Keeping Time: The Origin of B.C. & A.D. | Live Science

"A.D." stands for anno domini, Latin for “in the year of the lord,” and refers specifically to the birth of Jesus Christ. "B.C." stands for " ... Skiptomaincontent LiveScience Search Subscribe RSS HowItWorksMagazineHowItWorksMagazineWhysubscribe?Theultimateaction-packedscienceandtechnologymagazineburstingwithexcitinginformationabouttheuniverseEngagingarticles,amazingillustrations&exclusiveinterviewsIssuesdeliveredstraighttoyourdoor/in-boxFrom$7.15ViewDeal News Space&Physics Health PlanetEarth StrangeNews Animals History Forums More trendingPhysics&AstrophysicsComputerhistoryCOVID-19NewsCulturePregnancytips LiveScienceissupportedbyitsaudience.Whenyoupurchasethroughlinksonoursite,wemayearnanaffiliatecommission.Learnmore ThecornerstoneattheIowaStateCapitolreads,"IOWA.A.D.1873." (Imagecredit:IowaLegislature) Theideaofcountingyearshasbeenaroundforaslongaswehavewrittenrecords,buttheideaofsyncingupwhereeveryonestartscountingisrelativelynew.TodaytheinternationalstandardistodesignateyearsbasedonatraditionalreckoningoftheyearJesuswasborn—the“A.D.”and"B.C."system."A.D."standsforannodomini,Latinfor“intheyearofthelord,”andrefersspecificallytothebirthofJesusChrist."B.C."standsfor"beforeChrist."InEnglish,itiscommonfor"A.D."toprecedetheyear,sothatthetranslationof"A.D.2014"wouldread"intheyearofourlord2014."Inrecentyears,analternativeformofB.C./A.D.hasgainedtraction.Manypublicationsuse"C.E.,"or"commonera,"and"B.C.E.,"or"beforecommonera."Beforewetalkabouthowandwhythesystemwasinvented,let'sgetsomehistoricalcontext.WhenisEaster?IntheearlyMiddleAges,themostimportantcalculation,andthusoneofthemainmotivationsfortheEuropeanstudyofmathematics,wastheproblemofwhentocelebrateEaster.TheFirstCouncilofNicaea,inA.D.325,haddecidedthatEasterwouldfallontheSundayfollowingthefullmoonthatfollowsthespringequinox.Computus(Latinforcomputation)wastheprocedureforcalculatingthismostimportantdate,andthecomputationsweresetforthindocumentsknownasEastertables.Itwasononesuchtablethat,inA.D.525,amonknamedDionysiusExiguusofScythiaMinorintroducedtheA.D.system,countingtheyearssincethebirthofChrist.AnnoDiocletianitoAnnoDominiDionysiusdevisedhissystemtoreplacetheDiocletiansystem,namedafterthe51stemperorofRome,whoruledfromA.D.284toA.D.305.ThefirstyearinDionysius'Eastertable,“AnnoDomini532,”followedtheyear“AnnoDiocletiani247.”DionysiusmadethechangespecificallytodoawaywiththememoryofthisemperorwhohadbeenaruthlesspersecutorofChristians.DionysiusneversaidhowhedeterminedthedateofJesus'birth,butsomeauthorstheorizethatheusedcurrentbeliefsaboutcosmology,planetaryconjunctionsandtheprecessionofequinoxestocalculatethedate.DionysiusattemptedtosetA.D.1astheyearofJesusChrist’sbirth,butwasoffinhisestimationbyafewyears,whichiswhythebestmodernestimatesplaceChrist’sbirthat4B.C.[Related:EasterScience:6FactsAboutJesus]AddingintheyearsbeforeChristTheadditionoftheB.C.componenthappenedtwocenturiesafterDionysius,whentheVenerableBedeofNorthumbriapublishedhis"EcclesiasticalHistoryoftheEnglishPeople"in731.Upuntilthispoint,Dionysius’systemhadbeenwidelyused.Bede’sworknotonlybroughttheA.D.systemtotheattentionofotherscholars,butalsoexpandedthesystemtoincludeyearsbeforeA.D.1.Prioryearswerenumberedtocountbackwardtoindicatethenumberofyearsaneventhadoccurred“beforeChrist”or“B.C.”NoYearZero?AccordingtoCharlesSeifeinhisbook"Zero:TheBiographyofaDangerousIdea":“ToBede,alsoignorantofthenumberzero,theyearthatcamebefore1A.D.[sic]was1B.C.Therewasnoyearzero.Afterall,toBede,zerodidn’texist.”However,zerodidexist;ourmodernconceptionofzerowasfirstpublishedinA.D.628bytheIndianscholarBrahmagupta.TheideawouldnotspreadtomedievalChristianEurope,however,untilthe11thto13thcenturies.SpreadofthesystemTheB.C./A.D.systemgainedinpopularityintheninthcenturyafterHolyRomanEmperorCharlemagneadoptedthesystemfordatingactsofgovernmentthroughoutEurope.Bythe15thcentury,allofWesternEuropehadadoptedtheB.C./A.D.system.Thesystem'sinclusionwasimplicitinthe16th-centuryintroductionoftheGregoriancalendar,anditlaterwouldbecomeaninternationalstandardin1988whentheInternationalOrganizationforStandardizationreleasedISO8601,whichdescribesaninternationallyacceptedwaytorepresentdatesandtimes.CommonandvulgarerasThealternativeformof“BeforetheCommonEra”and“CommonEra”datesbackto1715,whereitisusedinanastronomybookinterchangeablywith“VulgarEra.”Atthetime,vulgarmeant“ordinary,”ratherthan“crude.”Theterm“VulgarEra”isevenolder,firstappearingina1615bookbyJohannesKepler.RationalesforthetransitionfromA.D.toC.E.include(1)showingsensitivitytothosewhousethesameyearnumberasthatwhichoriginatedwithChristians,butwhoarenotthemselvesChristian,and(2)thelabel“AnnoDomini”beingarguablyinaccurate,sincescholarsgenerallybelievethatChristwasbornsomeyearsbeforeA.D.1andthatthehistoricalevidenceistoosketchytoallowfordefinitivedating.Timetofindoutifyou'vebeenpayingattention!Proveitbytakingthetimetotakethisquiz:KeepingTime:KeepingTime:TheOriginofB.C.&A.D. LiveSciencenewsletter StayuptodateonthelatestsciencenewsbysigningupforourEssentialsnewsletter. ContactmewithnewsandoffersfromotherFuturebrands Receiveemailfromusonbehalfofourtrustedpartnersorsponsors ThankyouforsigninguptoLiveScience.Youwillreceiveaverificationemailshortly. Therewasaproblem.Pleaserefreshthepageandtryagain. MOSTREADMOSTSHARED110stunningswordsandotherancientweaponsuncoveredin20212Enormousseadragonfossilfrom180millionyearsagodiscoveredinEngland3Surgeonstransplantpig'sheartintodyinghumanpatientinafirst4Rare'bionic'armordiscoveredin2,500-year-oldChinaburial5PentagonlaunchesnewUFOoffice.Notallbelieversarehappyaboutit.1China's$1trillion'artificialsun'fusionreactorjustgotfivetimeshotterthanthesun2RemainsofamananddogtryingtoescapeancienttsunamifoundonAegeancoast3Rare'bionic'armordiscoveredin2,500-year-oldChinaburial4Enormousseadragonfossilfrom180millionyearsagodiscoveredinEngland5Omicron'snotthelastvariantwe'llsee.Willthenextonebebad? 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