The Jewish festivals and calendar

The calendrical substrate of the Torah rests on two complementary poles: the seven-day week, crowned by Shabbat, and the lunar cycle, whose new moon (Rosh Hodesh, ראש חודש) inaugurates each month. Genesis (1, 14) presents the stars as "signs for the festivals, the days and the years," conferring on time an immediately religious dimension. Leviticus (chap. 23), which constitutes the first great "liturgical calendar" of the Hebrew Bible, enumerates the festivals in their annual order: Shabbat, Pessah and Matsot, the festival of firstfruits (Bikkourim), Rosh Hashana, Yom Kippur, then Sukkot and Shemini Atzeret.

The Hebrew Bible designates the month of Nisan (Aviv) as the "first of the months" (Exodus 12, 2), making the Exodus from Egypt the founding event that reconfigures time itself. Pessah (פֶּסַח) celebrates this liberation each year on the 14th of Nisan, while commemorating the offering of the Paschal lamb and the march toward freedom. The festival of Shavuot (שָׁבוּעוֹת), counted seven weeks after Pessah, first celebrated the firstfruits of the harvest, before being interpreted by rabbinic tradition as the day of the giving of the Torah at Sinai. Sukkot (סוּכּוֹת), in autumn, recalls the forty years of wandering in the wilderness and closes the agricultural season.

These so-called "pilgrimage festivals" (Shalosh Regalim, שָׁלוֹשׁ רְגָלִים) — Pessah, Shavuot and Sukkot — required every male Israelite to "appear before the Lord" at the Temple in Jerusalem (Exodus 23, 14-17; Deuteronomy 16). They thus articulated agricultural festival, historical memory and sacred space in a single liturgical gesture. The biblical calendar is therefore simultaneously cosmological, agricultural and memorial: it inscribes the community in a double rhythm, that of the seasons and that of the history of salvation.

The Hebrew calendar is a lunisolar calendar: its months follow the cycle of the moon, while the year remains anchored in the solar cycle so that Passover always falls in spring, in accordance with the biblical prescription (hag ha-aviv, "feast of spring"). This double constraint — lunar months of 29 or 30 days, solar year of approximately 365.25 days — creates an annual discrepancy of about eleven days, which would accumulate inexorably if a thirteenth month were not periodically intercalated.

The Hebrew calendar is a lunisolar calendar composed of solar years, lunar months, and weeks of seven days beginning on Sunday and ending on Saturday, the day of Shabbat. The solution adopted by Jewish tradition is the Metonic cycle, named after the Greek astronomer, but whose use predates him in the Near Eastern world: a cycle of nineteen years during which seven years contain an additional month — Adar II (אֲדָר ב׳) — intercalated before Nisan. This system makes it possible to reconcile, with remarkable precision, the lunar cycle and the solar cycle.

In biblical times and throughout the entire Second Temple period, the beginning of each month was proclaimed by the Sanhedrin of Jerusalem on the basis of the testimony of two eyewitnesses who had seen the crescent of the new moon. Signal fires lit from hill to hill, then messengers, subsequently propagated the information to the diaspora communities. This living system, founded on direct observation, nevertheless had a structural fragility: Jews far from Jerusalem risked not receiving the information in time. This is why the diaspora developed the habit of celebrating a yom tov sheni (יוֹם טוֹב שֵׁנִי), a second day of festival, as a precaution — a practice preserved to this day in diaspora communities for biblical festivals, although the calendar is now calculated rather than observed.

In 358 of the Common Era, Rabbi Hillel II established a fixed system of calculation based on mathematical formulas to determine the new moon and thus fix the dates of the months and religious festivals, making direct observation unnecessary. This decisive reform, which took place in a context of persecutions making public assembly of the Sanhedrin dangerous, fixed the Hebrew calendar in the arithmetic form it has maintained since then. The era of the creation of the world (Anno Mundi, אַנְנוֹ מוּנְדִי), in which year 1 corresponds to Sunday, 6 September 3761 before the Common Era, thus became the universal anchor point of Jewish reckoning.

