Ayear zero does not exist in theAnno Domini (AD) calendar year system commonly used to number years in theGregorian calendar (or in its predecessor, theJulian calendar); in this system, the year1 BC is followed directly by yearAD 1 (which is the year of theepoch of the era). However, there is a year zero in both theastronomical year numbering system (where it coincides with the Julian year1 BC), and theISO 8601:2004 system, a data interchange standard for certain time and calendar information (where year zero coincides with the Gregorian year1 BC;see:Holocene calendar § Conversion). There is also a year zero in mostBuddhist andHindu calendars.
Dionysius Exiguus did not use "AD" years to date any historical event. This practice began with the English clericBede (c. 672–735), who used AD years in hisHistoria ecclesiastica gentis Anglorum (731), popularizing the era. Bede also used – only once – a term similar to the modern English term "before Christ", though the practice did not catch on for nearly a thousand years, when books byDenis Pétau treating calendar science gained popularity. Bede did not sequentially numberdays of the month, weeks of the year, or months of the year. However, he did number many of thedays of the week using the counting origin one inEcclesiastical Latin.[citation needed]
Previous Christian histories used several titles for dating events:anno mundi ("in the year of the world") beginning on the purported first day ofcreation; oranno Adami ("in the year ofAdam") beginning at the creation of Adam five days later (or the sixth day of creation according to theGenesis creation narrative) as used byAfricanus; oranno Abrahami ("in the year ofAbraham") beginning 3,412 years after Creation according to theSeptuagint, used byEusebius of Caesarea; all of which assigned "one" to the year beginning at Creation, or the creation of Adam, or the birth of Abraham, respectively. Bede continued this earlier tradition relative to the AD era.[citation needed]
In chapter II of book I ofEcclesiastical History, Bede stated thatJulius Caesar invaded Britain "in the year 693 after the building of Rome, but the sixtieth year before the incarnation of our Lord", while stating in chapter III, "in the year of Rome 798,Claudius" also invaded Britain and "within a very few days ... concluded the war in ... the forty-sixth [year] from the incarnation of our Lord".[3] Although both dates are wrong, they are sufficient to conclude that Bede did not include a year zero between BC and AD: 798 − 693 + 1 (because the years are inclusive) = 106, but 60 + 46 = 106, which leaves no room for a year zero. The modern English term "before Christ" (BC) is only a rough equivalent,not a direct translation, of Bede's Latin phraseante incarnationis dominicae tempus ("before the time of the lord's incarnation"), which was itself never abbreviated. Bede's singular use of 'BC' continued to be used sporadically throughout theMiddle Ages.[citation needed]
Neither the concept of nor a symbol for zero existed in the system ofRoman numerals. TheBabylonian system of the BC era had used the idea of "nothingness" without considering it a number, and the Romans enumerated in much the same way. Wherever a modern zero would have been used, Bede and Dionysius Exiguus did useLatin number words, or the wordnulla (meaning "nothing") alongside Roman numerals.[1][4][5] Zero was invented in India in the sixth century,[6] and was either transferred or reinvented by the Arabs by about the eighth century. TheArabic numeral for zero (0) did not enter Europe until the thirteenth century. Even then, it was known only to very few, and only entered widespread use in Europe by the seventeenth century.[citation needed]
Theanno Domini nomenclature was not widely used inWestern Europe until the 9th century, and the1 January to31 December historical year was not uniform throughout Western Europe until 1752. The first extensive use (hundreds of times) of 'BC' occurred inFasciculus Temporum byWerner Rolevinck in 1474, alongside years of the world (anno mundi).[7] The termsanno Domini,Dionysian era,Christian era,vulgar era, andcommon era were used interchangeably between theRenaissance and the 19th century, at least inLatin. Butvulgar era fell out of use in English at the beginning of the 20th century aftervulgar acquired the meaning of "offensively coarse", replacing its original meaning of "common" or "ordinary". Consequently, historians regard all these eras as equal.[citation needed]
Historians have never included a year zero. This means that between, for example,1 January500 BC and1 JanuaryAD 500, there are 999 years: 500 years BC, and 499 years AD preceding 500. In common usageanno Domini 1 is preceded by the year 1BC, without an intervening year zero.[8] Neither the choice of calendar system (whetherJulian orGregorian) nor the name of the era (Anno Domini orCommon Era) determines whether a year zero will be used. If writers do not use the convention of their group (historians or astronomers), they must explicitly state whether they include a year 0 in their count of years, otherwise their historical dates will be misunderstood.[9]
In astronomy, for the year AD 1 and later it is common to assign the same numbers as the Anno Domini notation, which in turn is numerically equivalent to the Common Era notation. But the discontinuity between 1 AD and 1 BC makes it cumbersome to compare ancient and modern dates. So the year before 1 AD is designated 0, the year before 0 is −1, and so on.
