I have lived in Israel for most of my life. Many mitzvot are only relevant in the land of Israel, but there is one question that only crossed my mind once I left my country. I had not contended with the issue of what to do when traveling abroad for a holiday. I knew that there were differing opinions but on the rare occasion when I did travel abroad, I followed a psak, halakhic ruling, to observe only one day of the holiday, while being careful not to do any melakha, prohibited activities, publicly in a Jewish community on the second day of the holiday.
However, this issue came to an abrupt head when I moved to the U.S. for a period of a few years to study at Yeshivat Maharat. During my first Sukkot in the U.S., I observed one day but felt an unsettling disquiet within. I was eventually able to put a name to it – I felt lacking in my halakhic integrity. As a future Maharat, it was time for me to do my own research and find out what was really going on behind the scenes of the halakha.
I had heard of a ruling requiring all Jews to observe one day while in Israel and two days when outside of Israel. This made sense to me as it matched the original customs observed within and without the land of Israel and seemed the best way to commemorate those customs.
The lunar month is either 29 or 30 days long. During the time of the Sanhedrin (supreme rabbinic court), Rosh Chodesh, the first day of the new month, was determined by eyewitnesses who actually saw the new moon. They would report to the Sanhedrin, which would then determine the date for Rosh Chodesh, and send out messengers to notify all the Jews living in Israel and in the diaspora of the appropriate date. These communities would then celebrate Sukkot and Pesach on the fifteenth of Tishrei and Nissan and subsequently count 49 days to Shavuot on the sixth of Sivan. The messengers always had enough time to reach the communities in Israel before the fifteenth of each month. However, the messengers would reach communities outside of Israel after the fifteenth of the month, which left them with a doubt as to the correct day to celebrate each holiday. They therefore observed two days of chag, just in case