They Ate Chametz On Pesach
‘Declared By A Beis Din Of Three’
(Sanhedrin 10b)
Until the era of Abaye and Rava of the Babylonian Talmud, the Sanhedrin in Eretz Yisrael would determine the beginning of each month according to witnesses who reported seeing the New Moon. Since then, our months and holidays are determined according to the calendar instituted by Hillel II in 4119 (357 C.E.). According to the Rambam (Hilchos Kiddush HaChodesh 5:2) it is a halacha handed down by Moshe from Mount Sinai that the calendar must be calculated mathematically in the absence of the Sanhedrin, whereas the Ramban (Hasagos to Sefer HaMitzvos, Mitzvah 153) goes even further and maintains that Hillel II declared and sanctified each eventual Rosh Chodesh in advance.
The Molad Factor
One of the rules instituted by Hillel II provides that Rosh Hashana should always coincide with the appearance of the New Moon, known as the molad (birth). The molad occurs every 29½ days, 44 minutes, and one chelek (or division – 1 chelek equals one hour divided by 1,080; one minute is 18 chalakim), when the moon, after disappearing, just began a new orbit around the earth. However, the rule that Rosh Hashana must coincide with the appearance of the New Moon has two limitations: a) The first day of Rosh Hashana must never fall on Sunday, Wednesday, or Friday. Should the molad occur on those days, the first day of Rosh Hashana is celebrated on the next day. b) If the molad occurs after midday, that day does not become Rosh Hashana (see Rambam, ibid. 7:2).
A Genizah Discovery
A far-reaching difference of opinion erupted in the era of Rabbeinu Saadya Gaon between 4681-84 (921-4 C.E.) but was unknown to modern historians until the discovery of the Genizah (storeroom of old books and documents) in Cairo. The rosh yeshiva in Eretz Yisrael was Rabbi Aharon ben Meir, descended from the original Nesiim and regarded as the primary Torah scholar in the country. He claimed that the rule of the molad occurring after midday was inexact and that it applied only if the molad occurred 642 chalakim or 35 minutes after midday. He asserted that he had received that tradition from his forefathers. Many tried to explain his reasoning, some insisting it was an error and some maintaining that it was an opinion rejected in the era of Hillel II (see Torah Sheleimah 8:9, and Aleh Yonah by Rabbi Yonah Merzbach).
A Major Controversy
In most years, the molad of Tishrei does not occur near midday, but in 4683 (923 C.E.) it occurred 237 chalakim after midday, and in the summer of 4681 (921 C.E.), Rabbi Aharon ben Meir had announced that he would determine the months of the next year according to his method. Rabbeinu Saadya Gaon was in Aleppo on his way from Eretz Yisrael to Babylonia when he heard about that decision, and pleaded with Rabbi Aharon ben Meir in a number of letters to change his opinion. The latter insisted steadfastly on his viewpoint, and on Hoshana Rabbah 4682, he announced on the Mount of Olives, where the Jews traditionally gathered and encircled, that Cheshvan and Kislev would have only 29 days.
The following Rosh Hashana would thus fall on Tuesday. However, according to the Babylonian calculation, Cheshvan and Kislev would have 30 days, with Rosh Hashana on Thursday. Meanwhile, Rabbeinu Saadya Gaon reached Babylonia and attacked Rabbi Aharon ben Meir’s approach with all his might.
“Fire” Breaks Out
Copies of his Sefer Zikaron Ledoros were sent to Jewish communities everywhere to prevent a division of the people but the fire of controversy broke out when most of the Jews in Eretz Yisrael changed the calendar to fit their leader’s system and ate chametz on the last two days of Pesach according to the Babylonian calendar.
Letters flew back and forth between Eretz Yisrael and Babylonia to convince the other side of the supposed truth. The letters discovered in the Cairo Genizah show that those in Eretz Yisrael claimed that the Nesiim replaced the Sanhedrin and were still allowed to determine the halacha of the calendar (see Nefesh Chayah 68, cited in Responsa Avnei Nezer, OrAch Chayyim 310).
Rabbi Aharon ben Meir, then, was assumed to be the only authority to determine the Jewish calendar. Those outside Eretz Yisrael insisted that Hillel II had been the last to institute these halachos and that the calendar could be regulated only according to his rules.
Rav Saadya Gaon Victorious
Rabbeinu Saadya Gaon became the rosh yeshiva at Sura and his opinion was eventually accepted all over, even in Eretz Yisrael. The tradition instituted by Hillel II persisted thanks to his efforts and, according to Rabbeinu Tam, “We live from the words of his mouth, as he handed the secret of the calendar down to us” (Shibbolei HaLekket 28).
