Year zero
From GeneaWiki - English
There is no year zero in the widely used Gregorian calendar, nor in its predecessor, the Julian calendar. However, there is a year zero in astronomical year numbering (where it coincides with the Julian year 1 BC) and in the calendar ISO 8601:2004 (where it coincides with the Gregorian year 1 BC) as well as in all Buddhist and Hindu lunar calendars.
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Julian and Gregorian calendars
Dionysius Exiguus (c.470–c.544) introduced the anno Domini era, which he used to identify the several Easters in his Easter table, but did not use it to date any historical event. When he devised his table, Julian calendar years were identified by naming the consuls who held office that year — he himself stated that the "present year" was "the consulship of Probus Junior Flavius Probus", which he also stated was 525 years "since the incarnation conception of our Lord Jesus Christ". How he arrived at that number is unknown. He invented a new system of numbering years to replace the Diocletian years that had been used in an old Easter table because he did not wish to continue the memory of a tyrant who persecuted Christians.
Bede (c.672–735) was the first historian to use a BC year, and hence the first one to choose 1 as the origin of the BC era, thus 1 BC, in his Historia ecclesiastica gentis Anglorum (Ecclesiastical history of the English people, 731). Previous Christian histories used anno mundi ("in the year of the world"), or anno Adami ("in the year of Adam", beginning five days later, used by Africanus), or anno Abrahami ("in the year of Abraham", beginning 3,412 years later according to the Septuagint, used by Eusebius), all of which assigned "one" to the year beginning at Creation, or the creation of Adam, or the birth of Abraham, respectively. All began with year 1, the most frequent origin for counting sets.
Bede did not sequentially number any other calendar entities (days of the month, weeks of the year, or months of the year).
It is often stated that Bede did not use a year zero because he did not know about the number zero. Although the Arabic numeral for zero (0) did not enter Europe until the eleventh century, two Latin words for zero, nulla and nihil, meaning "nothing", were normal in Latin speech. Nulla was used whenever zero was a member of a series of numbers, whether the other numbers were Roman numerals or Latin words. Dionysius Exiguus himself had used it in his Easter table, though not to label years.
The first extensive use (hundreds of times) of 'BC' occurred in Fasciculus Temporum by Werner Rolevinck in 1474, alongside years of the world (anno mundi). The anno Domini nomenclature was not widely used in Western Europe until the 9th century, and the 1 January to 31 December historical year was not uniform throughout Western Europe until 1752. The terms anno Domini, Dionysian era, Christian era, vulgar era, and common era were used interchangeably between the Renaissance and the 19th century, at least in Latin. But vulgar era was suppressed in English at the beginning of the twentieth century after vulgar acquired the meaning of "offensively coarse", replacing its original meaning of "common" or "ordinary". Consequently, historians regard all these eras as equal.
Historians
Since Bede, historians have not counted with a year zero. This means that between, for example, 500 BC, January 1 and AD 500, January 1 there are 999 years: 500 for the time taking place BC, and 499 for the part of AD. Common usage Anno Domini 1 is preceded by the year 1 BC, without an intervening year zero. Thus the year 2006 actually signifies "the 2006th year". Neither the choice of calendar system (whether Julian or Gregorian) nor the era (Anno Domini or Common 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. No historian includes a year 0 when numbering years in the current standard era. Thus, regardless of the appellation or calendar employed (Julian or Gregorian), 1 BC always immediately precedes AD 1. Historians even refuse to use a year 0 when using negative years before our positive era, hence their −1 immediately precedes 1 (for example, V. Grumel, La chronologie (1958), page 30).
Numerical explanation
There are two different ways of recording time:
- One is to use ordinal numbers (e.g. first, second, third, ...) or cardinal numbers (e.g. one, two, three, ...) This corresponds to treating time as a discrete variable, and the labels as counts. Under this point of view, the first year counted after the starting point will come immediately after the first year counted before the starting point. Thus 1 AD comes immediately after 1 BC.
