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An era is a span of time defined for the purposes of
chronology Chronology (from Latin ''chronologia'', from Ancient Greek , ''chrónos'', "time"; and , ''-logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of even ...
or
historiography Historiography is the study of the methods of historians in developing history as an academic discipline, and by extension is any body of historical work on a particular subject. The historiography of a specific topic covers how historians h ...
, as in the regnal eras 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 ...
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 date is the designation of a single and specific day within such a system. A calendar is also a phy ...
, or the
geological era The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochrono ...
s defined for the
history of Earth The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geologi ...
. Comparable terms are
epoch 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 ...
, 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 * Periodic sentence (or rhetorical period), a concept ...
, saeculum,
aeon The word aeon , also spelled eon (in American and Australian 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", "timele ...
(Greek ''aion'') and Sanskrit
yuga A ''yuga'', in Hinduism, is generally used to indicate an age of time. In the ''Rigveda'', a ''yuga'' refers to generations, a long period, a very brief period, or a yoke (joining of two things). In the ''Mahabharata'', the words ''yuga'' and ...
.


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 form of Literary Latin of late antiquity.Roberts (1996), p. 537. English dictionary definitions of Late Latin date this period from the , and continuing into the 7th century in t ...
''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, theologian, and archbishop of Seville. He is widely regarded, in the words of 19th-century historian Montalembert, as "the last scholar of ...
, 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 from the 5th century until the 15th, when it was phased out in favour of the ...
is calculated from 38 BC, Before Christ, 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 p ...
) levied in that year, or due to a miscalculation of the
Battle of Actium The Battle of Actium was a naval battle fought between a maritime fleet of Octavian led by Marcus Agrippa and the combined fleets of both Mark Antony and Cleopatra VII Philopator. The battle took place on 2 September 31 BC in the Ionian Sea, ...
, 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 Chronology (from Latin ''chronologia'', from Ancient Greek , ''chrónos'', "time"; and , ''-logia'') is the science of arranging events in their order of occurrence in time. Consider, for example, the use of a timeline or sequence of even ...
, 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 ...
" 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 () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by German philosopher ...
, 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 and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwa ...
".


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 era The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...
" refers to well-defined time spans. The next-larger division of geologic time is the
eon Eon or Eons may refer to: Time * Aeon, an indefinite long period of time * Eon (geology), a division of the geologic time scale Arts and entertainment Fictional characters * Eon, in the 2007 film '' Ben 10: Race Against Time'' * Eon, in the ...
. The
Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present, and it began with the Cambrian Period, when anim ...
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 agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedin ...
.
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, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Beca ...
"). The older
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided i ...
and
Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...
eons are also divided into eras.


