Tel Aviv study argues Qumran used its 364-day calendar until seasonal drift made it unusable

Run the shortfall out further than the release does. Fifty uncorrected years of a day-and-a-quarter deficit come to about 62 days ^[18]. Two months of slippage puts a spring festival in winter, which is roughly what Tel Aviv University describes after several decades of use ^[12]. The twenty-year case works out to 25 days exactly, which the release rounds up ^[17]. The community's festivals were bound to agriculture, harvests, first fruits and the seasonal cycle ^[13], so the error would have been visible in whether the crop was ready, as well as in the sky.

The obvious repair, inserting extra days, was the one adjustment this group had ruled out. Its members held that festival dates had been fixed by God at the Creation of the world and were not for human authorities to alter, which was their objection to the way the Temple in Jerusalem set dates ^[9]. They took the 52-week structure to reflect a perfect divine system ^[8].

For evidence that the calendar was more than a thought experiment, Prof. Eshbal Ratzon points to volume: nearly twenty of the scrolls found at Qumran deal with calendars and astronomy, an unusually large share ^[16]. That establishes how much the subject mattered to the community, and leaves open whether the 364-day year governed the working week. A day and a quarter a year makes a calendar unusable eventually. Two questions stay open: when the sect noticed, and which of the two pressures in the reconstruction ended the practice.

Tel Aviv University presents the sequence as a "proposed reconstruction," saying the sect "likely used the calendar during its early history" and that the system "may have been abandoned" later ^[19]. The abandonment is undated there ^[21]. Ratzon, of the Department of Jewish Philosophy and the Cohn Institute for the History and Philosophy of Science and Ideas, published the study in the Tarbiz Quarterly for Jewish Studies ^[5][6].