Editing Era

{{Short description|Span of time defined for the purposes of chronology or historiography}}
{{Other uses}}
{{Wiktionary|era}}
An '''era''' is a span of time defined for the purposes of [[chronology]] or [[historiography]], as in the [[regnal era]]s in the history of a given monarchy, a [[calendar era]] used for a given [[calendar]], or the [[geological era]]s defined for the [[history of Earth]].<ref>{{Cite web |title=Era {{!}} definition in the Cambridge English Dictionary |url=https://dictionary.cambridge.org/us/dictionary/english/era |access-date=2023-12-11 |website=Cambridge Dictionary}}</ref>

Comparable terms are [[Epoch]], [[age (geology)|age]], [[Periodization|period]], [[saeculum]], [[aeon]] (Greek ''aion'')<ref>{{Cite web |date=2023-12-06 |title=Thesaurus.com - The world's favorite online thesaurus! |url=https://www.thesaurus.com/browse/era |access-date=2023-12-11 |website=Thesaurus.com |language=en}}</ref> and Sanskrit [[yuga]].<ref name="Dictionary.com yuga">{{Dictionary.com|Yuga|access-date=2023-12-11}}</ref>

==Etymology==
The word has been in use in English since 1615,<ref>{{Cite web |title=Time Traveler by Merriam-Webster: Words from 1615 |url=https://www.merriam-webster.com/time-traveler/1615 |access-date=2023-12-11 |website=www.merriam-webster.com |language=en}}</ref> and is derived from [[Late Latin]] ''aera'' "an era or epoch from which time is reckoned," probably identical to Latin ''æra'' "counters used for calculation," plural of ''æs'' "brass, money".<ref>{{Cite book |last=Peón |first=Baltasar |url=https://books.google.com/books?id=ptay4FWMeI8C&pg=PA560 |title=Estudios de cronología universal |date=1863 |publisher=Imprenta Nacional |language=es}}</ref><ref>{{cite journal |first=Giorgio |last=Levi Della Vida |author-link=Giorgio Levi Della Vida |year=1943 |title=The 'Bronze Era' in Moslem Spain |journal=Journal of the American Oriental Society |volume=63 |issue=3 |pages=183–191 |doi=10.2307/593870 |jstor=593870}}</ref>

The Latin word use in chronology seems to have begun in 5th century [[Visigoths|Visigothic]] Spain, where it appears in the ''History'' of [[Isidore of Seville]],<ref>{{Cite book |last=Hispalensis |first=Isidorus |url=https://books.google.com/books?id=cLi2PgAACAAJ |title=Isidori Hispalensis Historia de regibus Gothorum, Vandalorum et Suevorum |date=1773 |language=la}}</ref> and in later texts. The [[Spanish era]] is calculated from 38 BC, Before Christ,<ref>{{cite book |title=A Handbook of Dates: For Students of British History |first1=Carl D. |last1=Cheney |first2=Michael |last2=Jones |publisher=Cambridge University Press |year=2000 |edition=Rev.|page=2}}</ref><ref>{{cite encyclopedia |last=Roth |first=Norman |title=Calendar |editor-first=E. Michael |editor-last=Gerli |encyclopedia=Medieval Iberia: An Encyclopedia |publisher=Routledge |year=2003 |isbn=978-0-415-93918-8 |page=190}}</ref> perhaps because of a tax (cfr. [[indiction]]) levied in that year, or due to a miscalculation of the [[Battle of Actium]], which occurred in 31 BC.<ref>{{Cite web |title=Actium, 31 BC: the beginning of the end for Mark Antony and Cleopatra |url=https://www.historyextra.com/period/roman/battle-actium-31-bc-mark-antony-downfall/ |access-date=2023-12-11 |website=HistoryExtra |language=en}}</ref>

Like epoch, "era" in English originally meant "the starting point of an age"; the meaning "system of chronological notation" is c. 1646; that of "historical period" is 1741.<ref>{{Cite web |date=2023-11-22 |title=Definition of EPOCH |url=https://www.merriam-webster.com/dictionary/epoch |access-date=2023-12-11 |website=www.merriam-webster.com |language=en}}</ref>

