Epoch

epochsEpoch (reference date)epoch eventepoch yearcalendar epochepochal yearfirst daythe origin of the calendar19801980-01-01
An epoch, for the purposes of chronology and periodization, is an instant in time chosen as the origin of a particular calendar era.wikipedia
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Calendar era

erayear numberingepoch
An epoch, for the purposes of chronology and periodization, is an instant in time chosen as the origin of a particular calendar era.
The instant, date, or year from which time is marked is called the epoch of the era.

Anno Domini

ADBCChristian era
This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AD counting years from the start of this epoch, and BC denoting years before the start of the era.

Before Present

BPB.P.YBP
Because the "present" time changes, standard practice is to use 1 January 1950 as the commencement date (epoch) of the age scale, reflecting the origin of practical radiocarbon dating in the 1950s.

Chronology

chronologicalchronological ordertimeline
An epoch, for the purposes of chronology and periodization, is an instant in time chosen as the origin of a particular calendar era.
An epoch is the date (year usually) when an era begins.

Olympiad

Cultural OlympiadOlympiadsfour years
Although the Ancient Olympic Games were established during Archaic Greece, it was not until the Hellenistic period, beginning with Ephorus, that the Olympiad was used as a calendar epoch.

Byzantine calendar

Byzantine eraEtos KosmouA.M.
The calendar was based on the Julian calendar, except that the year started on 1 September and the year number used an Anno Mundi epoch derived from the Septuagint version of the Bible.

Common Era

CEBCEC.E.
He attempted to number years from an initial reference date ("epoch"), an event he referred to as the Incarnation of Jesus.

Hebrew calendar

Jewish calendarHebrew monthHebrew
The era used since the Middle Ages is the Anno Mundi epoch (Latin for "in the year of the world"; לבריאת העולם, "from the creation of the world").

Islamic calendar

AHHijriHijri calendar
The Islamic calendar employs the Hijri era whose epoch was established as the Islamic New Year of 622 AD/CE.

Julian calendar

Old CalendarJulianO.S.
The Fasti Capitolini, an inscription containing an official list of the consuls which was published by Augustus, used an epoch of 752 BC.

Xinhai Revolution

1911 RevolutionChinese RevolutionChinese Revolution of 1911
1 January 1912, was set as the first day of the First Year of the ROC.

Thai solar calendar

B.E.Rattanakosin EraBE
The epoch (reference date) for Year 1 was 6 April 1782 with the accession of Rama I, the foundation of the Chakri Dynasty, and the founding of Bangkok (Rattanakosin) as capital.

French Republican calendar

French Revolutionary CalendarRepublican CalendarYear II
As the rapporteur of the commission, Charles-Gilbert Romme presented the new calendar to the Jacobin-controlled National Convention on 23 September 1793, which adopted it on 24 October 1793 and also extended it proleptically to its epoch of 22 September 1792.

Iranian calendars

H-ShIranian calendarPersian calendar
It specified the origin of the calendar to be the Hegira of Muhammad from Mecca to Medina in 622 CE).

Holocene calendar

Holocene eraHEHuman Era
Instead, HE uses the "beginning of human era" as its epoch, arbitrarily defined as 10,000 BC denoted year 1 HE, so that AD 1 matches 10,001 HE.

Periodization

periodperiodisationhistorical epochs
An epoch, for the purposes of chronology and periodization, is an instant in time chosen as the origin of a particular calendar era.

Point of no return

fait accompliburn one's boatcross the Rubicon
In a more gradual change, a deciding moment is chosen when the epoch criterion was reached.

Japanese era name

nengōera nameera
The official Japanese system numbers years from the accession of the current emperor, regarding the calendar year during which the accession occurred as the first year.

Emperor of Japan

EmperorMonarchJapanese Emperor
The official Japanese system numbers years from the accession of the current emperor, regarding the calendar year during which the accession occurred as the first year.