The letters "AD", "BC", "CE", or "BCE" are omitted. So 1 BC in historical notation is equivalent to 0 in astronomical notation, 2 BC is equivalent to −1, etc. Sometimes positive years are preceded by the + sign. This year numbering notation was introduced by the astronomerJacques Cassini in 1740.[10]
In 1627, the German astronomerJohannes Kepler, in hisRudolphine Tables, first used an astronomical year essentially as a year zero. He labeled itChristi and inserted it between years labeledAnte Christum andPost Christum—abbreviated BC and AD today,respectively—on the "mean motion" pages of the Sun, Moon, and planets.[11] In 1702, the French astronomerPhilippe de La Hire labeled a year asChristum0 and placed it at the end of the years labeledante Christum (BC), and immediately before the years labeledpost Christum (AD), on the mean motion pages in hisTabulæ Astronomicæ, thus adding the number designation0 to Kepler'sChristi.[12]
Finally, in 1740, the transition was completed by French astronomerJacques Cassini(Cassini II), who is traditionally credited with inventing year zero.[13] In hisTables astronomiques, Cassini labeled the year simply as0, and placed it at the end of years labeledavant Jesus-Christ (BC), and immediately before years labeledaprès Jesus-Christ (AD).[14]
ISO 8601:2004 (and previously ISO 8601:2000, but not ISO 8601:1988) explicitly uses astronomical year numbering in its date reference systems. (Because it also specifies the use of theproleptic Gregorian calendar for all years before 1582, some readers incorrectly assume that a year zero is also included in that proleptic calendar, but it is not used with the BC/AD era.) The "basic" format for year 0 is the four-digit form 0000, which equals the historical year 1 BC. Several "expanded" formats are possible: −0000 and +0000, as well as five- and six-digit versions. Earlier years are also negative four-, five- or six-digit years, which have anabsolute value one less than the equivalent BC year, hence -0001 = 2 BC. Because onlyISO 646 (7-bitASCII) characters are allowed by ISO 8601, the minus sign is represented by ahyphen-minus.
Most eras used withHindu andBuddhist calendars, such as theSaka era or theKali Yuga, begin with the year 0. These calendars mostly use elapsed, expired, or complete years, in contrast with most calendars from other parts of the world which use current years. A complete year had not yet elapsed for any date in the initial year of the epoch, thus the number 1 cannot be used. Instead, during the first year the indication of 0 years (elapsed) is given in order to show that the epoch is less than 1 year old. This is similar to the Western method of stating a person's age – people do not reach age one until one year has elapsed since birth (but their age during the year beginning at birth is specified in months or fractional years, not as age zero). However, if ages were specified in years and months, such a person would be said to be, for example, 0 years and 6 months or 0.5 years old. This is analogous to the way time is shown on a24-hour clock: during the first hour of a day, the time elapsed is 0 hours,n minutes.
^Blackburn, Bonnie; Holford-Strevens, Leofranc (2003).The Oxford Companion to the Year: An exploration of calendar customs and time-reckoning (corrected reprinting of 1999 ed.). Oxford University Press. pp. 778–779.ISBN9780192142313.
^While it is increasingly common to placeAD after a date by analogy to the use ofBC, formal English usage adheres to the traditional practice of placing the abbreviation before the year as in Latin (e.g.,100 BC, butAD 100).
^Richards, E. G. (2013). "Calendars". In Urban, Sean E.; Seidelmann, P. Kenneth (eds.).Explanatory Supplement to the Astronomical Almanac (3 ed.). Mill Valley, California: University Science Books. p. 591.ISBN978-1-891389-85-6.
