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An era is a span of time defined for the purposes of
chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European language ...
or
historiography Historiography is the study of the methods of historian ( 484– 425 BC) was a Greek historian who lived in the 5th century BC and one of the earliest historians whose work survives. A historian is a person who studies and writes about the p ...

historiography
, as in the
regnal era A regnal year is a year of the reign of a monarch, sovereign, from the Latin ''regnum'' meaning kingdom, rule. Regnal years considered the date as an ordinal number (linguistics), ordinal, not a cardinal number (linguistics), cardinal number. For ...
s in the history of a given monarchy, a
calendar era A calendar era is the period of time elapsed since one ''epoch'' of a calendar and, if it exists, before the next one. For example, it is the year as per the Gregorian calendar, which numbers its years in the Western Christian era (the Coptic Ort ...
used for a given
calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single, specific day within such a system. A calendar is al ...

calendar
, or the
geological eraA geologic era is a subdivision of geologic time that divides an Eon (geology), eon into smaller units of time. The Phanerozoic, Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middl ...
s defined for the
history of Earth The history of Earth concerns the development of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity ...
. Comparable terms are
epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
, age,
period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Period, a descriptor for a historical or period drama ...
,
saeculum A saeculum is a length of time roughly equal to the potential lifetime of a person or, equivalently, the complete renewal of a human population. The term was first used by the Etruscans The Etruscan civilization () of ancient Italy covered a t ...
,
aeon The word aeon , also spelled eon ( in American English), originally meant "life", "vital force" or "being", "generation" or "a period of time", though it tended to be translated as "age" in the sense of "ages", "forever", "timeless" or "for etern ...
(Greek ''aion'') and Sanskrit
yuga In Hinduism Hinduism () is an Indian religion and ''dharma'', or way of life. It is the Major religious groups, world's third-largest religion, with over 1.2 billion followers, or 15–16% of the global population, known as Hindus. The wor ...
.


Etymology

The word has been in use in English since 1615, and is derived from
Late Latin Late Latin ( la, Latinitas serior) is the scholarly name for the written Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area ar ...
''aera'' "an era or epoch from which time is reckoned," probably identical to Latin ''æra'' "counters used for calculation," plural of ''æs'' "brass, money". The Latin word use in chronology seems to have begun in 5th century
Visigothic The Visigoths (; la, Visigothi, Wisigothi, Vesi, Visi, Wesi, Wisi) were an early Germanic people who, along with the Ostrogoths, constituted the two major political entities of the Goths within the Roman Empire in Late Antiquity, or what is ...
Spain, where it appears in the ''History'' of
Isidore of Seville Isidore of Seville (; la, Isidorus Hispalensis; c. 560 – 4 April 636) was a Spanish scholar and cleric. For over three decades, he was Archbishop In many Christian denomination, Christian Denominations, an archbishop (, via Latin ...
, and in later texts. The
Spanish era The Spanish era ( la, Æra Hispanica), sometimes called the era of Caesar, was a calendar era (year numbering system) commonly used in the states of the Iberian Peninsula The Iberian Peninsula , ** * Aragonese and Occitan: ''Peninsula Iber ...
is calculated from 38 BC, perhaps because of a tax (cfr.
indiction An indiction ( la, indictio, impost) was a periodic reassessment of taxation in the Roman Empire which took place every fifteen years. In Late Antiquity, this 15-year cycle began to be used to date documents and it continued to be used for this pu ...
) levied in that year, or due to a miscalculation of the
Battle of Actium The Battle of Actium was a naval battle in the last war of the Roman Republic, fought between the fleet of Octavian Caesar Augustus (23 September 63 BC19 August AD 14) was the first Roman emperor, reigning from 27 BC until his death ...
, which occurred in 31 BC. 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.


Use in chronology

In
chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European language ...
, an "era" is the highest level for the organization of the measurement of time. A "
calendar era A calendar era is the period of time elapsed since one ''epoch'' of a calendar and, if it exists, before the next one. For example, it is the year as per the Gregorian calendar, which numbers its years in the Western Christian era (the Coptic Ort ...
" indicates a span of many years which are numbered beginning at a specific reference date (epoch), which often marks the origin of a political state or
cosmology Cosmology (from Ancient Greek, Greek κόσμος, ''kosmos'' "world" and -λογία, ''-logia'' "study of") is a branch of astronomy concerned with the study of the chronology of the universe. Physical cosmology is the study of the universe's ...
, dynasty, ruler, the birth of a leader, or another significant historical or mythological event; it is generally called after its focus accordingly as in "
Victorian era In the history of the United Kingdom, the Victorian era was the wikt:period, period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian era, Georgian period and preceded the Edwar ...
".


