beitzah

Beitzah (Hebrew: ביצה, "egg") is a tractate of the Mishnah and the Talmud in the order Moed. It is named Beitzah and is principally concerned with the laws of Jewish festivals and the calendar. The tractate surveys how months and holidays were determined in the Temple period, focusing on the process by which the new moon and month were declared, and the practical implications for holiday observance.

A central theme is calendrical calculation and uncertainty, including the methods used to fix months and the implications for when holidays occur. One well-known consequence discussed in Beitzah is the practice of observing two days of Yom Tov in the Diaspora, a safeguard against possibly miscalculating the calendar. The discussions also touch on the relationship between different festival days, the boundaries of appropriate holiday observance, and related legal rulings that affect how holidays are celebrated.

Beitzah exists in the Mishnah and is elaborated in the Babylonian Talmud and the Jerusalem Talmud. It has been a subject of extensive medieval and contemporary rabbinic commentary, contributing to the broader rabbinic understanding of festival law and calendar theory. The tractate’s name, meaning "egg," is traditional and tied to its early calendrical discussions, but the work covers a wider range of holiday-related legal issues. Beitzah remains a foundational source for Jewish festival practice and the historical development of calendar calculation in rabbinic Judaism.