Adding Adar Bet: Striking a Balance


This Hebrew year consists of thirteen months rather than twelve. Jews throughout the world will add (“intercalate”) a second month of Adar this year, in order to insure that Passover falls in the spring. Although we think of it as the Jewish calendar, the calendar of twelve “lunations”, 29 or 30 day months corresponding to the cycle of the moon – whose 354-day years are adjusted to the solar year of 365 days by intercalating a thirteenth month every two or three years – was the most common calendar in the ancient world.

It is true that the ancient Egyptians, Persians and Romans had solar calendars of various types, but the lunisolar calendar was more prevalent: it was common to the Celts of Gaul, most of the ancient Greeks, the Sumerians, the Babylonians, and many of the peoples leaving in the Indian subcontinent in ancient times, and to this day it is the calendar according to which the traditional festivals of China, Japan, Korea, Vietnam and other East Asian nations are celebrated. It was the secular calendar of the world-embracing Babylonian and Persian empires, and of the Macedonian Empire and Hellenistic world that succeeded them. For the Babylonians and Macedonian Greeks, this was merely a matter of imposing their own local calendar on their subject peoples; for the Persians, who had their own 365-day solar calendar, the exigencies of running the empire they inherited from the Babylonians made it prudent for them to adopt the dominant lunisolar calendar as the secular calendar of the empire, and they relegated their own calendar to ritual use in the Zoroastrian religion.

The Original Israelite Calendar May Have Been Solar
All this changed when the Romans, who had a solar calendar, subjugated most of the known world under their own empire in the last century BCE and the first centuries CE: the Julian calendar, a reformed version of an earlier Roman solar calendar that was instituted by Julius Caesar in the year 45 BCE, became the calendar of the Roman empire and the Western world, and by the twentieth century this solar calendar, slightly reformed over the years, was adopted as the secular calendar by virtually all modern nation-states, including those of East Asia.

The calendar that we consider “Jewish” was thus common to most ancient peoples. In fact, some scholars believe that the ancient Israelites, like the ancient Egyptians, were among the few ancient peoples who had a solar calendar! According to these scholars, the current Jewish calendar was adopted during the Babylonian exile in the sixth century BCE. To support this view they adduce the following arguments: Ancient Canaan, both before and after the Israelite conquest, was part of the Egyptian sphere of influence, and the ancient Egyptians, along with the Romans and the Zoroastrian Persians, were among the few peoples who had a solar calendar.

Moreover the calendar used in Jewish texts from the Second Temple period attributed to the more conservative of Second Temple texts, most notably the book of Jubilees and the Qumran documents, was an Egyptian-style 364-day solar calendar. The religious groups responsible for these writings took pride in the fact that they preserved what they considered to be the ancient Israelite solar calendar, and objected to what they believed to be the Jewish adoption of the dominant lunisolar calendar under Babylonian influence. Many contemporary scholars find their view of the history of the calendar convincing. The Qumran solar calendar consisted of 364 days, exactly 52 weeks, and began each year on Wednesday, the first of Nisan, the day the sun was created. The Jews of Qumran considered this calendar divinely ordained for the Torah’s festivals, unlike the Babylonian lunisolar calendar, our contemporary Jewish calendar, which required human intervention in the form of intercalation.

Ascendency of the Lunar “Jewish” Calendar
The Jews of Qumran thus perceived their solar calendar as uniquely divine and Israelite, despite its Egyptian roots, because they believed that the rest of the Jewish world, like the near East in general, had adopted a lunisolar calendar under Babylonian and Hellenistic influence. The reverse thought process took hold of the Rabbis in Roman times. As stated above, the calendar of the Hellenistic world was the lunisolar calendar that we consider “Jewish”. During the first centuries of the Common Era, however, the nations under Roman dominion adjusted their local lunisolar calendars, one by one, to correspond with the Julian calendar. The Jews refused to do so, maintaining steadfast allegiance to what they now considered the “Jewish” calendar, but which in the past they had shared with, and possibly even adopted from, the Babylonians and Greeks. In Rabbinic times, under Roman rule, the Jews felt unique in their allegiance to this calendar, and thus they came to see the moon-based calendar, and even the moon itself, as a symbol of Israel:

“This new moon is for you” (Exodus 12:2) – for you; Adam the first man did not calculate [the calendar] by means of it… foryou and not for the gentiles… from whence we derive that Israel calculates by the moon and the gentiles by the sun. It would not suffice for the Israelites if they were unable to raise their eyes to their father in heaven once every thirty days (Mekhilta Pisha 2).

The true creator, who acts faithfully, has told the moon to renew itself. It is a crown of glory for Israel, the people conceived by God, who will likewise renew themselves in the future, in order to proclaim the beauty of their Creator, for his glorious majesty … (Blessing on the new moon, Bavli Sanhedrin 42a).

