View source for International Date Line

{{short description|Imaginary line that demarcates the change of one calendar day to the next}}
{{Redirect|Date line||Dateline (disambiguation)}}
{{refimprove|date=July 2022}}
{{Use dmy dates|date=August 2016}}
{{en-US|date=January 2019}}
[[File:International Date Line.png|thumb|The International Date Line around the [[antimeridian]] (180° longitude).]]
The '''International Date Line''' ('''IDL''') is an internationally accepted demarcation of the [[Earth#Surface|surface of Earth]], running between the [[South Pole|South]] and [[North Pole]]s and serving as the boundary between one [[calendar day]] and the next. It passes through the [[Pacific Ocean]], roughly following the [[180th meridian|180.0°]] [[line of longitude]] and deviating to pass around some territories and island groups. Crossing the date line eastbound decreases the date by one day, while crossing the date line westbound increases the date.

==Geography==
[[File:Dateline-animation-3deg-borderonly-180px.gif|thumb|upright=1.3|A simplified illustration of the relation between date line, date and time of day. Each colour represents a different date.]]
[[File:international date line.png|thumb|280px|Example depicting situation at 04:00 [[Greenwich Mean Time|GMT]] Tuesday. (Times are approximate, since time zone boundaries generally do not exactly coincide with meridians. Night and day is illustrative only; daylight hours depend on latitude and time of year.)]]

===Circumnavigating the globe===

People traveling westward [[circumnavigation|around the world]] must set their clocks: 
*Back by one hour for every 15° of longitude crossed, and 
*Forward by 24 hours upon crossing the International Date Line.

People traveling eastward must set their clocks: 
*Forward by one hour for every 15° of longitude crossed, and 
*Back by 24 hours upon crossing the International Date Line.

Failing to do this would make their time inaccurate to the local time.

The 14th century Arab geographer [[Abulfeda]] predicted that circumnavigators would accumulate a one-day offset to the local date.<ref>{{cite book |last1=Gunn |first1=Geoffrey C. |title=Overcoming Ptolemy: The Revelation of an Asian World Region |date=15 October 2018 |publisher=Lexington Books |location=Lanham, Maryland |isbn=9781498590143 |pages=47–48}}</ref> This phenomenon was confirmed in 1522 at the end of the [[Magellan's circumnavigation|Magellan–Elcano expedition]], the first successful circumnavigation. After sailing westward around the world from Spain, the expedition called at [[Cape Verde]] for provisions on Wednesday, 9 July 1522 (ship's time). However, the locals told them that it was actually Thursday, 10 July 1522. The crew was surprised, as they had recorded each day of the three-year journey without omission.<ref>{{cite book|last=Neal|first=Larry|title=The Rise of Financial Capitalism: International Capital Markets in the Age of Reason|url=https://books.google.com/books?id=ey8h1WC5w7kC|year=1993|publisher=Cambridge University Press|isbn=978-0-521-45738-5|page=[https://books.google.com/books?id=ey8h1WC5w7kC&dq=%229+july%22+%2210+july%22&pg=PA8-IA1 1]}}</ref> Cardinal [[Gasparo Contarini]], the Venetian ambassador to Spain, was the first European to give a correct explanation of the discrepancy.<ref>{{cite book |last1=Winfree |first1=Arthur T. |title=The Geometry of Biological Time |edition=2nd |date=2001 |publisher=Springer Science & Business Media |location=New York |isbn=978-1-4757-3484-3 |page=10 |language=en}}</ref>

===Description===
{{refimprove section|date=July 2022}}
:''This description is based on the most common understanding of the ''de facto'' International Date Line. See {{slink||De facto and de jure date lines}} below, and map above at right.''
The IDL is roughly based on the [[Meridian (geography)|meridian]] of 180° longitude, roughly down the middle of the Pacific Ocean, and halfway around the world from the [[IERS Reference Meridian]], the successor to the historic [[Prime meridian (Greenwich)|Greenwich prime meridian]] running through the [[Royal Observatory, Greenwich|Royal Greenwich Observatory]]. In many places, the IDL follows the 180° meridian exactly. In other places, however, the IDL deviates east or west away from that meridian. These various deviations generally accommodate the political and/or economic affiliations of the affected areas.

Proceeding from north to south, the first deviation of the IDL from 180° is to pass to the east of [[Wrangel Island]] and the [[Chukchi Peninsula]], the easternmost part of Russian [[Siberia]]. (Wrangel Island lies directly on the meridian at 71°32′N 180°0′E, also noted as 71°32′N 180°0′W.)<ref name="wrengell">{{cite journal |title=Arctic Expeditions Commanded by Americans |journal=The National Geographic Magazine |volume=18 |pages=459–468 |url=https://books.google.com/books?id=_RAOAQAAIAAJ&pg=PA459|year=1907 |access-date=4 January 2017}}</ref> It then passes through the [[Bering Strait]] between the [[Diomede Islands]] at a distance of {{convert|1.5|km|mi}} from each island at 168°58′37″ W.<ref name="Russia-US maritime boundary">{{citation |last=Allen |first=Jared |date=11 January 2012 |title=United States – Russian Maritime Boundary and Exclusive Economic Zones |website=ArcticEcon |url=https://arcticecon.wordpress.com/2012/01/11/united-states-russian-maritime-boundary-and-exclusive-economic-zones/ |access-date=4 January 2017 |archive-date=5 January 2017 |archive-url=https://web.archive.org/web/20170105181513/https://arcticecon.wordpress.com/2012/01/11/united-states-russian-maritime-boundary-and-exclusive-economic-zones/ |url-status=live }}</ref> It then bends considerably west of 180°, passing west of [[St. Lawrence Island]] and [[St. Matthew Island]].

