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Jewish Calendar 2024

The Jewish calendar is a sophisticated, accurate system that has been in use for millennia. It’s also an important tool for spiritual growth.
by Tzvi Gluckin

What is the Jewish calendar?

The Jewish calendar is a type of lunisolar calendar, which is a lunar calendar with a solar adjustment. A lunar cycle—based on the synodic month, or complete cycle of phases of the moon as seen from the earth—is about 29.5 days, and that is calculated so the full moon always lands on the 15th of each month. To compensate for that extra half day, the different Hebrew months alternate between 29 and 30 days.

If you do the math, 12 lunar months only add up to 354 days, which is about 11 days less than a solar year (365.25 days). Without some type of adjustment, the holidays would be 11 days earlier every year. They would travel around the calendar and come back to the same spot only once every 33 years.

Yet that doesn’t happen because the Torah (Deuteronomy 16:1) mandates that Passover has to be celebrated in the spring1 (similar to the original Passover as chronicled in the book of Exodus). In order for that to work out, a system was eventually adopted that adds seven leap months over the course of a 19-year cycle, which works out to about once every three years.

Table of Contents

When did the Jewish calendar start?

Time is central to Jewish observance. The Torah starts with the creation of time, the establishment and naming of the different parts of the day,2 and the setting up of a weekly cycle that culminates with a Sabbath, or day of rest. The weekly cycle is significant in that unlike other demarcations of time—like the day, month, and year—it is not related to an astronomical cycle. In Jewish thought, the week is considered a spiritual system. It’s built around a weekly Sabbath, and is superimposed over—as well as supersedes—the other, “natural” time cycles.

Marking time is also important. The great medieval biblical commentator, Rashi (Rabbi Shlomo Yitzchaki, 1040-1105), says about Genesis 1:1, the Torah’s opening verse, “God need not have begun the Torah [with ‘In the beginning’], but from [Exodus 12:2] ‘This month shall be the head month to you,’ because that is the first commandment that Israel was commanded.” His point is that if the Torah is supposed to be a book of commandments, it should begin with the first time the Jewish people are given a command—as opposed to the creation story—and that is the commandment to establish a calendar.

As noted, that commandment is from Exodus 12, which describes the Passover sacrifice, both its preparation and application. But in order to explain when that process begins, it needs to set up a calendar, which is why Exodus 12:2 continues, “[This month] shall be the first month of the year.”3

The Jewish calendar starts with the birth of the Jewish people. Passover occurs in the first month, and the other holidays follow. Rosh Hashanah, the Jewish New Year, is celebrated on the first day of the seventh month,4 because the ordering of the months starts from the time of Passover and not the counting of the year. However, the Jewish year is counted from Rosh Hashanah, year zero being the creation of Adam and Eve, which took place on Day Six in the creation story (Genesis 1:26-30), and not from the start of creation.

How many months are in the Jewish calendar?

The Jewish year consists of 12 months. The Torah doesn’t name those months, but refers to them by number: the first month, when Passover is celebrated, is called “the first month,” the next month is called “the second month,” and so on. Following the Babylonian exile (around 370 BCE), the returning refugees adopted the Babylonian names for the months—which may come from the ancient Sumerian calendar—and those are the names still in use today.

According to the 13th century sage, Rabbi Moses Nachmonides,5 the Torah counts the months starting from Passover in order to help keep alive the memory of the exodus and the redemption from Egypt. Following the return from Babylonian captivity, the Jewish leaders at that time started using the Babylonian month names in order to preserve the memory of that redemption as well.