When the Jews of Qumran perceived the solar calendar as uniquely Israelite against the background of the Hellenistic world, they found religious significance in the divine nature of the solar calendar, in its freedom from human intervention. When the Rabbis of Roman times perceived the lunisolar calendar as uniquely Israelite, they found religious significance in Israel’s role in determining the months and years. They took pride in the fact that it was an opportunity for the Israelites to raise their eyes to their father in heaven once a month, proclaiming God’s glorious beauty and majesty, and the waxing and waning cycle of the moon was perceived as a promise of renewal and redemption for the Israelites themselves.

The solar calendar was thus preferred by the Qumran sect for its divine purity and its freedom from human intervention; the lunisolar calendar was preferred by the Rabbis for the role Israel played in its calculation. Both of these were examples of spiritual significance sought by Jews “after the fact”: neither the Egyptian-based Qumran calendar, nor the Babylonian-Hellenistic calendar of the Rabbis, was truly uniquely Jewish. Yet both the Qumran sect and the Rabbis maintained their calendars even after they had been replaced by those around them. Both perceived their own calendar as uniquely Israelite, and both took pride in the unique characteristics of their calendar, imbuing them with religious significance.

The Muslim Lunar Year: Intercalation, a Sin
Years later, similar spiritual significance would be found in the Koran’s legislation with regard to the Islamic calendar in the seventh century CE. The pre-Islamic tribes of the Arabian Peninsula, living as they did just outside the borders of the Roman and Byzantine Empires, did not undergo the transition to the Julian solar calendar at the turn of the millennium. Like the Jews, they retained the lunisolar calendar that dominated the East in pre-Roman times. This was a source of conflict among the tribes, who often fought among one another. The local tribes held four months a year “sacred” and free from warfare. The Quraish tribe of northern Arabia would occasionally intercalate the year, as is necessary, without telling the other tribes, leaving them defenseless in the face of an attack by the Quraish during a month which would have been sacred, had the previous year not been intercalated. This led to a sense that intercalation of the lunar year was not only “tampering” with the divinely ordained calendar, but morally untenable. The Koran therefore proclaimed the twelve-month lunar year divinely ordained, and forbade intercalation:

Surely the reckoning of months, in the sight of Allah, is twelve months, laid down in Allah’s decree on the day when He created the heavens and the earth; and out of these months four are sacred. That is the true ordainment. Do not, therefore, wrong yourselves, with respect to these months. And fight all together against those who associate others with Allah in His Divinity in the manner that they fight against you all together, and know well that Allah is with the God-fearing. Intercalation is an act of gross infidelity which causes the unbelievers to be led further astray. They declare a month to be lawful in one year and forbidden in another year in order that they may conform to the number of months that Allah has declared as sacred, and at the same time make lawful what Allah has forbidden. Their foul acts seem fair to them. Allah does not direct those who deny the Truth to the Right Way (Koran 9:36-37).

As is often pointed out, an unintercalated lunar calendar, in which every year consists of twelve lunar months, does not keep pace with the seasons. Nonetheless, the Koran maintains that this is the year ordained by God from creation – the pure, unadulterated, divine year. It should be noted that in a desert society, situated not far from the equator, agricultural seasons are practically non-existent, and thus the very concept of keeping pace with the seasons of the solar year is of meager significance. The divine purity of the Islamic calendar echoes the divine purity of a desert society, unencumbered by the vicissitudes of the agricultural cycle and human endeavor.

In contrast with the divine purity of the solar calendar advocated by the Jews of Qumran, and in contrast with the divine purity of the lunar calendar ordained by God according to Islam, classical rabbinic Judaism seeks spiritual significance in the partnership between God and Israel implicit in the intercalated lunisolar calendar. In this sense, the calendar can be seen as a metaphor for the religious life in general: for rabbinic Jews, the spiritual life is not always about conforming to an ideal of divine purity – sometimes it is about striking a balance between ideals, in a human partnership with God. The sun and the moon are two ideals, two manifestations of the divine will, and both are meant to serve as “signs, ordained times, days and years” according to Genesis 1:14. It is up to Israel to find the balance between them, encountering the divine Presence in the process and proclaiming God’s glory.

For further reading, see Sacha Stern, Calendar and Community, Oxford 2001; idem., Calendars in Antiquity, Oxford 2012.


Prof. Moshe Benovitz is professor of Talmud and Halakhah at the Schechter Institute of Jewish Studies. He is the recipient of numerous prizes and fellowships and is author of three books and many articles including Kol Nidre: Studies in the Development of Rabbinic Votive Institutions. In addition he has published several volumes of comprehensive critical commentary on sections of the Talmud, as well as numerous scholarly articles on various aspects of Talmudic scholarship and rabbinic history, including oaths and vows, liturgy, and Jewish festivals.