==Use in chronology==
In [[chronology]], an "era" is the highest level for the organization of the measurement of time. A "[[calendar era]]" indicates a span of many years which are numbered beginning at a specific [[epoch (reference date)|reference date (epoch)]],<ref>{{Cite book |last1=Richards |first1=E. G. |title=Explanatory Supplement to the Astronomical Almanac |date=2013 |publisher=Univ Science Books |isbn=978-1-891389-85-6 |editor-last1=Urban |editor-first1=Sean E. |edition=3 |location=Mill Valley, CA |chapter=Calendars |editor-last2=Seidelmann |editor-first2=P. Kenneth}}</ref> which often marks the origin of a political state or [[cosmology]], dynasty, ruler, the birth of a leader, or another significant historical or mythological event;<ref name=":0">{{Cite web |title=The Geological Society of London - How are Geological Periods Determined? |url=https://www.geolsoc.org.uk/Education-and-Careers/Ask-a-Geologist/Nomenclature/How-are-Geological-Periods-Determined |access-date=2023-12-11 |website=www.geolsoc.org.uk}}</ref> it is generally called after its focus accordingly as in "[[Victorian era]]".

===Geological era===
{{main|Era (geology)}}
In large-scale natural science, there is need for another time perspective, independent from human activity, and indeed spanning a far longer period (mainly prehistoric), where "[[Era (geology)|geologic era]]" refers to well-defined time spans.<ref name=":0" />
The next-larger division of geologic time is the [[aeon|eon]].<ref name="Keel">{{cite book |author=Martin Harweit |title=Astrophysical Concepts |publisher=Springer-Verlag |year=1991 |isbn=3-540-96683-8 |edition=2nd}} p. 4.</ref> The [[Phanerozoic]] Eon, for example, is subdivided into eras.<ref>Short, N.M. (2009). [http://rst.gsfc.nasa.gov/Sect2/Sect2_1b.html "Geologic Time"] {{webarchive|url=https://web.archive.org/web/20050418090602/http://rst.gsfc.nasa.gov/Sect2/Sect2_1b.html |date=2005-04-18 }} in [http://rst.gsfc.nasa.gov/ ''Remote Sensing Tutorial''] {{webarchive|url=https://web.archive.org/web/20091027181013/http://rst.gsfc.nasa.gov/ |date=2009-10-27 }}. [[NASA]].</ref> There are currently three eras defined in the Phanerozoic; the following table lists them from youngest to oldest (BP is an abbreviation for "[[before present]]").
{| class="wikitable"
|-
! Era<ref>Lide, D. R. (1990). ''Handbook of Chemistry and Physics''. Boca Raton: CRC Press. pp. 14–16.</ref><ref name=ICS_chart>{{cite web|url=http://www.stratigraphy.org/index.php/ics-chart-timescale |title=International Stratigraphic Chart |publisher=International Commission on Stratigraphy |url-status=dead |archive-url=https://web.archive.org/web/20140530005940/http://www.stratigraphy.org/index.php/ics-chart-timescale |archive-date=30 May 2014 }}</ref>
! Beginning (millions of years BP)
! End (millions of years BP)
|-
| [[Cenozoic]]
|66.038
|N/A
|-
| [[Mesozoic]]
| 252.17
| 66.038
|-
| [[Paleozoic]]
| 542
| 252.17
|}
The older [[Proterozoic]] and [[Archean]] eons are also divided into eras.<ref>{{Cite web |title=Proterozoic Eon {{!}} Oxygen Crisis, Animals, & Facts {{!}} Britannica |url=https://www.britannica.com/science/Proterozoic-Eon |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref><ref>{{Cite web |title=Archean Eon {{!}} Atmosphere, Timeline, and Facts {{!}} Britannica |url=https://www.britannica.com/science/Archean-Eon |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref>

===Cosmological era===
For periods in the  [[history of the universe]], the term "[[Epoch (cosmology)|epoch]]" is typically preferred, but "era" is used e.g. of the "[[Stelliferous Era]]".<ref>{{Cite web |title=Big Bang Timeline- The Big Bang and the Big Crunch - The Physics of the Universe |url=https://www.physicsoftheuniverse.com/topics_bigbang_timeline.html |access-date=2023-12-11 |website=www.physicsoftheuniverse.com}}</ref>