The ordinary Hebrew year contains 353, 354 or 355 days; the embolismic year (with Adar II) contains 383, 384 or 385. This variability is not a matter of chance: it responds to the rules known as the dechiyyot (דְּחִיּוֹת), "postponements," which prevent Rosh Hashana from falling on certain days of the week, notably Sunday, Wednesday or Friday, in order to avoid liturgical conflicts between Yom Kippur and Shabbat.

Among the many sources of tension that traversed Judaism during the Second Temple period, the question of the calendar was one of the most intense and structuring. The Manuscripts of the Dead Sea, discovered from 1947 onward in caves overlooking the site of Khirbet Qumrân, reveal that a community — long identified with the Essenes — had adopted a calendar system radically different from the lunisolar calendar in use at the Temple of Jerusalem: a solar calendar of 364 days.

Nearly twenty of the scrolls found at Qumrân deal with calendars and astronomy, attesting to the capital importance the community accorded to this question. This 364-day calendar — a number perfectly divisible by seven — guaranteed that each festival always fell on the same day of the week from year to year. Pessah, for example, invariably arrived on a Wednesday. This regularity was not merely a practical advantage: it meant that the divine order of time was perfect, immutable, removed from the contingency of human observation of the moon.

The Book of Jubilees, a central apocryphal text in the Qumrân library, vigorously attacks the dominant lunar calendar and presents the 364-day solar calendar as the "original calendar" received by Moses on Sinai. For the Qumrân sect, this calendar reflected the perfect divine order; it was also a symbol of rebellion against the political and religious leadership of Jerusalem, which determined the important dates of Jewish life.

This system nevertheless presented a fatal flaw: a year of 364 days runs behind the actual solar year by 1.25 days annually. Within a few decades, the Qumrân festivals would have drifted out of their natural seasons. For decades, scholars debated whether this defective calendar had ever been used in practice. Some suggested that the sect had periodically added days or weeks, while others believed that this calendar had never been used in the real world, serving only as a theoretical framework.

It is to this academic controversy, now more than half a century old, that Professor Eshbal Ratzon of Tel Aviv University brings an answer in 2026, in a study published in the peer-reviewed journal Tarbiz. Her conclusion resolves a debate that has divided Qumrân specialists since the 1950s, and she does so by taking seriously something that earlier researchers had dismissed. According to Ratzon, the 364-day calendar was indeed used by the community in its early years, in the 2nd century before the Common Era. It would then have been gradually abandoned as its cumulative drift from the seasons became untenable — an abandonment facilitated by a new political context: the rapprochement between the sect and the Hasmonean dynasty under Alexander Jannaeus. This shift would have allowed the community to return to the practical calendar of the Temple, while preserving the 364-day calendar as a valid theoretical concept at the time of Creation, capable of being restored at the end of times.

This study, widely reported in mid-July 2026 by the Jerusalem Post, the Times of Israel, JNS, and Archaeology Wiki, does not rest on the discovery of new archaeological materials, but on a historiographical reevaluation of documents long known [study by Eshbal Ratzon, Tarbiz, 2026, reported by the Jerusalem Post].

The three pilgrimage festivals constitute the backbone of the Jewish liturgical calendar. Each articulates several layers of meaning — agrarian, historical, eschatological — that have accumulated over the centuries like sediment.

Pessah (פֶּסַח) — "Passover". Celebrated from the 15th to the 21st (or 22nd in the Diaspora) of Nisan, it commemorates the Exodus from Egypt. The Seder meal (seder, "order"), organized according to the rite of the Haggadah, is its living heart: one recites, sings, discusses and eats symbolic foods — unleavened bread (matsa), bitter herbs (maror), haroset — while actualizing the memory of slavery and liberation. The prohibition of hamets (leaven) throughout the entire week imposes a complete transformation of dishes and diet, making Pessah the festival that most profoundly reconfigures domestic life. Rabbinic tradition progressively elaborated the Seder as a night of transmission par excellence: "In each generation, each person is duty-bound to regard oneself as if one had personally gone out from Egypt" (Haggadah).

