(In regards to the shiur that Horav Shloimo Miller Shlit”a gave recently I have some questions.)

Q. What exactly are the different opinions in regards to the dateline in Halacha and what is Horav Miller’s opinion?

A. There are three main opinions in regards to what the dateline is in Halacha. (Kav Hata’arich HaIsraeli, ch.26 quotes thirteen different points of view)

1) The opinion of the Chazon Ish (Kuntres Yud Ches Sha’os), is also the view of the Kuzari (2:19-20) and various other Rishonim, including the Baal Hamaor‘s (Rosh Hashana 20b.)
The dateline runs in principle 90 degrees east of Yerushalayim, where the time is six hours later. This line is at 125.2°E and runs technically through Russia, China, North Korea, the Philippines, and Australia. See next question in regards to the “nigrar” issue and what is in practice is the Chazon Ish dateline.

2) A second opinion best known as the Sefer Hayomam B’Kadur Ha’aretz from Rav Yechiel Michel Tukachinsky, zt”l, reflects the Yesod Olam and Matteh Dan’s view. Horav Henken zt”l evinces a similar opinion in Edus L’Yisroel p. 119. (See also Bnei Tzion 1: 14). This outlook is based on the fact that Yerushalayim is considered to be “the centre of the world.”  Creation proceeded from there. Thus, the Halacha Dateline would be located at the exact opposite side of the world, 180 degrees away. This meaning, that 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 through the State and Gulf of Alaska and down the Pacific Ocean east of Hawaii, placing the entire state of Hawaii on the other side of the Dateline.

3) The third opinion is the Mid-Pacific. It places the Halacha dateline between the Bering Straits and Alaska. This opinion considers such a line as the “natural” dividing line of the world, separating the earth into two hemispheres. According to this view the Halacha Dateline is very close to the International Dateline and only some relatively minor Pacific islands fall into a “variance zone.” The exact location of this dateline varies among Poskim.  The Bnai Tzion’s (2: 10) Dateline slants westward through the Bering Straits (between Alaska and Siberia), touching the Siberian coast, through the Pacific Ocean at approximately 177°E (west of Fiji), then turns east of New Zealand. 
Other Mid-Pacific Poskim, including Rabbi B. Rabinowitz Theumim (Hapardes Iyar 5714),Atzei Sodeh and Alei Yonah are of the opinion that the line is at 169.7°W , and runs from the eastern tip of Siberia, directly southward through the Pacific Ocean, 10° east of the Civil Dateline.
According to these opinions, Japan and New Zealand are on the western side of the Dateline (similar to Asia), and residents of these locations observe Shabbos on the local Saturday.  Hawaii is on the eastern side of the Dateline (similar to America), and residents also observe Shabbos on their local Saturday.

As far as practical Halacha today; Horav Moshe Heinemann’s shlit’a position, (quoted in Star K online by Rabbi Dovid Heber) is that one should follow the majority of opinions of the above mentioned Poskim in determining which day is observed as Shabbos, and also observe Dinei d’Oraisa shel Shabbos, Shabbos prohibitions of the Torah, on the day of the minority opinion.  However, Rabbinic prohibitions, such as shopping and the handling of muktzah, are permissible on the day which the minority opinion considers Shabbos.  In addition, performing even a biblically proscribed violation of Shabbos through a shinui, or an unusual manner, or through the action of a Gentile, would be permitted on the day which the minority opinion considers Shabbos.

Horav Shlomo Miller’s Shlit’a opinion is that the view of the Chazon Ish is most important as it is reflected on the opinion of the Rishonom (Kuzary and Ba’al Hamaor). However, the Halacha issue remains still unsettled. He also recommends to follow Horav Heinemann’s Shlit’a advice above in areas of conflict. He also quoted Horav Moshe Feinstein zt”l who asserted that people should avoid residence or visiting areas of Shabbos uncertainty.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a