BIBLE HISTORY DAILY

Understanding the Jewish Calendar

Why Jewish holidays shift each year

Ever wondered why the days for holidays like Hanukkah and Passover seem to shift around from year to year? The simple answer is that these holidays are determined not by the Gregorian calendar utilized by many countries, but by the Jewish calendar. However, the days of the year are not the only difference between these calendars; the years themselves are too. Although many elements of this calendrical system can be seen in the pages of the Bible, other features developed only much later. So, what exactly is the Jewish calendar?

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Dating in Judaism

As the name implies, the modern Jewish calendar is utilized today within Jewish religious settings, as well as by the State of Israel. This calendar was first established by the Jewish sage Hillel II in 358/9 CE. It was heavily based on earlier Jewish calendars, and various alterations have been made since then. Many features of the modern Jewish calendar will seem familiar to those who use the Gregorian calendar, including seven-day weeks and days of 24 hours. Within these features, the most significant differences are that Saturday is the last day of the Jewish week, and each day ends at sundown rather than midnight.

Where the calendar begins to diverge more significantly is in its calculation of months. Like many calendars, the Jewish calendar is lunisolar, meaning that it attempts to combine months corresponding to lunar cycles with years that correspond to the solar cycle. As such, the Jewish calendar consists of 12 months, each containing 29 or 30 days. Yet, as the lunar and solar cycles do not perfectly align, the Jewish calendar uses an intercalary month in which an extra month is added every several years. In the biblical period, the beginning of a new month was established by the physical sighting of a new moon. Between the first and 12th centuries, however, this was slowly replaced by a mathematical model.

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As can be seen throughout the Bible, the names of the months are also very different than those used in the Gregorian calendar. Just as the Gregorian months were borrowed from the Roman Julian calendar, the names for the Jewish months were borrowed from Mesopotamia, specifically the month names and system formalized in the religious capital of Nippur during the early second millennium BCE. This borrowing is easily seen in the names of the first two Jewish months (Nisan and Iyar) compared to the first two Mesopotamian months (Nisanum and Ayarum).

One interesting feature of the Jewish calendar is its own disagreement about the start of the year, with both a civil and an ecclesiastical new year. Despite this, the festival of Rosh Hashana (literally, “head of the year”), which occurs in either September or October, is considered the first day of the year for counting new years. So how, then, are Jewish years counted?

As would be expected, years within the Jewish calendar bear no connection to the birthdate of Jesus (Anno Domini). Instead, the years of the Jewish calendar are calculated based on the age of the world (Anno Mundi). This age is determined based on calculations of the biblical text by Rabbi Yose Ben Halafta in the second century CE. According to his calculations, the world was created on Monday, October 7, 3761 BCE. Thus, if you want to know what Jewish year it is, just add 3761 to the current Gregorian year.

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The Eras Tour

Determining eras, and thereby what year it is, has always been tricky. Many ancient cultures utilized regnal years, in which the year was named by the number of years the current king or queen had reigned. This system is frequently seen in the Hebrew Bible. However, this system is far less common today, with most modern systems working according to a fixed start date. Although the Jewish year is based on the calculated age of the world, the Gregorian system is based on the birth of Jesus as calculated by the sixth-century monk Dionysius Exiguus. However, his calculations were off by a few years. The Gregorian system divides dates into two eras: those after the birth of Jesus (AD: Anno Domini) and those before the birth of Jesus (BC: Before Christ).

In more recent history, AD and BC have begun to be replaced by the more neutral CE (Common Era) and BCE (Before the Common Era), which is utilized by a majority of scholars in the fields of archaeology and biblical studies. While this shift in terminology is contentious, it is certainly not the first time that such a shift has occurred, with the prevalent use of AD only being a little over a millennium old, and BC being a more modern and explicitly English term. Meanwhile, the term “Common Era” (or analogous terms) was already in use by at least 1615.

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Related reading in Bible History Daily

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