The Jewish calendar is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions, yahrzeits (dates to commemorate the death of a relative), and daily Psalm readings, among many ceremonial uses. In Israel, it is used for religious purposes, provides a time frame for agriculture and is an official calendar for civil purposes, although the latter usage has been steadily declining in favor of the Gregorian calendar.
The Jewish calendar is based on both the moon and the sun. Months are based on the lunar cycle, while years are based on the solar cycle. This leads to a varying number of days in the year, unlike the Gregorian calendar which has 365 days in every year. The Jewish calendar coordinates the 19-year Metonic cycle of the solar year with the 235 months of the lunar calendar so that the lunar months fall in the same season every 19 years. It maintains a relation to the Gregorian calendar but differs in the way leap days and leap months are implemented.
The calendar era uses the creation of the world based on Biblical chronology as its epoch; however, the months start from Nisan in the spring because of Exodus 12:2 which states: “This month shall mark for you the beginning of the months; it shall be the first of the months of the year for you.”
The structure of the Jewish calendar can be summarized in the following key points:
- Lunisolar calendar – Based on both the moon and sun cycles
- Starts from Biblical Creation (3761 BCE) but months start from Nisan in spring
- 12 or 13 months per year
- Months follow the lunar cycle (new moon to new moon): 29 or 30 days per month
- Years follow the solar cycle: 12 or 13 months to total 353-385 days per year
- Leap years have 13 months (Adar I and Adar II) to maintain alignment of solar and lunar cycles
- Leap years follow a 19-year Metonic cycle
- Month names are Babylonian in origin: Tishrei, Heshvan, Kislev, Tevet, Shevat, Adar, Nisan, Iyar, Sivan, Tammuz, Av, Elul
- Days begin at sunset
- Extra day added to Kislev or Adar II (Adar Rishon/Adar Bet) to keep Passover in the spring
- Coordination with the Gregorian calendar through calculated postponements
Epoch
The Jewish calendar era counts from the biblical Creation of the world based on the Seder Olam Rabbah, a 2nd-century CE Jewish chronology. According to this traditional counting, the current Jewish year is 5783 AM (anno mundi, “in the year of the world”). The epoch of the modern Jewish calendar is equivalent to sunset on the Julian Day Number (JDN) 2457585.5 (Monday, 6 October 3761 BCE in the proleptic Julian calendar).
Months
The months of the Jewish calendar, and their usual relation to Gregorian calendar months, are as follows:
- Tishrei – September-October
- Heshvan – October-November
- Kislev – November-December
- Tevet – December-January
- Shevat – January-February
- Adar – February-March
- Nisan – March-April
- Iyar – April-May
- Sivan – May-June
- Tammuz – June-July
- Av – July-August
- Elul – August-September
The extra month Adar I is added after Shevat in leap years. In non-leap years, only the month of Adar exists.
The months originate from the Babylonian calendar and are referred to in the Hebrew Bible. They reflect West Asian names, such as Nisan, which refers to first fruits and the springtime. The current names are derived from Akkadian, the language of Babylon.
Days
In the Jewish calendar, days begin and end at sunset. This contrasts with the civil calendar in Israel where days end at midnight. The day commonly identified as the “first day of the week” is Saturday, the Jewish Sabbath, due to Creation beginning on the first day. Sunday is considered the first day in the civil Israeli calendar, analogous to the Gregorian calendar.
Years
Years in the Jewish calendar follow solar years of around 365 days. However, adjustments are made to ensure Passover falls in the spring. This means years can have 12 or 13 months.
In leap years, an extra month (Adar I) is added after Shevat to synchronize the lunar and solar calendars. The extra month keeps holidays in the seasons they are meant to be celebrated. For example, Passover needs to occur in the spring for its agricultural significance.
Leap years with 13 months occur 7 times in the 19-year Metonic cycle. This cycle approximates the tropical year of 365.24 days.
An ordinary year can have 353, 354 or 355 days while leap years have 383, 384 or 385 days. This variability arises from the tropical year not being exactly 365.24 days long, but closer to 365 days and 5 hours. The calendar accounts for this difference in the lengths of each month.
Postponements
The Jewish calendar coordinates with the civil calendar through the use of postponements. These delay the start of the year to ensure certain holy days don’t conflict with Shabbat or fall too close together.