Geological era

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 eraA geologic era is a subdivision of geologic time that divides an Eon (geology), eon into smaller units of time. The Phanerozoic, Phanerozoic Eon is divided into three such time frames: the Paleozoic, Mesozoic, and Cenozoic (meaning "old life", "middl ...
" refers to well-defined time spans. The next-larger division of geologic time is the eon. The
Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontolo ...
Eon, for example, is subdivided into eras.Short, N.M. (2009)
"Geologic Time"
i
''Remote Sensing Tutorial''
.
NASA The National Aeronautics and Space Administration (NASA; ) is an independent agencies of the United States government, independent agency of the Federal government of the United States, U.S. federal government responsible for the civilian Lis ...

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 Before Present (BP) years is a time scale used mainly in archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. Archaeology is often considered a branch of socio-cultural ...
"). The older
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 541million years ago. It is the most recent part of the Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part ...
and
Archean The Archean Eon ( , also spelled Archaean or Archæan) is one of the four geologic Geology (from the Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient w ...

Archean
eons are also divided into eras.


Cosmological era

For periods in the
history of the universe The chronology of the universe describes the history and future of the universe according to Big Bang The Big Bang theory A theory is a reason, rational type of abstraction, abstract thinking about a phenomenon, or the results of such t ...

history of the universe
, the term "
epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-E ...
" is typically preferred, but "era" is used e.g. of the " Stelliferous Era".


Calendar eras

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 The Book of Genesis,, "''Bərēšīṯ''", "In hebeginning" the first book of the Hebrew Bible The Hebrew Bible or Tanakh (; Hebrew: , or ), is the Biblical canon, canonical collection of Hebrew language, Hebrew scriptures, including the ...

Book of Genesis
. In Jewish religious contexts one of the versions is still used, and many
Eastern Orthodox The Eastern Orthodox Church, officially the Orthodox Catholic Church, is the List of Christian denominations by number of members, second-largest Christian church, with approximately 220 million baptised members. It operates as a Communion ( ...
religious calendars used another version until 1728. Hebrew year 5772 AM began at sunset on 28 September 2011 and ended on 16 September 2012. In the Western church, ''
Anno Domini The terms (AD) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendar The Gregorian calendar is the calendar used in most of the world. It was introduced in October 1582 by Pope Gregory XIII as a ...
'' (''AD'' also written '' CE''), counting the years since the birth of Jesus on traditional calculations, was always dominant. The
Islamic calendar The Hijri calendar ( ar, ٱلتَّقْوِيم ٱلْهِجْرِيّ '), also known as the Lunar Hijri calendar and (in English) as the Islamic, Muslim or Arabic calendar, is a lunar calendar A lunar calendar is a calendar based on the mon ...
, which also has variants, counts years from the Hijra or emigration of the Islamic prophet
Muhammad Muhammad ibn AbdullahHe is referred to by many appellations, including Messenger of Allah, The Prophet Muhammad, Allah's Apostle, Last Prophet of Islam, and others; there are also many variant spellings of Muhammad, such as Mohamet, Mohammed, ...

Muhammad
from
Mecca Mecca, officially Makkah al-Mukarramah ( ) and commonly shortened to Makkah ( ),Quran 48:22 ' () is a city and administrative center of the Mecca Province of Saudi Arabia, and the Holiest sites in Islam, holiest city in Islam. It is inland ...

Mecca
to
Medina Medina,, ', "the radiant city"; or , ', (), "the city" officially Al Madinah Al Munawwarah (, ), commonly simplified as Madīnah or Madinah (, ), is the second holiest city in Islam Islam (;There are ten pronunciations of ''Islam'' in Eng ...

Medina
, which occurred in 622 AD. The Islamic year is some days shorter than 365; January 2012 fell in 1433 AH ("After Hijra"). For a time ranging from 1872 to the
Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a World war, global war that lasted from 1939 to 1945. It involved World War II by country, the vast majority of the world's countries—including all of the gr ...
, the Japanese used the imperial year system (''kōki''), counting from the year when the legendary
Emperor Jimmu was the Legend, legendary first emperor of Japan according to the ''Nihon Shoki'' and ''Kojiki''. His accession is traditionally dated as 660 BC.Kelly, Charles F"Kofun Culture"
Emperor Jimmu
founded Japan, which occurred in 660 BC. Many Buddhist calendars count from the death of the
Buddha Gautama Buddha, popularly known as the Buddha (also known as Siddhattha Gotama or Siddhārtha Gautama or Buddha Shakyamuni), was an Śramaṇa, ascetic, a religious leader and teacher who lived in History of India#Iron Age (1500 – 200 BCE ...

Buddha
, which according to the most commonly used calculations was in 545–543 BCE or 483 BCE. Dates are given as "BE" for "Buddhist Era"; 2000 AD was 2543 BE in the
Thai solar calendar The Thai solar calendar ( th, ปฏิทินสุริยคติ, , "solar calendar") was adopted by King Chulalongkorn Chulalongkorn, also known as King Rama V, reigning title Phra Chula Chom Klao Chao Yu Hua) (Thai language, Thai: ...
. Other calendar eras of the past counted from political events, such as the
Seleucid era The Seleucid era or (literally "year of the Greeks" or "Greek year"), sometimes denoted "AG", was a system of numbering years in use by the Seleucid Empire The Seleucid Empire (; grc, Βασιλεία τῶν Σελευκιδῶν, ''Basileía ...
and the Ancient Roman ''
ab urbe condita 300px, Antoninianus of Pacatianus, Roman usurper, usurper of Roman emperor Philip the Arab, Philip in 248. It reads ''ROMAE AETERANMIL ESIMOET PRIMO'', 'To eternal Rome, in its one thousand and first year.' ''Ab urbe condita'' ( ...
'' ("AUC"), counting from the foundation of the city.


