In I got It!
‘Shabbos on Sunday’
An interesting halachic query arose regarding the real Shabbos day.
In the year 1942/5703 the Chazon Ish brought out a pamphlet ‘The Eighteen Hours’, in which he ruled, on the basis of the words of the Kuzari, that Shabbos in Japan should take place on Sunday rather than Saturday, as was the custom until that time.
This new ruling came about because of a question raised by the Mir Yeshiva, who had taken refuge in Shanghai, and then Japan, during their escape from Europe in the Second World War. They asked how they should fix the times of Shabbos and Yom Tov (Festivals).
The background for this question: The time difference that exists between every line of longitude (the distance between the lines is 15°), is one hour. The imaginary line that stretches round the 180° longitude, and is parallel to the 0° longitude passing through Greenwich, is known as the International Date Line. So someone who crosses this line, is actually crossing a time zone whereby the actual date changes.
So it works out, that on the western side of the date-line the time is twelve hours before the time in Greenwich, and on the eastern side it is twelve hours later. So the difference between the two sides of the line is 24 hours, thus, a person who crosses from one side of the line to the other, is in essence gaining or losing an entire day. Understandably, this situation was a problem regarding when Shabbos and Yom Tov should fall, and required a Halachic ruling.
The opinion of the Chazon Ish, as mentioned, was – that Shabbos in Japan falls on Sunday.
In practice, we follow a different opinion - one that is supported by many Rabbanim, amongst them Rabbi Yechiel Tikochinski (author of many Halachic works) and the Imrei Emes of Gur, who ruled that the seventh day (Saturday) must be sanctified, as it had always been until the question was brought up.
‘..And they rested on the seventh day’.