===Calendar eras===
{{main|Calendar era}}
Calendar eras count the years since a particular date (epoch), often one with religious significance.  ''[[Anno mundi]]'' (year of the world) refers to a group of calendar eras based on a [[Dating creation|calculation of the age of the world]], assuming it was created as described in the [[Book of Genesis]].<ref>{{Cite web |title=Anno mundi {{!}} Jewish Calendar, History & Origins {{!}} Britannica |url=https://www.britannica.com/topic/anno-mundi |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref> In Jewish religious contexts one of the versions is still used, and many [[Eastern Orthodox]] religious calendars used another version until 1728.  Hebrew year 5772 AM began at sunset on 28 September 2011<ref>{{Cite web |title=Hebrew Date Converter - September 28, 2011 after sunset / 1st of Tishrei, 5772 |url=https://www.hebcal.com/converter?gd=28&gm=9&gy=2011&gs=on&g2h=1 |access-date=2023-12-11 |website=www.hebcal.com}}</ref> and ended on 16 September 2012.<ref>{{Cite web |title=Hebrew Date Converter - September 16, 2012 after sunset / 1st of Tishrei, 5773 |url=https://www.hebcal.com/converter?gd=16&gm=9&gy=2012&gs=on&g2h=1 |access-date=2023-12-11 |website=www.hebcal.com}}</ref>  In the Western church, ''[[Anno Domini]]'' (''AD'' also written ''[[Common era|CE]]''), counting the years since the birth of Jesus on traditional calculations, was always dominant.<ref>{{Cite web |title=Chronology - Christian History, Dates, Events {{!}} Britannica |url=https://www.britannica.com/topic/chronology/Christian |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref>

The [[Islamic calendar]], which also has variants, counts years from the [[Hijra (Islam)|Hijra]] or emigration of the Islamic prophet [[Muhammad]] from [[Mecca]] to [[Medina]], which occurred in 622 AD.<ref>{{Cite web |date=2023-11-14 |title=Islamic calendar {{!}} Months, Definition, & Facts {{!}} Britannica |url=https://www.britannica.com/topic/Islamic-calendar |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref>  The Islamic year is some days shorter than 365; January 2012 fell in 1433 AH ("After Hijra").<ref>{{Cite web |title=Hijri to Gregorian Date Converter - Islamic Date Converter |url=https://www.islamicfinder.org/islamic-date-converter/ |access-date=2023-12-11 |website=IslamicFinder |language=en}}</ref>

For a time ranging from 1872 to the [[World War II|Second World War]], the Japanese used the imperial year system (''kōki''),<ref>{{Cite book |last=Louis-Frédéric |url=https://books.google.com/books?id=p2QnPijAEmEC&pg=PA514 |title=Japan Encyclopedia |date=2002 |publisher=Harvard University Press |isbn=978-0-674-01753-5 |language=en}}</ref> counting from the year when the legendary [[Emperor Jimmu]] founded Japan, which occurred in 660 BC.<ref>Gubbins, John Harrington. (1922). [https://books.google.com/books?id=0MwNAAAAIAAJ&pg=PA71 ''The Making of Modern Japan,'' p. 71]; Mossman, Samuel. (1873). [https://books.google.com/books?id=ryEPAAAAYAAJ&pg=PA462 ''New Japan, the Land of the Rising Sun,'' p. 462].</ref>

Many [[Buddhist calendar]]s count from the death of the [[Buddha]], which according to the most commonly used calculations was in 545–543 BCE or 483 BCE.<ref name=":1">{{Cite web |title=Calendar systems and their role in patent documentation {{!}} Epo.org |url=https://www.epo.org/en/searching-for-patents/helpful-resources/patent-knowledge-news/calendar-systems-and-their-role-1#:~:text=In%20Thailand,%20Cambodia%20and%20Laos,and%20Myanmar%20to%20544%20BC. |access-date=2023-12-11 |website=www.epo.org}}</ref> Dates are given as "BE" for "Buddhist Era"; 2000 AD was 2543 BE in the [[Thai solar calendar]].<ref name=":1" />

Other calendar eras of the past counted from political events, such as the [[Seleucid era]]<ref>Denis C. Feeney, ''Caesar's Calendar,'' [[University of California Press]], Berkeley 2007, p. 139.</ref> and the Ancient Roman ''[[ab urbe condita]]'' ("AUC"), counting from the foundation of the city.<ref name=":2">Wiseman, Timothy Peter (1995). ''Remus: A Roman Myth''. Cambridge University Press. {{ISBN|978-0-521-48366-7}}.</ref>

