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According to halakha, where is the international date line?

More specifically, I have heard that some people say you should observe Shabbat on Sunday in Japan & New Zealand and/or on Friday in Hawaii. Should I worry about this if I go to these places?

Also, what if I am on an eastward nonstop flight from Beijing to New York, that departs on Saturday night and also arrives on Saturday night. However, as I am flying over California it is Shabbat there. Is this a problem?

Also, what if I circumnavigate the Earth during the Omer, thereby inserting or deleting a day between Pesach and Shavuot? How would I conduct my Omer count? Also what if I just cross the International Date Line temporarily and return back the same way, all during the Omer?

Are there any other international date line issues I should be concerned about?

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Rabbi Blumenkranz ZT"L has an article about it in his Pesach book "The Laws of Pesach". He is known to be a strict authority, but he basically recommends not spending Pesach in Hawaii. –  andrewmh20 Mar 28 '13 at 14:29
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5 Answers

If I recall reading from the Star-K, the basic three "families" of opinion with regard to the dateline are:

A.) 90 degrees East of Jerusalem, and a landmass that's on the 90°-east line gets entirely included on one side. This means the entire Asian and Australian mainlands, but nothing east of that.
B.) Somewhere close to the International line.
C.) 180° east of Jerusalem, and any mainland included on one side. This means that everything west of Alaska is on the other day.

Their recommendation is to go for two out of the three opinions, and therefore:

Regardless, keep Shabbat on Saturday. Avoid Torah-prohibited (as opposed to Rabbinic-prohibited) "work" in Japan on Sunday. Avoid Torah-prohibited "work" in Hawaii on Friday.

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Another issue to be concerned about that I've heard of: If you follow Opinion A in Shalom's answer, then when it's Sunday in Australia, it's Shabbat off the Eastern coast thereof. So, I've heard that there are those who forbid swimming or boating off the Eastern coast of Australia on a Sunday, since as soon as you get in the water, you should be observing Shabbat.

YUTorah.org has a bunch of lectures on the topic that you may find useful.

If this issue confronts you practically, that is, if you find yourself travelling to or passing through the Far East or the Pacific, I recommend that you talk to the local Rabbi wherever you're going (assuming there is one, and of course, check with your own Rabbi first). This sort of Halachic situation exists as a theoretical concept for most people, but as a reality for communities that live with it and for their Rabbis. As such, the local Rabbi will be familiar with all of the issues facing his region and will be ready with approaches that are practical, Halachically sound, and communally accepted.

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As far as Japan goes, listen to this shiur by Rabbi Dovid Horowitz about his trip to Japan with YU students. I believe that the first part is dateline related (and the rest is pretty interesting also).

There is an RJJ Journal article by Rabbi David Pahmer that goes back about 15 years that sums up a lot of the issues. And, of course, if you have a lot of free time, there is Rav Menachem Kasher's book on the subject.

In a related vein, Rabbi Frand has an audio shiur about the Great North, meaning the Arctic Circle, where the sun barely sets for 6 months. It includes the question about what happens if the switchover occurs on a Shabbat, and therefore perhaps it is Shabbat for 6 months - what happens if you fly over that zone during such a time? I think that the Lubavitcher Rebbe dealt with it, but you would have to find the shiur to confirm.

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Aaron, Welcome to mi.yodeya, and thanks very much for the very informative answer! Please consider registering your account by clicking on register, above, and following the prompts. This will give you access to all of mi.yodeya's features and will allow you to get full credit for your contributions. –  Isaac Moses Mar 4 '10 at 3:42
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Ah, if only this could be addressed in one simple post. Just to add to what's been mentioned:

  • Link to Star-K Article

  • Some audio shiurim Look for the ones by R' Heber, who just happens to be the author of aforementioned article

  • Try to find this book which is an abridged and translated version of תאריך ישראל
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There is a book "Ḳaṿ ha-taʾarikh be-khadur ha-arets" by a R. Leib Blum, which essentially is a massive compilation containing photocopies of every source ever written regarding this topic, plus a (relatively) short guide at the end by R. Blum himself.

There are two versions: The first, published in 1990, runs close to 1000 pages. The second, published in 1997 following demand for a more concise text, is only 350 pages long, containing the most important sources plus a small amount of new material. Both were published in Jerusalem and contain fold-out maps.

If you are interested in obtaining either of these volumes, the only practical advice I can suggest is to do what I did and gain access to a University library that contains every obscure Jewish book ever published.

As for the content of the book, I haven't had a chance to go through it yet, so I'll have to report back later...

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For those of us who do not have access to a university library, there is always Otzar HaChochma: otzar.org/wotzar/Book.aspx?15295&BOOKS –  Dave Mar 24 '11 at 17:25
Re "gain access to a University library that contains every obscure Jewish book ever published": possibly via interlibrary loan. –  msh210 Jun 11 '13 at 19:29
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