Calendrical Cycle

In this brief Judeo-Arabic calendar manual, preserved in the Cairo Geniza, Josiah al-‘Aqūlī presents one of the earliest accounts of the 247-year calendar. The Jewish calendar addresses the discrepancy between the lunar and solar years by adding an extra month in thirteen out of nineteen years. In addition, two months can be either “defective” with twenty-nine days or “full” with thirty days. Here, Josiah tells his readers to subtract 1,000 from the Seleucid era (termed the “years of Alexander”) and then to subtract (“cast out”) all multiples of 247 from that sum. The remainder then corresponds to a number in his chart; the sequence starts with “15, 42 . . .” The chart then indicates whether a year will be “defective,” with two months of twenty-nine days, or “plain”—that is, with no extra month. The “sign” summarizes the information. Here it is referred to as bet-ḥet-gimel, which indicates that Rosh Hashanah will be on Monday, the second day (bet) of the week, the months are defective (ḥet for ḥaserim, “defective”), and Passover will be on Tuesday, the third (gimel) day of the week. Finally, it tells the reader upon which days the various holidays will fall. Until the discovery of this text, the detailed 247-year cycle was only known from Judeo-Persian texts, where it was called dūlābī, “waterwheel-like.”