existing Jewish communities. For example, residents of the Jewish communities of Japan, New Zealand, Hawaii, and French Polynesia all observe Shabbat on local Saturday. However, there is not unanimity as to how Jewish law reaches that conclusion. For this reason, some authorities rule that certain aspects of Sabbath observance are required on Sunday (in Japan and New Zealand) or Friday (in Hawaii and French Polynesia) in addition to Saturday. Additionally, there are differences of opinion as to which day or days individual Jews traveling in the Pacific region away from established Jewish communities should observe Shabbat. For individuals crossing the date line, the change of calendar date influences some aspects of practice under Jewish law. Yet other aspects depend on an individual's experience of sunsets and sunrises to count days, notwithstanding the calendar date. Cultural references and traditions The Island of the Day Before The date line is a central factor in Umberto Eco's book The Island of the Day Before (1994), in which the protagonist finds himself on a becalmed ship, with an island close at hand on the other side of the IDL. Unable to swim, the protagonist indulges in increasingly imaginative speculation regarding the physical, metaphysical and religious importance of the date line. Around the World in Eighty Days The concept behind the IDL (though not the IDL itself, which did not yet exist) appears as a plot device in Jules Verne's book Around the World in Eighty Days (1873). The main protagonist, Phileas Fogg, travels eastward around the world. He had bet with his friends that he could do it in 80 days. To win the wager, Fogg must return by 8:45 p.m. on Saturday, 21 December 1872. However, the journey suffers a series of delays and when Fogg reaches London, it is 8:50 p.m. on Friday, 20 December, although he believes it is Saturday, 21 December and that he has lost the wager by a margin of only five minutes. The next day, however, it is revealed that the day is Saturday, not Sunday, and Fogg arrives at his club just in time to win the bet. Verne explains: In journeying eastward he had gone towards the sun, and the days therefore diminished for him as many times four minutes as he crossed degrees in this direction. There are three hundred and sixty degrees on the circumference of the earth; and these three hundred and