Shavuos is the only Yom Tov that does not have a set date in the Torah. All the other Yomim Tovim have a set date in the month; we know the 15th day of Nissan is Pesach, the 15th day of Tishrei is Succos, the only thing it says about Shavuos is that one should count forty-nine days from Pesach, and the 50th day should be celebrated as Shavuos.
A Yom Tov Without a Set Date
The Alter Rebbe states in Shulchan Aruch (Orach Chayim, siman 494:4) that Shavuos could either be on the 5th, 6th, Or 7th of Sivan [depending on whether Rosh Chodesh Iyar and Sivan are one or two days]. The Alter Rebbe is obviously referring to the time before Hillel II made a set calendar, when it was possible for any month to be 29 days long, or 30 days long. Nowadays we have a set calendar, and Nissan is always 30 days long, and Iyar 29 days long, which puts Shavuos on the 6th of Sivan.
The Rebbe brings down (Likkutei Sichos vol. III, p. 998) that even now — after the calendar was set — there are times when Shavuos would fall out on another date, that being the case when someone crosses the international dateline.
The international dateline is an imaginary line running from the north pole to the south pole through the Pacific Ocean (according to most Halachic opinions) that separates the calendar dates.
Being that the Torah says about Sefiras HaOmer “U’sfartem lachem”, that every individual needs to count on his own, someone that flies westward from the United States to Australia, for example, would be losing a day, and would thus end up counting the 50th day on the 7th day of Sivan, a day later.
The opposite is also true, someone traveling eastward from Australia to the United States would arrive on the same calendar date he left, and would thus celebrate Shavuos a day early – on the 5th of Sivan, a day earlier.
Does “Zman Matan Toraseinu” have a set date?
The Rebbe writes quite a few times, that being that it’s such a big chidush, one should avoid crossing the dateline during sefira and only in a case of great need, one should celebrate Shavuos on a different day.
[This position can create an anomaly, in which someone celebrating Shavuos on the 5th of Sivan will have to omit from his davening the words “Zman Matan Toraseinu,” as that event does have a definitive date – the sixth of Sivan.]
When bochurim asked Rabbi Marlow about traveling to the far east for Shlichus, Rabbi Marlow would tell them, that if it’s a bigger expense to fly the long way, and it’s coming from public charity funds, it’s considered a big need, and they may fly over the dateline instead, and celebrate Shavuos on their 50th day.
“Gut Shabbos, Gut Yom Tov!”
One year Shavuos fell on a Sunday and Monday, and R’ Yoel Kahn had a Guest over at his house for Shabbos and Yom Tov.
The guest mentioned at the Friday night meal that he recently traveled from Japan to the United States, and R’ Yoel realized and told him that it wasn’t just Shabbos for him, but Yom Tov for him as well. After somewhat of a debate among the rabbis in 770 which reached no definitive conclusion, R’ Yoel suggested that the man stand on the line of people whom the Rebbe greeted after leaving shul and tell the Rebbe a few words, “I was in Japan.”
As the Rebbe walked out from his place to his room, he wished everyone a “Gut Shabbos,” but when he passed this guest of R’ Yoel, he turned to him and wished him a “Gut Shabbos, Gut Yom Tov.”
When R’ Yoel spoke to the Rebbe about this on Motzei Shabbos, the Rebbe told him to make sure that this guest wraps Tefillin the next day (he was a Jew from Eretz Yisrael), being that it’s not Yom Tov for him anymore.
From all of the above, we see that the Rebbe’s opinion is that one should avoid crossing the international dateline, and if one does, he should celebrate Shavuos on his 50th day. ■
Lightly edited from a video on StumpTheRabbi.com — Made possible by The Chanin Fund, and Reliable Fast Cash.