Chavouot (שָׁבוּעוֹת) — "the Weeks". Fifty days after Pessah (whence the Greek name "Pentecost"), this festival marks the conclusion of the sefirat ha-omer (ספירת העומר), the count of forty-nine days begun on the evening of the 16th of Nisan. Biblically an agricultural festival of the first fruits of wheat, it was interpreted very early by rabbinic Judaism as the day of the revelation of the Torah at Sinai — a synthesis that makes it the festival of the Book and the Covenant. The custom of studying all night (tikkoun leïl Chavouot) became established from the sixteenth century onward, notably under the influence of the Kabbalist masters of Safed.

Souccot (סוּכּוֹת) — "the Booths". From the 15th to the 21st of Tishri, families construct and inhabit a succa (a booth with a vegetable roof that allows the stars to be seen), recalling the precarious shelters of the forty years in the desert. The four plant species (arba minim) — lulav (palm), etrog (citron), hadass (myrtle), aravah (willow) — are waved ritually each morning in the synagogue. The festival closes with Shemini Atseret and Simhat Torah, a day of joy on which one concludes and recommences the annual cycle of Torah reading. Souccot is designated in the Bible as the "festival" par excellence (he-hag), a sign of its centrality in the ancient calendar.

If the Shalosh Regalim are festivals of collective joy and pilgrimage, the first ten days of Tishri constitute what the liturgy calls the Yamim Noraïm (יָמִים נוֹרָאִים), the "awesome days" or "days of awe": a period of inner reckoning, repentance (teshouva) and divine judgment.

Rosh Hashana (ראש הַשָּׁנָה), the 1st of Tishri, is the Hebrew "New Year," but also, in rabbinic theology, the "Day of Judgment" (Yom ha-Din) and the "Day of Remembrance" (Yom ha-Zikaron). The Talmud (Rosh Hashana 16b) teaches that three books open on this day: that of the perfectly righteous, that of the wicked, and that of the intermediate—whose fate hangs in the balance until Yom Kippour. The sounding of the shofar (ram's horn) is the central rite of the festival: one hundred blasts (according to Ashkenazi practice) divided into tekia, shevarim and terua each call to spiritual awakening. Rosh Hashana is biblically designated as "day of the blowing of the trumpet" (Yom Terua, Numbers 29, 1) and does not yet bear in the Torah the name of New Year, a title that rabbinic development would confer upon it.

Yom Kippour (יוֹם כִּפּוּר), the 10th of Tishri, is the "Day of Atonement," unique in the calendar for its absolute character: a fast of twenty-five hours, five prayers, prohibition of bathing, perfume, leather shoes and conjugal relations. It was the only day of the year when the High Priest entered the Holy of Holies to perform the rite of the scapegoat (Azazel) described in Leviticus (chap. 16). After the destruction of the Temple in 70 of the Common Era, Yom Kippour was entirely refounded in collective prayer, notably around the Kol Nidré—a formula for the annulment of vows sung on the evening of the festival's beginning, whose melody has become one of the most recognizable in all of Jewish liturgy.

The ten days separating Rosh Hashana from Yom Kippour (Asseret Yemei Teshouva) are devoted to reconciliation with others: tradition teaches that God cannot forgive offenses committed against one's neighbor until the victim himself has granted forgiveness.

To the biblical festivals, rabbinic tradition added celebrations instituted in remembrance of historical events after the closure of the Pentateuch. These festivals do not have the status of mitzvot of the Torah, but their observance is deeply rooted in collective identity.