The names of the 12 months of the Jewish calendar are:

  • Nisan (ניסן)
  • Iyar (אייר)
  • Sivan (סיון)
  • Tammuz (תמוז)
  • Av (אב)
  • Elul (אלול)
  • Tishrei (תשרי)
  • Marcheshvan (מרחשון)
  • Kislev (כסלו)
  • Tevet (טבת)
  • Shevat (שבט)
  • Adar (אדר)

Leap years in the Hebrew Calendar

The Jewish calendar is a lunar calendar with a solar adjustment. A lunar month, based on the synodic month—or complete cycle of phases of the moon as seen from the earth—is about 29.5 days, which, if multiplied by 12 months equals only 354 days. That number is about 11 days less than a solar year—the time required for the earth to travel around the sun—which is about 365.25 days. Without some type of correction, any given Hebrew date would occur 11 days “earlier” each year in relation to the solar cycle and the seasons (which are based on the earth's position vis a vis the sun).

The Torah (Deuteronomy 16:1) requires Passover, which begins on the 15th of Nisan, to be celebrated in the spring. In order for that to work out, an extra month is added seven times over a 19-year period, or roughly once every three years. That added month is a second Adar, and Jewish leap years contain an Adar I and an Adar II, called Adar Alef (אדר א) and Adar Beit (אדר ב). During a Jewish leap year, the holiday of Purim, which takes place on the 14th and 15th of Adar, is celebrated in Adar Beit.

For much of Jewish history, the courts decided when to add a leap year based on seasonal factors and visual observations, but at some point—due to Roman persecution and a growing diaspora—that was no longer tenable. In the year 358, the Talmudic sage, Hillel (often referred to as Hillel II so as not to be confused with first century scholar, Hillel the Elder), created the calendar system that’s still in use today.

Calculating the Hebrew Calendar

As noted above, the Hebrew month is a synodic month6 (the complete cycle of phases of the moon as seen from the earth), which should not be confused with the sidereal month7 (the time needed for the moon to return to the same place against the background of the stars). The length of a synodic month is about 29.5 days, and to compensate for that extra half day, the different Hebrew months alternate between 29 and 30 days.

Initially, the Jews high court, called the Sanhedrin, declared each month based on eyewitness testimony. Witnesses testified that they saw the first sliver of the new moon, called the molad (מולד), and the court determined, based on various factors, the start of the new month. With the dissolution of the Sanhedrin, that was no longer possible, and a fixed system of months, as well as a set leap year cycle, was established (see above).

The Hebrew calendar is considered a type of Metonic calendar. Meton of Athens was a Greek astronomer, and in 432 BCE introduced the Attic, or Athenian, calendar. Meton’s cycle is a system made up of 235 synodic months, which is a period of about 19 years.8 Over the course of those 19 years, seven of them include a leap year. In the Jewish system, those leap years occur in the third, sixth, eighth, 11th, 14th, 17th, and 19th years. Those leap years are 13-month years, as opposed to the regular 12.

The Jewish system differs from the Metonic calendar in a number of ways, and may have developed alongside the Babylonian calendar. In any event, the number needed for those calculations was known for millennia. According to the Talmud,9 which was compiled in the fifth century, the synodic month is 29.5 days plus 793/1080 parts of an hour, or, in modern parlance, 29.530594 days. That number isn't unique to Jewish tradition, although carrying it to the sixth decimal point is an unusual level of accuracy.10

When Hillel standardized the calendar in 358, he made a number of other adjustments—particularly in terms of the lengths of the months Marcheshvan and Kislev—to make sure that Yom Kippur never occurs on a Sunday or Friday, so as to not negatively impact the fast or its preparations.

Understanding the Jewish calendar as a tool for growth

In Jewish thought, you travel through the calendar, and arrive at various stations along the way.11 That trip repeats itself each year, but those stations—which include the Sabbath, holidays, and other significant times—are the same. Each station is an opportunity that’s available only then. If you’re prepared, when you arrive at a particular station you can take advantage of that particular opportunity. If not, the opportunity will pass you by. What you make of it is up to you.

