Daily Halacha Wednesday 30th Tishreiy: The Clash That Nearly Split the Jewish World: The Rasag–Ben Meir Calendar Controversy

The dispute of Rav Sadya Gaon [Rasag] and Rebbe Ahron Ben Meir of Eretz Yisrael:[1]

The history of the Jewish calendar is as much a story of astronomical precision as it is of profound communal significance. In the tenth century, a dramatic dispute arose between two towering rabbinic figures—Rav Sadya Gaon (Rasag) of Babylon and Rebbe Ahron Ben Meir of Eretz Yisrael—over the seemingly technical question of the Molad Zakein, the “old Molad.” Yet, beneath this debate lay critical questions about religious authority, tradition, and the unity of the Jewish people. The controversy threatened not only the synchrony of holiday observance, but also the very fabric of Jewish communal life, as different communities risked celebrating Rosh Hashanah and Pesach on divergent dates. Drawing upon rare correspondence and centuries-old sources, this article explores the origins, details, and lasting impact of the Rasag–Ben Meir dispute. It aims to shed light on the technicalities of the Jewish calendar, the passionate arguments that defined this chapter in Jewish history, and the ultimate resolution that ensured the continued unity of Jewish practice.

A. Background concepts and laws:

Molad Zakein:[2] Molad Zakein literally means the old Molad. This refers to when the Molad falls between midday and night of a given day, which is approximately the last six hours of the day. It is called an old Molad because it is falling at the latest possible opportunity of that date. The Molad Zakein has special significance in the calendar of today, as although in general we try to set the day of Rosh Chodesh on the day of the Molad [if it falls on a permissible day], nevertheless this only applies if the Molad falls prior to midday. If, however, the Molad falls after midday, then we differ Rosh Chodesh until the next day. In other words, we do not set Rosh Chodesh on the day of a Molad Zakein even if it is a day that is permitted to have Rosh Chodesh fall on.[3] [The above rule of Molad Zakein only applies to the month of Tishrei, as once we have set the date of Rosh Chodesh Tishrei, we follow from there a set order of Malei and Chaseir, as explained in the previous Halacha.] The debate we are about to learn centers on the exact definition of a Molad Zakein, regarding how much time after midday it must fall.

Days on which Rosh Hashanah will never fall:[4] The Sages established that Rosh Hashanah, which is Rosh Chodesh Tishrei, cannot fall out on certain days of the week even if the Molad is on that day. It cannot fall on Sunday, Wednesday or Friday. In the event that the Molad falls on one of these days, Rosh Chodesh is pushed off a further day.[5] Some Rishonim[6] explain the reason for the avoidance of the above weekdays is because doing so would cause Yom Kippur to fall a day before or a day after Shabbos and they did not want there to be two consecutive days of prohibited food preparation. Likewise, they did not want Hoshana Rabbah to fall on Shabbos which would nullify the Mitzvah of Arava. The Rambam[7] however explains the reason this is done is in order to have Rosh Chodesh fall on the Cheshbon Haamiti of when the moon will be seen and not on the Molad, which is the Cheshbon Haemtzai. This decree effected that the Rosh Chodesh of every month cannot fall on certain days, as once we force Rosh Chodesh Tishrei to only fall on certain days, and the remaining months follow an automatic pattern of Malei and Chaseir, it effects that every Rosh Chodesh has only certain days on which it can fall. Practically, the following are the dates in which Rosh Chodesh can and cannot fall on:

B. The debate:

In the times of Rav Sadya Gaon [882-942] erupted one of the most infamous disputes with regards to the Jewish calendar that threatened a catastrophic split amongst the Jewish people regarding the dates of Rosh Chodesh and the subsequent Holidays. The precise date of the debate was in year 921 [4682] and impacted the years 921-924. If, Heaven forefend, this dispute would not have come to a closure there would be different dates in which Jews celebrated the new months and the Holidays; while one Jew would celebrate Rosh Hashanah on Monday, another might celebrate Rosh Hashanah on Tuesday, depending on which opinion in the debate he decided to follow. The debate threatened to end the consensus of all Jewry as to the dates of Rosh Chodesh and the Holidays. What was the topic of debate? The debate surrounded the day of Rosh Hashanah and as to when on the calendar it is to be set. Earlier we explained that Rosh Hashanah cannot fall on certain days of the week and likewise cannot fall on the Molad Zakein. These matters are not up for debate and had consensus of all Jewry. What was debatable however was the precise definition of the Molad Zakein. How long after midday is a Molad considered a Molad Zakein which causes Rosh Hashanah to be differed to the next day? This was the subject of debate between Rav Sadya Gaon and Ben Meir. We will attempt here to give a general summary of this debate:

