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The '''Hebrew calendar''' or '''Jewish calendar''' is the [[calendar]] used in [[Judaism]]. It is used to set the dates of the [[Holiday#Jewish holidays|Jewish holidays]] and the weekly public reading of the [[Torah]]. It is used to set the date for a [[Bar Mitzvah]] or [[Bat Mitzvah]], the day a young person is considered an adult in Judaism. It sets the ''[[Yahrzeit]],'' the [[anniversary]] of the death of a [[kinship|relative]]. The daily Jewish [[Service of worship#Judaism|prayer service]] changes depending on the day of the Hebrew calendar.

==Basic rules==
[[File:Beit Alpha.jpg|250px|thumb|right|[[Mosaic]] floor of a [[zodiac]] in the 6th century [[synagogue]] at Beit Alpha, [[Israel]].]]
[[File:DetailOfMedievalHebrewCalendar.jpg|thumb|This [[wikt:figure#noun|figure<sup>''n''2</sup>]], from a [[medieval]] Hebrew calendar, reminded Jews of the [[palm tree|palm branch]] ''([[lulav]]),'' the [[myrtle]] twigs, the [[willow]] branches, and the [[citron]] ''([[etrog]])'' used during the holiday of [[Sukkot]].]]The Hebrew calendar is a [[lunisolar calendar]] which depends on both the [[moon]] and the [[sun]]. [[Month]]s of the Hebrew calendar are based on the [[wikt:appearance|appearance]] of the [[Phases of the Moon|new moon]].<ref name=Rosh>{{bibleverse||Exodus|12:1-2|HE}}: "This month is the first month for you".</ref> At the same time, the holiday of [[Passover]] must be in the [[Spring (season)|spring]].<ref>{{bibleverse||Deuteronomy|16:1|HE}}. "Spring" refers to [[northern hemisphere]] spring.</ref> For this reason, [[year]]s of the Hebrew calendar are based on the sun.

One solar (sun-based) year lasts about 365 [[day]]s, but twelve lunar (moon-based) months only last about 354 days. For this reason, the Hebrew calendar adds an extra lunar month seven times in each [[wikt:cycle|cycle]] of 19 years. This rule makes the [[average]] Hebrew calendar year about the same length as a solar year, 365 days.<ref><math>354+\frac{7}{19}\times30\approx365</math>. This is an example; the exact rules are more [[wikt:complicated|complicated]].</ref>

The seven-day [[week]] is used to figure out the day for [[Shabbat]], the day of rest. The week does not depend on the solar year or lunar month. Instead, it depends on a count of seven days that is believed to go back to [[ancient history|ancient]] times. The week is also an important part of the Hebrew calendar.

==History==
According to the Book of [[Exodus]], Jews have been using a lunisolar calendar since the time they left Egypt. The first [[:wikt:commandment|commandment]] the Jewish people received as a nation was the commandment to determine the New Moon.<ref name=Rosh /> Very soon after that, the Jews received the commandment to make sure that Passover falls in the spring.<ref name=onethreefour />

In the [[Tanak|Tanakh]] (the [[Hebrew Bible]]), the months are usually numbered rather than named. (See [[#Months of the Hebrew calendar year|table below]].) Only four month names appear in the Tanakh from before the Babylonian [[Exile]] (see [[#Months of the Hebrew calendar year|table]]). The month names of the [[wikt:modern|modern]] Hebrew calendar were taken from the month names in the [[Babylonian]] calendar during the Babylonian Exile (6th century [[Common Era|BCE]]).<ref name="DeVaux">''Ancient Israel: Its Life and Institutions'' (1961) by Roland De Vaux, John McHugh, Publisher: McGraw–Hill, {{ISBN|978-0-8028-4278-7}}.</ref>