- In some contexts, however, such as astronomy, it can be more convenient to regard time as a continuous variable, and label time periods as ranges on a continuous scale, that is as measurements of the total time elapsed since the start of the era. According to this interpretation, elapsed time year 1 begins exactly one full year after the starting point, and the first year is year 0 (meaning that zero full years have elapsed since the starting point).
The first way of reckoning described above is the traditional one in historiography and in common usage to label years, centuries, and millennia. The second is used, for example, with a person's age.
A similar distinction occurs in numbering the floors of a building, and the exits of a highway. See Floor numbering and Exit 0.
Third millennium
The 3rd millennium of the Gregorian calendar began on 1 January 2001 (rather than the popularly-celebrated 1 January 2000). This is a direct consequence of the absence of a year zero in the Common Era. Had there been a year zero, which might be considered part of the first millennium, then 1 January 2000 would indeed mark 2000 years since the year numbering datum and be the start of the third millennium.
Note that this also applies to centuries. Thus, the 20th century didn't really begin until 1901.
Astronomical year numbering
Astronomers
Astronomers, for whom ease of mathematical calculation is more important, have used for several centuries a defined leap year zero equal to BC 1 of the traditional Christian era. The first use of an astronomical year 0 is traditionally attributed to Jacques Cassini whose stated reasons for including a year zero were:
But Philippe de La Hire had used a year zero earlier in 1702 in his Tabulæ Astronomicæ (Astronomical Tables) in the form Christum o. ("Christ 0"), without explanation. Both Cassini and La Hire used BC years before their year 0 and AD years thereafter (hence the sequence 1 BC, 0, AD 1). That is why Cassini stated that their sum yielded the interval. For example, 1 + 1 = 2. Beginning in the 19th century, some astronomers began to use negative years before their year 0, while other astronomers continued to use BC years before their year 0. By the mid 20th century, all astronomers were using negative years before year 0 (hence the sequence −1, 0, 1). Thus modern astronomers would state that the years' difference yields the interval, just as it does if the years are both positive or both negative. For example, 1 − (−1) = 2, and 2000 − 1999 = 1. Although 'AD' is omitted from later years, leaving a bare number, a positive sign (+) is sometimes prefixed to the number. Because of possible confusion with the earlier use of an astronomical BC, only in the modern version can it be said that astronomical year 0 equals the historical year 1 BC.
ISO 8601
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 the proleptic Gregorian calendar for all years before 1582, some readers incorrectly assume that a year zero is also included in that proleptic calendar, whereas that is unusual. 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 an absolute value one less than the equivalent BC year, hence -0001 = 2 BC. Because only ISO 646 (7-bit ASCII) characters are allowed by ISO 8601, the minus sign is represented by a hyphen-minus.
Other traditions
South Asian Moon calendars
All eras used with Hindu and Buddhist calendars, such as the Saka era or the Kali Yuga, begin with the year 0. All these calendars show elapsed, expired, or complete years, in contrast with most other calendars 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 the clock: during the first hour of a day, the time elapsed is 0 hours, xx minutes.
Maya historiography
Many Maya historians, but not all, assume (or used to assume) that a year 0 exists in the modern calendar and thus specify that the epoch of the Mesoamerican Long Count calendar occurred in 3113 BC rather than 3114 BC. This would require the sequence 1 BC, 0, AD 1 as in early astronomical years.
Popular culture
- In the movie Back to the Future, Dr. Emmett Brown, the inventor of a time machine, enters the input date of the "birth of Jesus|Christ" on a keypad as December 25, 0000, implying that he uses the astronomical year numbering. It should be noted that the DVD commentary clearly points out that the date was a joke.
- In the movie, The Beach, Leonardo DiCaprio is, during his mental instability, crazed about the term Year 0.
- The fictitious theologian Franz Bibfeldt's most famous work relates to the year 0: a 1927 dissertation submission to the University of Worms entitled "The Problem of the Year 0".
- The Zork timeline included with the comedy game Zork Grand Inquisitor features the year 0 GUE with the annotation: "As the year zero begins, people feel fairly confident that something big is about to happen."