The IDL crosses between the U.S. [[Aleutian Islands]] ([[Attu Island]] being the westernmost) and the [[Commander Islands]], which belong to Russia. It then bends southeast again to return to 180°. Thus, all of Russia is to the west of the IDL, and all of the United States is to the east except for the insular areas of [[Guam]], the [[Northern Mariana Islands]], and [[Wake Island]], reaching the hypothetical, but not used UTC–13:00 time zone.

The IDL remains on the 180° meridian until passing the [[equator]]. Two U.S.-owned uninhabited atolls, [[Howland Island]] and [[Baker Island]], just north of the equator in the central Pacific Ocean (and ships at sea between 172.5°W and 180°), have the earliest time on Earth ([[UTC−12:00]] hours).

The IDL circumscribes [[Kiribati]] by swinging far to the east, almost reaching the [[150th meridian west|150°W meridian]]. Kiribati's easternmost islands, the southern [[Line Islands]] south of [[Hawaii]], have the latest time on Earth, [[UTC+14:00]] hours.

South of Kiribati, the IDL returns westwards but remains east of 180°, passing between [[Samoa]] and [[American Samoa]].<ref name=BorneoPost>[http://www.theborneopost.com/2011/06/30/samoa-confirms-dateline-switch/ Samoa confirms dateline switch] {{Webarchive|url=https://web.archive.org/web/20111008180735/http://www.theborneopost.com/2011/06/30/samoa-confirms-dateline-switch/ |date=8 October 2011 }} Borneo Post online. Accessed 11 August 2011.</ref> Accordingly, Samoa, [[Tokelau]], [[Wallis and Futuna]], [[Fiji]], [[Tonga]], [[Tuvalu]], and New Zealand's [[Kermadec Islands]] and [[Chatham Islands]] are all west of the IDL and have the same date. American Samoa, the [[Cook Islands]], [[Niue]], and [[French Polynesia]] are east of the IDL and one day behind.

The IDL then bends southwest to return to 180°. It follows that meridian until reaching [[Antarctica]], which has [[Time in Antarctica|multiple time zones]]. Conventionally, the IDL is not drawn into Antarctica on most maps. (See {{slink||Cartographic practice and convention}} below.)

===Facts dependent on the IDL===
{{refimprove section|date=July 2022}}
According to the clock, the first areas to experience a new day and a [[New Year]] are islands that use UTC+14:00. These include portions of the [[Republic of Kiribati]], including [[Millennium Island]] in the Line Islands. The first major cities to experience a new day are [[Auckland]] and [[Wellington]], New Zealand ([[UTC+12:00]]; [[UTC+13:00]] with daylight saving time).{{cn|date=July 2022}}

A 1994 realignment of the IDL made Caroline Island one of the first points of land on Earth to reach January 1, 2000, on the calendar (UTC+14:00). As a result, this [[atoll]] was renamed [[Millennium Island]].<ref name="Millennium">{{cite web |work= Pacific Islands Report |title= Kiribati's Caroline Island renamed Millennium Island |date= September 2002 |url= http://www.pireport.org/articles/1997/08/11/kiribatis-caroline-island-renamed-millennium-island |access-date= 4 January 2017 |archive-url= https://web.archive.org/web/20190822120549/http://www.pireport.org/articles/1997/08/11/kiribatis-caroline-island-renamed-millennium-island |archive-date= 22 August 2019 |url-status= dead }}</ref>

The areas that are the first to see the daylight of a new day vary by the season. Around the [[June solstice]], the first area would be any place within the [[Kamchatka Time|Kamchatka Time Zone]] (UTC+12:00) that is far enough north to experience [[midnight sun]] on the given date. At the [[equinox]]es, the first place to see daylight would be the uninhabited Millennium Island in Kiribati, which is the easternmost land located west of the IDL.{{cn|date=July 2022}}

Near the [[December solstice]], the first places would be [[Research stations in Antarctica|Antarctic research stations]] using [[New Zealand Time]] (UTC+13:00) during summer that experience midnight sun. These include [[Amundsen-Scott South Pole Station]], [[McMurdo Station]], [[Scott Base]] and [[Zucchelli Station]].<ref>{{cite web|title=The World Clock-Query Results|url=http://www.timeanddate.com/worldclock/?query=Antarctica|website=Time and date.com|access-date=20 May 2016|postscript=,|archive-date=17 June 2016|archive-url=https://web.archive.org/web/20160617194222/http://www.timeanddate.com/worldclock/?query=Antarctica|url-status=live}} and click through to the individual stations' pages. With respect to Scott Base, see [[Ross Dependency]].</ref>

== De facto and de jure date lines ==
{{unsourced section|date=July 2022}}
There are two ways [[time zone]]s and thereby the location of the International Date Line are determined, one on land and adjacent [[territorial waters]], and the other on open seas.{{cn|date=July 2022}}

All nations unilaterally determine their standard [[time zone]]s, applicable only on land and adjacent territorial waters. This date line can be called ''[[de facto]]'' since it is not based on international law, but on national laws. These national zones do not extend into international waters.{{cn|date=July 2022}}

The [[nautical date line]], not the same as the IDL, is a ''[[de jure]]'' construction determined by international agreement. It is the result of the 1917 [[Anglo-French Conference on Time-keeping at Sea]], which recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas. The United States adopted its recommendation for U.S. military and merchant marine ships in 1920. This date line is implied but not explicitly drawn on time zone maps. It follows the [[180th meridian|180° meridian]] except where it is interrupted by territorial waters adjacent to land, forming gaps—it is a pole-to-pole dashed line. The 15° [[Gore (segment)|gore]] that is offset from UTC by 12 hours is bisected by the nautical date line into two 7.5° gores that differ from UTC by ±12 hours.

