Eliezer Beilin and David Bar Ya’akov of Lomza. Sepher Ivronoth.

A comprehensive handbook and presentation of the astronomical and mathematical calculations required for determining the cycles of the Jewish calendar. The Jewish calendar is lunisolar - the months are reckoned by the moon and the year by the sun. The astronomical expertise required to make the necessary adjustments, mandated an interest by religious Jews in astronomy. This popular book first appeared in Basle, 1526. The Lublin 1640 edition contains corrections and additional material by David Bar Ya’akov of Lomza. The present manuscript contains the additional material both in the introduction (f. 2a-b) and throughout the text, explaining the various diagrams. The section “Luach HaChaga’oth” (ff. 33-36) notes the Christian holidays observed in Germany, Poland and Russia, as well as dates of the fairs and market days held throughout the year. Some of the towns and cities mentioned include: Cracow, Belz, Kalisch, Lissa, Leipnik, Nikolsberg and Mehzritch.