era

The word has been in use in English since 1615,{{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}} 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".{{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}}{{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}}

The Latin word use in chronology seems to have begun in 5th century Visigothic Spain, where it appears in the History of Isidore of Seville,{{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}} and in later texts. The Spanish era is calculated from 38 BC, Before Christ,{{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}}{{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}} 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.{{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}}

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.{{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}}

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 reference date (epoch),{{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}} 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;{{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}} it is generally called after its focus accordingly as in "Victorian 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 "geologic era" refers to well-defined time spans.

The next-larger division of geologic time is the eon.{{cite book |author=Martin Harweit |title=Astrophysical Concepts |publisher=Springer-Verlag |year=1991 |isbn=3-540-96683-8 |edition=2nd}} p. 4. The Phanerozoic Eon, for example, is subdivided into eras.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. 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").

The older Proterozoic and Archean eons are also divided into eras.{{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}}{{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}}

For periods in the history of the universe, the term "epoch" is typically preferred, but "era" is used e.g. of the "Stelliferous Era".{{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}}

{{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 calculation of the age of the world, assuming it was created as described in the Book of Genesis.{{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}} 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{{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}} and ended on 16 September 2012.{{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}} In the Western church, Anno Domini (AD also written CE), counting the years since the birth of Jesus on traditional calculations, was always dominant.{{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}}

The Islamic calendar, which also has variants, counts years from the Hijra or emigration of the Islamic prophet Muhammad from Mecca to Medina, which occurred in 622 AD.{{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}} The Islamic year is some days shorter than 365; January 2012 fell in 1433 AH ("After Hijra").{{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}}

For a time ranging from 1872 to the Second World War, the Japanese used the imperial year system (kōki),{{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}} counting from the year when the legendary Emperor Jimmu founded Japan, which occurred in 660 BC.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].

Many Buddhist calendars count from the death of the Buddha, which according to the most commonly used calculations was in 545–543 BCE or 483 BCE.{{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}} Dates are given as "BE" for "Buddhist Era"; 2000 AD was 2543 BE in the Thai solar calendar.

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

{{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.{{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}} The use of regnal years 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). 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.{{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}} The name of each was a motto or slogan chosen by the emperor. Different East Asian countries utilized slightly different systems, notably:

• Chinese eras
• Japanese era
• Korean eras
• 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, so that "61 & 62 Vict c. 37" refers to the Local Government (Ireland) Act 1898{{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}} passed in the session of Parliament in the 61st/62nd year of the reign of Queen Victoria.{{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}}

"Era" can be used to refer to well-defined periods in historiography, such as the Roman era, Elizabethan era, Victorian era, etc.{{Cite web |title=Historiography {{!}} NMU Writing Center |url=https://nmu.edu/writingcenter/historiography |access-date=2023-12-11 |website=nmu.edu |language=en}}

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 era", "disco era", etc.{{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}}{{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}}

• Periodization
• List of time periods
• List of archaeological periods
• {{anl|Epoch}}

{{Reflist}}

{{Chronology}}

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

Category:Chronology

Category:Units of time