Determining the Day of the Bar-Misva When Crossing the International Date Line

A fascinating question arises in the case of a boy whose family travels across the International Date Line to celebrate his Bar-Misva. If, for example, the boy was born and raised in the U.S., and the family travels to Australia via the Pacific Ocean, they cross the Date Line during the trip, thus jumping one day ahead. The question becomes whether the boy becomes Bar-Misva on his birthday in Australia, or if he must wait another day, until it is his birthday back in the United States where he was born. Some Poskim maintain that in such a case, he indeed does not become a Bar-Misva until the next day. Since he moved ahead one day during his flight, the date in his current location does not determine his halachic status as a Bar-Misva. If, however, the family traveled to Australia eastward, such that they did not cross the International Date Line, then he becomes Bar-Misva once the date of his birthday arrives in Australia. In this case, he follows the date of his current location, even though his birthday has yet to arrive back home which is in a later time zone. This ruling would apply in the reverse case, as well, if an Australian boy travels to the U.S. for his Bar-Misva. If the family travels eastward, arriving in the U.S. via the Pacific Ocean, and thus having crossed the International Date Line and moving back one day, the boy becomes a Bar-Misva a day before the date of his birthday in the U.S., since this is the day of his Bar-Misva in Australia. If, however, the family traveled westward, reaching the U.S. via the Atlantic Ocean, then since he did not cross the Date Line, he does not become a Bar-Misva until the date of his birthday in the U.S. Rav Yosef Shalom Elyashiv (Jerusalem, 1910-2012) disagreed. He maintained that the boy becomes a Bar-Misva on the date of his birthday in his current location, and crossing the International Date Line has no effect on the timing of his becoming a halachic adult. This is the accepted Halacha. Another intriguing case, is that of a boy who crosses the Date Line on the day of his Bar-Misva, moving him back one day. In such a case, after becoming a Bar-Misva, the boy enters a region where his thirteenth birthday had not yet arrived. A number of Poskim, including Rav Haim Kanievsky, ruled that once a child becomes a Bar-Misva, there is no possibility of him losing this status and reverting to being a minor, and thus crossing the Date Line would not affect the boy's status in this case.