R. Isaac ibn al-Aḥdab · c. 1396 (composed in Syracuse, Sicily; this is a later manuscript copy)
Read the translation (PDF) · Editorial footnotes (PDF)
A set of astronomical tables by Isaac ibn al-Aḥdab (Sicily, late 14th c.) for computing the true conjunctions and oppositions of the Sun and Moon — the Orah Selulah, “The Paved Way,” one of the most widely copied Hebrew astronomical table-works, surviving in some twenty-five manuscripts.
A short preface and a pair of opening gates explain the method; everything after that is table. The body is built from lunar and solar equation tables — the argument-correction tables (luaḥ ḥeq levanah) and double-entry equation tables that turn a mean position into a true one — laid out with rubricated headers in red so a user can find the right column at speed. A planetary-hours table sits among them.
The title is an argument in miniature. A conjunction or opposition can be computed from first principles, but the work is long and the chances of error many; a well-made table paves the way, so that the same result is reached by lookup and interpolation. What the book offers is not new astronomy but a smoothed road through it.
Conjunctions and oppositions are what the Hebrew calendar turns on — the molad governs the months, and eclipse prediction depends on the same quantities. That practical necessity is why table-works like this one were copied far more often than treatises: they were used. Twenty-five surviving manuscripts is a large number for a Hebrew scientific text, and it measures how thoroughly the Orah Selulah embedded itself in practice.
The translated witness is the colour manuscript BnF Hébreu 1086, composed in Syracuse around 1396 and copied later. Its front matter preserves the accidents of a working codex — guard leaves with pen-trials and jottings, a shelfmark on a blank flyleaf, a cataloguer’s leaf — before the incipit begins.