions , such as
between two new moons. Since the actual length of a synodic month varies
by several hours from month to month, the calendar is based on a long-term
average length called the *mean synodic month*. The virtual lunar
conjunctions at the start of each mean synodic month are called molads .
The mean synodic month used in the Hebrew calendar is exactly
\tfrac{765433}{25920} days, or 29 days, 12 hours, and 793 parts (44+^1
/_18 minutes) (ie 29.5306 days). This interval exactly matches the mean
synodic month determined by the Babylonians before 250 BCE^[50] and as
adopted by the Greek astronomer Hipparchus and the Alexandrian astronomer
Ptolemy . Its remarkable accuracy (less than one second from the true
value) is thought to have been achieved using records of lunar eclipses
from the eighth to fifth centuries BCE.^[51]

Traditional new moon

A "new moon " is the day on which the first /visible/ crescent of the moon
is observed. It occurs 29 or 30 days after the preceding visible crescent
and traditionally signaled the start of a Jewish lunar month.

Combining the observation method with the scientific lunar month length
works as follows. Assume one begins at a particular new month of 29 days.
As the mean lunar month is 29.5306 days long, there would be a carry
forward into the next month of 0.5306 days (ie 12 hours, 44+^1 /_18
minutes). Adding that carry forward amount to the next month will make it
equal 30.0612 days (30 days, 1 hour and 24+^2 /_18 minutes). So the second
month would be 30 days long, and 0.0612 days (or 1 hour 24+^2 /_18
minutes) would be carried forward to be added to the next cycle, and so
on. Then every 17 lunar months the carry forward amounts would exceed 24
hours (0.0612 x 17 = 1.0404), which would require an additional day to be
added to that month. In summary, the progression becomes: year 1 | 29 –
30 – 29 – 30 – *29* – *30* – 29 – 30 – 29 – 30 – 29 –
30 | year 2 | 29 – 30 – 29 – 30 – *30* – *29* – etc.


[edit ] Pattern of calendar years

The Jewish calendar is based on the Metonic cycle of 19 years, of which 12
are common years (12 months) and 7 leap years (13 months). A Metonic cycle
equates to 235 lunar months in each 19-year cycle. This gives an average
of 6939 days, 16 hours and 595 parts for each cycle.

But due to the Rosh Hashanah postponement rules (see below), a cycle of 19
Jewish years can be either 6939, 6940, 6941, or 6942 days in duration.
Since none of these values is evenly divisible by seven, the Jewish
calendar repeats exactly only following 36,288 Metonic cycles, or 689,472
Jewish years. There is a near-repetition every 247 years, except for an
excess of 50 minutes (905 parts).

There are 14 different patterns that Jewish years may take. Each of these
patterns is called a "/keviyah/" / "/קביעה/" (Hebrew for "a setting"
or "an established thing"), and is distinguished by the day of the week
for Rosh Hashanah of that particular year and by that particular year's
length.

A Jewish non-leap year can only have 353, 354, or 355 days. A leap year
can have 383, 384, or 385 days (always 30 days longer than the non-leap
length).

* A /chaserah/ year (Hebrew for "deficient" or "incomplete") is 353 or 383
days long. Both Kislev and Cheshvan have 29 days. The Hebrew letter ×—
"het", and the letter for the weekday denotes this pattern. * A /kesidrah/
year ("regular" or "in-order") is 354 or 384 days long. Kislev has 30 days
and Cheshvan has 29 days. The Hebrew letter ×› "kaf", and the letter for
the week-day denotes this pattern. * A /shlemah/ year ("abundant" or
"complete") is 355 or 385 days long. Both Kislev and Cheshvan have 30
days. The Hebrew letter ש "shin", and the letter for the week-day denotes
this pattern.


[edit ] Determining leap years

The Jewish leap years are years 3, 6, 8, 11, 14, 17, and 19 of the Metonic
cycle. To determine whether a year is a leap year, find the remainder when
dividing the Jewish year number by 19. If the remainder is 3, 6, 8, 11, 14
or 17, the year is a leap year and an extra month, Adar I, is added,
preceding Adar II (sometimes called "the real Adar"). If the remainder is
zero, the year is also a leap year since year 19 of the Metonic cycle is a
year exactly divisible by 19. Another way to check a specific year is to
find the remainder in the following calculation: ( 7 x the Jewish year
number + 1 ) / 19. If the remainder is less than 7, the year is a leap
year.

