calendar era

A calendar era is the year numbering system used by a calendar. For example, the Gregorian calendar numbers its years in the Western Christian era (the Coptic and Ethiopic churches have their own Christian eras, see below). The instant, date, or year from which time is marked is called the epoch of the era. There are many different calendar eras.

In antiquity, regnal years were counted from the ascension of a monarch. This makes the Chronology of the ancient Near East very difficult to reconstruct, based on disparate and scattered king lists, such as the Sumerian King List or the Babylonian Canon of Kings. In East Asia, reckoning by era names chosen by ruling monarchs remained current until the 20th century, except for Japan, where they are still used.

Hellenistic period

Olympiads are periods of four years each, with the first year of the first Olympiad beginning in 776 BC, in use from the 4th century BC until the 3rd or 4th century AD; the "modern olympiad" began in 1896.
The Seleucid era, called the Era of Contracts by Jews, formerly used in much of the Middle East from the 4th century BC to the 6th century AD, uses the epoch 312 BC, the year when Seleucus I Nicator captured Babylon and began his reign over the Asian portions of Alexander the Great's empire.
A.U.C. (or AUC) — for the Latin ab urbe condita, meaning from the founding of the city (of Rome), was introduced by Marcus Terentius Varro in the 1st century BC. The first day of its year was Founder's Day (April 21), although most modern historians assume that it coincides with the modern historical year (January 1 to December 31). It was rarely used in the Roman calendar and in the early Julian calendar — naming the two consuls that held office in a particular year was dominant. 2007 is the same as AUC 2760 (2007 + 753).

Late Antiquity and Middle Ages

Most of the traditional calendar eras in use today were introduced at the time of transition from Late Antiquity to the Early Middle Ages, roughly between the 6th and 10th centuries.

Christian

The Aetos Kosmou of the Byzantine Greek Calendar places Creation at the beginning of its year 1, September 5509 BC. Its first known use occurred in the 7th century AD, although its precursors were developed about AD 400. The year 7516 of this era begins in September 2007.
Era of Diocletian, Era of the Martyrs Reckoned from the beginning of the reign of Roman Emperor Diocletian; the first year of this era was 284/5. It was not the custom to use regnal years in Rome, but it was the custom in Roman Egypt, which the emperor ruled through a prefect (the king of Egypt). The year number changed on the first day of the Egyptian month Thoth (29 August three years out of four, 30 August the year before a Roman leap year.) Diocletian abolished the special status of Egypt, which then followed the normal Roman calendar: consular years beginning on 1 January. This era was used in the Easter tables prepared in Alexandria long after the abdication of Diocletian, even though Diocletian was a notorious persecutor of Christians. The Era of Diocletian was retained by the Coptic Church and used for general purposes, but by 643 the name had been changed to Era of the Martyrs. ^[1]
The Incarnation Era is used by Ethiopia. Its epoch is 29 August 8 in the Julian calendar.
The Armenian calendar has its era fixed at AD 552.

Dionysian "Common Era"

Main articles: Anno Domini and Common Era

The era based on the Incarnation of Christ was introduced by Dionysius Exiguus in 525 and is in continued use with various reforms and derivations. The distinction between the Incarnation being the conception or the Nativity of Jesus was not drawn until the late ninth century.^[2]

A.D. (or AD) — for the Latin Anno Domini, meaning in the year of (our) Lord. This is the dominant or Western Christian Era; AD is used in the Gregorian calendar. Anno Salutis, meaning in the year of salvation is identical to this era. Originally intended to number years from the Incarnation of Jesus, in fact the calculation was a few years off. Traditionally, years preceding AD 1 are numbered using the BC era (see below), avoiding zero or negative numbers. AD was also used in the medieval Julian calendar as well, but the first day of the year was either March 1, Easter, March 25, September 1, or December 25, not January 1. To distinguish between them, O.S. and N.S. were often added to the date, especially during the 17th and 18th centuries, when both calendars were in common use. Old Style (O.S.) was used for the Julian calendar and for years not beginning on January 1. New Style (N.S.) was used for the Gregorian calendar and for Julian calendar years beginning on January 1. Many countries switched to using January 1 as the start of the numbered year when switching from the Julian calendar to the Gregorian calendar, but others switched earlier or later.

B.C. (or BC) — Before Christ. Used for years prior to AD 1, counting backwards so the year n BC is the year 1-n AD. Using these two calendar eras as historians use them means that there is no year 0 or negative year numbers.
C.E. (or CE) — meaning Common Era, equivalent to the Anno Domini era. This use is similar to that of the Era Vulgaris (or EV) used in the past. B.C.E. (or BCE) — meaning Before the Common Era. Equivalent to B.C..

Dionysian-derived

Some modern calendar eras are directly tied to the Dionysian era:

Astronomical year numbering equates its year 0 with 1 BC, and counts negative years from 2 BC backward (−1 backward), so 100 BC is −99.
The Holocene calendar proposed by Cesare Emiliani placed its year 1 at 10,000 BC.
Anno Lucis of Freemasonry adds 4000 years to the AD year.
The Year of Our Lady of Discord of the Discordian calendar adds 1166 years to the AD year.