Hanukkah (חֲנֻכָּה), "inauguration," lasts eight days beginning on the 25th of Kislev (November–December). It commemorates the revolt of the Maccabees against the forced Hellenization attempt of Antiochus IV Epiphanes (175–164 before the common era) and the rededication of the Temple of Jerusalem. Its central rite is the lighting of the menorah (eight-branched candelabrum plus the shamash), which recalls the miracle of the oil: according to the Talmud (Shabbat 21b), a flask of pure oil, sufficient for a single day, is said to have fueled the great candelabrum of the Temple for eight days. Hanukkah, a minor festival in the halakhic hierarchy, has acquired considerable cultural visibility in diaspora contexts, particularly due to its calendrical proximity to Christmas.

Purim (פּוּרִים), on the 14th of Adar, commemorates the deliverance of the Jews of Persia recounted in the Book of Esther. The festival is characterized by a festive inversion typical of carnival cultures: the reading of the Megillah (scroll of Esther) accompanied by noise and whistling at the name of Haman, costumes, mishloach manot (sending of food gifts) and feasting. The Talmud (Megillah 7b) even permits an intoxication such that one can no longer distinguish Mordecai from the cursed Haman — a unique liturgical license in rabbinic law. Purim in Jerusalem, a city surrounded by ramparts in the time of Joshua according to tradition, is celebrated on the 15th of Adar (Shushan Purim).

Tisha be-Av (תִּשְׁעָה בְּאָב), the 9th of the month of Av, is the great day of mourning in the Jewish calendar. It commemorates the destruction of the First Temple (586 before the common era) and the Second Temple (70 of the common era), to which rabbinic tradition has added other national catastrophes: the fall of Betar (135 of the common era), the expulsion of Jews from Spain (1492), and others still. The fast of twenty-five hours is accompanied by the reading of the Lamentations (Eikha) and kinot (elegies), creating a liturgy of collective mourning without equivalent in the calendar.

The founding of the State of Israel in 1948 gave the Hebrew calendar a civic dimension unprecedented since Antiquity. The Hebrew calendar is used to calculate the dates of religious festivals, and it begins year one at the supposed date of the creation of the world (Anno Mundi); throughout the world, including in Israel, Jewish communities use the Gregorian calendar as their civil calendar.

The State of Israel integrated into the official calendar several days of modern Memory: Yom ha-Shoah (27 Nisan), dedicated to remembrance of the Shoah and the resisters; Yom ha-Zikaron (4 Iyar), a day of remembrance for fallen soldiers and victims of terrorism; Yom ha-Atsmaout (5 Iyar), Independence Day. These three consecutive dates form a deliberate emotional and narrative sequence: from mourning the destruction to the proclamation of national rebirth.

In diaspora communities, the Jewish calendar continues to structure collective life, but selectively and sometimes negotiated with the civil calendar: the major festivals — Rosh Hashana, Yom Kippour, Pessah — remain strong identity markers even for non-observant Jews, while festivals such as Tisha be-Av or minor fasts (Guedalia, Esther, Tamouz, Tevet) are less universally observed. The question of yom tov sheni, the second day of festival in the diaspora, remains a point of debate among different religious sensibilities: Orthodoxy maintains it, while the Conservative movement accepts in certain contexts its suppression, and the Reform movement has largely abandoned it.

The relationship to liturgical time has also been profoundly reconfigured by the Shoah. Entire communities that marked the seasons according to the Hebrew calendar were annihilated. The reconstruction of Jewish life after 1945 made it imperative to take up this calendar again, to live it anew — an act of resistance as much as of fidelity. Poets like Paul Celan, theologians like Emil Fackenheim reflected on the way in which the Memory of genocide inscribes itself in — and sometimes against — traditional sacred temporality.