A mnemonic word in Hebrew is GUCHADZaT "גוחאדז"ט" (the Hebrew
letters gimel-vav-het aleph-dalet-zayin-tet, i.e. 3, 6, 8, 1, 4, 7, 9. See
Hebrew numerals ). A variant of this pattern of naming includes another
letter which specifies the day of the week for the first day of Pesach
(Passover) in the year.

Another memory aid notes that intervals of the major scale follow the same
pattern as do Jewish leap years, with /do/ corresponding to year 19 (or
0): a whole step in the scale corresponds to two common years between
consecutive leap years, and a half step to one common year between two
leap years. This connection with the major scale is more remarkable in the
context of 19 equal temperament .


[edit ] Special holiday rules

Adjustments are made to ensure certain holy days and festivals do or do
not fall on certain days of the week.

Yom Kippur

Adjustments are made to ensure that Yom Kippur , on which no work can be
done, does not fall on Friday (the day prior to the Sabbath ) to avoid
having Yom Kippur's restrictions still going on at the start of Sabbath,
or on Sunday (the day after Shabbat) to avoid having the Shabbat
restrictions still going on at the start of Yom Kippur.

The Rosh Hashanah postponement rules are the mechanism used to make the
adjustments. As Yom Kippur falls on Tishrei 10, and Rosh Hashanah falls on
the 1st, the adjustment is made so that Rosh Hashanah does not fall on a
Wednesday or Friday.

Rosh Hashanah postponement rules

Day of week Number of days Monday 353 355 383 385 Tuesday 354 384 Thursday
354 355 383 385 Saturday 353 355 383 385

To ensure that Yom Kippur does not directly precede or follow Shabbat ,
and that Hoshana Rabbah is not on a Shabbat, in which case certain
ceremonies would be lost for a year, the first day of Rosh Hashanah may
only occur on Mondays, Tuesdays, Thursdays, and Saturdays (the "four
gates"). Adjustments are made to ensure that Rosh Hashanah does not fall
on the other three days. To achieve that result the year may be made into
a short (chaser) year (both Kislev and Cheshvan have 29 days) or full
(maleh) year (both Kislev and Cheshvan have 30 days). (see table)

The day of the week on which Rosh Hashanah falls in any given year will
also be the day on which Sukkot and Shmini Atzeret will occur.

Short or full years

A leap year (ie. one which has 13 months) has an average length of 383½
days, so that in discrete numbers a leap year may have either 383 or 384
days.

Also, whether either Chesvan or Kislev both have 29 days, or both have 30
days, or one has 29 days and the other 30 days depends upon the number of
days needed in each year.

The period from 29 Adar (or Adar II, in leap years) to 29 Heshvan contains
all of the festivals specified in the Bible - Pesach (15 Nisan), Shavuot
(6 Sivan), Rosh Hashanah (1 Tishrei), Yom Kippur (10 Tishrei), Sukkot (15
Tishrei), and Shemini Atzeret (22 Tishrei). This period is fixed, during
which no adjustments are made.

Days of week of holidays

Main article: Days of week on Hebrew calendar

Purim Passover (first day)  Shavuot (first day)  17 Tammuz / Tisha B'Av
Rosh Hashanah / Sukkot / Shmini Atzeret / (first day)  Yom Kippur Chanukah
(first day)  10 Tevet Tu Bishvat Sun Tue Wed Tue Thu Sat Wed or Thu Wed,
Thu, or Fri Tue, Wed, or Thu Tue Thu Fri Thu Sat Mon Fri or Sat Fri or Sun
Thu or Sat Thu Sat Sun Sun* Mon Wed Sun or Mon Sun or Tue Sat or Mon Fri
Sun Mon Sun Tue Thu Mon Tue Mon
	*Postponed from Shabbat


[edit ] Measurement of hours

Every hour is divided into 1080 /halakim/ or parts. A part is 3â…“ seconds
or ^1 /_18 minute. The ultimate ancestor of the /helek/ was a small
Babylonian time period called a /barleycorn/, itself equal to ^1 /_72 of a
Babylonian /time degree/ (1° of celestial rotation).^[52] Actually, the
barleycorn or /she/ was the name applied to the smallest units of all
Babylonian measurements, whether of length, area, volume, weight, angle,
or time.

