International Dateline

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Rabbi Kaganoff

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Jan 21, 2026, 1:18:41 PM (9 days ago) Jan 21

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International Dateline

By Rabbi Yirmiyohu Kaganoff

Question #1: International

Does the International Dateline have any halachic ramifications?

Question #2: Date

Can you change your date?

Question #3: Line

Did the Torah create a line where, if you crossed it, you could mysteriously leave Shabbos and then cross it back and return to Shabbos?

The International Dateline follows a path near the 180° longitude but deviates to accommodate national borders.

Foreword

Where, what and why is the International Dateline (IDL)?

From virtually every place on earth you can move east or west. If two people start from the same point, one traveling eastward and the other westward, wherever they meet again on the globe, they will be observing different days of the week. The reason is that one has been observing sunset later each day as he moves west, whereas the other has been observing it earlier each day as he moves east. Eventually, the combined differences of their travels add up to a full day.

There is no such thing as the easternmost “beginning” of world time or the “last” place to observe Shabbos, unless one establishes a point, line or boundary to be the beginning. When mankind began traversing the globe in the sixteenth century, the European colonizers usually established the day of the week according to which way they had traversed the globe and not with any regard to the location of the colony. Thus, Indonesia, which the Dutch colonized by circumnagiating Africa, followed the day of the week as it was observed in Europe, whereas the Spanish who colonized the Phillipines on their travels westward from the Americas used the next day. If you look at a map, you will see that the Phillipines lie due north of Indonesia.

In the nineteenth century, nations decided that it was a good idea to establish an accepted demarcation line, east of which would be considered as far as you can go west on the day later, and west of which is as far as you can go east and is on the day earlier. Once you cross that line eastward, you have “gained” a calendar day, and you repeat the calendar day you just lived through. Crossing it westward, you skip 24 hours ahead, i.e., you lose a calendar day. This line is the International Date Line (IDL). The IDL runs from the North Pole to the South Pole and is at the 180^th meridian, i.e., halfway around the world from the prime meridian (0° longitude), which runs through Greenwich, UK. The IDL is not straight, but curves around landmasses and national borders. It tilts east around Siberia at the Bering Strait, westward around the Aleutian Islands, and eastward in the central Pacific to allow countries that are composed of islands to keep the entire nation on the same date. The 180^th meridian was selected as the basis for the International Dateline because it runs mostly through a very sparsely populated area in the vast middle of the Pacific Ocean.

Introduction

Since the time of the rishonim, there has been halachic discussion that revolves around the following: Except for the flat earthers (which no rishonim accept), all halachic authorities recognized the observable proofs that the earth is basically round and that, therefore, from virtually every place on earth you can move east or west.

As described above, an international dateline was established in the nineteenth century, which follows 180 degrees from Greenwich Mean Time, with certain exceptions. The IDL passes almost exclusively through water – predominantly the Arctic, Pacific and Antarctic Oceans, going over land only in Antarctica, which affects only a few penguins and researchers.

Our question is whether and where is the halachic dateline? Although halachic authorities have wrestled with this question for almost a thousand years, its relevance to practical halacha began in the nineteenth century, when Jews began populating Australia, Siberia, China, Japan, the Philippines, Alaska, Hawaii, Korea, New Zealand and similar areas, as we will soon see. Literally, dozens of books and essays have analyzed the topic, and many different conclusions have been reached. As always, this article is to provide background, and any individual who intends to travel in the areas that will be discussed here should ask their rav or posek what to do.

Stopover in the Far East

I am going to pose a very curious shaylah that I was recently asked which most people would not even realize involves this issue. Someone who lives in Eretz Yisrael had a family emergency on the Pacific coast of the United States and quickly booked a ticket to leave Israel on Thursday and arrive at their destination on Friday morning. They were so appreciative of finding a connection that had them arriving before Shabbos that they did not realize that they had any shaylah until they settled in on their flight. Their flight connection was through Seoul, South Korea, but they could just as easily have made a booking that connected through Tokyo. As we will see in the course of our discussion, either of these stopovers might create a serious halachic shaylah.

Opinions of halachic authorities

Perhaps the earliest authority who discusses the ramification of where halacha might place a dateline was the Kuzari (Book 2, Section 20). This work is devoted to hashkafah and the beauty and importance of Torah, Jewish thought and values and it is not usually considered a halachic work. Yet, based on his explanation of a passage of Gemara (Rosh Hashanah 20b), the Kuzari concludes that halacha recognizes a dateline that is 90 degrees east and 270 degrees west of Yerushalayim. Any point east of this line follows the date of the Americas, and any point west of this line starts its day earlier than Yerushalayim.

The Kuzari’s approach to understanding both the topic and the passage of Gemara is followed by the Ba’al Hama’or in his commentary to the Rif’s Halachos on Rosh Hashanah. However, this is only one approach to explaining the passage of that Gemara. For example, according to Rashi’s approach, which is explained brilliantly by the Ben Aryeh (to Rosh Hashanah 20b) and Rav Henkin (Lev Ivra, pages 51-60), this passage of Gemara has nothing to do with the concept of a halachic dateline.