For example, that’s why the Torah calls Passover, “the time of our freedom,” and Sukkot, “the time of our joy.” Those times are opportunities to focus on the Jewish concepts of freedom and joy. You can work on freedom and joy at other times, too, but when you pull into the station, it’s in the air. It’s easier—it’s the season, or the right time—to work on those things.

That idea is true for the other important times on the Jewish calendar as well.

Summary

The Jewish, or Hebrew, calendar is a lunar calendar with a solar adjustment. That adjustment is necessitated by the Torah, which requires the holiday of Passover to be celebrated in the spring. The Torah implies the need for a calendar, which was adjusted regularly by the Sanhedrin, or Jewish high court. The current calendar was established in the year 358 by the Talmudic sage, Hillel II. His system is based on a number of complex calculations, and is a 19-year cycle with seven leap years that occur about every three years. The calendar is adjusted to make sure Yom Kippur never falls on a Sunday or Friday. The Jewish calendar also has a spiritual dimension, and is considered an important tool for personal growth.

FAQs

What year is it in the Jewish calendar?

According to Jewish tradition, the current Jewish year is 5784.

What is the first month of the Jewish calendar?

That’s actually a trick question. In the Torah, Nisan, which usually occurs in March and/or April, is called “the first month.” However, the year is counted from Rosh Hashanah, which falls on the first day of Tishrei, which is called “the seventh month” in the Torah.

What is the Jewish calendar based on?

The Jewish calendar is considered a type of Metonic calendar, although it’s not necessarily based on a Meton’s calculations, and some think it developed alongside the Babylonian calendar. The Torah is very specific about certain aspects of the calendar, including the timing of the holidays, the establishment of each month, and the imposition of the week (which, unlike the other aspects of the calendar, is spiritual in nature and isn’t based on astronomical observations). The current Jewish calendar was established by Hillel II in the year 358, and is a 19 year system that contains seven leap years over the course of that cycle.
  1. Deuteronomy 16:1: “Safeguard the month of standing grain (חדש האביב) so that you will be able to keep the Passover to God your Lord, since it was in the month of standing grain that God your Lord brought you out of Egypt at night.”
  2. Genesis 1:5: “God named the light ‘Day,’ and the darkness He named ‘Night.’ It was evening and it was morning, one day.”
  3. See Maimonidies, Sefer HaMitzvahs, Positive Commandment 153: "God commanded us to sanctify the months [or to calculate the months] and years."
  4. Leviticus 23:23: “The first day of the seventh month shall be a day of rest. It is a sacred holiday for remembrance and sounding of the ram’s horn.”
  5. See Nachmonides’s commentary on Exodus 12:2
  6. The synodic month, or complete cycle of phases of the moon as seen from earth, averages 29.530588 mean solar days in length (i.e., 29 days 12 hours 44 minutes 3 seconds); because of perturbations in the moon’s orbit, the lengths of all astronomical months vary slightly.
  7. The sidereal month is the time needed for the moon to return to the same place against the background of the stars, 27.321661 days (i.e., 27 days 7 hours 43 minutes 12 seconds); the difference between synodic and sidereal lengths is due to the orbital movement of the earth–moon system around the sun. This definition, as well as the note above, were taken from here: https://www.britannica.com/science/month#ref225843
  8. The Metonic cycle, in chronology, is a period of 19 years in which there are 235 lunations, or synodic months, after which the moon’s phases recur on the same days of the solar year, or year of the seasons. The cycle was discovered by Meton (fl. 432 BC), an Athenian astronomer. Computation from modern data shows that 235 lunations are 6,939 days, 16.5 hours; and 19 solar years, 6,939 days, 14.5 hours. Taken from here: https://www.britannica.com/science/Metonic-cycle#ref102869
  9. Rosh Hashanah 25A
  10. Want your mind blown? Here’s how that number is derived from classical Jewish sources: https://www.torahcode.net/first_els/first_els.shtml
  11. Michtav M’Eliyahu, volume 2, page 21, by Rabbi Eliyahu Dessler
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