June 9, 2024
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Rav Mordechai Kuber’s ‘Crossing the Dateline’: International Dateline Halachic Issues Finally Resolved

Part I

Introduction: An Indispensable Sefer

One of the most intriguing contemporary halachic discussions is the many and varied ramifications of the International Dateline (IDL). Many sefarim and articles have been written on this beautiful topic. Therefore, I was hardly surprised when TABC talmid Aidan Samet told me that his uncle, who serves as a rav in Yerushalayim, recently released a sefer on this topic. However, when leafing through the set that Aidan and his parents gifted me of Rav Mordechai Kuber’s three-volume collection titled “Crossing the Dateline,” I very quickly realized that this is not just a sefer on the IDL. It is the Sefer on the IDL. Moreover, the author is not merely a rav in Yerushalayim but is an exceedingly talented posek whose word carries considerable weight.

Together with more than 30 TABC students, we devoted our recent intersession to delving into this magnificent sefer. We even had the fabulous opportunity to hear directly from Rav Kuber the last Sunday evening.

It is well worth sharing highlights of Rav Kuber’s monumental work since the situations he addresses are becoming commonplace.

The Location of the Dateline: The Primary Opinions

We first must determine the location of the halachic dateline. While a plethora of opinions has emerged, there are three primary views.

Intuitively, the halachic dateline should lie 180 degrees from Yerushalayim. The most famous proponent of this view is Rav Yechiel Michel Tukachinsky, an important mid-20th-century Yerushalayim-based rav. Rav Tukachinsky writes that “Yerushalayim is the Jewish Greenwich.”

However, the Chazon Ish fiercely disagrees and vigorously argues that the dateline lies 90 degrees east of Yerushalayim. The Chazon Ish interprets the Baal Hamaor and Kuzari’s understanding of Rosh Hashanah 20b. However, Rav Tukachinsky hotly debates the Chazon Ish’s interpretations, making this one of the most celebrated halachic debates of the 20th century.

Other poskim, such as Rav Betzalel Stern (who served as rav in Australia and wrote extensively about the IDL), notes the absence of clear evidence from the Gemara about the dateline’s site, apparently leaving it to us to decide upon its position. Therefore, he argues, we may adopt the civil dateline as the halachic IDL.

Halachic Challenges

The Chazon Ish and Rav Tukachinsky datelines differ from the IDL and generate significant challenges. Since Japan and New Zealand lie east of the Chazon Ish’s dateline and the west of the civil international dateline, one observes Shabbat on Sunday in these countries in his view! On the other hand, since Hawaii and most of Alaska lie to the west of Rav Tukachinsky’s line but east of the IDL, one observes Shabbat on Friday in these areas according to his view!

Although most of Australia and the easternmost portions of Russia and China lie west of the 90-degree line, the Chazon Ish extends his line along the eastern coast of Asia and Australia. Thus, all of Australia, China and Russia observe Shabbat on Saturday in his view.

The Star-K posts a magnificent map that very clearly outlines the issues. https://www.star-k.org/articles/wp-content/uploads/2015/12/IDL_Map.pdf

The Location of the Dateline: Resolving the Debate

Different opinions prevail. For example, Yeshiva University roshei yeshiva offer widely differing views. Rav Schachter adopts the 90-degree line, Rav Willig follows the 180-degree line, and Rav Baruch Simon advocates for a line that hews closely to the IDL.

Rav Kuber’s first critical contribution to this topic is establishing that the consensus opinion regards the halachic dateline as 180 degrees from Yerushalayim. This consensus emerges from a rabbinic conference held in 1941 and prominent late-20th-century-authorities’ decisions.

In 1941, a sizable group of Lithuanian Jews (including the Mirrer Yeshiva’s students) were granted visas by the righteous Japanese consul Chiune Sugihara, escaped from the clutches of the evil Nazis and arrived in Japan. Along with the other refugees, the yeshiva students were unsure about the halachic dateline location. After the refugees sent telegrams to Israel’s Ashkenazic Chief Rabbi Herzog for direction, he invited the leading poskim in Eretz Yisrael to Yerushalayim to deliberate and issue a definitive decision.

Rav Herzog’s rabbinic summit concluded that Shabbat is observed on the Japanese Saturday and wired the decision to the Jews in Japan. This decision did not resolve the issue conclusively, though, since the Chazon Ish did not attend the conference (he sent an emissary to communicate his views). After the Jerusalem rabbis sent their telegram to Japan, the Chazon Ish wired the Jews in Japan a dissenting ruling to observe Shabbat on Sunday!

This question became particularly acute in regard to Yom Kippur. In his 1976 work “Japanese, Nazis, and Jews,” Dr. David Kranzler reports that there were a few yeshiva students who, believe it or not, fasted two days of Yom Kippur due to this debate!

The next generation of poskim debate whether Rav Herzog’s conference resolved the issue. Two great late-20th-century Jerusalem sages, Rav Shlomo Zalman Auerbach and Rav Yosef Shalom Eliashiv, follow the decision of the 1941 summit and state that the halachic dateline lies 180 degrees from Yerushalayim.

Rav Kuber cites a report that Rav Moshe Feinstein also adopts the 180-degree line. Finally, the late 20th century Bnei Brak sage Rav Shmuel Wosner fundamentally assumes the 180-degree line, despite his typical allegiance to the Chazon Ish’s rulings. Rav Wosner’s decision clinches Rav Kuber’s assessment that there is a halachic consensus to follow Jerusalem’s 180-degree line.

Tentative Conclusion

Rav Mordechai Kuber believes that the halachic consensus accepts the 180-degree line as the dateline following the decision of Rav Tukachinsky and the 1941 Jerusalem Summit. With Hashem’s help, we will continue with this fascinating discussion next week.


Rabbi Haim Jachter is the spiritual leader of Congregation Shaarei Orah, the Sephardic Congregation of Teaneck. He also serves as a rebbe at Torah Academy of Bergen County and a dayan on the Beth Din of Elizabeth.

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