Cosmological era

For periods in the
history of the universe History (derived ) is the systematic study and the documentation of the human activity. The time period of event before the invention of writing systems is considered prehistory. "History" is an umbrella term comprising past events as well ...
, the term "
epoch 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 ...
" 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 (from Latin "in the year of the world"; he, לבריאת העולם, Livryat haOlam, lit=to the creation of the world), abbreviated as AM or A.M., or Year After Creation, is a calendar era based on the biblical accounts of the creation of ...
'' (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 (from Greek ; Hebrew: בְּרֵאשִׁית ''Bəreʾšīt'', "In hebeginning") is the first book of the Hebrew Bible and the Christian Old Testament. Its Hebrew name is the same as its first word, ( "In the beginning" ...
. In Jewish religious contexts one of the versions is still used, and many
Eastern Orthodox Eastern Orthodoxy, also known as Eastern Orthodox Christianity, is one of the three main branches of Chalcedonian Christianity, alongside Catholicism and Protestantism. Like the Pentarchy of the first millennium, the mainstream (or " canonical ...
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 calendars. The term is Medieval Latin and means 'in the year of the Lord', but is often presented using "our Lord" instead of "the Lord" ...
'' (''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, translit=al-taqwīm al-hijrī), also known in English as the Muslim calendar and Islamic calendar, is a lunar calendar consisting of 12 lunar months in a year of 354 ...
, which also has variants, counts years from the
Hijra Hijra, Hijrah, Hegira, Hejira, Hijrat or Hijri may refer to: Islam * Hijrah (often written as ''Hejira'' in older texts), the migration of Muhammad from Mecca to Medina in 622 CE * Migration to Abyssinia or First Hegira, of Muhammad's followers ...
or emigration of the Islamic prophet
Muhammad Muhammad ( ar, مُحَمَّد;  570 – 8 June 632 CE) was an Arab religious, social, and political leader and the founder of Islam. According to Islamic doctrine, he was a prophet divinely inspired to preach and confirm the mon ...
from
Mecca Mecca (; officially Makkah al-Mukarramah, commonly shortened to Makkah ()) is a city and administrative center of the Mecca Province of Saudi Arabia, and the holiest city in Islam. It is inland from Jeddah on the Red Sea, in a narrow v ...
to
Medina Medina,, ', "the radiant city"; or , ', (), "the city" officially Al Madinah Al Munawwarah (, , Turkish: Medine-i Münevvere) and also commonly simplified as Madīnah or Madinah (, ), is the Holiest sites in Islam, second-holiest city in Islam, ...
, 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 that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...
, the Japanese used the imperial year system (''kōki''), counting from the year when the legendary
Emperor Jimmu was the legendary first emperor of Japan according to the '' Nihon Shoki'' and ''Kojiki''. His ascension is traditionally dated as 660 BC.Kelly, Charles F"Kofun Culture"Buddhist calendar The Buddhist calendar is a set of lunisolar calendars primarily used in Cambodia, Laos, Myanmar, India, Sri Lanka, and Thailand as well as in Malaysia, Singapore and Vietnam by Chinese populations for religious or official occasions. W ...
s count from the death of the
Buddha Siddhartha Gautama, most commonly referred to as the Buddha, was a wandering ascetic and religious teacher who lived in South Asia during the 6th or 5th century BCE and founded Buddhism. According to Buddhist tradition, he was born in L ...
, 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 (Rama V) in 1888 CE as the Siamese version of the Gregorian calendar, replacing the Thai lunar calendar as the lega ...
. Other calendar eras of the past counted from political events, such as the
Seleucid era The Seleucid era ("SE") or (literally "year of the Greeks" or "Greek year"), sometimes denoted "AG," was a system of numbering years in use by the Seleucid Empire and other countries among the ancient Hellenistic civilizations. It is sometimes r ...
and the Ancient Roman ''
ab urbe condita ''Ab urbe condita'' ( 'from the founding of the City'), or ''anno urbis conditae'' (; 'in the year since the city's founding'), abbreviated as AUC or AVC, expresses a date in years since 753 BC, the traditional founding of Rome. It is an ex ...
'' ("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, from the Latin ''regnum'' meaning kingdom, rule. Regnal years considered the date as an ordinal, not a cardinal number. For example, a monarch could have a first year of rule, a second 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 Romulus () was the legendary founder and first king of Rome. Various traditions attribute the establishment of many of Rome's oldest legal, political, religious, and social institutions to Romulus and his contemporaries. Although many of these ...
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 East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea ...
, 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 * 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, are texts of law passed by the legislative body of a jurisdiction (often a parliament or council). In most countries with a parliamentary system of government, acts of parliament be ...
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 ...
, 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 that established a system of local government in Ireland similar to that already created for England, ...
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: representing the electorate, making laws, and overseeing the government via hearings and inquiries. Th ...
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. Her reign of 63 years and 216 days was longer than that of any previ ...
.


Historiography

"Era" can be used to refer to well-defined periods in historiography, such as the
Roman era In modern historiography, ancient Rome refers to Roman civilisation from the founding of the city of Rome in the 8th century BC to the collapse of the Western Roman Empire in the 5th century AD. It encompasses the Roman Kingdom (753–509 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 in English history. The symbol of Britannia (a female personific ...
,
Victorian era In the history of the United Kingdom and the British Empire, the Victorian era was the period of Queen Victoria's reign, from 20 June 1837 until her death on 22 January 1901. The era followed the Georgian period and preceded the Edwa ...
, etc. Use of the term for more recent periods or topical history might include
Soviet era The history of Soviet Russia and the Soviet Union (USSR) reflects a period of change for both Russia and the world. Though the terms "Soviet Russia" and "Soviet Union" often are synonymous in everyday speech (either acknowledging the dominance ...
, 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). ''Fu ...
, such as the "
big band era A big band or jazz orchestra is a type of musical ensemble of jazz music that usually consists of ten or more musicians with four sections: saxophones, trumpets, trombones, and a rhythm section. Big bands originated during the early 1910s and ...
", "
disco era Disco is a genre of dance music and a subculture that emerged in the 1970s from the United States' urban nightlife scene. Its sound is typified by four-on-the-floor beats, syncopated basslines, string sections, brass and horns, electric pia ...
", etc.


See also

*
Periodization In historiography, periodization is the process or study of categorizing the past into discrete, quantified, and named blocks of time for the purpose of study or analysis.Adam Rabinowitz. It's about time: historical periodization and Linked Ancie ...
*
List of time periods The categorisation 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