On the 364-day solar calendar

CALENDAR MYSTERY: Dead Sea Scrolls mystery: Qumran’s 364-day calendar may have been real, until it failed. Tel Aviv University study argues the calendar was not only a religious ideal but was used by the sect in its early years, before seasonal drift and political changes made it impractical (YNet News).

The study suggests that the calendar was indeed used in practice during the sect’s early period and even stood at the heart of the dispute that led to its separation from the Jerusalem religious establishment. Over time, however, the calendar was abandoned because of a built-in flaw that made it impossible to maintain and because of political changes that brought the sect closer to the Hasmonean leadership under Alexander Jannaeus.

The study was conducted by Prof. Eshbal Ratzon of Tel Aviv University’s Department of Jewish Philosophy and its Cohn Institute for the History and Philosophy of Science and Ideas. It was published in the journal Tarbiz.

The article is publsihed in Tarbiz 91.1-2 (2026). Tarbiz is a Hebrew journal that seems to be available only in print form.

Whether anyone actually used the Jewish 364-day solar calendar is an old problem. I have touched on it occasionally over the years, notably here (especially), here, here, here, here, and here. I have not read this Tarbiz article, but Prof. Ratzon's case as summarized in the YNet article seems plausible. I doubt we will ever know for sure.

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