Hebrew calendar

The **Hebrew calendar** or **Jewish calendar** is the calendar used in Judaism. It is used to set the dates of the 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 relative. The daily Jewish prayer service changes depending on the day of the Hebrew calendar.

## Basic rules

The Hebrew calendar is a lunisolar calendar which depends on both the moon and the sun. Months of the Hebrew calendar are based on the appearance of the new moon. At the same time, the holiday of Passover must be in the spring.

## History

According to the Book of Exodus, Jews have been using a lunisolar calendar since the time they left Egypt. The first commandment the Jewish people received as a nation was the commandment to determine the New Moon. Very soon after that, the Jews received the commandment to make sure that Passover falls in the spring.

In the Tanakh (the Hebrew Bible), the months are usually numbered rather than named. (See table below.) Only four month names appear in the Tanakh from before the Babylonian Exile (see table). The month names of the modern Hebrew calendar were taken from the month names in the Babylonian calendar during the Babylonian Exile (6th century BCE).

At first, a new month began when witnesses came to the Sanhedrin (high rabbinical court) and testified that they saw the new crescent moon in the sky. 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 destruction of the Second Temple in 70 CE, it became harder for the Sanhedrin to meet and hear witnesses. For that reason, the Sanhedrin established a fixed, rule-based form of the calendar. Maimonides fully described the modern Hebrew calendar around the year 1178 CE.

In the modern Hebrew calendar, years are counted as _Anno Mundi_ (Latin for "year of the world"). This represents the traditional count of years since the creation of the world as described in Genesis. This year is _anno mundi_ .

### 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.

## Days of the Hebrew calendar week

|Day of the week (Hebrew) !! Translation !! Day starts from sundown !! style="border-left:dotted darkgray 2px" | Day continues until sundown|
| --- |
|<span style="direction:rtl;">יום ראשון</span> _yom rishon_||first day||Saturday||style="border-left:dotted darkgray 2px" |Sunday|
|<span style="direction:rtl;">יום שני</span> _yom sheni_||second day||Sunday||style="border-left:dotted darkgray 2px" |Monday|
|<span style="direction:rtl;">יום שלישי</span> _yom shelishi_||third day||Monday||style="border-left:dotted darkgray 2px" |Tuesday|
|<span style="direction:rtl;">יום רביעי</span> _yom revi'i_||fourth day||Tuesday||style="border-left:dotted darkgray 2px" |Wednesday|
|<span style="direction:rtl;">יום חמישי</span> _yom hamishi_||fifth day||Wednesday||style="border-left:dotted darkgray 2px" |Thursday|
|<span style="direction:rtl;">יום ששי</span> _yom shishi_||sixth day||Thursday||style="border-left:dotted darkgray 2px" |Friday|
|<span style="direction:rtl;">שבת</span> _shabbat_||Shabbat (Sabbath)||Friday||style="border-left:dotted darkgray 2px" |Saturday|

## Months

|Month in Bible|Month name in English !! Month name in Hebrew !! Number of days !! Time of year !! Notes|||||
| --- | --- | --- | --- | --- | --- |
|1|Nisan||30|March–April|pre-exile name _Aviv_ ("spring") Month of Passover|
|2|Iyar||29|April–May|pre-exile name _Ziv_ ("light")|
|3|Sivan||30|May–June|Month of Shavuot|
|4|Tammuz||29|June–July||
|5|Ab||30|July–August|Month of Tisha B'Av|
|6|Elul||29|August–September||
|7|Tishrei||30|September–October|pre-exile name _Etanim_ ("strong") Month of Rosh Hashanah, Yom Kippur and Sukkot|
|8|Heshvan (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 || October–November || pre-exile name _Bul_|||||
|9|Kislev||30 or 29|November–December|Month of Hanukkah|
|10|Tevet||29|December–January||
|11|Shevat||30|January–February||
|12|Adar||29|February–March|Month of Purim — In a leap year:  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  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|

### The day and the week

In the Hebrew calendar, the meaning of _day_ is taken from the Hebrew Bible: "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 nightfall.

People who print calendars, or who write calendar programs for computers, 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 assume that people reading a Hebrew calendar know the sundown rule. Whenever a 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. 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 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. (See table 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,  seconds.

### 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 adaptation<sup>n 2</sup> of the Metonic cycle, a calendar cycle that was well known in ancient times. By 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:
1. _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.
1. _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.
Once Rosh Hashanah for this year is calculated, the Rosh Hashanah for next year is calculated, starting with the time either 12 or 13 _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  days. Since a month must have a whole number of days, calculating the calendar starts with alternating months of 30 and 29 days. This gives an average of  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 above.)

### Calendar months and the astronomical new moon

The first day of the Hebrew calendar month, known as _Rosh Hodesh_ (), is always close to the astronomical new moon. It often is not exactly on the astronomical new moon. There are two reasons for that:
1. The calendar calculations are based on the _average_ length of a moon cycle. The _actual_ length of individual moon cycles varies over time.
1. 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 factors.

## 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._
- Jewish Calendar Details various Jewish points-of-view about the history of the Jewish calendar/Hebrew calendar. Includes several charts.
- Jewish Calendar with Zmanim - Halachic times and date converter chabad.org
- Jewish Encyclopedia: Calendar
- Jewish calendar  More detailed, scientific explanation at the NASA web site
- Calendar Hebrew for Christians website

### Date converters

- Kaluach - Hebrew/civil calendars
- Hebcal Hebrew Date Converter
- Chabad Hebrew date converter
- The _Kalendis_ Calendar Calculator  (freeware)