But by the twelfth century that source had been forgotten, causing
Maimonides to speculate that there were 1080 parts in an hour because that
number was evenly divisible by all numbers from 1 to 10 except 7. But the
same statement can be made regarding 360. The weekdays start with Sunday
(day 1) and proceed to Saturday (day 7). Since some calculations use
division, a remainder of 0 signifies Saturday.

While calculations of days, months and years are based on fixed hours
equal to ^1 /_24 of a day, the beginning of each /halachic/ day is based
on the local time of sunset . The end of the Shabbat and other Jewish
holidays is based on nightfall (/Tzeth haKochabim/) which occurs some
amount of time, typically 42 to 72 minutes, after sunset. According to
Maimonides, nightfall occurs when three medium-sized stars become visible
after sunset. By the seventeenth century this had become three
second-magnitude stars. The modern definition is when the center of the
sun is 7° below the geometric (airless) horizon, somewhat later than
civil twilight at 6°. The beginning of the daytime portion of each day is
determined both by dawn and sunrise . Most /halachic/ times are based on
some combination of these four times and vary from day to day throughout
the year and also vary significantly depending on location. The daytime
hours are often divided into /Sha`oth Zemaniyoth/ or "Halachic hours" by
taking the time between sunrise and sunset or between dawn and nightfall
and dividing it into 12 equal hours. The nighttime hours are similarly
divided into 12 equal portions, albeit a different amount of time than the
"hours" of the daytime. The earliest and latest times for Jewish services
, the latest time to eat Chametz on the day before Passover and many other
rules are based on /Sha`oth Zemaniyoth/. For convenience, the modern day
using /Sha`oth Zemaniyoth/ is often discussed as if sunset were at 6:00pm,
sunrise at 6:00am and each hour were equal to a fixed hour. For example,
/halachic/ noon may be after 1:00pm in some areas during daylight saving
time . Within the Mishnah , however, the numbering of the hours starts
with the "first" hour after the start of the day. ^[53]


[edit ] Accuracy


[edit ] Seasonal drift

The Hebrew calendar's mean year is 365.2468 days long (exactly 365 days 5
hours 55 minutes and 25+^25 /_57 seconds - ie. the molad/monthly interval
× 235 months per 19-year cycle ÷ 19 years per cycle). As the present-era
mean northward equinoctal year is about 365.2424 days long, the Hebrew
calendar mean year is slightly longer than this tropical year. This
results in a "drift" of the Hebrew calendar of about a day every 224
years.

Also, the mean Gregorian calendar year is 365.2425 days long (365 days 5
hours 49 minutes and 12 seconds), resulting in a drift of the Hebrew
calendar in relation to the Gregorian calendar of about a day every 231
years.

The impact of the drift is reflected in the drift of the date of Passover
from the vernal full moon:

Comparison of vernal full moon to actual dates of Passover:
2001–2020^[54] In Gregorian dates Year Astronomical vernal full moon
Passover* 2001 8 April 8 April 2002 28 March 28 March 2003 16 April 17
April 2004 5 April 6 April 2005 *25 March* *24 April* 2006 13 April 13
April 2007 2 April 3 April 2008 *21 March* *20 April* 2009 9 April 9 April
2010 30 March 30 March 2011 18 April 19 April 2012 6 April 7 April 2013 27
March 26 March 2014 15 April 15 April 2015 4 April 4 April 2016 *23 March*
*23 April* 2017 11 April 11 April 2018 31 March 31 March 2019 *21 March*
*20 April* 2020 8 April 9 April *Passover commences at sunset preceding
the date indicated.


