I heard there is a shailah about when to keep Shabbos when staying in New Zealand due to the date line. How do we pasken?
There is a dispute among authorities concerning the time of Shabbos in New Zealand. According to most poskim, Shabbos should be kept on Saturday. Some, however (based on the opinion of Baal Hame’or, which is ruled by several rishonim and by the Chazon Ish), maintain that Shabbos should be kept on Sunday. Teshuvos Vehanhagos writes that due to the doubt, one should avoid all Torah prohibitions on Sunday. However, kiddush, Shabbos prayers, and so on, should be recited on Saturday alone (and tefillin should be worn on Sunday).
Sources: See Teshuvos Vehanhagos, I:269, III, 86; IV:66.