Introduction
This website was designed to introduce the traveler to the concept of the date line and how it relates to Halacha. Every effort has been made to make the subject understandable to all. While some may undoubtedly find the material confusing, an attempt was made to simplify as much as possible.
With the advent of extensive travel to the Far East by the Mitzva observant, halacha as it relates to the date line has become a topic of interest. Halacha sensitive Jews have been presented with a vast array of halachic questions ranging from when to daven midflight to when Shabbos is to be observed in various locations.
Because there are such differing opinions by leading poskim on almost any specific question, we have based the halachos on conclusions reached by Rabb Yisroel Taplin of Beth Medrash Govoha in Lakewood, who has researched the topic extensively, has personally discussed the matter with the greatest poskim of the past half century, and who has written a 700 page sefer on this subject, Sefer Taarich Yisroel. His conclusions are not the final word on the subject. All are advised to discuss the matter with their own posek as they relate to halacha lema’aseh. This website should however be a good introduction to the issues and offer the reader a solid background to enable one to know wherein lie the questions.
The website is divided into the following sections:
Where is the Date Line
International Date Line vs Halachik Date Line
How to Use the Location and Time Charts
In addition we have attached 2 appendices to this website.
Appendix A – Location and time charts that can be used on trips to and from the Far East that are helpful in planning time observance of mitzvos
Appendix B- The original text of the English adaptation of Sefer Taarich Yisroel published in 1999. While on the one hand it offers a deeper understanding of much of the subject, some of the practical halacha lemaaseh questions have changed as a result of the introduction of transpolar flight,
Overview
The Great Bar Mitzvah Paradox
Rabbi and Mrs. Cohen, teachers in the Hebrew Day School of Hawaii, would like to celebrate the bar mitzvah of their twins, Moshe and Aharon, in Yerushalayim. Rabbi Cohen’s elderly parents live in New York, while Mrs. Cohen’s parents live in Hong Kong. As they plan to celebrate the bar mitzvah in Eretz Yisroel, the Cohens decide that Rabbi Cohen will take Moshe to visit his parents in New York on the way to Eretz Yisroel, and Mrs. Cohen will take Aharon to Eretz Yisroel via Hong Kong to enable her parents to partake in the simcha.
The bar mitzvah is scheduled for Thursday, 7 Adar. On Monday, 4 Adar, they board their respective flights, the father and Moshe to New York and then to Eretz Yisroel, and the mother and Aharon to Hong Kong and then on to Eretz Yisroel.
Each leg of each flight is about 12 hours.
The eastbound flight to New York departs Hawaii on Monday at 1 p.m. local time, flies into the sunset and through the night, and arrives in New York 12 hours later, on Tuesday morning at 6 a.m.. (1 a.m. Hawaii time plus 5 hours, as New York is 5 hours ahead of Hawaii). They visit their relatives and leave New York that evening. After a 12-hour stopover, they depart New York at 6 p.m., they observe Tuesday’s sunset, fly through the night, and arrive in Eretz Yisroel on Wednesday at 1 p.m. (6 a.m. New York time plus 7, as Eretz Yisroel time is 7 hours ahead of New York). The bar mitzvah is scheduled for the next morning.
In the meantime, Mrs. Cohen, traveling with Aharon, leaves Hawaii at the same time as her husband, 1 p.m., in a westbound direction. They land in Hong Kong 12 hours later, where the local time is Tuesday 7 p.m. (Hawaii time 1 a.m., minus 6, as Hong Kong time is 6 hours behind Hawaii. However, because they crossed the International date line the day advances from Monday to Tuesdya). The entire flight took place during daylight. Mrs. Cohen visits her parents, and after a 12-hour stopover in Hong Kong, she and Aharon depart to Eretz Yisroel the next morning. local time Wednesday 7 a.m. Being that this flight is also in a westbound direction, they are flying “with the sun,” so that when they arrive 12 hours later in Eretz Yisroel, the local time is Wednesday 1 p.m. (Hong Kong time 7 p.m., minus 6, as Eretz Yisroel time is 6 hours behind Hong Kong time.)
Rabbi Cohen and Moshe arrive at the same time, and together they take a cab to Yerushalayim.
That night, as they compare notes of their journeys, something fascinating surfaces. As Rabbi Cohen flew eastward, “against the sun,” time kept on advancing. He and Moshe saw two sunsets along the way. Mrs. Cohen and Aharon, on the other hand, flew westward. As they flew with the sun, time kept moving back, resulting in their experiencing only one sunset since leaving Hawaii.
While it may be true that both Moshe and Aharon consider their landing time in Israel to be Wednesday 1 p.m., their days coincide only because Aharon crossed the International Date Line, an imaginary line in the Pacific that pushed the day forward as he crossed it. The question is, does halacha recognize this event? If halacha does not, but rather considers a day change to take place only at sunset, Moshe and Aharon’s days do not coincide.
Moshe lived through one more sunset than his twin Aharon did. Is he, in fact, a day older? Aharon observed a Monday night sunset shortly after he landed in Hong Kong, but he never did get to see a Tuesday night sunset. Is today in fact his Tuesday, 5 Adar? And if it is Wednesday, how did he get there without having seen a Tuesday sunset?
