The International Date Line (IDL) is an internationally accepted demarcation on the surface of Earth, running between the

South South is one of the cardinal directions or Points of the compass, compass points. The direction is the opposite of north and is perpendicular to both east and west. Etymology The word ''south'' comes from Old English ''sūþ'', from earlier Pro ...

and

North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's axis of rotation meets its surface. It is called the True North Pole to distinguish from the Mag ...

s and serving as the boundary between one

calendar day {{Short pages monitor, started the year 2000 before any other country, a feature upon which the Kiribati government capitalized as a potential tourist draw.

Date lines according to religious principles

Christianity

Generally, the Christian calendar and Christian churches recognize the IDL.

Christmas Christmas is an annual festival commemorating Nativity of Jesus, the birth of Jesus, Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people Observance of Christmas by country, around t ...

for example, is celebrated on 25 December (according to either the Gregorian or the

Julian calendar The Julian calendar, proposed by Roman consul Julius Caesar in 46 BC, was a reform of the Roman calendar. It took effect on , by edict. It was designed with the aid of Greek mathematicians and astronomers such as Sosigenes of Alexandr ...

, depending upon which of the two is used by the particular church) as that date falls in countries located on either side of the Date Line. Thus, whether it is Western Christmas or Orthodox Christmas, Christians in Samoa, immediately west of the Date Line, will celebrate the holiday a day before Christians in ''American'' Samoa, which is immediately ''east'' of the Date Line. A problem with the general rule above arises in certain Christian churches that solemnly observe a Sabbath day as a particular day of the week, when those churches are located in countries near the Date Line. Notwithstanding the difference in dates, the same sunrise happened over American Samoa as happens over Samoa a few minutes later, and the same sunset happens over Samoa as happened over American Samoa a few minutes earlier. In other words, the secular days are ''legally'' different but they are ''physically'' the same; and that causes questions to arise under religious law. Because the Date Line was an arbitrary imposition, the question can arise as to which Saturday on either side of the Date Line (or, more fundamentally, on either side of 180 degrees longitude) is the "real" Saturday. This issue (which also arises in

Judaism Judaism ( he, ''Yahăḏūṯ'') is an Abrahamic, monotheistic, and ethnic religion comprising the collective religious, cultural, and legal tradition and civilization of the Jewish people. It has its roots as an organized religion in the ...

) is a particular problem for Seventh Day Adventists, Seventh Day Baptists, and similar churches located in countries near the Date Line. In

Tonga Tonga (, ; ), officially the Kingdom of Tonga ( to, Puleʻanga Fakatuʻi ʻo Tonga), is a Polynesian country and archipelago. The country has 171 islands – of which 45 are inhabited. Its total surface area is about , scattered over in ...

, Seventh Day Adventists (who usually observe Saturday, the

seventh-day Sabbath The seventh-day Sabbath, observed from Friday evening to Saturday evening, is an important part of the beliefs and practices of seventh-day churches. These churches emphasize biblical references such as the ancient Hebrew practice of beginning a ...

) observe Sunday due to their understanding of the International Date Line, as Tonga lies east of the 180° meridian. Sunday as observed in Tonga (West of the Date Line, as with Kiribati, Samoa, and parts of Fiji and Tuvalu) is considered by the Seventh-day Adventist Church to be the same day as Saturday observed East of the Date line. Most Seventh Day Adventists in

Samoa Samoa, officially the Independent State of Samoa; sm, Sāmoa, and until 1997 known as Western Samoa, is a Polynesian island country consisting of two main islands (Savai'i and Upolu); two smaller, inhabited islands (Manono Island, Manono an ...

planned to observe Sabbath on Sunday after Samoa's crossing the date line in December 2011, but SDA groups in Samatau village and other places (approx. 300 members) decided to accept the IDL adjustment and observe the Sabbath on Saturday. Debate continues within the Seventh-day Adventist community in the Pacific as to which day is really the seventh-day Sabbath. The Samoan Independent Seventh-day Adventist Church, which is not affiliated to the worldwide Seventh-day Adventist Church, has decided to continue worshiping on Saturday, after a six-day week at the end of 2011.