[edit ] Molad intervals

The value 29^d 12^h 793^p for the molad interval is identical to the value
in the Babylonian System B (about 300 BCE), and in Ptolemy's /Almagest/
(2nd century CE), and is approximately equal to 29.530594 days.^[52] This
is as close to the correct value of 29.530589 days as it is possible for a
value to come that is rounded off to whole parts (^1 /_18 minute). So the
molad interval is about 0.6 seconds too long. Put another way, if the
molad is taken as the time of mean conjunction at some reference meridian,
then this reference meridian is drifting slowly eastward. If this drift of
the reference meridian is traced back to the mid-4th century CE, the
traditional date of the introduction of the fixed calendar, then it is
found to correspond to a longitude midway between the Nile River and the
end of the Euphrates River . The modern molad moments match the mean solar
times of the lunar conjunction moments near the meridian of Kandahar ,
Afghanistan , more than 30° east of Jerusalem.

In the present era actual lunar conjunction intervals can be as short as
29 days 6 hours and 30 minutes to as long as 29 days and 20 hours, a
variation range of about 13 hours and 30 minutes. Furthermore, due to the
eccentricity of Earth's orbit, series of shorter lunations alternate with
series of longer lunations. Consequently the actual lunar conjunction
moments can range from 12 hours earlier than to 16 hours later than the
molad moment, in terms of Jerusalem mean solar time.

Furthermore, the discrepancy between the molad interval and the mean
synodic month is accumulating at an accelerating rate, since the mean
synodic month is progressively shortening due to gravitational tidal
effects. Measured on a strictly uniform time scale, such as that provided
by an atomic clock , the mean synodic month is becoming gradually longer,
but since the tides slow Earth's rotation rate even more, the mean synodic
month is becoming gradually shorter in terms of mean solar time.


[edit ] Implications for Jewish ritual



This figure, in a detail of a medieval Hebrew calendar, reminded Jews of
the palm branch (Lulav ), the myrtle twigs, the willow branches, and the
citron (Etrog ) to be held in the hand and to be brought to the synagogue
during the holiday of sukkot , near the end of the autumn holiday season.

Although the molad of Tishrei is the only molad moment that is not
ritually announced, it is actually the only one that is relevant to the
Hebrew calendar, for it determines the provisional date of Rosh Hashanah,
subject to the Rosh Hashanah postponement rules. The other monthly molad
moments are announced for mystical reasons. With the moladot on average
almost 100 minutes late, this means that the molad of Tishrei lands one
day later than it ought to in (100 minutes) ÷ (1440 minutes per day) = 5
of 72 years or nearly 7% of years!

Therefore the seemingly small drift of the moladot is already significant
enough to affect the date of Rosh Hashanah, which then cascades to many
other dates in the calendar year and sometimes, due to the Rosh Hashanah
postponement rules, also interacts with the dates of the prior or next
year. The molad drift could be corrected by using a progressively shorter
molad interval that corresponds to the actual mean lunar conjunction
interval at the original molad reference meridian. Furthermore, the molad
interval determines the calendar mean year, so using a progressively
shorter molad interval would help correct the excessive length of the
Hebrew calendar mean year, as well as helping it to "hold onto" the
northward equinox for the maximum duration.

If the intention of the calendar is that Passover should fall near the
/first/ full moon after the northward equinox, or that the northward
equinox should land within one lunation before 16 days after the /molad/
of /Nisan/, then this is still the case in about 80% of years, but in
about 20% of years Passover is a month late by these criteria (as it was
in Hebrew year 5765, an 8th year of the 19-year cycle = Gregorian 2005
AD). Presently this occurs after the "premature" insertion of a leap month
in years 8, 19, and 11 of each 19-year cycle, which causes the northward
equinox to land at exceptionally early moments in such years. This problem
will get worse over time, and so beginning in Hebrew year 5817 the 3rd
year of each 19-year cycle will also be a month late. Furthermore, the
drift will accelerate in the future as perihelion approaches and then
passes the northward equinox, and if the calendar is not amended then
Passover will start to land on or after the summer solstice around Hebrew
year 16652, or about 10885 years from the present. (The exact year when
this will begin to occur depends on uncertainties in the future tidal
slowing of the Earth rotation rate, and on the accuracy of predictions of
precession and Earth axial tilt.)