A disciple of the Rosh named Rav Yitzchak Yisraeli authored a work on astronomy entitled Yesod Olam, in which he discusses the contributions of the Kuzari and the Ba’al Hama’or on the subject and objects very strongly to their conclusions. Among the concerns that he raises is that their calculations assume that Yerushalayim is on the east-west midpoint of the Eurasian landmass and that the distance eastward from the easternmost point of the Eurasian landmass to its westernmost point is approximately the same as the east-west distance of Eurasia. He notes that neither of these calculations is at all accurate. He further notes that, according to the opinion of the Kuzari, two people could stand together and be observing two different days of Shabbos, because the imaginary line 90 degrees east of Yerushalayim stands between them. He objects to this possibility. He understands that the proper place of the halachic dateline should not be 90 degrees of Yerushalayim, but should be at the east-west midpoint of the Eurasian landmass, which is considerably to the east of Yerushalayim.

The Yesod Olam, himself, locates the halachic dateline 23.5 degrees further east than do the Kuzari and the Ba’al Hama’or. This places it east of most of Japan, although it still runs through Australia, placing both Sydney and Melbourne on the “wrong” side of the dateline, although the Yesod Olam would have had no way to know that. It is possible that, if the Yesod Olam had the geographic information that we currently have, he would have determined the line to be farther east, off the eastern coast of Siberia, and this is the conclusion of the Atzei Hasadeh (page 66) and several other authorities.

In the early 16^th century, the Radbaz (Shu’t Haradbaz 1:76), probably the greatest halachic authority of his era, also weighed in on the subject, concluding that there is no halachic date line. In his opinion, each individual should continue his count of the days of the week from where he left. When a community is established, it will determine when its Shabbos is, based on the starting point of most of its membership. The community will then have an established day for Shabbos that will be binding on all its members and visitors. Should two nearby communities be established, one of people who traveled from the east and the other of people who traveled from the west, we could indeed have the phenomenon of two nearby communities that observe Shabbos on different days. However, each community, and all members of that community, will always observe Shabbos on the same day each week, seven days after they did the previous week, which is seven days after the week before, going back to when their community first established itself.

Date

The second of our opening questions was: “Can you change your date?” What this question means is -- can the date in a certain place be changed to a day earlier or a day later?

Indeed, I am aware of at least two times that this happened:

The first “westerners” to visit Alaska were fur trappers from Russia. Thus, Russia was the first state to place a claim on possessing Alaska. When this claim was made by the czar of Russia, the date in Alaska was observed according to eastern Asia, as the earliest point – the easternmost point -- of the world. When Alaska was sold to the United States in 1867, its date was changed so that it became the last time zone of the United States, that is, the westernmost point of the Americas, rather than the easternmost point of Asia. Suddenly, what had been considered Friday night and Saturday now became Thursday night and Friday.

A second place where this happened was the Philippines. Although these are islands off the eastern coast of mainland Asia, they were colonized by Spain who governed them as a sub-colony of Mexico, very far to the east. When the Spaniards did this, they counted the days in the Philippines as the westernmost point of the Americas, rather than part of the Far East. This is indeed strange, since Taiwan, Indonesia, Australia and New Zealand, all island nations lying far to the east of the Philippines, kept their days the same as mainland Asia. Thus, someone traveling from any nearby country to the Philippines found themselves a day in the week earlier.

During the sixteenth and seventeenth centuries, Holland and Spain were frequently at war in the Far East. At the time, Holland controlled many east Asian islands that eventually became Taiwan and Indonesia. The Dutch repeatedly attempted to wrest the Philippines from Spain by attacking either Manila Harbor or the Spanish navy. Although the Dutch did not succeed in colonizing the Philippines, they did at times capture Spanish prisoners of war, who discovered that, not only were they now slaves, but they also had to change their days of the week to accomodate their new masters!

This situation existed in the Philippines from the sixteenth century until the 1820’s when Spain lost Mexico and almost all of its new world colonies. Once Spain no longer governed the Philippines from Mexico, they eventually changed its date to the same as the rest of the east Asian world.

There apparently was no Jewish community in the Philippines when this change occurred. Had there been one, they would have had to ask a shaylah whether they are now to observe Shabbos on Friday!

The Mid-19^th Century

Slightly past the middle of the 19^th century, such great luminaries as Rav Shemuel Mohliver and Rav Alexander Moshe Lapidus wrote works on the topic of the halachic dateline. They were well aware of the contributions on the subject by the Kuzari and the other rishonim that we have quoted. Most of these scholars contended that, notwithstanding that the Kuzari appears to be the only rishon who provided an opinion on the subject of the dateline, his approach was not accepted by the majority of rishonim and early halachic opinion. In addition, Rav Shemuel Mohliver noted that neither the Kuzari nor the Ba’al Hama’or ever expressly stated that they were ruling that there is a halachic dateline to determine when Shabbos begins. However, Rav Lapidus concluded that the dateline is 90 degrees east of Yerushalayim. Thus, he ruled that Japan, Korea, Kamchatka, Harbin, Melbourne, Sydney, New Zealand and eastern Indonesia should observe Shabbos, Yom Kippur and other Jewish laws as if they are part of the Americas, a day later than mainland Asia.

This article will be continued next week.