The Shabbos That Vanished: Halacha on the High Seas When Crossing The Dateline
Question:
Rabbi, I’m on a cruise ship traveling from Hawaii toward Australia, and late Friday afternoon the ship crossed the International Date Line. According to the ship’s clocks, we skipped completely over Saturday daytime and jumped straight to Saturday night. I’m an observant Jew and had prepared to keep Shabbat normally, but now it feels like Shabbat vanished. Should I still keep Shabbat based on where I started, follow the ship’s local time, or treat this as a special case? How should I observe Shabbat when a full day disappears like this?
Answer:
In a situation like yours, you keep Shabbat as you normally would, beginning at sunset of what would have been Friday night for you — even though the ship’s clock now says Saturday night. You observe Shabbat until nightfall of what the ship calls Sunday night, because that is the first opportunity for a full halachic Shabbat to end. Once that Shabbat is complete, you resume the regular weekly cycle based on your new location. That means the coming Friday night you will begin Shabbat again — which, on the ship’s calendar, will arrive only about five days later. Although the gap feels shorter than a full week, it is the correct halachic practice after crossing the Date Line in this manner.
Explanation:
The halachic discussion about crossing the International Date Line in a way that causes a person to “lose” or “gain” a day first arose in later centuries, particularly in the era when long‑distance sea travel became common in Eastern Europe, including regions such as Ukraine. Only once Jews began traveling across the Pacific — something practically impossible in earlier eras — did this question become realistic and urgently relevant within the Jewish world.
To understand the problem, it’s important to grasp how the International Date Line works. The world is divided into 24 time zones of roughly equal width. When one travels far enough eastward [i.e. Travels From the direction of Africa to Past New Zealand], after crossing a certain boundary, the local calendar jumps backward by one day. Travel far enough westward [i.e. Travels From Past New Zealand towards the direction of Africa], and the calendar jumps forward by one day. This is not because nature changes, but simply due to the need for a consistent global calendar.
For example, someone flying from Auckland to Honolulu can leave on a Friday morning and arrive on Thursday night. In the opposite direction, traveling far enough westward—such as flying from Hawaii toward New Zealand and then onward toward Africa—the instant you cross the Date Line the calendar jumps forward by one day, so a traveler leaving Honolulu on Thursday morning may land in Auckland on Friday afternoon. Nothing physical changes at that boundary; it’s simply a global bookkeeping system that keeps the world’s calendar consistent as we move through 24 time zones.
Now, halacha must determine how Shabbos behaves when a person forcibly “skips” a day or “repeats” one. The poskim framed the issue as follows:
Is Shabbos personal, or is it geographical?
- The personal‑count model:
Shabbos is the seventh day counted from Day One of Creation. A person continuously counts seven‑day cycles from the moment humanity began observing Shabbos. Under this logic, one’s seventh day arrives after six ordinary intervening days — regardless of what the local calendar says. Therefore, if a traveler crosses the Date Line and a calendar day disappears, their personal Day Seven still arrives right on schedule — even if the local clock says it is already Saturday night or Sunday. According to this model, their Shabbos simply shifts and occurs earlier or later relative to the local community. The Sefer Habris indeed writes accordingly that in certain circumstances it is entirely possible for two Jews standing side‑by‑side — even on the very same ship — to be keeping Shabbos on different days. Imagine one traveler who came from the west, who never crossed the Date Line, and another traveler who came from the east and did cross it. Although they now stand together in the same spot, their personal seven‑day counts differ. For one of them, today is the seventh day and thus Shabbos; for the other, Shabbos will not be until the following day. Each one must keep Shabbos according to their own halachic calculation, even though they see each other, speak to each other, and share the same deck at the same moment.
- The geographic‑reality model:
Shabbos is not a personal cycle but a worldwide objective state, tied to natural sunrise and sunset in each location. According to this view, when one crosses the Date Line and enters a region where Shabbos has already ended — or never arrived — then the traveler has, in effect, stepped into a place where the local population already passed Shabbos. In such a scenario, one might conclude that the traveler simply misses Shabbos that week, and would not observe it until the next local Saturday.
This became a major debate among the halachic authorities.
And what is the ruling?
The accepted conclusion among the poskim is that we act stringently according to both major halachic models. On the one hand, we follow the personal seven‑day cycle: a person must keep Shabbos on what is personally the seventh day since the previous Shabbos, even if the local calendar has jumped and the ship’s clock insists it is already Saturday night or Sunday. On the other hand, we are also stringent for the approach that Shabbos is a geographical reality, a fixed state tied to the location one currently occupies.
Because we take both views into account, complex and unusual situations can occur. For example, it is entirely possible that a traveler will keep Shabbos in a place where the local population is already observing Sunday, simply because according to their personal seven‑day count, Shabbos has arrived. Likewise, if someone crosses the Date Line from east to west, turning Sunday back into Saturday, they may need to observe Shabbos again, keeping it once in their original location and then a second time in the new location, in order to satisfy the possibility that the local halachic Shabbos has re‑entered.
This dual stringency reflects the severity and weight of the opposing positions: one view holds that a traveler could entirely lose Shabbos for that week, while the other maintains that local Shabbos remains binding regardless of one’s personal count. Because each opinion carries significant halachic implications, the poskim rule that one must avoid either extreme outcome by observing Shabbos according to both considerations whenever the situation applies.
