Introduction
Theearthisaplanetinthesolarsystem.Inadditiontorevolvingaroundthesun,italsorotatesonceaday.Therefore,thehalfsphereoftheearthirradiatedbysunlightformstheday,andtheotherhalfofthespherethatbearsthesunlightisthenight.Thetransitionzonebetweenthemisearlymorninganddusk.Theearthkeepsturningfromwesttoeast,andthemorning,day,dusk,andnightontheearthalsokeepmovingfromeasttowest,appearingcyclicallyeverywhere.
Allpartsoftheworldusethepositionofthesunthattheyseeasthestandardfordeterminingaday,andameridianontheothersideoftheearthcorrespondingtowheretheyarelocatedisregardedasthe"datechangeline",alsocalledtheinternationaldayboundary.Inthisway,therearemany"datechangelines",whichisveryinconvenienttouse.Inordertosolvethisproblem,a"datechangeline"thatiscommontothewholeworldandcanbecomparedshouldbestipulated.Withtheestablishmentofthezonetimesystemforstandardtimekeeping,theeasternandwesternzonesoverlap,withthesametimingbutdifferentdates.Toavoidconfusion,the180°meridianisrecognizedasthedatechangelinebecauseitisbasedon"GreenwichMeanTime".This"dateline"iscalledthe"internationaldateline".
This"internationaldateline"crossingthePacificOceanavoidssomeislandsandregionsinordertofacilitatelocallife.Thisistopreventthemfrombeingdividedintotwodates.Therefore,itisnotastraightline.Instead,thereareseveraltortuouscurves.
Theturnoftheinternationaldatelineisroughlyasfollows:thefirstisintheeasternpartofRussia,theBeringStrait,thesecondisinAlaskaandtheAleutianIslandsintheUnitedStates,andthethirdisintheSouthPacific,protrudingeastward,LettheFijiIslandsbelongtotheEast12thDistrict(thatis,thewesternpartoftheEast-West12thDistrict).(Picture1isthefirstturn,andPicture2isthethird)
Background
Inordertoavoiddateconfusion,the1884InternationalLongitudeConferencestipulatedaninternationaldatechangeString.Thislineofchangeislocatedonthe180°meridianinthePacificOcean,asthedividinglinebetween"today"and"yesterday"ontheearth,soitiscalledthe"internationaldateline".
Inordertoavoidtheexistenceoftwodatesinacountry,thedatelineisnotastraightline,butabrokenline.ItstartsfromtheNorthPoleinthenorth,passesthroughtheBeringStrait,thePacificOcean,andreachestheSouthPole.Inthisway,thedatelinenolongercrossesanycountry.Midnightonthisline,thatis,midnightlocaltime,isthedemarcationtimeofthedate.Accordingtoregulations,thedatewillchangewheneverthislineofchangeiscrossed:whencrossingthisboundaryfromeasttowest,thedatemustbeaddedbyoneday,andwhencrossingtheboundaryfromwesttoeast,thedatemustbesubtractedbyoneday.Alsocalled"artificialdateline".
Thetheoryproposed
Theearthrotatesfromwesttoeasteveryday,dawn,noon,duskandmidnight,(fromthesouthpoleoftheearth,italsorotatesclockwisefromwesttoeast)Repeatedlyappearinginvariouspartsoftheworld.Whereshouldanewdayonearthbeginandwhereshoulditend?Regardingthisissue,therehavebeenmanycontroversiesinhistory,andmanymisunderstandingsandtroubleshavealsooccurred.Itissaidthatinthe19thcenturyinasmalltownnearIrkutsk,Russia,apostalofficertookatelegramtotheChicagoPostOfficeat7o'clockinthemorningonSeptember1,butthecallbacksaid"At9:28onAugust31Receivedacall..."Thisissimplyinexplicable.HowcouldatelegramtakeninSeptemberbereceivedinAugust?Misunderstandingslikethishappenedalmosteverydayatthattime.Thereasonfortheconfusionliesintheuseoflocaltime.Therefore,thereisanurgentneedtostandardizetheestablishmentofadatechangesystemtofacilitatetimekeepinginplaceswherepeopleliveinvariousplacesandavoidglobaltimekeepingconfusion.
