Letter on the Calendar Controversy

This Hebrew letter, preserved in the Cairo Geniza, contains instructions for scheduling Passover for the coming year based on the sighting of the new moon and other calculations. The calendar assumed by this letter is largely in agreement with the one used in Jewish communities today, but the document shows that the Jewish calendar had not yet been fully fixed at this point, and also that Palestinian authorities (referred to here as the ḥavurah and the ḥaverin, meaning “the fellows [of the Palestinian academy]”) remained in control of the calendar at least until the middle of the ninth century. The acronyms in the letter are shorthand for long-standing calendrical rules. First, lo BaDU Pesaḥ indicates that the first day of Passover (Pesaḥ) may not fall on the second (B), fourth (D), or sixth (U) day of the week. Similarly, lo GaHaZ ‘Atzeret says that the festival of Shemini Atzeret may not fall on the third (G), fifth (H), or seventh (Z) day of the week. Finally, lo ADU Rosh Hashanah indicates that Rosh Hashanah may not fall on the first (A), fourth (D), or sixth (U) day of the week. These rules were considered when determining the calendar for the year to come, which was done by declaring individual months longer or shorter by a day, or by adding an extra month. The “great festival of the Willow” is Hoshana Rabbah, which in the Middle Ages (and especially in Palestine) had paramount status.