On Shemini Atzeret, we add in the Amida the prayer “mashib ha-ruach umorid ha-geshem”, praising HaShem for creating and directing the mechanism of precipitation (=rain). But we still refrain from asking HaShem to grant us the blessing of rain. Why?
ISRAEL
Once Shemini Atzeret ends, the rain season begins, and we should be asking God immediately for rain; our Chakhamim, however, postponed this request in remembrance of the days of the Bet haMiqdash. In those days, once the holidays were over, the people had to go back home, and for these Jews walking back home, rain would not have been a blessing. Some of them lived very far away, within the borders of ancient Babylonia, and it would take them up to 14 days to get home. And this is why in Israel, Jews start praying for rain two weeks after Shemini Atzeret, on the evening of the seventh of Cheshvan. We kept this tradition to remember the glorious days when our beautiful Temple was standing.
JEWISH DIASPORA
At the time this ruling was established, the Jews who lived outside of the Land of Israel did not need rain so early, so the Rabbis ruled that in Babylonia, the Jews would begin praying for rain on the 60th day of the season (tequfat) Tishri, or the “Hebrew calendar autumn”. The Rabbis gave a round number for determining the beginning of each Hebrew calendar season. A season consists of 91 days, 7 hours, and 30 minutes. This makes each year precisely 365 days and 6 hours long, about 11 minutes longer than the actual astronomical calculation of a solar year.
All Jews living outside of Israel, therefore, follow the practice of the Jews of Babylonia. Consequently, it has become a tradition for all Jews living in the Diaspora to ask for rain in their prayers, as the Babylonian Jews did. Based on this calculation, we start saying Barekh Alenu from December 5th at night.
