Jacob ben Samson (attrib.) · c. 1123 (composition; this is a later manuscript copy)
Read the translation (PDF) · Editorial footnotes (PDF)
An early Ashkenazi commentary on the “secret of the calendar” (sod ha-ibbur) — the computation of the Hebrew calendar: the molad (lunar conjunction), the tequfot (seasonal points), the nineteen-year intercalation cycle, and the rules governing leap years and festival dates.
The calendar is the subject, and the calendar in Jewish practice is an astronomical problem with legal consequences: the molad must be reckoned, the seasons tracked, the nineteen-year cycle of intercalation applied, and from those computations the dates of the festivals follow. The commentary works through that apparatus for a reader who needs to understand the reasoning rather than merely apply a rule.
Its manuscript context is part of the text’s character. The commentary does not stand alone but sits within a miscellany, and the surrounding leaves carry material of a quite different kind — a paytanic composition in numbered strophes, an admonition-poem, the text of the mezuzah with a scribal note on tefillin, blessings on seeing, the Wayfarer’s Prayer. The calendar science is embedded in a devotional compilation rather than isolated as a technical treatise.
Calendar computation was one of the few domains where medieval Ashkenazi scholarship engaged sustained mathematical astronomy, because the liturgical year could not be kept without it. This commentary is an early witness to how that knowledge was taught in northern France in the generation around Rashi — close to the world of the great Talmudic commentators, and showing what astronomy looked like when it was pursued inside it.
The attribution is to Jacob bar Samson, an early-twelfth-century French scholar of Rashi’s school and an early Ashkenazi authority on the calendar; the corpus entry marks it attrib. accordingly. The text survives within the North French Hebrew Miscellany (British Library Add MS 11639), copied in northern France in the late thirteenth century — so the manuscript translated here is roughly a century and a half later than the composition, and the translation follows folios 511r–545v of that codex.