The seriousness of the spring equinox drift is widely discounted on the
grounds that Passover will remain in the spring season for many millennia,
and the text of the Torah is generally not interpreted as having specified
tight calendrical limits. On the other hand, the mean southward
equinoctial year length is considerably shorter, so the Hebrew calendar
has been drifting faster with respect to the autumn equinox, and at least
part of the harvest festival of Sukkot is already more than a month after
the equinox in years 9, 1, 12 and 4 of each 19-year cycle (these are the
same year numbers as were mentioned for the spring season in the previous
paragraph, except that they get incremented at Rosh Hashanah). This
progressively increases the probability that Sukkot will be cold and wet,
making it uncomfortable or impractical to dwell in the traditional
/succah/ during Sukkot. The first winter seasonal prayer for rain is not
recited until /Shemini Atzeret/, after the end of Sukkot, yet it is
becoming increasingly likely that the rainy season in Israel will start
before the end of Sukkot.


[edit ] "Rectifying" the Hebrew calendar

Given the importance in Jewish ritual of establishing the accurate timing
of monthly and annual times, some futurist writers and researchers have
considered whether a "corrected" system of establishing the Hebrew date is
required, due to the small but accelerating changes in the actual lunar
cycle interval. Further religious questions include how such a system
might be implemented and administered throughout the diverse aspects of
the world Jewish community.

It is traditionally held that the fixed arithmetic Hebrew calendar was
established on the authority of Hillel ben Yehudah , President of the
Sanhedrin in Hebrew year 4119, and therefore only an equal authority (a
modern Sanhedrin ) can either amend it or reinstate the observational
Hebrew calendar.

A 353-year leap cycle of 4366 months, including 130 leap months, along
with use of a progressively shorter /molad/ interval, could keep an
amended fixed arithmetic Hebrew calendar from drifting for more than 7
millennia.^[55]


[edit ] Irregularities and "Missing Years"

Main article: Missing years (Hebrew calendar)


The traditional dates of events in Jewish history are often used
interchangeably with the modern secular dates according to the Gregorian
calendar . For example, the traditional Jewish date for the destruction of
the First Temple (3338 AM = 423 BCE) differs from the modern scientific
date, which is usually expressed using the Gregorian calendar (586 BCE).
Implicit in this practice is the view that if all the differences in
structure between the Hebrew and Gregorian calendars are taken into
consideration, the two dates can be derived from each other. This is not
the case. If the traditional dates of events before the Second Temple era
are assumed to be using the standard Hebrew calendar, they refer to
different objective years than those of the secular dates. The discrepancy
is some 165 years.

The conflict does not necessarily imply that either the traditional dates
or the secular dates must be objectively wrong. It is possible that the
traditional dates did not use a consistent calendar matching the year
count of the standard Hebrew calendar. It could be that one or more
substantial calendar shifts have occurred, or the years counted might in
certain periods have differed from astronomical years. Taking into account
the possibility of a changing structure of the Hebrew calendar,
theoretically, both the traditional dates and those of secular scholars
could be correct. Even so, the account of history in the traditional
sourcebook Seder Olam Rabba , and in particular its description of the
period of Persian domination, seems to be irrevocably at odds with modern
scientific understanding.

Furthermore, the modern Hebrew calendar cannot be used to calculate
Biblical dates because new moon dates may be in error by ±2 days and
months may be in error by ±2 months. The latter accounts for the
irregular intercalation (adding of extra months) that was performed in
three successive years in the early second century, according to the
Talmud .^[/citation needed /]


[edit ] Usage in contemporary Israel

Early Zionist pioneers were impressed by the fact that the calendar
preserved by Jews over many centuries in far-flung diasporas, as a matter
of religious ritual, was geared to the climate of their original country:
the Jewish New Year marks the moment of transition from the Dry Season to
the Rainy one, and major Jewish Holidays such as Sukkot, Passover or
Shavuot correspond to major points of the country's agricultural year such
as planting and harvest.

