Finding it difficult to fast on Yom Kippur? What do you think about the fact that in ancient times, some people fasted for two days? The foundation for this extraordinary and nearly incomprehensible practice stems from the fact that Jews living outside the Land of Israel didn't always know when the Hebrew month started.
The individuals who established the starting date of a Hebrew month were members of the Jewish court residing in the Land of Israel, first in Jerusalem and later in the town of Yavneh after its destruction. This situation led to many regions in the Jewish world being uncertain whether a new month had already been declared in the Land of Israel or if the declaration was delayed by one day. This situation evolved because they needed to wait for two witnesses to testify about it.
Due to this reason, Jews throughout the world continue to observe holidays twice to this day. Passover Seder is observed for two nights, Shavuot is observed for two days, and so forth. This became an established and obligatory practice despite the fact that nowadays the procedure for establishing months in the Hebrew calendar is predetermined and not decided based on witness testimony.
The Yom Kippur exception
The doubling that developed from communication gaps should theoretically have affected Yom Kippur too, as it wasn't clear when the court declared Rosh Chodesh Tishrei. Yet here, authorities determined not to require the community to fast two days, partly since this was a religious requirement that obviously most Jews couldn't meet, and also because it presents life-threatening risks.
However, every principle has its exceptions. Such a person was the Babylonian Amora Rava, who strictly fasted on the 10th day of Tishrei and the 11th, fearing that the month's declaration was delayed by a day in the Land of Israel. The Amora Bar Avuy of Shmuel bar Rav Yitzchak likewise fasted two days, though his body couldn't endure it, and in one year this practice caused his death.
Either way, theoretically, once the Hebrew calendar was finalized and people stopped waiting for the court's decision in the Land of Israel, there was no reasonable justification to fast two days, as it was evident when Yom Kippur occurred. Yet some still fasted for two days.
Testimony to this appears in the liturgical and legal text Machzor Vitry, composed by Rabbi Simcha ben Shmuel of Vitry, Rashi's disciple. In the machzor, Rashi's student recounts that "I heard regarding the Geonim R' Yehuda bar Baruch and R' Yitzchak bar Yehuda, may their memory be blessed, that they fasted on the day following Yom Kippur. Their children and disciples continue this practice."
The debate over Yom Kippur observance in Japan
The practice of fasting for two days for Yom Kippur was dismissed by the majority of Jews and their leadership and disappeared entirely. Yet during World War II, the issue resurfaced when the Mir Yeshiva and additional European refugees escaped via Russia to Japan. Reaching Japan prompted questions about when the Sabbath occurs and when festivals take place in the remote island country.
The issue was – where does Jewish law place the date boundary separating the globe's two sections? Certain rabbinic scholars maintained the decisive line sits directly across from Jerusalem on the globe's opposite side, specifically 180 degrees from Jerusalem. Still, others maintained the line runs through East Asia roughly where China starts – specifically, 90 degrees from Jerusalem.
This created a difficulty, since sections of Japan sit precisely between these two boundaries – meaning the Sabbath and Yom Kippur, for instance, would fall on separate days according to each rabbinic view. The difference between these two views, with both backed by numerous prominent rabbinic figures, resulted in some Mir Yeshiva students planning to fast two days. Ultimately, for various reasons, a major gathering convened in Jerusalem under the leadership of Chief Rabbi Yitzchak Herzog determined that the date boundary lies 180 degrees from Jerusalem. Most rabbinic scholars adopted this view, although discussions concerning this matter persist to this day.