===Regnal eras===
{{main|Regnal year}}
The word era also denotes the units used under a different, more arbitrary system where time is not represented as an endless continuum with a single reference year, but each unit starts counting from one again as if time starts again.<ref>{{Cite web |title=Regnal Years - The University of Nottingham |url=https://www.nottingham.ac.uk/manuscriptsandspecialcollections/researchguidance/datingdocuments/regnalyears.aspx |access-date=2023-12-11 |website=www.nottingham.ac.uk}}</ref> The use of [[regnal year]]s is a rather impractical system, and a challenge for historians if a single piece of the historical chronology is missing, and often reflects the preponderance in public life of an absolute ruler in many ancient cultures.  Such traditions sometimes outlive the political power of the throne, and may even be based on mythological events or rulers who may not have existed (for example Rome numbering from the rule of [[Romulus]] and [[Remus]]).<ref name=":2" /> In a manner of speaking the use of the supposed date of the birth of Christ as a base year is a form of an era.

In [[East Asia]], each emperor's reign may be subdivided into several reign periods, each being treated as a new era.<ref>{{Cite web |title=Calendar systems and their role in patent documentation {{!}} Epo.org |url=https://www.epo.org/en/searching-for-patents/helpful-resources/patent-knowledge-news/calendar-systems-and-their-role |access-date=2023-12-11 |website=www.epo.org}}</ref> The name of each was a motto or slogan chosen by the emperor. Different East Asian countries utilized slightly different systems, notably:

*[[Chinese era name|Chinese eras]]
*[[Japanese era name|Japanese era]]
*[[Korean era name|Korean eras]]
*[[Vietnamese era name|Vietnamese eras]]

A similar practice survived in the United Kingdom until quite recently, but only for formal official writings: in daily life the ordinary year A.D. has been used for a long time, but [[Acts of Parliament]] were dated according to the years of the reign of the current [[Monarch of the United Kingdom|monarch]], so that "61 & 62 Vict c. 37" refers to the [[Local Government (Ireland) Act 1898]]<ref name="beckett">{{cite book |last=Beckett |first=J C |title=The Making of Modern Ireland 1603 – 1923 |publisher=Faber & Faber |year=1966 |isbn=0-571-09267-5 |location=London |page=406}}</ref> passed in the session of [[Parliament of the United Kingdom|Parliament]] in the 61st/62nd year of the reign of [[Victoria of the United Kingdom|Queen Victoria]].<ref>{{cite book |title=Sweet & Maxwell's Guide to Law Reports and Statutes |publisher=Sweet & Maxwell's Guide |year=1962 |edition=Fourth |location=London |pages=20–33 |chapter=Chapter Five: Table of regnal year of English Sovereigns |ref={{harvid|Sweet & Maxwell's Guide|1962}} |chapter-url=https://guides.library.harvard.edu/ld.php?content_id=12548485}}</ref>

===Historiography===
"Era" can be used to refer to well-defined periods in historiography, such as the [[Roman era]], [[Elizabethan era]], [[Victorian era]], etc.<ref>{{Cite web |title=Historiography {{!}} NMU Writing Center |url=https://nmu.edu/writingcenter/historiography |access-date=2023-12-11 |website=nmu.edu |language=en}}</ref>
Use of the term for more recent periods or topical history might include [[Soviet era]], and "musical eras" in the history of modern [[popular music]], such as the "[[Big Band|big band era]]", "[[disco era]]", etc.<ref>{{Cite web |title=Big Bands and the Swing Era |url=https://acousticmusic.org/research/history/musical-styles-and-venues-in-america/big-bands-and-the-swing-era/ |access-date=2023-12-11 |website=Acoustic Music |language=en-US}}</ref><ref>{{Cite web |date=2023-12-09 |title=Disco {{!}} Origins, Genres & Cultural Impact {{!}} Britannica |url=https://www.britannica.com/art/disco |access-date=2023-12-11 |website=www.britannica.com |language=en}}</ref>

==See also==
*[[Periodization]]
*[[List of time periods]]
*[[List of archaeological periods]]
*{{anl|Epoch}}

== References ==
{{Reflist}}

{{Chronology}}

{{Authority control}}
{{Use dmy dates|date=August 2019}}


[[Category:Chronology]]
[[Category:Units of time]]