Regnal eras

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. The use of
regnal year A regnal year is a year of the reign of a sovereign Sovereign is a title which can be applied to the highest leader in various categories. The word is borrowed from Old French ''souverain'', which is ultimately derived from the Latin Latin ...
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 Romulus () was the legendary founder Founder or Founders may refer to: Places *Founders Park, a stadium in South Carolina, formerly known as Carolina Stadium * Founders Park, a waterside park in Islamorada, Florida#In popular culture, Islamorad ...
and
Remus
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 East Asia is the eastern region of Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, Hemispheres. It shares the ...

East Asia
, each emperor's reign may be subdivided into several reign periods, each being treated as a new era. 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 Japanese may refer to: * Something from or related to Japan, an island country in East Asia * Japanese language, spoken mainly in Japan * Japanese people, the ethnic group that identifies with Japan through culture or ancestry ** Japanese diaspora ...
* 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 Acts of parliament, sometimes referred to as primary legislation In parliamentary systems and presidential systems of government, primary legislation and secondary legislation, the latter also called delegated legislation or subordinate legislat ...
were dated according to the years of the reign of the current
monarch A monarch is a head of stateWebster's II New College DictionarMonarch Houghton Mifflin. Boston. 2001. p. 707. Life tenure, for life or until abdication, and therefore the head of state of a monarchy. A monarch may exercise the highest authority a ...
, so that "61 & 62 Vict c. 37" refers to the
Local Government (Ireland) Act 1898 The Local Government (Ireland) Act 1898 (61 & 62 Vict. c. 37) was an Act of the Parliament of the United Kingdom of Great Britain and Ireland In modern politics and history, a parliament is a legislative body of government. Generally, a ...
passed in the session of
Parliament In modern politics and history, a parliament is a legislative body of government. Generally, a modern parliament has three functions: Representation (politics), representing the Election#Suffrage, electorate, making laws and overseeing the g ...
in the 61st/62nd year of the reign of
Queen Victoria Victoria (Alexandrina Victoria; 24 May 1819 – 22 January 1901) was Queen of the United Kingdom of Great Britain and Ireland from 20 June 1837 until her death in 1901. Known as the Victorian era, her reign of 63 years and seven months was Lis ...

Queen Victoria
.


Historiography

"Era" can be used to refer to well-defined periods in historiography, such as the
Roman era In historiography, ancient Rome is Roman people, Roman civilization from the founding of the Italian city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD, encompassing the Roman Kingdom (753 BC ...
,
Elizabethan era The Elizabethan era is the epoch in the Tudor period of the history of England during the reign of Queen Elizabeth I (1558–1603). Historians often depict it as the Golden age (metaphor), golden age in English history. The symbol of Britannia ...
,
Victorian era In the history of the United Kingdom, the Victorian era was the wikt:period, period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian era, Georgian period and preceded the Edwar ...
, etc. Use of the term for more recent periods or topical history might include
Soviet era The history of Soviet union and the Soviet Union reflects a period of change for both Russia and the world. Though the terms "Russian Soviet Federative Socialist Republic#Early years (1917–1920), Soviet Russia" and "Soviet Union" often are sy ...
, and "musical eras" in the history of modern
popular music Popular music is music with wide appeal that is typically distributed to large audiences through the music industry. These forms and styles can be enjoyed and performed by people with little or no musical training.Popular Music. (2015). ''Funk & ...
, such as the "
big band era
big band era
", "
disco era Disco is a genre Genre () is any form or type of communication in any mode (written, spoken, digital, artistic, etc.) with socially-agreed-upon conventions developed over time. In popular usage, it normally describes a Category of being, categ ...
", etc.


See also

*
Periodization Periodization is the process or study of categorizing the past into discrete, quantified named blocks of time.Adam Rabinowitz. It’s about time: historical periodization and Linked Ancient World Data'. Institute for the Study of the Ancient Wo ...
*
List of time periods The categorization of the past into discrete, quantified named blocks of time is called periodization.Adam Rabinowitz. And kingIt’s about time: historical periodization and Linked Ancient World Data'. Study of the Ancient universe Papers, 2014 ...
*
List of archaeological periods The names for archaeological periods in the list of archaeological periods vary enormously from region to region. This is a list of the main divisions by continent and region. Dating also varies considerably and those given are broad approximations ...
*


References

{{Use dmy dates, date=August 2019 Chronology Units of time