Accordingly, in the early 20th Century the Hebrew Calendar was
re-interpreted as an agricultural rather than religious calendar. The
Kibbutz movement was especially inventive in creating new rituals fitting
this interpretation.

With the creation of the State of Israel the Hebrew Calendar was made one
of its official calendars (along with the Gregorian calendar). New
holidays and commemorations not derived from previous Jewish tradition
invariably were to be defined according to their Hebrew dates — notably
the Israeli Independence Day on 5 Iyar, Jerusalem Reunification Day on 28
Iyar, and the Holocaust Commemoration Day on 27 Nisan (close to the Hebrew
date of the start of the Warsaw Ghetto Uprising ).

Nevertheless, since the 1950s the Hebrew calendar steadily declined in
importance in Israeli daily life, in favor of the worldwide Gregorian
Calendar . At present, Israelis — except for the minority of religiously
observant — conduct their private and public life according to the
Gregorian Calendar, although the Hebrew calendar is still widely
acknowledged, appearing in public venues such as banks (where it is legal
for use on checks and other documents, though only rarely do people make
use of this option) and on the mastheads of newspapers.

The Jewish New Year (Rosh Hashanah) is a two-day public holiday in Israel.
However, since the 1980s an increasing number of secularist Israelis had
taken up the habit of celebrating the Gregorian New Year (usually known as
"Sylvester Night" — "ליל סילבסטר") by holding all-night
parties on the night between 31 December and 1 January. Prominent Rabbis
have on several occasions sharply denounced this practice, but with no
noticeable effect on the secularist celebrants. ^[/citation needed/ ]

The disparity between the two calendars is especially noticeable with
regard to commemoration of the assassinated Prime Minister Yitzchak Rabin
. The official Day of Commemoration, instituted by a special Knesset law,
is marked according to the Hebrew Calendar - on 12 Heshvan. However,
left-leaning Israelis, who revere Rabin as a martyr for the cause of peace
and who are predominantly secularist, prefer to hold their own mass
memorial rallies on 4 November. In some years the two competing Rabin
Memorial Days are separated by as much as two weeks.

The wall calendars commonly used in Israel are hybrids — organised
according to Gregorian rather than Jewish months, but beginning in
September, where the Jewish New Year usually falls, and providing the
Jewish date in small characters.


[edit ] Notes

/This article incorporates text from the 1901–1906 Jewish Encyclopedia ,
a publication now in the public domain ./

1. *^ * Exodus 12:2

2. *^ * The Babylonians also employed a lunisolar calendar derived from
the Sumerian calendar . 3. *^ * Josephus, /Antiquities/ 3.248-251, Loeb
Classical Library, 1930, pp. 437-438. 4. *^ * Tosefta /Sanhedrin/ 2.2,
Herbert Danby, Trans., /Tractate Sanhedrin Mishnah and Tosefta/, Society
for Promoting Christian Knowledge, London and New York, 1919, p. 31. Also
quoted in Sacha Stern, /Calendar and Community: A History of the Jewish
Calendar Second Century BCE-Tenth Century CE,/ Oxford University Press,
2001, p. 70. 5. *^ * Gen 1:5 , Gen 1:8 , Gen 1:13 , Gen 1:19 , Gen 1:23 ,
Gen 1:31 and Gen 2.2 . 6. *^ * "In higher latitudes, where during the
summer the sun does not sink below the horizon, and during the winter does
not rise above it, the days are counted in summer from midday., i.e., from
one upper crossing of the meridian by the sun to the next crossing; in the
winter, from midnight to midnight, i.e., from one lower crossing of the
meridian by the sun to the next," Entry "Calendar" in /The Jewish
Encyclopedia/ Volume 3, Funk and Wagnalls, New York, 1916. 7. *^ * For
example, according to Morfix מילון מורפיקס, Morfix Dictionary
, which is based upon Prof. Yaakov Choeka 's Rav Milim dictionary. But the
word meaning a non-Talmudic week is שָׁבוּע /(shavuʻa)/, according
to the same "מילון מורפיקס". 8. *^ * For example, when
referring to the daily psalm recited in the morning prayer (Shacharit ).
9. *^ * Numbers 10:10 . 10. *^ * Sanctification of the New Moon.