There are four potential postponements:
- Rosh Hashana – Prevented from falling on a Sunday, Wednesday or Friday
- Yom Kippur – Prevented from falling the day before or after Shabbat
- Hoshana Rabbah – Prevents it falling on Shabbat
- Pesach/Passover – Prevented from falling the day before or after Shabbat
These postponements mean Rosh Hashana cannot occur on a Wednesday or Friday, pushing it back to a Thursday, for instance. The year can then start 1-4 days later to accommodate them.
Coordination with Civil Calendar
The Jewish calendar coordinates with the Israeli civil calendar mainly through the use of leap years. Although the Gregorian dates drift relative to the Jewish calendar, leap years keep Passover in the spring season.
The civil calendar adopted the leap year synchronization once every 19 years. However, the month numbering differs. In the civil calendar the extra month is known as Adar Alef whereas in the religious calendar it is Adar I, with Adar II following.
The civil New Year starts at Rosh Hashana. However, mandatory military conscription, contracts and other civil documents use Gregorian dates. The civil calendar also replaced the 7th day week with a continuous week cycle of days 1-7.
History
The calendar began as a simple lunisolar calendar based on observation of the new moon crescent. King David introduced a calendar modeled on the Egyptian solar calendar divided into 12 months. After Babylonian exile, the current version emerged based on Babylonian month names and traditions. Until the 9th century CE, authorities in Jerusalem determined dates through witnesses and astronomical calculations.
The calendar was fully codified by Maimonides in the Mishneh Torah in the 12th century CE. He described rules for calculating leap years, months, postponements and coordination with the civil calendar. His work reduced controversies between Jewish communities using variant systems.
There have been a few minor variations in practice between Jewish communities since. Some differences arose due to persecution and communication challenges. However, the calendar structure has remained stable since Maimonides’ codification.
Significance
The Jewish calendar holds great significance spiritually and culturally for the Jewish people. Religious life and worship revolve around it. As it is lunisolar, it links the cycles of the moon and sun. The moon represents renewal, growth and community while the sun represents constancy and permanence. Each new month represents a renewed hope.
The months reflect the seasons of Israel’s climate. Jewish agriculture was based on rains in fall and spring. Nisan, in the spring, is the first month as Passover celebrates new harvests.
The calendar preserves Jewish identity and ties to Hebrew tradition. It connects the Jewish people to their roots and heritage. It also reflects the values of continuity and consistency through its structured rules and intercalations.
Biblical References
The Jewish calendar system has its origins in the Hebrew Bible. Some relevant biblical passages include:
- Exodus 12:2 – Establishes month of Nisan as first month
- Numbers 10:10 – Trumpets to be blown at start of months
- Numbers 28:11-15 – Sacrifices specified for start of months
- 1 Kings 4:7; 1 Chronicles 27:1-15 – Organization of year into 12 months
- Ezekiel 45:18-25; 46:3-6 – Sacrifices and festivals for specified months
- Psalms 81:3 – Blowing trumpets on the new moon
- Isaiah 66:23 – Worshiping monthly at new moons
- Amos 8:5 – Regulation of business at the new moon
The Bible emphasizes the significance of each new month (“Rosh Chodesh”) as a period of restoration, celebration, worship and community reflection. While the modern calendar emerged later, its roots lie in the biblical importance of months.
Controversies and Criticisms
There have been some controversies and criticisms about the Jewish calendar throughout history:
- Difficulties in communicating start of new month led to Jewish communities using divergent calendars at times.
- Karaites rejected the modern fixed calendar and relied solely on observation of moon.
- Some claim the modern calendar was postponed from the correct biblical month beginnings.
- Questions around accuracy of biblical date for Creation which starts the calendar era.
- Occasional conflict between Jewish and civil dates for holidays.
- Debates around adapting the calendar given modern astronomical knowledge.
However, most modern Jewish communities unite behind the standardized calendar. Astronomical calculations provide reliability. The calendar system balances tradition and continuity with seasonal requirements.
Conclusions
In summary, the Jewish calendar provides the basis for Jewish religious and cultural life. Its foundations lie in the Torah but it evolved through history into the form codified by Maimonides. The metaphysical meaning behind the calendar connects Jews to their heritage. The structured lunar-solar design ensures consistency and seasonal alignment. Hence, the calendar continues to play a vital role in modern Jewish identity and worship today.