Islam

Similarly, the

Islamic calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...

and

Muslim Muslims ( ar, المسلمون, , ) are people who adhere to Islam, a monotheistic religion belonging to the Abrahamic tradition. They consider the Quran, the foundational religious text of Islam, to be the verbatim word of the God of Abrah ...

communities recognize the convention of the IDL. In particular, the day for holding the ''

Jumu'ah In Islam, Friday prayer or Congregational prayer ( ar, صَلَاة ٱلْجُمُعَة, ') is a prayer ('' ṣalāt'') that Muslims hold every Friday, after noon instead of the Zuhr prayer. Muslims ordinarily pray five times each day accordin ...

'' prayer appears to be local Friday everywhere in the world. The IDL is not a factor in the start and end of Islamic lunar months. These depend solely on sighting the new crescent moon. As an example, the fasts of the month of Ramadan begin the morning after the crescent is sighted. That this day may vary in different parts of the world is well known in Islam. (See .)

Judaism

The concept of an international date line in Jewish law is first mentioned by 12th-century decisors. But it was not until the introduction of improved transportation and communications systems in the 20th century that the question of an international date line truly became a question of practical Jewish law. As a practical matter, the conventional International Date Line—or another line in the Pacific Ocean close to it—serves as a ''de facto'' date line for purposes of Jewish law, at least in existing Jewish communities. For example, residents of the Jewish communities of Japan, New Zealand,

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

, 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 Umberto Eco (5 January 1932 – 19 February 2016) was an Italian medievalist, philosopher, semiotician, novelist, cultural critic, and political and social commentator. In English, he is best known for his popular 1980 novel ''The Name of th ...

's book ''

The Island of the Day Before ''The Island of the Day Before'' ( it, L'isola del giorno prima) is a 1994 historical fiction novel by Umberto Eco set in the 17th century during the historical search for the secret of longitude. The central character is Roberto della Griva, an ...

'' (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 Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...

's book '' Around the World in Eighty Days'' (1873). The main protagonist,

Phileas Fogg Phileas Fogg () is the protagonist in the 1872 Jules Verne novel ''Around the World in Eighty Days''. Inspirations for the character were the American entrepreneur George Francis Train and American writer and adventurer William Perry 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 sixty degrees, multiplied by four minutes, gives precisely twenty-four hours — that is, the day unconsciously gained. In other words, while Phileas Fogg, going eastward, saw the sun pass the meridian eighty times, his friends in London only saw it pass the meridian seventy-nine times.

Fogg had thought it was one day later than it actually was, because he had forgotten this simple fact. During his journey, he had added a full day to his clock, at the rhythm of an hour per fifteen degrees, or four minutes per degree, as Verne writes. At the time, the concept of a ''de jure'' International Date Line did not exist. If it did, he would have been made aware that it would be a day less than it used to be once he reached this line. Thus, the day he would add to his clock throughout his journey would be thoroughly removed upon crossing this imaginary line. But a ''de facto'' date line did exist since the U.K., India, and the U.S. had the same calendar with different local times, and he should have noticed when he arrived in the U.S. that the local date was not the same as in his diary (his servant

Jean Passepartout Jean Passepartout () is a fictional character in Jules Verne's novel '' Around the World in Eighty Days'', published in 1873. He is the French valet of the novel's English main character, Phileas Fogg. His surname translates literally to "goe ...

kept his watch set to London time, despite the clues from his surroundings).

Line-crossing ceremonies relating to the IDL

Ceremonies aboard ships to mark a sailor's or passenger's first crossing of the Equator, as well as crossing the International Date Line, have been long-held traditions in navies and in other maritime services around the world.

References

{{Coord, 0, N, 180, W, display=title Bering Sea Chukchi Sea Kiribati Samoa Pacific Ocean Time