From Wikipedia, the free encyclopedia
Reference point from which time is measured
In
chronology
and
periodization
, an
epoch
or
reference epoch
is an
instant
in time chosen as the origin of a particular
calendar era
. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided by congruity, or by following conventions understood from the epoch in question. The epoch moment or date is usually defined from a specific, clear event of change, an
epoch event
. In a more gradual change, a
deciding moment
is chosen when the
epoch criterion
was reached.
Calendar eras
[
edit
]
Pre-modern eras
[
edit
]
Modern eras
[
edit
]
- The
Baha'i calendar
is dated from the
vernal equinox
of the year the
Bab
proclaimed his religion (AD 1844). Years are grouped in
Va?ids
of 19 years, and
Kull-i-Shay
of 361 (19×19) years.
[5]
- 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. Except for this era, it is the Gregorian calendar.
- In the
French Republican Calendar
, a calendar used by the French government for about twelve years from late 1793, the epoch was the beginning of the "Republican Era", September 22, 1792 (the day the
French First Republic
was proclaimed, one day after the Convention abolished the
Ancien Regime
).
- The
Indian national calendar
, introduced in 1957, follows the
Saka era
(AD 78).
- The
Minguo calendar
used by officials of
Taiwan
and
its predecessor
dates from January 1, 1912, the first year after the
Xinhai Revolution
, which overthrew the
Qing Empire
.
- North Korea
uses a system that starts in 1912 (=
Juche
1), the year of the birth of its founder
Kim Il-Sung
.
- The
Fascist Era
dates to
Mussolini
's
March on Rome
in 1922, and was in use only in countries under hegemony of the Fascist regime of Benito Mussolini. It has been defunct since the fall of the
Italian Social Republic
in 1945.
- In the scientific
Before Present
system of numbering years for purposes of
radiocarbon dating
, the reference date is January 1, 1950 (though the specific date January 1 is quite unnecessary, as radiocarbon dating has limited precision).
[6]
[7]
- Different branches of
Freemasonry
have selected different years to date their documents according to a Masonic era, such as the
Anno Lucis
(A.L.).
- The
Holocene calendar
uses 10,000 BC as the epoch, the beginning of the
Holocene epoch
on the
geological time scale
.
Regnal eras
[
edit
]
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. A similar
system
existed in
China
before 1912, being based on the accession year of the emperor (1911 was thus the third year of the
Xuantong
period). With the establishment of the
Republic of China
in 1912, the republican era was introduced. It is still very common in
Taiwan
to date events via the republican era. The People's Republic of China adopted the common era calendar in 1949 (the 38th year of the Chinese Republic).
Other applications
[
edit
]
An
epoch in computing
is the time at which the representation is zero. For example,
Unix time
is represented as the number of seconds since 00:00:00 UTC on 1 January 1970, not counting
leap seconds
.
An
epoch in astronomy
is a reference time used for consistency in calculation of positions and orbits. A common astronomical epoch is J2000, which is noon on January 1, 2000,
Terrestrial Time
.
An epoch in
Geochronology
is a period of time, typically in the order of tens of millions of years. The current epoch is the
Holocene
.
See also
[
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]
References
[
edit
]
- ^
Solomin, Rachel M.
"Counting the Jewish Years"
.
myjewishlearning.com
.
Archived
from the original on 2020-02-12
. Retrieved
2016-12-27
.
- ^
Lee, Scott E. (2006).
"Overview of Calendars"
.
rosettacalendar.com
.
Archived
from the original on 2020-08-20
. Retrieved
2006-10-23
.
- ^
Dershowitz, Nachum
;
Reingold, Edward M.
(2008).
Calendrical Calculations
(3rd ed.). Cambridge University Press. p.
289
.
ISBN
978-0-521-70238-6
.
- ^
Blackburn, B; Holford-Strevens, L (2003). "Incarnation era".
The Oxford Companion to the Year: An exploration of calendar customs and time-reckoning
. Oxford University Press. p. 881.
- ^
Richards, E. G. (2013). "Calendars". In Urban, S. E.; Seidelman, P. K. (eds.).
Explanatory Supplement to the Astronomical Almanac
(3rd ed.). Mill Valley, CA: University Science Books. pp. 616?617.
- ^
Higham, Thomas
.
"Radiocarbon dating ? Age calculation"
.
c14dating.com
. Thomas Higham (archaeologist).
Archived
from the original on June 10, 2007
. Retrieved
December 31,
2009
.
- ^
Stuiver, Minze; Polach HA (1977).
"Discussion; reporting of C-14 data"
.
Radiocarbon
.
19
(3). University of Arizona: 355?363.
Bibcode
:
1977Radcb..19..355S
.
doi
:
10.1017/S0033822200003672
.
S2CID
56572650
.
Archived
from the original on August 17, 2020
. Retrieved
October 5,
2018
.