Islamic

A.H. (or AH) — for the Latinized Anno Hegirae, meaning in the year of the Hijra, Prophet Muhammad's migration from Mecca to Medina in September 622, which occurred in its first year, used in the Islamic calendar. Since the Islamic calendar is a purely lunar calendar of about 354 days, its year count increases faster than that of solar and lunisolar calendars.
A.H.S. (or AHS)^{[citation needed]} is used by the Iranian calendar to denote the number of solar years since the Hijra. The year beginning at the vernal equinox equals the number of the Gregorian year beginning at the preceding January 1 minus 621.

Hindu

Hindu calendar, counting from the start of the Kali Yuga, with its epoch on 18 February 3102 BC Julian (23 January 3102 BC Gregorian).
Vikrama Samvat, 56-57 BC, introduced about the 12th century.
S.E. or (SE) — for the Saka Era, used in some Hindu calendars and in the Indian national calendar, with an epoch near the vernal equinox of year 78 (its year 0).

Zoroastrian

The Zoroastrian calendar used regnal years since the reform by Ardashir I, but after the fall of the Sassanid empire, the ascension of the last Sassanid ruler, Yazdegerd III of Persia, crowned 16 June 632, continued to be used as the reference year, abbreviated Y.Z. or "Yazdegerd era".

Jewish

A.M. (or AM) — for the Latin Anno Mundi, meaning in the year of the world, has its epoch in the year 3761 BC. This was first used to number the years of the modern Hebrew calendar in 1178 by Maimonides. Precursors with epochs one or two years later were used since the 3rd century, all based on the Seder Olam Rabba of the 2nd century. The year beginning in the northern autumn of 2000 was 5761 AM).

Modern

Political

The Republican Era of the French Republican Calendar was dated from 22 September 1792, the day of the proclamation of the French First Republic. It was used in Revolutionary France from October 24, 1793 (on the Gregorian calendar) to December 31, 1805.
The Positivist calendar of 1844 takes 1789 as its epoch.
The Republican era is used by the Republic of China (Taiwan) since 1929, assigning year one to 1912, the first year of the republic. Coincidentally, this is the same as the Juche era used in North Korea, the year of the birth of its founder Kim Il-Sung. Juche means self-reliance.
The Italian Fascists used Roman numerals to denote the number of years since the establishment of the Fascist government in 1922. Therefore, 1934, for example, was Year XII. This era was abolished with the fall of fascism in Italy on July 25, 1943.
China traditionally reckoned by the regnal year of its emperors, see Chinese era name. Most Chinese do not assign numbers to the years of the Chinese calendar, but the few who do, like expatriate Chinese, use a continuous count of years from the reign of the legendary Yellow Emperor, using 2698 BC as year 1. Western writers begin this count at either 2637 BC or 2697 BC (see Chinese calendar). Thus the Chinese years 4637, 4697, or 4698 began in early 2000.
In Korea, from 1952 until 1961 years were numbered via Dangi years, where 2333 BC was regarded as the first such year.
The Assyrian calendar introduced in the 1950s has its era fixed at 4750 BC.
The Japanese calendar dates from the accession of the current Emperor of Japan. The current emperor took the throne in early 1989, which became Heisei 1, which was until then Shōwa 64 (for its first seven days).

Religious

B.E. — for the Buddhist Era, introduced by Vajiravudh in 1912, which has an epoch (origin) of 544 BC. This year is called year 1 in Sri Lanka and Burma, but year 0 in Thailand, Laos and Cambodia. Thus the year 2500 B.E. occurred in 1956 in the former countries, but in 1957 in the latter. In Thailand in 1888 King Chulalongkorn decreed a National Thai Era, dating from the founding of Bangkok on April 6 1782. In 1912 New Year's Day was shifted to April 1. In 1941, Prime Minister Phibunsongkhram decided to count the years since 543 BC. This is the Thai solar calendar using the Thai Buddhist Era aligned to the western solar calendar.
B.E. — The Bahá'í calendar dates from the year of the declaration of the Báb. Years are counted in the Bahá'í Era (BE), which starts its year 1 from March 21, 1844.

Practical

B.P. — for Before Present, specifically, the number of radiocarbon years before 1950.
The Unix epoch is set at midnight of 1 January 1970.
The Julian day number counts days, not years, and has its era fixed at noon 1 January 4713 BC in the proleptic Julian calendar. This equals November 24 4714 BC in the proleptic Gregorian calendar. From noon of this day to noon of the next day was day 0. Multiples of 7 are Mondays. Negative values can also be used. Apart from the choice of the zero point and name, this Julian day and Julian date are not related to the Julian calendar. It does not count years, so, strictly speaking, it has no era, but it does have an epoch. Today (noon-to-noon UTC) the value is Expression error: unrecognised word "expression".

References

^ Bonnie Blackburn & Leofranc Holford-Strevens. (1999, 2003). The Oxford Companion to the Year: an exploration of calendar customs and time-reckoning (corrected printing). Oxford University Press. ISBN 978-0-19-214231-3. 766–7.
^ Bonnie Blackburn & Leofranc Holford-Strevens. (1999, 2003). The Oxford Companion to the Year: an exploration of calendar customs and time-reckoning (corrected printing). Oxford University Press. ISBN 978-0-19-214231-3. Glossary s. v. Incarnation era.

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