Hebrew Calendar
A 3,500-year continuous lunisolar calendar. The religious year begins with Nisan in remembrance of the Exodus from Egypt; the civil year begins with Tishrei in remembrance of Creation. The shift from observation to calculation in 358 CE; every month begins with the new crescent, every seventh day with rest, every seventh year with the rest of the land, every fiftieth year with a full reset, a mathematical map of sacred time.
Why This Reconstruction?
The Hebrew calendar is the oldest calendar system of the ancient world still in living use. While Mesopotamia's cuneiform tablets, Egypt's stone walls, and the Greek parapegma sit in museums, the Hebrew calendar rhythms the daily lives of roughly 15 million people worldwide. Shabbat still begins on Friday evening, Pesach is still celebrated on the 15th of Nisan, Yom Kippur is still the longest fast on the 10th of Tishrei. An ancient calendar, a modern life.
Moreover, this calendar fuses three distinct strata of time into a single system: the Moon (each month begins with the new crescent, 29 or 30 days), the Sun (Pesach must always fall in spring each year), and the Week (every seventh day is Shabbat). Unlike Egypt's strict solar reckoning, Babylon's pure lunisolar system, or Islam's purely lunar one, it harmonises three astronomical cycles within a seven-tiered mathematics. This is the most complex calendrical engineering of the ancient world.
But the matter is not mathematics alone. The Hebrew calendar is an expression of a theology of sacred time. Rest on the seventh day (Shabbat), rest of the land on the seventh year (Shemitah), and after seven times seven years, the Yovel (a full reset in the fiftieth year, manumission of slaves and restoration of lands to their original owners). The cosmic repetition of the number seven across seven months, seven days, seven years, and seven-times-seven years; the mathematical rhythm of the cosmos bound to socio-economic justice. No other calendar system in the ancient world has established so comprehensive a sacred-time ethic.
This tool unfolds that system in sequence. For the Hebrew year you select, the 12 months (13 in leap years) are laid out; for each month you see its Babylonian-derived name, its older Canaanite/biblical name (Aviv, Ziv, Eitanim, Bul), its season, agricultural cycle, attendant festivals and significant days. The Three Pilgrimage Festivals (Pesach, Shavuot, Sukkot) and Yamim Noraim (Rosh Hashanah, Yom Kippur, and the Days of Repentance between them) are treated in their own sections. The Shemitah and Yovel cycles are explained; Hillel II's reform (the shift from observation to calculation, 358 CE) and the Metonic mathematics behind it are demonstrated. The Gezer Calendar (10th century BCE, the oldest known Hebrew inscription) is presented as archaeological evidence of the agricultural-calendrical weave.
There is no outward grandeur of Babylon, no monumentality of Egypt, no philosophy of Greece, no law of Rome here. Instead, there is living time: a cosmological system that pauses every seven days, returns to its land every seven years, and resets every fifty years. The Hebrew calendar is the most enduring fragment of the ancient world, and it is still speaking.
Year Selector
The Hebrew year (Anno Mundi, AM) and its position in the 19-year Metonic cycle. Tishrei 1 and Nisan 1 are computed from the molad and the four dehiyyot, following the arithmetic system fixed by Hillel II in 358 CE. AM 1, in Jewish tradition, is the year of Creation (3761 BCE).
The Dual New Year System
A distinctive feature of the Hebrew calendar: two separate beginnings within the same year. The Mishnah (ca. 200 CE) in fact recognises four new years; two of them are central.