A Further Point of Debate
Beyond the theoretical dispute about what a person should do when personally crossing the International Date Line, the poskim raised a second, very practical debate: Where exactly is the halachic Date Line?
The modern International Date Line is a human convention agreed upon by governments for the sake of civil timekeeping. But halacha does not necessarily follow political agreements. Thus, the question arose: Does halacha adopt the world’s International Date Line, or is there a halachic Date Line determined by Torah‑based principles, which might fall in an entirely different location?
This debate among the poskim is extensive and unresolved. Various halachic authorities place the halachic Date Line in different possible longitudes — some aligning closely with the modern line, and others positioning it far from the international one, in a way that could drastically change what day of the week it “is” in a given location.
The practical result is this:
It is entirely possible that a traveler may cross the civil International Date Line while not crossing the halachic Date Line. If so, then even though the ship’s captain, the local clocks, and the calendar insist it is “Saturday,” halachically it may still be Friday night. In such a case, the ship has simply chosen to label the day incorrectly from a halachic standpoint. This mistake has no more force than if the newspapers suddenly declared that one week would skip from Friday straight to Sunday. Their statement would not change the actual sequence of days; it would merely reflect a human decision that does not alter reality.
This possibility adds a second layer of uncertainty and is one of the reasons the poskim warn strongly that one should avoid placing oneself in situations where crossing the Date Line near Shabbos becomes relevant. Even if a person believes they have entered “Saturday,” halachically they may not have left Friday at all.
The Lubavitcher Rebbe’s view
According to the Rebbe’s view as implied from various talks and letters, Shabbos follows only the geographical reality of the place a person is in, with no halachic weight given to one’s personal seven‑day count. Based on this, it is entirely possible for a person crossing the International Date Line to either miss Shabbos completely or to observe two consecutive days of Shabbos if the calendar “moves backward” upon crossing from east to west. This raises practical questions for Chabad chassidim traveling such routes — for example, if one crosses from west to east and the local clock jumps to Saturday night, should one now put on tefillin? Should one keep Shabbos? What prayers should be recited? These issues parallel the stringencies applied to someone lost in the desert who keeps a rabbinic seventh‑day Shabbos out of doubt.
The Rebbe further states that there is no inherent halachic obligation to ensure that one always experiences a seventh day called Shabbos; therefore, even initially, one could cross the Date Line and “lose” Shabbos according to this view. The only complication is that the precise location of the halachic Date Line is not definitively known, and therefore even for Chabad chassidim the matter remains a halachic doubt. This uncertainty extends to related questions, such as whether tefillin should be worn with a conditional stipulation: that if it is indeed Shabbos, the tefillin are not being worn as a mitzvah, and if it is not Shabbos, they are being worn properly. Since these and other practical issues remain unresolved, such scenarios should certainly be avoided whenever possible.
Sources:
See Tiferes Yisarel beginning of Brachos; Shoel Umeishiv Daled 2:154; Eretz Tzevi 1:44-45; Kaf Hachaim 261:19; Erav Poalav Sod Yesharim 4; Minchas Elazar 4:42; Divrei yehosef 8; Even Yikarah Kama 11; Chavalim Beni’imim 4:3; Bnei Tziyon 1:14; Betzel Hachochma 5:103; Or Letziyon 1:14; Hazemanim Behalacha 8; Vayivarech David 2:168; Sefer Agan Hasohar p. 436; Igros Kodesh 21:310; Likkutei Sichos 37:183; Shulchan Menachem 2:155; Piskeiy Teshuvos 344:3 footnote 26; Migdal Or Los Angeles 7:111-383 Shaar Sheiyni
See regarding if Shabbos follows ones personal seven-day count or the day of the local population: Nachlas Meir 18; Radbaz 1:76; Shabbos 69b; Admur Basra 1:8; Sefer Habris 1 Mamar 4:11; Piskeiy Teshuvah 252; Sefer Agan Hasohar p. 436; Igros Kodesh 21:310; Likkutei Sichos 37:183; Shulchan Menachem 2:155; Piskeiy Teshuvos 344:3 footnote 26; Migdal Or Los Angeles 7:111-383 Shaar Sheiyni
See regarding keeping Shabbos as the 7th day of one’s count: Admur 344:1; Michaber 344:1; Tur 344; Rav Huna Shabbos 69b; Radbaz 1:76, brought in Likkutei Sichos Volume 8 Parshas Naso 3; Likewise, the Kabbalists maintain that the seventh day of one’s personal count is not merely symbolic but carries the status of an actual Biblical Shabbos. Their reasoning is rooted in the concept that within the spiritual realms there exists a unique point of holiness called Shabbos, which can be drawn from every day of the week. When a person, uncertain of the true Shabbos, designates a specific day as Shabbos and sanctifies it accordingly, that day becomes connected to this mystical Shabbos energy. Consequently, for that individual, the chosen day attains the essence of a true Shabbos on a Biblical level. [Reishis Chachmah Shaar Hakedusha 2:27 in name of Ramak; Shelah hakadosh Miseches Chulin Torah Or; Magid Meisharim of Beis Yosef of Beis Yosef Parshas Mishpatim in name of Parshas Derachim Derush 23; Piskeiy Teshuvos 344:1 footnote 9]