At first, a new month began when [[witness]]es came to the Sanhedrin (high rabbinical court) and [[wikt:testified|testified]] that they saw the new [[crescent]] moon in the sky.<ref>The [[Islamic calendar]], which is lunar, still uses a similar procedure today.</ref> The Sanhedrin also decided when an extra month should be added to the calendar to keep Passover in the spring. (See [[Metonic cycle]].) After the [[wikt:destruction|destruction]] of the [[Second Temple]] in [[70]] [[Common Era|CE]], it became harder for the Sanhedrin to meet and hear witnesses. For that reason, the Sanhedrin [[wikt:established|established]] a [[wikt:fixed|fixed]], rule-based form of the calendar. [[Maimonides]] fully described the modern Hebrew calendar around the year [[1178]] CE.<ref>''The Code of Maimonides ''(Mishneh Torah),'' Book Three (Book of "Times" or "Seasons"), Treatise Eight: Laws of the Sanctification of the New Moon.'' See [[#References|reference]] below.</ref>

{{anchor|AM}}In the modern Hebrew calendar, years are counted as ''Anno Mundi'' ([[Latin]] for "year of the world"). This represents the [[tradition]]al count of years since the [[Creation myth#Judeo-Christian-Islamic account|creation]] of the world as described in [[Genesis]]. This year is ''anno mundi'' {{#time:xjY}}<!--automatically updates on Rosh Hashanah; might have to refresh the cache-->.

===In Karaite Judaism===
In the small [[Karaite Judaism]] community, the calendar is very similar. However, Karaites use witnesses to set the date of the new crescent moon. They still use the ripening of barley to decide whether to add an extra month to the year. For those reasons, the Karaite calendar can be slightly different from the main Jewish calendar.<ref>[http://www.karaite-korner.org/holiday_dates.shtml Karaite Korner calendar web site]</ref>

==Days of the Hebrew calendar week==
{| class="wikitable" style="text-align:center"
! Day of the week<br />(Hebrew) !! Translation !! Day starts from<br />sundown !! style="border-left:dotted darkgray 2px" | Day continues until<br />sundown
|-
|<span style="direction:rtl;">יום ראשון</span><br />''yom rishon''||first day||[[Saturday]]||style="border-left:dotted darkgray 2px" |[[Sunday]]
|-
|<span style="direction:rtl;">יום שני</span><br />''yom sheni''||second day||Sunday||style="border-left:dotted darkgray 2px" |[[Monday]]
|-
|<span style="direction:rtl;">יום שלישי</span><br />''yom shelishi''||third day||Monday||style="border-left:dotted darkgray 2px" |[[Tuesday]]
|-
|<span style="direction:rtl;">יום רביעי</span><br />''yom revi'i''||fourth day||Tuesday||style="border-left:dotted darkgray 2px" |[[Wednesday]]
|-
|<span style="direction:rtl;">יום חמישי</span><br />''yom hamishi''||fifth day||Wednesday||style="border-left:dotted darkgray 2px" |[[Thursday]]
|-
|<span style="direction:rtl;">יום ששי</span><br />''yom shishi''||sixth day||Thursday||style="border-left:dotted darkgray 2px" |[[Friday]]
|-
|<span style="direction:rtl;">שבת</span><br />''shabbat''||[[Shabbat]]<br />(Sabbath)||Friday||style="border-left:dotted darkgray 2px" |Saturday
|}