If we carry the argument to its logical conclusion, that Moshe is in fact older than Aharon by a day because he experienced an extra sunset, then as they both stood at the airport in Eretz Yisroel after they landed, for Moshe it was Wednesday and his bar mitzvah would be the next day, Thursday, while for Aharon it was only Tuesday, and his bar mitzvah would not take place for another two days — on his Thursday, which is Moshe’s Friday. Is that possible? When Friday night comes for Moshe, will it be Thursday night for Aharon? When Moshe is making Kiddush, can it be a weekday for Aharon? That is clearly impossible. How, then, do we reconcile Aharon’s calendar?
The short answer to the Cohens’ question lies in the fact that someone crossed the date line somewhere along the way.
As the Cohens traveled, two of them east and two of them west, together they circumnavigated the world. Only one pair of them crossed the date line. I hesitate to say which one did as this is, in fact, a major disagreement among poskim. The Chazon Ish would claim that Mrs. Cohen and Aharon crossed the date line as they approached Asia, catapulting them a day forward, while other poskim would say that Rabbi Cohen and Moshe crossed the date line shortly after they took off from Hawaii, somewhere between Hawaii and California, moving them backward in time. Just how this works and why the poskim disagree is the subject of the website. The fact of the matter is that one of them crossed the date line, resulting in their simultaneous arrival in Eretz Yisroel on the same day regardless of how many sunsets each experienced.
Welcome to the World of the Date Line in Halacha.
The date line question in halacha was not seriously dealt with until the Jews fleeing the Nazis during World War II found themselves in the Far East. They were unsure where the date line was and on which side of it they stood. The questionwas sent to Eretz Yisroel by telegram, and two major conflicting opinions emerged — opinions that severely impacted their daily lives by concluding which day to keep Shabbos and on which day to fast on Yom Kippur.
In broad strokes, the date line question can be broken down into two major issues.
One: Is there a halachic date line? And if so, where is it?
Two: Halachically, what happens when you cross the date line?
The first question regarding where the date line is has major ramifications regarding the determination as to what day of the week it is at each point on the planet. Just to cite one example, according to the Chazon Ish (CI), Shabbos in Japan is to be observed on the day that the Japanese call Sunday. According to Rav Yechiel Michel Tukatzinsky (RYM) and most other poskim, Shabbos in Hawaii is to be observed on the local Friday.
The second question, what impact does crossing the date line have on halacha, has created an entirely new area of study heretofore unexplored.
A few cases in point:
One is on a flight from New York to Hong Kong. On Monday afternoon, at 3 PM local time, he davens Mincha. Shortly thereafter, he crosses the date line. The day is pushed forward, and local time is now Tuesday 4 PM Must he daven Mincha again? Furthermore, since it is now Tuesday, and he never wore Tefillin on Tuesday, must he don them for Mincha?
Or consider a baby born in New York on Monday, 2 Kislev, who travels westward to have his bris in Hong Kong the following Monday, 9 Kislev. When this baby date line crosses the and the day is pushed forward, by the time it is Monday, 9 Kislev, in Hong Kong, for this baby it is still the seventh day! What difference does it make if he crossed some invisible geographic line in the Pacific Ocean? Bottom line is that this baby is only seven days old. May we perform the bris on Monday?
On eastbound flights, the day is pushed backward as the date line is crossed; in other words, the calendar shows the date on the east side of the date line to be a day earlier, hence the day repeats itself. All the above questions then arise in the reverse. If one davened Mincha on Monday, and he then crosses the date line in an eastbound direction, thereby pushing the day/date back to Sunday, when it is time for Mincha the next day, on Monday, in New York, must he daven again? After all, he davened Monday’s Mincha already! On the other hand, as far as this individual is concerned, this “second” Monday is a new day for him. The questions are endless. Interestingly, contemporary poskim have very different opinions on each case. Their understanding of which mitzvos are determined by the calendar day/date and which mitzvos are determined by one’s personal day based on sunrise and sunset experiences are quite diverse.
Why Must There Be A Date Line At All?
Before directly addressing this matter, it is important to gain an appreciation of the geography involved, a subject that some may have found distasteful back in ninth grade, but so very essential for an understanding of the dateline. Let us reacquaint ourselves with how one’s latitude affects seasons and the number of daylight hours at a particular location, and how one’s longitude determines day/date and the hour of the day at any particular location.
The vertical lines on the globe are longitude lines. When traveling in an east-west or west-east direction, you are changing longitude. Longitude is measured by 360 vertical lines that go from the North Pole to the South Pole. However, unlike latitude, longitudinal lines are not parallel to each other. At the Equator, the widest point of the Earth, which measures approximately 25,000 miles in circumference, the distance between each longitude degree is approximately 70 miles. As you move away from the Equator toward the poles (as latitude increases), the circumference of the Earth decreases to the point where all 360 longitude degrees converge at the Poles, and the distance between longitude lines is reduced to zero. Geographers have set up a system of plotting points on the globe using longitude and latitude coordinates. The point where a specific longitude meets a specific latitude is called its coordinates.