The Hebrew calendar (, ), also called the Jewish calendar, is a lunisolar calendar used today for Jewish religious observance and as an official calendar of Israel. It determines the dates of Jewish holidays and other rituals, such as , and the scheduling of public Torah readings. In Israel, it is used for religious and agriculture purposes, and is also an official calendar for civil holidays alongside the Gregorian calendar.
Like other lunisolar calendars, the Hebrew calendar consists of months of 29 or 30 days that begin and end at approximately the time of the new moon. As 12 such months comprise a total of just 354 days, an extra lunar month is added every 2 or 3 years so that the long-term average year length closely approximates the actual length of the solar year.
Originally, the beginning of each month was determined based on physical observation of a new moon, while the decision of whether to add the leap month was based on observation of natural agriculture-related events in ancient Israel.Tosefta Sanhedrin 2:2 "The year may be intercalated on three grounds: [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."; also quoted in ; see also Talmud, Sanhedrin 11b Between the years 70 and 1178, these empirical criteria were gradually replaced with a set of mathematical rules. Month length now follows a fixed schedule that is adjusted based on the molad interval (a mathematical approximation of the mean time between new moons) and several other rules, while leap months are now added in 7 out of every 19 years according to the Metonic cycle.
Nowadays, Hebrew years are generally counted according to the system of (Latin: "in the year of the world"; , "from the creation of the world", abbreviated AM) according to traditional Jewish interpretation of the chronology of the Hebrew Bible. This system attempts to calculate the number of years since the creation of the world according to the Genesis creation narrative. The current Hebrew year, AM , began at sunset on and will end at sunset on .
Components
Hours
Judaism uses multiple systems for dividing hours. In one system, the 24-hour day is divided into fixed hours equal to of a day, while each hour is divided into 1080 (parts, singular: ). A is seconds ( minute). The ultimate ancestor of the was a Babylonian unit of time called a barleycorn, equal to of a Babylonian time degree (1° of celestial rotation). These measures are not generally used for everyday purposes; their best-known use is for calculating and announcing the molad.
In another system, the daytime period is divided into 12 relative hours (, also sometimes called "halachic hours"). A relative hour is defined as of the time from sunrise to sunset, or dawn to dusk, as per the two opinions in this regard. Therefore, an hour can be less than 60 minutes in winter, and more than 60 minutes in summer; similarly, the 6th hour ends at solar noon, which generally differs from 12:00. Relative hours are used for the calculation of prayer times (zmanim); for example, the Shema must be recited in the first three relative hours of the day.Mishna Berachot 1:2. Note that the mishna specifies that the Shema may be recited "until three hours"; this is understood to mean "until the end of the third hour".
Neither system is commonly used in ordinary life; rather, the local civil clock is used. This is even the case for ritual times (e.g. "The latest time to recite Shema today is 9:38 AM").See e.g. Zmanim: Jerusalem
Days
Based on the classic rabbinic interpretation of ("There was evening and there was morning, one day"), a day in the rabbinic Hebrew calendar runs from sunset (the start of "the evening") to the next sunset. Similarly, Yom Kippur, Passover, and Shabbat are described in the Bible as lasting "from evening to evening".; ; regarding Shabbat () only the beginning time is mentioned. The days are therefore figured locally.
Halachically, the exact time when days begin or end is uncertain: this time could be either sundown () or else nightfall (, "when the stars appear"). The time between sundown and nightfall () is of uncertain status. Thus (for example) observance of Shabbat begins before sundown on Friday and ends after nightfall on Saturday, to be sure that Shabbat is not violated no matter when the transition between days occurs.
Instead of the International Date Line convention, there are varying opinions as to where the day changes.."Appendix II: Baal HaMaor's Interpretation of 20b and its Relevance to the Dateline" in Talmud Bavli, Schottenstein Edition, Tractate Rosh HaShanah, Mesorah Publications Ltd. ("ArtScroll") 1999, where "20b" refers to the 20th page 2nd folio of the tractate. (See International date line in Judaism.)
Weeks
The Hebrew week (, ) is a 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 are simply the day number within the week. The week begins with Day 1 (Sunday) and ends with Shabbat (Saturday). (More precisely, since days begin in the evening, weeks begin and end on Saturday evening. Day 1 lasts from Saturday evening to Sunday evening, while Shabbat lasts from Friday evening to Saturday evening.)
Since some calculations use division, a remainder of 0 signifies Saturday.
In Hebrew, these names may be abbreviated using the numerical value of the Hebrew letters, for example (Day 1, or ()): Hebrew name Abbreviation Translation English equivalent Yom Rishon (יום ראשון) First day Sunset on Saturday to sunset on Sunday Yom Sheni (יום שני) Second day Sunset on Sunday to sunset on Monday Yom Shlishi (יום שלישי) Third day Sunset on Monday to sunset on Tuesday Yom Revii (יום רביעי) Fourth day Sunset on Tuesday to sunset on Wednesday Yom Hamishi (יום חמישי) Fifth day Sunset on Wednesday to sunset on Thursday Yom Shishi (יום שישי) Sixth day Sunset on Thursday to sunset on Friday Yom Shabbat (יום שבת) Sabbath day Sunset on Friday to sunset on Saturday
The names of the days of the week are modeled on the seven days mentioned in the Genesis creation account.Hebrew-English Bible, For example, Genesis 1:8 "... And there was evening and there was morning, a second day" corresponds to meaning "second day". (However, for days 1, 6, and 7, the modern name differs slightly from the version in Genesis.)