==Months==
{| class="wikitable"
! Month in Bible !! Month name<br>in English !! Month name<br>in Hebrew !! Number<br>of days !! Time of year !! Notes
|-
| align="center"| 1 || Nisan || align="right"| {{Hebrew|נִיסָן}} || align="center" | 30 || [[March]]–[[April]] || pre-exile name ''Aviv''<ref name=onethreefour>See {{bibleref|Exodus|13:4|HE}}.</ref> ("[[Spring (season)|spring]]"<ref>Particularly, ''aviv'' means "the [season of the] [[ripening]] of [[barley]]" ({{bibleref|Exodus|9:31|HE}}).</ref>)<br>Month of [[Passover]]
|-
| align="center"| 2 || Iyar || align="right"| {{Hebrew|אִייָר}} || align="center" | 29 || April–[[May]] || pre-exile name ''Ziv''<ref>{{bibleref|1Kings|6:1|HE}}</ref> ("light")
|-
| align="center"| 3 || Sivan || align="right"| {{Hebrew|סִיוָן}} || align="center" | 30 || May–[[June]] || Month of [[Shavuot]]
|-
| align="center"| 4 || Tammuz || align="right"| {{Hebrew|תַּמּוּז}} || align="center" | 29 || June–[[July]] ||
|-
| align="center"| 5 || Ab || align="right" | {{Hebrew|אָב}} || align="center" | 30 || July–[[August]] || Month of [[Tisha B'Av]]
|-
| align="center"| 6 || Elul || align="right"| {{Hebrew|אֱלוּל}} || align="center" | 29 || August–[[September]] ||
|-
| align="center"| 7 || [[Tishrei]] || align="right"| {{Hebrew|תִּשְׁרֵי}} || align="center" | 30 || September–[[October]] || pre-exile name ''Etanim''<ref>{{bibleref|1Kings|8:2|HE}}</ref> ("strong")<br>Month of [[Rosh Hashanah]],<br>[[Yom Kippur]] and [[Sukkot]]
|-
| align="center"| 8 || Heshvan<br>(or Marheshvan) || align="right"| <div class="script-hebrew" style='font-size:125%; font-family:"SBL Hebrew", David, Narkisim, "Times New Roman", "Ezra SIL SR", FrankRuehl, "Microsoft Sans Serif", "Lucida Grande", "DejaVu Sans"; direction:"rtl";>מַרְ)חֶשְׁוָן)</div> || align="center" | 29 or 30<ref name=or>These can change because of [[technical]] calendar rules. See [[#Calculating the calendar|Calculating the calendar]] above.</ref> || October–[[November]] || pre-exile name ''Bul''<ref>{{bibleref|1Kings|6:38|HE}}</ref>
|-
| align="center"| 9 || Kislev || align="right"| {{Hebrew|כִּסְלֵו}} || align="center" | 30 or 29<ref name=or/> || November–[[December]] || Month of [[Hanukkah]]
|-
| align="center"| 10 || Tevet || align="right"| {{Hebrew|טֵבֵת}} || align="center" | 29 || December–[[January]] ||
|-
| align="center"| 11 || Shevat || align="right"| {{Hebrew|שְׁבָט}} || align="center" | 30 || January–[[February]] ||
|-
| align="center"| 12 || Adar || align="right" | {{Hebrew|אֲדָר}} || align="center" | 29 || February–March || Month of [[Purim]]<br />—<br />In a [[leap year]]:<br>&nbsp;12a: Adar I (<span class="script-hebrew" style='font-size:125%; font-family:"SBL Hebrew", David, Narkisim, "Times New Roman", "Ezra SIL SR", FrankRuehl, "Microsoft Sans Serif", "Lucida Grande", "DejaVu Sans"; direction:"rtl";>'אֲדָר א</span>), 30 days<br>&nbsp;12b: Adar II (<span class="script-hebrew" style='font-size:125%; font-family:"SBL Hebrew", David, Narkisim, "Times New Roman", "Ezra SIL SR", FrankRuehl, "Microsoft Sans Serif", "Lucida Grande", "DejaVu Sans"; direction:"rtl";>'אֲדָר ב</span>), 29 days
|}

==Details==
===The day and the week===
In the Hebrew calendar, the meaning of ''day'' is taken from the [[Tanakh|Hebrew Bible]]:<ref>[[wikisource:Bible_(Jewish_Publication_Society_1917)/Genesis|Genesis 1:5]]</ref> "And there was evening, and there was morning, one day". Because "evening" comes before "morning", a ''day'' in the Hebrew calendar starts in the evening. For many purposes, the ''day'' in the Hebrew calendar begins at [[sunset]]. But when it is important to make sure the previous day is completely over, the day begins at [[wikt:nightfall|nightfall]].<ref>{{cite web|title=The Jewish Day|url=http://www.chabad.org/library/article_cdo/aid/526873/jewish/The-Jewish-Day.htm|publisher=Chabad.org|access-date=11 May 2016}}</ref>

People who print calendars, or who write calendar programs for computers, [[wikt:ignore|ignore]] that rule. They treat the Hebrew calendar date and the [[Gregorian calendar]] date that has the same [[midnight]] as being the same day. They [[wikt:assume|assume]] that people reading a Hebrew calendar know the sundown rule. Whenever a [[Holiday#Jewish holidays|holiday]], birthday or anniversary appears on a printed calendar, it actually begins on the day before, at sundown.

In the Hebrew calendar, every seventh day is [[Shabbat]], the day of rest.<ref>Based on {{Bibleref|Genesis|2:1-3|HE}}.</ref> The ''week'' is the cycle of counting out each set of seven days ending in Shabbat. The week is not affected by any other calendar [[wikt:calculation|calculation]]. In Hebrew, the only name for the first six days of the week is a counting name: "First day", "Second day", etc. The only day of the week with a special name is the seventh day—Shabbat.<ref>See, for example, [http://www.he.chabad.org/calendar/view/month.htm Calendar in Hebrew (from he.chabad.org)] {{Webarchive|url=https://web.archive.org/web/20160519032235/http://www.he.chabad.org/calendar/view/month.htm |date=2016-05-19 }}.</ref> (See table [[#Days of the Hebrew calendar week|above]].)

===The ''molad''===
The calculation of the Hebrew calendar year and month start with the ''molad''. ''Molad'' is a Hebrew word meaning "birth". The word refers to the "birth" of the [[new moon]] each month. The modern Hebrew calendar uses a calculated ''molad:'' the ''average'' length of the cycle from new moon to new moon over many years. The length of the molad is 29 days, 12 hours, 44 minutes, {{frac|3|1|3}} seconds.<ref>{{cite web|last=Bromberg|first=Dr. Irving|title=Moon and the Molad of the Hebrew Calendar|url=http://individual.utoronto.ca/kalendis/hebrew/molad.htm|access-date=19 May 2016}}</ref>

===Regular years and leap years===
A year of 12 lunar months would be 354 days long; but a Hebrew calendar year must be a solar year—about 365 days long. Also, a Hebrew calendar year must have either 12 months or 13 months. It is not allowed to have "part" of a month, so a thirteenth month is added seven times in every cycle of nineteen years. This is an [[wikt:adaptation|adaptation<sup>n 2</sup>]] of the [[Metonic cycle]], a calendar cycle that was well known in ancient times.<ref>{{cite web|last=Jacobs|first=James Q.|title=Eclipses, Cosmic Clockwork of the Ancients|url=http://www.jqjacobs.net/astro/eclipse.html#metonic|access-date=19 May 2016}}</ref> By [[wikt:convention#Noun|convention<sup>n 3</sup>]], the Hebrew calendar adds the extra month during years 3, 6, 8, 11, 14, 17 and 19 of the cycle.

===Calculating Rosh Hashanah for this year and next year===
Hebrew calendar months are supposed to be lunar months. For that reason, the calculation of [[Rosh Hashanah]], the Jewish new year, starts with the ''molad'' for the month of [[Tishrei]]. Starting from there, the calendar rules allow two main reasons to delay Rosh Hashanah by one or more days:<ref>{{cite web|last=Bromberg|first=Dr. Irving|title=The Purpose of the Hebrew Calendar Rosh HaShanah Dehiyyot (Postponements of the First Day of Tishrei)|url=http://individual.utoronto.ca/kalendis/hebrew/postpone.htm|access-date=19 May 2016}} There are actually a total of four postponement rules. The other two are very rare. They are used to make the year the right length in days.</ref>
# ''Postponing Rosh Hashanah if the time of the ''molad'' (in [[Jerusalem]]) is after 12:00 noon.'' If not for this rule, Rosh Hashanah would be the day ''before'' the ''molad'' in parts of the world east of Jerusalem.
# ''Postponing Rosh Hashanah so that it does not start on Sunday, Wednesday or Friday.'' This rule prevents [[Yom Kippur]] from being the day before or after [[Shabbat]]. It also prevents Hoshana Rabba, the seventh day of [[Sukkot]], from being on Shabbat.<br />Once Rosh Hashanah for this year is calculated, the Rosh Hashanah for next year is calculated, starting with the time either 12 or 13<ref>(depending on whether it is to be a leap year or not)</ref> ''molad'' periods in the future.