Changeoflocation
OnJanuary1,1995,theauthoritiesofKiribati,anislandnationinthecentralPacific,revisedtheinternationaldatechangelinetotheeasternboundaryofitswatersandorderedthePhoenixIslandstobeintheUTC-11timezone.(PhoenixIslands)andLineIslands(LineIslands)inUTC-10timezoneuseUTC+13andUTC+14,respectively,whichisonefulldayearlierthanHawaiiantime,inordertoeliminatethe22hoursto23hoursdelaywiththecapitalTarawaTheinconvenience.
OnDecember29,2011,SamoaandTokelauadjustedtheirtimezonesfromeastoftheinternationaldatelinetowestoftheinternationaldateline.Asaresultofthechanges,thetwocountrieslostDecember30(Friday),andwentdirectlyfromDecember29(Thursday)toDecember31(Saturday).ThepurposeofthechangeistostrengtheneconomicexchangeswithAustralia,NewZealandandAsia,andtosynchronizetimewiththeseregions.Localresidentswillstartcelebrationactivitiesat0:00onDecember31towelcomethe"early"NewYear.HotelguestsinWesternSamoadonothavetopaytherentonDecember30,buttheirwagesstillhavetobepaidonthesameday.However,thishasdisruptedthelivesofresidents,andmembersoftheSeventh-dayAdventistChurchinWesternSamoaarerequiredtoworshiponSundayinsteadofSaturday.TheSamoaIslandsweresetonthewestsideoftheInternationalDateLinebeforeJuly4,1892,synchronizedwiththeWesternPacific.Duringtheimplementationofdaylightsavingtime,WesternSamoatimeis14hoursfasterthanCoordinatedUniversalTime,butbecauseAmericanSamoahasnotfollowed,thiswillcauseafull-daytimedifferenceinSamoa.
Theestablishmentofthestandardsystem
In1879,theCanadianrailwayengineerFlemingproposedtheconceptof"zonetime".Thisproposalwasrecognizedataninternationalconferencein1884.Formallyestablishedthe"zonetimesystem"thatunifiestheworld'stimemeasurement.The"zonetimesystem"stipulatesthatevery15°longituderangeontheearthisregardedasatimezone(thatis,thelongitudethatthesuntravelsinonehour).Inthisway,theentiresurfaceoftheearthisdividedinto24timezones.The“centralmeridian”ofeachtimezoneisspecifiedas0°(ie,“primarymeridian”),east-westlongitude15°,east-westlongitude30°,east-westlongitude45°...until180°longitude,ontheeastandwestsidesofeachcentralmeridian.Foralllocationswithintherangeof7.5°,eachtimezonemeasurestimeaccordingtoitscentralmeridian,thatis,theplacewhereitscentralmeridianisusedisusuallycalledstandardtime.
"Standardtimetiming"haslargelysolvedthechaoticphenomenonoftimeinvariousplaces.Thereareonly24differenttimesintheworld,andthetimedifferencebetweenadjacenttimeintervalsisexactly1hour.Timeconversionindifferenttimeintervalsbecomesextremelysimple.Therefore,forahundredyears,thistimezonesystemisstillusedallovertheworld.
Specifiesthezonetimesystembasedonstandardtime.Thereisstillaproblem:ifyoutraveltheworldfromwesttoeast,everytimeyoucrossatimezone,yourwatchwillbeadvancedbyonehourplusyourtravelTimewasted,sothatwhenyoucross24timezonesandreturntotheoriginalplace,yourwatchis24hoursfasterthanthepeoplearoundyou;onthecontrary,whenyoutraveltheworldfromeasttowest,yourwatchisbetterthanothers24hoursslow.(Forexample,Mr.JulesVerne'snoveltraveledaroundtheworldfor80days,andMr.Foggtraveledaroundtheworldfromwesttoeastfor24hours,andalmostdidn'tgetabetof20,000pounds.)InordertoavoidthisThephenomenonof"datingdisorder"mustsolvetheproblemofdatechange.