In theory, ships are supposed to adopt the standard time of a country if they are within its territorial waters within {{convert|12|nmi|mi km}} of land, then revert to international time zones (15° wide pole-to-pole [[Gore (segment)|gore]]s) as soon as they leave. In practice, ships use these time zones only for radio communication and similar purposes. For internal (within-ship) purposes, such as work and meal hours, ships use a time zone of their own choosing.{{cn|date=July 2022}}

===Cartographic practice and convention===
The IDL on the map in this article and all other maps is based on the ''de facto'' line and is an artificial construct of cartographers, as the precise course of the line in international waters is arbitrary. The IDL does not extend into Antarctica on the world time zone maps by the United States [[Central Intelligence Agency]] (CIA)<ref name=CIA>{{cite web |url=https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf |title=Standard Time Zones of the World by the CIA |access-date=23 September 2014 |archive-date=8 January 2018 |archive-url=https://web.archive.org/web/20180108181645/https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/physical/pdf/standard_time_zones_of_the_world.pdf |url-status=dead }}</ref> or the United Kingdom's [[HM Nautical Almanac Office|His Majesty's Nautical Almanac Office]] (HMNAO).<ref name=HMNAO>{{cite web |url=http://astro.ukho.gov.uk/nao/miscellanea/WMTZ/Wmtz160224.pdf |title=Standard Time Zones by HM Nautical Almanac Office |publisher=HM Nautical Almanac Office and US Naval Observatory (jointly) |access-date=20 May 2016 |archive-date=11 June 2016 |archive-url=https://web.archive.org/web/20160611172910/http://astro.ukho.gov.uk/nao/miscellanea/WMTZ/Wmtz160224.pdf |url-status=dead }} {{selfref inline|Note that this map uses the opposite sign convention for time zones from that used in Wikipedia.}}</ref> The IDL on modern CIA maps now reflects the most recent shifts in the IDL<ref name=CIA /> (see {{slink||Historic alterations}} below). The current HMNAO map does not draw the IDL in conformity with recent shifts in the IDL; it draws a line virtually identical to that adopted by the UK's Hydrographic Office about 1900.<ref>A. M. W. Downing, [http://articles.adsabs.harvard.edu/full/1900JBAA...10..176D "Where the day changes"] {{Webarchive|url=https://web.archive.org/web/20170721110851/http://articles.adsabs.harvard.edu/full/1900JBAA...10..176D |date=21 July 2017 }}, ''Journal of the British Astronomical Association'', vol x, no 4, 1906, pp. 176–178.</ref> Instead, HMNAO labels island groups with their time zones, which do reflect the most recent IDL shifts.<ref name=HMNAO /> This approach is consistent with the principle of national and nautical time zones: the islands of eastern Kiribati are actually "islands" of Asian date (west side of IDL) in a sea of American date (east side of IDL). Similarly, the western Aleutian Islands are islands of American date in a sea of Asian date.{{cn|date=July 2022}}

No international organization, nor any treaty between nations, has fixed the IDL drawn by cartographers: the 1884 [[International Meridian Conference]] explicitly refused to propose or agree to any time zones, stating that they were outside its purview. The conference resolved that the Universal Day, midnight-to-midnight [[Greenwich Mean Time]] (now redefined and updated as [[Coordinated Universal Time|Coordinated Universal Time, or UTC]]), which it did agree to, "shall not interfere with the use of local or standard time where desirable".<ref name=imc>{{cite web|title=International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884. Protocols of the proceedings.|url=http://www.gutenberg.org/files/17759/17759-h/17759-h.htm|publisher=Project Gutenberg|page=134|access-date=20 May 2016|year=1884|archive-date=11 September 2015|archive-url=https://web.archive.org/web/20150911112200/http://www.gutenberg.org/files/17759/17759-h/17759-h.htm|url-status=live}} Quote is from the session of 14 October.</ref>  From this comes the utility and importance of UTC or "Z" ("Zulu") time: it permits a single universal reference for time that is valid for all points on the globe at the same moment.{{cn|date=July 2022}}

==Historic alterations==

===<span class="anchor" id="Philippines"></span>Philippines (1521 and 1844)===
{{main|Philippine Standard Time}}
[[Image:Datumsgrenze MK1888.png|thumb|left|Erroneous International Date Line from the 1888 Encyclopædia the {{Lang|de|[[Meyers Konversations-Lexikon]]}}, running between the Spanish [[History of the Philippines (1565–1898)|Philippine Islands]] and British [[History of Hong Kong (1800s–1930s)|Hong Kong]]. The Philippine Islands and the rest of [[New Spain]] are shown on the eastern side of the IDL, even though they were moved to the western side in 1845. Also placed to the east of the IDL were the [[Bonin Islands]] and [[Fiji]], which are actually to the west of the line.]]

[[Ferdinand Magellan]] claimed the Philippines for Spain on Saturday, {{nowrap|16 March 1521}}, having sailed westwards from [[Seville]] across the [[Atlantic Ocean]] and the [[Pacific Ocean]]. As part of [[New Spain]], the [[Philippines]] had its most important communication with [[Acapulco]] in [[Mexico]], so it was on the eastern side of the IDL despite being on the western edge of the [[Pacific Ocean]]. As a result, the Philippines was one day behind its [[Asia]]n neighbours for 323 years, 9 months and 4 days from Saturday, 16 March 1521 ''(Julian Calendar)'' until Monday, 30 December 1844 ''(Gregorian Calendar)''.<ref>{{Cite web|first=Anri|last=Ichimura|url=https://www.esquiremag.ph/long-reads/features/philippines-international-date-line-time-a00304-20210217-lfrm|title=For Over 300 Years, the Philippines Was One Day Behind Every Country in Asia|publisher=EsquireMag.ph|date=February 17, 2021|access-date=2023-03-01|language=EN|archive-date=1 March 2023|archive-url=https://web.archive.org/web/20230301123820/https://www.esquiremag.ph/long-reads/features/philippines-international-date-line-time-a00304-20210217-lfrm|url-status=live}}</ref>

After Mexico gained its independence from Spain on 27 September 1821, Philippine trade interests turned to [[Qing dynasty|Imperial China]], the [[Dutch East Indies]] and adjacent areas, so the Philippines decided to join its Asian neighbours on the west side of the IDL.<ref>{{cite web|url=https://webspace.science.uu.nl/~gent0113/idl/idl_philippines.htm|title=A History of the International Date Line|author=R. H. van Gent|publisher=Webspace.science.uu.nl|access-date=30 December 2011|archive-date=9 August 2020|archive-url=https://web.archive.org/web/20200809023245/https://webspace.science.uu.nl/~gent0113/idl/idl_philippines.htm|url-status=live}}{{self-published source|date=July 2022}}</ref>{{self-published source|date=July 2022}} To advance the calendar by one day, on 16 August 1844 the then governor-general [[Narciso Clavería y Zaldúa|Narciso Claveria]], ordered that Tuesday, {{nowrap|31 December 1844}} should be removed from the calendar. Monday, {{nowrap|30 December 1844}} was followed immediately by Wednesday, {{nowrap|1 January 1845}}. The change also applied to the other remaining Spanish colonies in the Pacific: the [[Caroline Islands]], [[Guam]], [[Mariana Islands]], [[Marshall Islands]] and [[Palau]] as part of the [[Captaincy General of the Philippines]].<ref>{{Cite web |title=Time Zone & Clock Changes in Saipan, Northern Mariana Islands |url=https://www.timeanddate.com/time/zone/usa/saipan |access-date=2022-11-14 |website=www.timeanddate.com |language=en |archive-date=8 January 2017 |archive-url=https://web.archive.org/web/20170108093519/https://www.timeanddate.com/time/zone/usa/saipan |url-status=live }}</ref><ref>{{Cite web|url=https://faroutliers.wordpress.com/2007/08/27/missing-date-in-philippines-history-31-december-1844/|title=Missing Date In Philippines History: 31 December 1844|website=wordpress.com|language=en-US|date=27 August 2007|access-date=March 7, 2022|archive-date=1 March 2023|archive-url=https://web.archive.org/web/20230301124733/https://faroutliers.wordpress.com/2007/08/27/missing-date-in-philippines-history-31-december-1844/|url-status=live}}</ref> Western publications were generally unaware of this change until the early 1890s, so they erroneously gave the International Date Line a large western bulge for the next half century.<ref>{{cite book |last=Schedler |first=Joseph |date=1878 |title=An illustrated manual for the use of the terrestrial and celestial globes |url=https://archive.org/details/illustratedmanua00sche |location=New York |page=[https://archive.org/details/illustratedmanua00sche/page/27 27]}}</ref>

===<span class="anchor" id="Tahiti"></span>Tahiti & French Polynesia (early 1797 and late 1846)===
On 5 March 1797, missionaries of the [[London Missionary Society]] arrived on [[Tahiti]] from England. They had first tried to pass [[Cape Horn]], but failing that, went along [[Cape of Good Hope]] and the [[Indian Ocean]] instead. As such, they introduced the date of the eastern hemisphere on the island.<ref>{{Citation|title=Missionary writing in Polynesia|date=2003-08-07|url=http://dx.doi.org/10.1017/cbo9780511550324.008|work=Missionary Writing and Empire, 1800–1860|pages=136–164|publisher=Cambridge University Press|doi=10.1017/cbo9780511550324.008|isbn=9780521826990|access-date=2022-02-16|archive-date=16 February 2022|archive-url=https://web.archive.org/web/20220216101216/https://www.cambridge.org/core/books/abs/missionary-writing-and-empire-18001860/missionary-writing-in-polynesia/3579B3E6922B2AA7D43114D5870CA301|url-status=live}}</ref> It was not until the ending of the [[Franco-Tahitian War]] and the restoration of the French [[Protectorate]] over the Tahitian Kingdom (which Tahitian nationalists had tried to fight off for two years of intense war with more than 1000 deaths) that the French commissioner [[Armand Joseph Bruat]]  and the regent of the Tahitian Kingdom Paraita ordered that Tahiti had to follow the western hemisphere on 29 December 1846.<ref>{{Cite book|last=Saura|first=Bruno|year=1965|url=http://worldcat.org/oclc/933526850|title=Histoire et mémoire des temps coloniaux en Polynésie française|publisher=Au vent des îles éditions |isbn=978-2-36734-081-4|oclc=933526850|access-date=16 February 2022|archive-date=16 February 2022|archive-url=https://web.archive.org/web/20220216110540/https://www.worldcat.org/oclc/933526850|url-status=live}}</ref><ref>{{Cite book|author1=Maurice Graindorge |author2=Roger Parodi |title=Le ciel de Tahiti et des mers du Sud|publisher=Papeete: Editions Haere Pō nō, Tahiti, 1988|pages=105}}</ref><ref>{{Cite book|author=Louise Peltzer|title=Chronologie des événements politiques, sociaux et culturels de Tahiti et des archipels de la Polynésie française|publisher=Papeete: Éditions Au Vent des Îles, 2002|pages=55}}</ref>
{{clear|left}}

===<span class="anchor" id="Alaska"></span>Alaska (1867)===
{{See also|Alaska Time Zone|Time in Alaska}}
Alaska was on the western side of the International Date Line, since Russian settlers reached Alaska from [[Siberia]]. In addition, the [[Russian Empire]] was still using the [[Julian calendar]], which had fallen 12 days behind the [[Gregorian calendar]]. In 1867, the United States purchased [[Russian America]] and moved the territory to the east side of the International Date Line. The transfer ceremony took place at 3:30{{nbs}}p.m. local mean time (00:31 GMT) in the capital of New Archangel ([[Sitka, Alaska|Sitka]]), on Saturday, {{nowrap|7 October 1867}} (Julian), which was Saturday, {{nowrap|19 October 1867}} (Gregorian) in Europe. Since Alaska moved to the eastern side of the International Date Line, the date and time also moved back to 3:30{{nbs}}p.m. local time Friday, {{nowrap|18 October 1867}} (00:31 GMT Saturday), now known as [[Alaska Day]].<ref name=transfer>[https://books.google.com/books?id=n2lHAQAAIAAJ&pg=RA15-PA4 Alaska: ... The transfer of territory from Russia to the United States], Executive document 125 in ''Executive documents printed by order of the House of Representatives during the second session of the fortieth Congress, 1867–'68'', vol. 11, Washington: 1868. "18th of October ... fixed the hour of three and a half o'clock that day for the transfer"</ref><ref name=Sumner>Charles Sumner, [https://books.google.com/books?id=KawSAAAAYAAJ&pg=PA348 The cession of Russian America to the United States] in ''The Works of Charles Sumner'', vol. 11, Boston: 1875, pp. 181–349, p. 348. Sumner released the written version of his speech on Thursday,{{nowrap|24 May 1867}}, having written it during the immediately preceding Congressional recess following notes on a single page that he actually used on Tuesday, {{nowrap|9 April}}.</ref>

===<span class="anchor" id="Samoan Islands and Tokelau"></span>Samoan Islands and Tokelau (1892 and 2011)===
{{See also|Samoa Time Zone}}
The [[Samoan Islands]], now divided into [[Samoa]] and [[American Samoa]], were on the west side of the IDL until 1892.  In that year, King [[Malietoa Laupepa|Mālietoa Laupepa]] was persuaded by American traders to adopt the American date (three hours behind California) to replace the former Asian date (four hours ahead of Japan). The change was made by repeating {{nowrap|Monday, 4 July 1892}}, [[Independence Day (United States)|American Independence Day]].<ref>{{Cite journal |last=Lamont |first=Roscoe |date=1921-06-01 |title=The International Date Line |url=https://ui.adsabs.harvard.edu/abs/1921PA.....29..340L |journal=Popular Astronomy |volume=29 |pages=340–348 |bibcode=1921PA.....29..340L |issn=0197-7482 |access-date=3 July 2022 |archive-date=3 July 2022 |archive-url=https://web.archive.org/web/20220703101305/https://ui.adsabs.harvard.edu/abs/1921PA.....29..340L |url-status=live }}</ref>

In 2011, Samoa shifted back to the west side of the IDL by removing Friday, {{nowrap|30 December 2011}} from its calendar.<ref name=nypost>{{cite news|url=http://www.nypost.com/p/news/international/where_day_go_QeLR87EP23V9wJrdvAXJdO| title=Where'd Day Go? |publisher=[[Associated Press]] via the [[New York Post]]|date=31 December 2011|archive-url=https://web.archive.org/web/20120101004950/http://www.nypost.com/p/news/international/where_day_go_QeLR87EP23V9wJrdvAXJdO|archive-date=1 January 2012|url-status=live}}</ref> This changed the time zone from [[UTC−11:00]] to [[UTC+13:00]] ([[UTC-10]] to [[UTC+14:00|UTC+14]] [[Dst]] ).<ref name=HeraldSun>{{cite news|first=Tamara|last= McLean|url=http://www.heraldsun.com.au/news/breaking-news/samoas-dateline-jump-passes-into-law/story-e6frf7jx-1226083970021 |title=Samoa's dateline jump passes into law|location=Melbourne, Australia| publisher=[[Australian Associated Press]] via the [[Herald Sun]]| access-date=11 August 2011| archive-url = https://web.archive.org/web/20120101004714/http://www.heraldsun.com.au/news/breaking-news/samoas-dateline-jump-passes-into-law/story-e6frf7jx-1226083970021| archive-date=1 January 2012|url-status=live}}</ref>  Samoa made the change because [[Australia]] and [[New Zealand]] have become its biggest trading partners, and also have large communities of expatriates. Being 21 hours behind made business difficult because having weekends on backward days meant only four days of the week were shared [[Workweek|workday]]s.<ref>{{cite news|url=https://www.bbc.co.uk/news/business-13330592 |title=Samoa to Jump Forward in Time by One Day |work=BBC News |date=9 May 2011 |access-date=27 November 2011|archive-url=https://web.archive.org/web/20111231024932/http://www.bbc.co.uk/news/business-13330592|archive-date=31 December 2011|url-status=live}}</ref>

The IDL now passes between Samoa and American Samoa, which remains on the east (American) side of the line.<ref>{{Cite news |last=Mydans |first=Seth |date=2011-12-29 |title=Samoa Sacrifices a Day for Its Future |language=en-US |work=The New York Times |url=https://www.nytimes.com/2011/12/30/world/asia/samoa-to-skip-friday-and-switch-time-zones.html |access-date=2022-07-03 |issn=0362-4331 |archive-date=8 May 2021 |archive-url=https://web.archive.org/web/20210508014807/https://www.nytimes.com/2011/12/30/world/asia/samoa-to-skip-friday-and-switch-time-zones.html |url-status=live }}</ref>

[[Tokelau]] is a territory of New Zealand north of Samoa whose principal transportation and communications links with the rest of the world pass through [[Samoa]]. For that reason, Tokelau crossed the IDL along with Samoa in 2011, albeit strictly speaking 1 hour later, as they did not do Summer Time (Daylight Saving Time in American English), which Samoa did then.<ref name="Tokelau">{{Cite web |title=Tokelau: Wrong local time for over 100 years |url=https://www.timeanddate.com/news/time/tokelau-wrong-time.html |access-date=2022-07-03 |website=www.timeanddate.com |language=en |archive-date=3 June 2022 |archive-url=https://web.archive.org/web/20220603212619/https://www.timeanddate.com/news/time/tokelau-wrong-time.html |url-status=live }}</ref>

===<span class="anchor" id="Kwajalein"></span>Kwajalein (c. 1945 and 1993)===
[[Kwajalein]] atoll, like the rest of the [[Marshall Islands]], passed from Spanish to German to Japanese control during the nineteenth and twentieth centuries. During that period it was west of the IDL. Although Kwajalein formally became part of the [[Trust Territory of the Pacific Islands]] with the rest of the Marshalls after World War II, the United States established a military installation there. Because of that, Kwajalein used the Hawaiian date, so was effectively east of the International Date Line (unlike the rest of the Marshalls). Kwajalein returned to the west side of the IDL by removing Saturday, {{nowrap|21 August 1993}} from its calendar. Moreover, Kwajalein's work week was changed to Tuesday through Saturday to match the Hawaiian work week of Monday through Friday on the other side of the IDL.<ref>{{cite news |url=https://query.nytimes.com/gst/fullpage.html?res=9F0CE1D6163EF931A1575BC0A965958260&sec=&spon=&partner=permalink&exprod=permalink |title=In Marshall Islands, Friday Is Followed by Sunday |work=[[The New York Times]] |date=22 August 1993 |access-date=2007-09-24 |archive-date=14 October 2007 |archive-url=https://web.archive.org/web/20071014214125/http://query.nytimes.com/gst/fullpage.html?res=9F0CE1D6163EF931A1575BC0A965958260&sec=&spon=&partner=permalink&exprod=permalink |url-status=live }}</ref>

===<span class="anchor" id="Eastern Kiribati"></span>Eastern Kiribati (1994)===
{{main|Time in Kiribati}}
As a British colony, the [[Kiribati]] colony was centered in the [[Gilbert Islands]], just west of the IDL of the time. Upon independence in 1979, it acquired the claim to the [[Phoenix Islands|Phoenix]] and [[Line Islands]], east of the IDL, from the United States. As a result, the country straddled the IDL. Government and commercial concerns on opposite sides of the line could only conduct routine business by radio or telephone on the four days of the week which were weekdays on both sides. To eliminate this anomaly, [[Kiribati]] introduced a change of date for its eastern half by removing Saturday, {{nowrap|31 December 1994}} from its calendar. Because of this, Friday, 30 December 1994, was followed by Sunday, 1 January 1995. After the change, the IDL in effect moved eastwards to go around the entire country. Strictly legal, the 1917 nautical IDL convention is still valid. For example, when it is Monday on Kiribati's islands, it is still Sunday in the surrounding ocean, though maps are usually not drawn this way.<ref>{{citation |last1=Ariel |first1=Avraham |last2=Berger |first2=Nora Ariel |title=Plotting the Globe: Stories of Meridians, Parallels, and the International Date Line |url=https://books.google.com/books?id=2xTJt3b3SHUC&pg=PP1 |publisher=Greenwood Press |date=2005 |page=149 |isbn=0275988953}}</ref>

As a consequence of the 1994 change, Kiribati's easternmost territory, the [[Line Islands]], including the inhabited island of [[Kiritimati|Kiritimati (Christmas Island)]]<!--All areas in UTC+14 have midnight and new year simultaneously-->, started the year 2000 before any other country, a feature upon which the Kiribati government capitalized as a potential tourist draw.{{cn|date=July 2022}}

==Date lines according to religious principles==

===Christianity===
{{refimprove section|date=July 2022}}
{{further|Seventh-day Adventist Church of Tonga#Date Line controversy}}
Generally, the Christian calendar  and Christian churches recognize the IDL.  [[Christmas]] for example, is celebrated on 25 December (according to either the [[Gregorian calendar|Gregorian]] or the [[Julian calendar]], depending upon which of the two is used by the particular church) as that date falls in countries located on either side of the IDL.  Thus, whether it is Western Christmas or Orthodox Christmas, Christians in Samoa, immediately west of the IDL, will celebrate the holiday a day before Christians in ''American'' Samoa, which is immediately ''east'' of the IDL.{{cn|date=July 2022}}

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 IDL. 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; that causes questions to arise under religious law.{{cn|date=July 2022}} Because the IDL is an arbitrary imposition, the question can arise as to which Saturday on either side of the IDL (or, more fundamentally, on either side of 180 degrees longitude) is the "real" Saturday.  This issue (which also arises in [[#Judaism|Judaism]]) is a particular problem for Seventh Day Adventists, [[Seventh Day Baptists]], and similar churches located in countries near the IDL.{{cn|date=July 2022}}

In [[Tonga]], [[Seventh-day Adventist Church of Tonga|Seventh Day Adventists]] (who usually observe Saturday, the [[seventh-day Sabbath]]) observe Sunday because Tonga lies east of the 180° meridian. Sunday as observed in Tonga (west of the IDL, 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 IDL.<ref>{{Cite journal | last = Hay | first = Davi | title = Tonga's Common Day of Worship | journal = Record | volume = 93 | issue = 3 | page = 6 | publisher = Signs Publishing Company | location = Warburton, Victoria, Australia | date = 30 January 1988 | url = http://www.adventistarchives.org/docs/AAR/AAR19880130-V93-03__C.pdf#view=fit | access-date = 2 January 2012 }}{{Dead link|date=January 2020 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite web |publisher=Record |url=http://record.adventistconnect.org/site_data/88/assets/0034/6941/RECORD_2_lowrez.pdf |title=Date Line Changed in Somoa |date=4 Feb 2012 |pages=3 & 10 |access-date=16 April 2013 |archive-date=27 May 2013 |archive-url=https://web.archive.org/web/20130527055651/http://record.adventistconnect.org/site_data/88/assets/0034/6941/RECORD_2_lowrez.pdf |url-status=live }}</ref>

Most Seventh Day Adventists in [[Samoa]] planned to observe Sabbath on Sunday after Samoa's crossing the IDL in December 2011, but SDA groups in Samatau village and other places (approximately 300 members) decided to accept the IDL adjustment and observe the Sabbath on Saturday.<ref>{{cite news|title=Samoa Seventh Day Adventists diverge over impact of Dateline switch|url=http://www.rnzi.com/pages/news.php?op=read&id=65275|access-date=28 December 2011|newspaper=Radio New Zealand International|date=28 December 2011|archive-date=5 March 2012|archive-url=https://web.archive.org/web/20120305012004/http://www.rnzi.com/pages/news.php?op=read&id=65275|url-status=live}}</ref> Debate continues within the Seventh-day Adventist community in the Pacific as to which day is really the seventh-day Sabbath.{{cn|date=July 2022}}

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.{{cn|date=July 2022}}

===Islam===
The [[Islamic calendar]] and [[Muslim]] communities recognize the convention of the IDL. In particular, the day for holding the ''[[Jumu'ah]]'' prayer appears to be local Friday everywhere in the world.{{efn|There has been some discussion that the [[meridian (geography)|meridian]] directly opposite [[Mecca]], approximately 140°W, would be an appropriate date line for Islam.  See {{cite web|last1=Deen|first1=S.M.|title=Ramadan and Prayer Times in the Lands under Midnight Sun|url=http://scienceunderislam.blogspot.com/2011/05/scid03-ramadan-and-prayer-times-in.html|website=Science Digest for Muslim Thinkers|access-date=18 May 2016}} However, this appears to be an unusual, or at least only a theoretical, position. Muslims in areas that would be affected, such as Alaska<ref>{{cite web|title=Praying Time|url=http://alaskamasjid.com/PrayingTimes.html|website=Islamic Community Center Anchorage Alaska|access-date=15 November 2017|df=dmy-all|archive-date=15 November 2017|archive-url=https://web.archive.org/web/20171115225838/http://alaskamasjid.com/PrayingTimes.html|url-status=dead}}</ref> and Hawaii,<ref>{{cite web|title=About us|url=http://www.iio.org/the-masjid/about-us|website=Muslim Association of Hawaii|access-date=18 May 2016|archive-date=27 April 2016|archive-url=https://web.archive.org/web/20160427005647/http://www.iio.org/the-masjid/about-us|url-status=live}}</ref> in fact hold ''Jumu'ah'' on local Friday, not local Thursday.}} The IDL is not a factor in the start and end of Islamic lunar months. These depend solely on sighting the [[Hilal (crescent moon)|new crescent moon]].<ref>{{cite web|title=Quran 2:185|url=http://quran.com/2/185|access-date=19 July 2012|archive-date=11 July 2012|archive-url=https://web.archive.org/web/20120711235126/http://quran.com/2/185|url-status=live}} , [http://irebd.com/quran/english/surah-2/verse-185/ Quran Surah Al-Baqara ( Verse 185 )] {{Webarchive|url=https://web.archive.org/web/20180127083933/http://irebd.com/quran/english/surah-2/verse-185/ |date=27 January 2018 }}</ref> 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 {{slink|Ramadan|Beginning}}.)

===Judaism===
{{Details|International date line in Judaism}}
The concept of an International Date Line in Jewish law is first mentioned by 12th-century decisors.<ref name=kashrus>{{cite web|url=http://www.star-k.org/articles/kashrus-kurrents/493/a-travelers-guide-to-the-international-dateline/|last=Heber|first=Rabbi Dovid|title=A Traveller's Guide To The International Dateline|date=15 August 2013|publisher=Star-k.org|access-date=26 April 2016|archive-date=12 November 2020|archive-url=https://web.archive.org/web/20201112030813/https://www.star-k.org/articles/kashrus-kurrents/493/a-travelers-guide-to-the-international-dateline/|url-status=live}}</ref><ref name=chabad>{{cite web|last1=Shurpin|first1=Rabbi Yehuda|title=The Sabbath, the International Date Line and Jewish Law|url=http://www.chabad.org/library/article_cdo/aid/1736567/jewish/|website=Chabad.org|publisher=Chabad-Lubavitch|access-date=26 April 2016|archive-date=31 October 2020|archive-url=https://web.archive.org/web/20201031053414/https://www.chabad.org/library/article_cdo/aid/1736567/jewish/Shabbat-the-International-Date-Line-and-Jewish-Law.htm|url-status=live}}</ref> 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.{{efn|The fleeing of [[Jewish refugees]], including members of the [[Mir Yeshiva (Jerusalem)#Establishment in Jerusalem|Mir Yeshiva]], from the Nazis to China and Japan during World War II was a major impetus to the codification of this aspect of Jewish law. Many of the modern-era opinions cited in <ref name=kashrus /> and <ref name=chabad /> were produced in response to this situation.}}

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,<ref>[http://www.jccjapan.or.jp/ Jewish Community of Japan] {{Webarchive|url=https://web.archive.org/web/20060117013448/http://www.jccjapan.or.jp/ |date=17 January 2006 }}, [http://www.jcckobe.org/ Jewish Community of Kansai] {{Webarchive|url=https://web.archive.org/web/20130129074850/http://www.jcckobe.org/ |date=29 January 2013 }}. Accessed April 2016.</ref> New Zealand,<ref>[http://www.chc.org.nz/ Canterbury Hebrew Congregation] {{Webarchive|url=https://web.archive.org/web/20160516031051/http://www.chc.org.nz/ |date=16 May 2016 }}, [http://ahc.org.nz/category/events/ Auckland Hebrew Congregation] {{Webarchive|url=https://web.archive.org/web/20210119001718/https://chc.org.nz/ |date=19 January 2021 }}. Accessed April 2016.</ref> [[Hawaii]],<ref>[http://sofmaarav.org/ Congregation Sof Maarav] {{Webarchive|url=https://web.archive.org/web/20160507061042/http://sofmaarav.org/ |date=7 May 2016 }}, [http://www.mauijews.org/#!events/c17et Jewish Congregation of Maui] {{Webarchive|url=https://web.archive.org/web/20201031191200/http://sofmaarav.org/#!events/c17et |date=31 October 2020 }}. Accessed April 2016.</ref> and [[French Polynesia]]<ref>{{cite news|last1=Harris|first1=Andrew|title=Shabbat in Tahiti paradise|url=http://www.jewishnews.net.au/shabbat-in-tahiti-paradise/14535|access-date=27 April 2016|work=The Australian Jewish News|date=July 28, 2010|archive-date=27 March 2019|archive-url=https://web.archive.org/web/20190327161514/https://www.jewishnews.net.au/shabbat-in-tahiti-paradise/14535|url-status=live}}</ref> 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.<ref name=kashrus /><ref name=chabad />

For individuals crossing the IDL, 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.<ref name=kashrus /><ref name=chabad />

==Cultural references and traditions==
===''The Island of the Day Before''===
The IDL 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 IDL.{{cn|date=July 2022}}

===''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&nbsp;days. To win the wager, Fogg must return by 8:45&nbsp;p.m. on Saturday, 21&nbsp;December 1872. However, the journey suffers a series of delays and when Fogg reaches London, it is 8:50&nbsp;p.m. on Friday, 20&nbsp;December, although he believes it is Saturday, 21&nbsp;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:
<blockquote>In journeying eastward he {{grey|[Fogg]}} 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.<ref>{{cite book |first=Jules |last=Verne |author-link=Jules Verne |date=15 May 2008 |orig-year=1873 |title=Around the World in Eighty Days |publisher=Project Gutenberg |url=http://www.gutenberg.org/files/103/103-h/103-h.htm |chapter=Chapter&nbsp;XXXVII |chapter-url=https://www.gutenberg.org/files/103/103-h/103-h.htm#chap37 |access-date=8 September 2013 |archive-date=9 June 2012 |archive-url=https://web.archive.org/web/20120609024111/http://www.gutenberg.org/files/103/103-h/103-h.htm |url-status=live }}</ref></blockquote>

Fogg had thought it was one day later than it actually was, because he had not accounted for this 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]] kept his watch set to London time, despite the clues from his surroundings).{{cn|date=July 2022}}

===Line-crossing ceremonies relating to the IDL===
{{See also|Line-crossing ceremony}}
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.{{cn|date=July 2022}}
== Notes ==
{{notelist}}
== References ==
{{reflist|25em}}

{{Time measurement and standards}}
{{Coord|0|N|180|W|display=title}}

[[Category:Bering Sea]]
[[Category:Chukchi Sea]]
[[Category:Kiribati]]
[[Category:Samoa]]
[[Category:Pacific Ocean]]
[[Category:Time]]