Once the dates for this year's and next year's Rosh Hashanahs are known, calculating the calendar in between is easy.

===Calculating the calendar===
The length of a ''molad'' is just a little over {{frac|29|1|2}} days. Since a month must have a whole number of days, calculating the calendar starts with [[wikt:alternating|alternating]] months of 30 and 29 days. This gives an average of {{frac|29|1|2}} days and a 12-month total of 354 days. Starting from there, the month lengths are changed as follows:
* When the extra month is added, it is month six (counting from Tishrei), and always has 30 days.
* When the number of days between this Rosh Hashanah and next is 355 days in a regular year (or 385 days in a leap year), an extra day is needed. It is added to ''Heshvan'' (month two counting from Tishrei), which then has 30 days.
* When the number of days between this Rosh Hashanah and next is 353 days in a regular year (or 383 days in a leap year), one fewer day is needed. It is taken away from ''Kislev'' (month three counting from Tishrei), which then has 29 days.
(See the table of months [[#Months of the Hebrew calendar year|above]].)

===Calendar months and the astronomical new moon===
The first day of the Hebrew calendar month, known as ''[[Rosh Hodesh]]'' ({{Hebrew|רׂאשׁ חוֹדֶש}}), is always close to the [[astronomical]] new moon. It often is not exactly on the astronomical new moon. There are two reasons for that:
# The calendar calculations are based on the ''average'' length of a moon cycle. The ''actual'' length of individual moon cycles [[wikt:vary|varies]] over time.
# The rules for postponing Rosh Hashanah (see above) push ''Rosh Hodesh'' away from the astronomical new moon. The people who created the calculations decided having ''Rosh Hodesh'' close to the new moon was less important than other [[wikt:factor#Noun|factor]]s.

==Notes==
{{Reflist}}

== References ==
* ''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.
* Bonnie Blackburn and Leofranc Holford-Strevens. ''The Oxford Companion to the Year: An Exploration of Calendar Customs and Time-reckoning''. Oxford University Press; USA, 2000. pp 723–730.

== Other websites ==
''The English of these sites may not be Simple English.''
* [http://www.angelfire.com/pa2/passover/jewish-calendar-hebrew.html Jewish Calendar] Details various Jewish points-of-view about the history of the Jewish calendar/Hebrew calendar. Includes several charts.
* [http://www.chabad.org/calendar/ Jewish Calendar with Zmanim - Halachic times and date converter] chabad.org
* [http://jewishencyclopedia.com/view.jsp?artid=44&letter=C&search=Year%20of%20Creation Jewish Encyclopedia: Calendar]
* [http://www-spof.gsfc.nasa.gov/stargaze/Sjewcale.htm Jewish calendar] {{Webarchive|url=https://web.archive.org/web/20200618001657/http://www-spof.gsfc.nasa.gov/stargaze/Sjewcale.htm |date=2020-06-18 }} More detailed, scientific explanation at the [[NASA]] web site
* [http://www.hebrew4christians.com/Holidays/Calendar/calendar.html Calendar] Hebrew for Christians website

=== Date converters ===
* [http://kaluach.org/ Kaluach - Hebrew/civil calendars]
* [http://www.hebcal.com/converter/ Hebcal Hebrew Date Converter]
* [http://www.chabad.org/calendar/1000year.asp?AID=6225 Chabad Hebrew date converter]
* [http://www.sym454.org/kalendis/ The ''Kalendis'' Calendar Calculator] (freeware)

[[Category:Calendars]]
[[Category:Judaism]]