The seventh day, Shabbat, as its Hebrew name indicates, is a day of rest in Judaism. In Talmudic Hebrew, the word () can also mean "week",Jastrow: שַׁבָּת so that in ritual liturgy a phrase like "Yom Reviʻi beShabbat" means "the fourth day in the week".For example, when referring to the daily psalm recited in the morning prayer.
Days of week of holidays
Jewish holidays can only fall on the weekdays shown in the following table:
PurimPassover(first day)Shavuot(first day)17 Tammuz/Tisha B'AvRosh Hashanah/Sukkot/Shmini Atzeret(first day)Yom KippurChanukah(first day)10 TevetTu BishvatPurim Katan(only in leap years)ThuSatSunSun*MonWedSun or MonSun or TueSat or MonSun or TueFriSunMonSunTueThuMonTueMonTueSunTueWedTueThuSatWed or ThuWed, Thu, or FriTue, Wed, or ThuWed or FriTueThuFriThuSatMonFri or SatFri or SunThu or SatFri or Sun *Postponed from Shabbat
The period from 1 Adar (or Adar II, in leap years) to 29 Marcheshvan contains all of the festivals specified in the Bible (Purim, Passover, Shavuot, Rosh Hashanah, Yom Kippur, Sukkot, and Shemini Atzeret). The lengths of months in this period are fixed, meaning that the day of week of Passover dictates the day of week of the other Biblical holidays. However, the lengths of the months of Marcheshvan and Kislev can each vary by a day (due to the Rosh Hashanah postponement rules, which are used to adjust the year length). As a result, the holidays falling after Marcheshvan (starting with Chanukah) can fall on multiple days for a given row of the table.
A common mnemonic is "", meaning: "Rosh HaShana cannot be on Sunday, Wednesday or Friday, and Passover cannot be on Monday, Wednesday or Friday" with each day's numerical equivalent, in gematria, is used, such that א' = 1 = Sunday, and so forth. From this rule, every other date can be calculated by adding weeks and days until that date's possible day of the week can be derived.
Months The Hebrew calendar is a lunisolar calendar, meaning that months are based on lunar months, but years are based on solar years. The calendar year features twelve lunar months of 29 or 30 days, with an additional intercalary lunar month added periodically to synchronize the twelve lunar cycles with the longer solar year. These extra months are added in seven years (3, 6, 8, 11, 14, 17, and 19) out of a 19-year cycle, known as the Metonic cycle (See Leap months, below).
The beginning of each Jewish lunar month is based on the appearance of the new moon. Although originally the new lunar crescent had to be observed and certified by witnesses (as is still done in Karaite Judaism and Islam), nowadays Jewish months have generally fixed lengths that approximate the period between new moons. For these reasons, a given month does not always begin on the same day as its astronomical conjunction.
The mean period of the lunar month (precisely, the synodic month) is very close to 29.5 days. Accordingly, the basic Hebrew calendar year is one of twelve lunar months alternating between 29 and 30 days:
Month number Hebrew month Length Range of possible Gregorian dates Biblical / after Exodus Civil / currently used First day Last day 1 7 Nisan 30 12 March to 11 April 10 April to 10 May 2 8 Iyar 29 11 April to 11 May 9 May to 8 June 3 9 Sivan 30 10 May to 9 June 8 June to 8 July 4 10 Tammuz 29 9 June to 9 July 7 July to 6 August 5 11 Av 30 8 July to 7 August 6 August to 5 September 6 12 Elul 29 7 August to 6 September 4 September to 4 October 7 1 Tishrei 30 5 September to 5 October 4 October to 3 November 8 2 Cheshvan (or Marcheshvan) 29 (or 30) 5 October to 4 November 3 November to 2 December 9 3 Kislev 30 (or 29) 4 November to 3 December 2 December to 31 December 10 4 Tevet 29 3 December to 1 January 1 January to 29 January 11 5 Shevat 30 1 January to 30 January 30 January to 28 February 12 6 Adar I (this is added only in leap years) 30 31 January to 12 February 1 March to 12 March 12 6 Adar (this is called Adar II in leap years) 29 11 February to 13 March 11 March to 10 April Total 354 (or 353 or 355) 30 days more in leap years
Thus, the year normally contains twelve months with a total of 354 days. In such a year, the month of Marcheshvan has 29 days and Kislev has 30 days. However, due to the Rosh Hashanah postponement rules, in some years Kislev may lose a day to have 29 days, or Marcheshvan may acquire an additional day to have 30 days.
Normally the 12th month is named Adar. During leap years, the 12th and 13th months are named Adar I and Adar II (Hebrew: and —"first Adar" and "second adar"). Sources disagree as to which of these months is the "real" Adar, and which is the added leap month.Which is the true Adar?
Justification for leap months The Bible does not directly mention the addition of leap months (also known as "embolismic" or "intercalary" months). The insertion of the leap month is based on the requirement that Passover occur at the same time of year as the spring barley harvest ()., ; see למועד חודש האביב (Since 12 lunar months make up less than a solar year, the date of Passover would gradually move throughout the solar year if leap months were not occasionally added.) According to the rabbinic calculation, this requirement means that Passover (or at least most of Passover) should fall after the March equinox. Similarly, the holidays of Shavuot and Sukkot are presumed by the Torah to fall in specific agricultural seasons., ; ;
Maimonides, discussing the calendrical rules in his Mishneh Torah (1178), notes: