Base on: Rabbi Dovid Heber and Rabbi Y. Rimler
What is the International Dateline? The International Dateline accepted worldwide (hereafter referred to as the Civil Dateline) is an imaginary line zig-zagging around 180° longitude through the Pacific Ocean (see attached map), separating one day from the other. If it is 1:00 p.m. Monday on the eastern side of the Dateline, it is 1:00 p.m. Tuesday on the western side.
Therefore, if one travels from the United States to China, a day is “lost”. For example, if one crosses at noon Monday, one would turn his watch (with date display) ahead from noon Monday to noon Tuesday as he crosses the line traveling westbound, “skipping” Monday afternoon and night, and Tuesday morning. When one travels from China to the United States, a day is “gained,” as one would turn his watch back from noon Tuesday to noon Monday. This person will experience Monday afternoon and night, as well as Tuesday morning, twice.
Halacha addresses two aspects of the Dateline: The location and halachic implications of crossing the Dateline.
I. Location:
Various Rishonim, early commentators, and many Acharonim, later commentators, have written extensively on this topic. The three major opinions are as follows:
A. The Chazon Ish bases his opinion on the Baal Hamaor‘s explanation of a gemara in Rosh Hashana. The Dateline “technically” runs 90 degrees east of Yerushalayim, where the time is six hours later. This line is at 125.2°E and runs through Australia, the Philippines, China, North Korea and Russia.
However, if this was the Dateline it would cut through land. For example, it would intersect Dongfeng Street in Changchun, China. Families on the eastern strip of Dongfeng Street would recite kiddush while families a block to the west would recite havdala. It may be possible for those who want two days of Shabbos to walk one block eastbound, down Dongfeng Street, after Seuda Shlishis and start Shabbos again. Those who want to skip almost all of Shabbos could take a short stroll westbound, and go from sunset Friday to sunset Saturday. However, halacha does not allow for such a situation. Instead, we consider the eastern land masses tafel (secondary) to the western land masses of these same continents. Therefore, eastern landmasses of Asia and Australia observe the same day for Shabbos as the western sections. This is known as graira.
Therefore, the halachic Dateline of the Chazon Ish avoids going through land by gerrymandering along the Asian coast (see map), then along the 125.2°E longitude line, through the East China Sea, Philippines, and Indonesia. Finally, the line cuts eastward, around most of the northern, eastern and southern coasts of Australia, and then at 125.2o E turns south towards Antarctica. According to the Chazon Ish, Japan, New Zealand, Tasmania, and Fiji are on the same side of the Dateline as the United States. When the Japanese and New Zealand residents say it is Saturday, halacha says it is Friday. When they say it is Sunday, it is halachically Shabbos. This would also apply to parts of Indonesia and the Philippines.
B. Rav Yechiel Michel Tukatzinsky, zt”l, bases his ruling on Chazal‘s Judaic principle that Yerushalayim is “the center of the world.” If so, the Earth “starts and ends” (i.e. the Dateline) on the exact opposite side of the Earth, halfway around the globe at 144.8°W. This line runs from the Gulf of Alaska through the Pacific Ocean east of Hawaii, placing the entire state of Hawaii on the “other side of the Dateline” from the United States. Hawaii would then be nineteen hours ahead of Baltimore, rather than five hours behind, as it is on the same side of the Dateline as Asia. The day Hawaiians call Friday is halachically Shabbos, and the day they call Saturday is halachically Sunday.
C. “Mid-Pacific Poskim“ – Several Poskim, including the Bnai Tzion,