Translated from the Hebrew by Solomon Gandz; supplemented,
introduced, and edited by Julian Obermann; with an astronomical
commentary by Otto Neugebauer. Yale Judaica Series, Volume 11, New
Haven: Yale University Press, 1956
11. *^ * Gen 7:11
says
"... on the /seventeenth day of the second month/—on that day all
the springs of the great deep burst forth..." and Gen 8:3-4
say
"...At the end of the /hundred and fifty days/ the water had gone
down, (4) and on the /seventeenth day of the seventh month/ the
ark came to rest on the mountains of Ararat..." There is an
interval of 5 months and 150 days, making each month 30 days long.
12. *^ * See Maaser Rishon , Maaser
Sheni , Maaser Ani .
13. *^ * Josephus, /Antiquities/
1.81, Loeb Classical Library, 1930.
14. *^ * The barley had to be "eared out" (ripe) in
order to have a wave-sheaf offering of the first fruits according
to the Law. Jones, Stephen (1996). /Secrets of Time/. 
15. *^ * Edwin Thiele, /The Mysterious Numbers of the
Hebrew Kings /,
(1st ed.; New York: Macmillan, 1951; 2d ed.; Grand Rapids:
Eerdmans, 1965; 3rd ed.; Grand Rapids: Zondervan/Kregel, 1983).
ISBN 082543825X , 9780825438257
16. *^ * /The Code of Maimonides (Mishneh Torah), Book
Three, Treatise Eight: Sanctification of the New Moon/. Translated
by Solomon Gandz. Yale Judaica Series Volume XI, Yale University
Press, New Haven, Conn., 1956.
17. *^ * M. /Rosh Hashanah/ 1, in Herbert Danby, trans.,
/The Mishnah/, Oxford University Press, 1933, p. 188.
18. *^ * A minority opinion places Creation on 25 Adar
AM 1, six months earlier, or six months after the modern epoch.
19. *^ * The Karaite Korner: The New Moon in the Hebrew
Bible 
20. *^ * The Karaite Korner: Aviv (Barley)