Hillel II (c. 320 – c. 385 CE) — Patriarch (Nassi) of the Jewish community in Palestine, he established in 358 CE a fixed system of calculation based on mathematical formulas to determine the new moon and set the dates of religious festivals, rendering obsolete the procedure of visual observation of the crescent. This reform, occurring in a context of decline in the authority of the Patriarchate and increasing Roman persecutions, fixed the Hebrew calendar in the arithmetic form it has retained to this day. Hillel II is thus the father of the Jewish calendar as it is practiced throughout the world. Sources on his life remain scarce, and his exact biography remains partially conjectural.

Eshbal Ratzon (dates unknown, active researcher in 2026) — Professor in the Department of Jewish Philosophy and at the Cohn Institute for the History and Philosophy of Science and Ideas at Tel Aviv University, she is one of the most recognized contemporary specialists in ancient Jewish calendars. Her study published in 2026 in the journal Tarbiz on the 364-day calendar of the Qumran sect reopened an academic debate that had lain dormant for several decades, proposing that this solar calendar, long held to be purely theoretical, was indeed used in practice by the community in its early years before being gradually abandoned under Hasmonean influence. [study by Eshbal Ratzon, Tarbiz, 2026, reported by the Jerusalem Post]

Rabbi Yohanan ben Zakkaï (c. 30 BCE – c. 90 CE) — Founding figure of Rabbinic Judaism after the destruction of the Second Temple, he is, according to Talmudic tradition, the one who obtained from Vespasian permission to found the academy of Yavneh. Without the Temple and its rites, Yohanan ben Zakkaï undertook a complete refoundation of the liturgical calendar: the shofar had to be sounded thereafter in the synagogue on the days of Rosh Hashana falling on a Shabbat, something that had been reserved for the Temple alone; the four species of Sukkot were taken for seven days, as in the Temple. These halakhic decisions allowed the festive calendar to survive the catastrophe of 70 CE.

Maimonides — Rabbi Moses ben Maimon, RaMBaM (1138–1204) — Great codifier of medieval Jewish law, he devoted an entire section of his Mishneh Torah (Hilkhot Kiddush ha-Hodesh, "Laws of the Sanctification of the Month") to a rigorous exposition, both halakhic and astronomical, of the Hebrew calendar, including the calculation of the new moon, the rules of intercalation and the history of the transition from visual observation to fixed calculation. His treatise remains a fundamental reference for the theoretical and practical understanding of the Jewish calendar.

Shalom Spiegel (1899–1984) — American-Israeli scholar, professor at the Jewish Theological Seminary in New York, author notably of The Last Trial (Akedah), he was among the first to study scientifically the liturgy of the Yamim Noraïm and the piyyutim (liturgical poems) of ancient times associated with Rosh Hashana and Yom Kippur. His work shed light on the depth and complexity of the poetic layers that compose the liturgy of the Days of Awe.

The Jewish calendar is not a simple instrument for measuring time: it is a lived theology, an architecture of Memory, and a political act. From the oral proclamation of the new moon by the Sanhedrin to the algebraic formulas of Hillel II; from the solar calendar of Qumran — emblem of radical dissidence against the Temple — to the lunisolar rabbinical system that traversed two millennia of diaspora; from the biblical Shalosh Regalim to the days of modern memory established by the State of Israel, the question of sacred time has always been inseparable from the question of identity, authority, and transmission.

The study by Professor Ratzon published in 2026 reminds us with striking force that this calendar is also not an inert object: ancient sources continue to reveal their complexity as historiographical tools become more refined. The debate over the actual practice of the Qumran calendar — used, then abandoned, then preserved as an eschatological horizon — illustrates how a community can simultaneously inhabit two times: the time of the world as it is, and time as it should be. This tension between the ideal and the practicable, between the perfection of divine order and the contingency of human history, lies at the very heart of the Jewish relationship to time.

In each generation, the festivals of the Hebrew calendar accomplish what the liturgy of Pesach formulates most clearly: they make present what was, they anticipate what must come, they transform Memory into a living obligation.