1. The position of Rav Sadya Gaon [Rasag]:

Rav Sadya Gaon [i.e. Rasag] was the leading Rabbinical figure of Bavel in the 900’s and was considered the absolute leader of Babylonian Jewry together with the Rosh Galusa, Ben Zakaiy. The Rasag held, as did most of Jewry, that a Molad Zakein begins immediately after midday, which is 18 hours from the previous night. This means that if the Molad of Tishrei falls prior to midday [18 hours into that day] then Rosh Hashanah is to be set on the day of the Molad. If however it falls after midday then the concept of Molad Zakein is in effect and Rosh Hashanah is delayed until the next day. [See Halacha G!]

The year of debate: In the year 923/4684 the Molad fell on Shabbos, 237 Chalakim [13 minutes] after midday. According to the Rasag, due to the Molad Zakein, Rosh Hashanah had to be pushed to Monday. In order to organize the calendar accordingly, the year 921/4682 had to be a Shleima [with 30 days in both Cheshvan and Kisleiv]. This caused Pesach of 4682 to fall on Tuesday.

1. The position of Ben Meir:

Rav Ahron Ben Meir was the leading Rabbinical figure of Eretz Yisrael in the 900’s. He held a tradition that a Molad Zakein only begins 642 Chalakim after midday, which is 35.5 minutes after midday. This means that if the Molad of Tishrei falls prior to 35.5 minutes after midday [18 hours and 35.5 minutes into that day] then Rosh Hashanah is to be set on the day of the Molad. If, however, it falls after the 35.5 minutes after midday then the concept of Molad Zakein is in effect and Rosh Hashanah is delayed until the next day. The Rasag argued that there is no basis in our tradition for the opinion of Ben Meir, and so was held by the majority of Jewry. Ben Meir however countered that he was the leader of Eretz Yisrael and the setting of the new month was given only to the Sages of Eretz Yisrael and hence the Rasag has no right to argue on his ruling.

The year of debate: In the year 923/4684 the Molad fell on Shabbos, 237 Chalakim [13 minutes] after midday. According to Ben Meir, due to it not being considered a Molad Zakein in his opinion, Rosh Hashanah would be on Shabbos, two days earlier than the Rosh Hashanah of the Rasag. Now, in order to organize the calendar accordingly, the year 921/4682 had to be a Chaseira [with 29 days in both Cheshvan and Kisleiv]. This caused Pesach of 4682 to fall on Sunday.

1. The outcome of the debate:

During the year of the debate in 921/4682 the residents of Bavel and majority of the Diaspora celebrated Pesach on Tuesday, as directed the Rasag, while the residents of Eretz Yisrael celebrated Pesach on Sunday as directed Ben Meir. This threatened to split the global Jewish community and confuse the dates of all the holidays. The Sages of Bavel implored Ben Meir to retract his position in face of the great calamity this would befall the Jewish people, although to avail. Ben Meir wrote counter arguments and vehemently argued that it is the Rasag who has to back down from his position, as he was the leader of Eretz Yisrael and held the sole jurisdiction in the matter of the Luach. Ben Meir viewed the Rasag as the sole person responsible for the dispute and the great calamity that it threatened. Seeing that Ben Meir would not back down, the camp of the Rasag then went on to a worldwide campaign to convince world Jewry to reject the position of Ben Meir and so it was that even the Sages of Eretz Yisrael adapted the ruling of the Rasag. This dispute came to end by the year 4684, as by that year even the residents of Eretz Yisrael adapted the ruling of the Rasag and this is the final ruling today which we follow in our calendar.

[1] Based on the correspondence of letters between the Rasag and Ben Meir recently discovered in Geniza Mitzrayim and published in the Sefer “Hamachlokes” of Rav Chaim Yechiel Borenshtein [Poland 1904, author of Simas Ayin]; Torah Shleima 13:9

[2] Rambam ibid 7:2; See Torah Sheleima ibid 8:2 [p. 114-115]; Understanding the Jewish Calendar chapter 10

[3] The reason: See Torah Sheleima ibid for various reasons given behind this deferral.

[4] Michaber 428:1-3; Rambam Kiddush Hachodesh 7

[5] Rambam ibid 7:1

[6] Raavad 7:7

[7] Rambam ibid 7:7