21. *^ * Sacha Stern, "The Babylonian Calendar at
Elephantine", /Zeitschrift für Papyrologie und Epigraphik/ 130 ,
159–171(2000).
22. *^ * Lester L. Grabbe, A /History of the Jews and
Judaism in the Second Temple Period, Volume 1: Yehud: A History of
the Persian Province of Judah/, T&T Clark, London, 2004, p. 186.
23. *^ * M. /Rosh Hashanah/ 1.7
24. *^ * M. /Rosh Hashanah/ 2.6-8
25. *^ * b. Rosh Hashanah 20b: "This is what Abba the
father of R. Simlai meant: 'We calculate the new moon's birth. If
it is born before midday, then certainly it will have been seen
shortly before sunset. If it was not born before midday, certainly
it will not have been seen shortly before sunset.' What is the
practical value of this remark? R. Ashi said: Confuting the
witnesses." I. Epstein, Ed., /The Babylonian Talmud Seder Mo'ed,/
Soncino Press, London, 1938, p. 85.
26. *^ * M. /Rosh Hashanah/ 2.2
27. *^ * b. /Betzah/ 4b
28. *^ * Sacha Stern, /Calendar and Community/, Oxford
University Press, 2001, pp. 162ff.
29. *^ * James B. Pritchard, ed., /The Ancient Near
East: An Anthology of Texts and Pictures/, Vol. 1, Princeton
University Press, p. 213.
30. *^ * M. /Sanhedrin/ 5.3: "If one testifies, 'on the
second of the month, and the other, 'on the third of the month:'
their evidence is valid, for one may have been aware of the
intercalation of the month and the other may not have been aware
of it. But if one says, 'on the third', and the other 'on the
fifth', their evidence is invalid."
31. *^ * M. /Baba Metzia/ 8.8.
32. *^ * Solomon Gandz, "The origin of the Two New Moon
Days", /Jewish Quarterly Review/ (New Series), v. 40, 1949-50.
Reprinted in Shlomo Sternberg, ed., /Studies in Hebrew Astronomy
and Mathematics by Solomon Gandz/, KTAV, New York, 1970, pp. 72-73.
33. ^ ^/*a*/  ^/*b*/ 
E.S. Kennedy, "Al-Khwarizmi on the Jewish calendar", /Scripta
Mathematica/ *27* (1964) 55–59.
34. ^ ^/*a*/  ^/*b*/
"al-Khwarizmi", /Dictionary of
Scientific Biography/, VII: 362, 365.
35. *^ * See /The Remaining Signs of Past Centuries
/.
36. *^ * Sacha Stern, /Calendar and Community/.
37. *^ * Julian, Letter 25, in John Duncombe, /Select
Works of the Emperor Julian and some Pieces of the Sophist
Libanius/, Vol. 2, Cadell, London, 1784, pp. 57-62.
38. *^ * Epiphanius, /Adversus Haereses/ 30.4.1, in
Frank Williams, trans., /The Panarion of Epiphanius of Salamis
Book I (Sects 1-46),/ Leiden, E. J.Brill, 1987, p. 122.
39. *^ * H. Graetz, Popular History of the Jews, (A. B.
Rhine, trans.,) Hebrew Publishing Company, New York, 1919, Vol.
II, pp. 410-411. Quoted in Sacha Stern, /Calendar and Community/,
p. 216.
40. *^ * S Lieberman, "Palestine in the 3rd and 4th
Centuries", Jewish Quarterly Review, New Series 36, pp.
329-370(1946). Quoted in Sacha Stern, /Calendar and Community,/
pp. 216-217.
41. *^ * Sacha Stern, /Calendar and Community: A History
of the Jewish Calendar Second Century BCE-Tenth Century CE/,
Oxford University Press, 2001. In particular section 5.1.1,
discussion of the "Persecution theory."
42. *^ * Samuel Poznanski , "Ben
Meir and the Origin of the Jewish Calendar", /Jewish Quarterly
Review/, Original Series, Vol. 10, pp. 152-161(1898).
43. *^ * "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." Entry
"Calendar", /Encyclopedia Judaica/, Keter, Jerusalem, 1971.
44. *^ * Samuel Poznanski ,
"Calendar (Jewish)", /Encyclopaedia of Religion and Ethics/, vol.
3 .
45. *^ * Yerushalmi /Megillah/ 70b.
46. *^ * Yerushalmi /Sukkah/ 54b.
47. *^ * Eduard Schwartz, /Christliche und jüdische
Ostertafeln,/ (Abhandlungen der königlichen Gesellschaft der
Wissenschaften zu Göttingen. Philologisch-Historische Klasse. Neue
Folge, Band viii, Berlin, 1905.
48. *^ * Peter of Alexandria, quoted in the /Chronicon
Paschale/. /Corpus Scriptorum Historiae Byzantinae, Chronicon
Paschale/ Vol. 1, Weber, Bonn, 1832, p. 7
49. *^ * Sacha Stern, Calendar and Community, pp. 87-97,
146-153.
50. *^ * Neugebauer, /Astronomical cuneiform texts/, Vol
1, pp 271-273
51. *^ * G. J. Toomer, Hipparcus' Empirical Basis for
his Lunar Mean Motions, /Centaurus/, Vol 24, 1980, pp. 97-109
52. ^ ^/*a*/  ^/*b*/
Otto Neugebauer, "The astronomy of
Maimonides and its sources", /Hebrew Union College Annual/ *23*
(1949) 322–363.
53. *^ * See, for example, Berachot

chapter 1, Mishnah 2.
54. *^ * Towards a common date of Easter
World Council of
Churches , 1997.
55. *^ * Bromberg, Irv. ""The Rectified Hebrew
Calendar."
".
http://individual.utoronto.ca/kalendis/hebrew/rect.htm. Retrieved
2007-10-31.