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Annum is a Latin noun meaning year. It is the accusative singular of the second declension masculine noun annus (nominative), anni (genitive) [1].

As a unit of time, it is defined as exactly 365.25 days (that is, the average length of a year in the Julian calendar) of 86,400 SI seconds each, representing the duration of one revolution of the Earth around the Sun. Although there is no universally accepted symbol for the year, NIST[1] and ISO 31-1[2] suggest the symbol a (in the International System of Units a is also the symbol for the are unit of area, but context is usually enough to disambiguate). In English, the deprecated abbreviation yr is still frequently used.

The Unified Code for Units of Measure[3] disambiguates the symbology by using

ar for are (unit), and:


at = a_t = 365.24219 days for the mean tropical year


aj = a_j = 365.25 days for the mean Julian year


ag = a_g = 365.2425 days for the mean Gregorian year


a = 1 aj year (without further qualifier)
  • Per annum means "yearly".
  • kiloannum, usual symbol ka, is a unit of time equal to one thousand years.
  • megaannum, usual symbol Ma, is a unit of time equal to one million (106) years. It is commonly used in scientific disciplines such as geology, paleontology, and celestial mechanics to signify very long time periods in the past. For example, the dinosaur species Tyrannosaurus rex was abundant approximately 65 Ma (65 million years) ago (ago may not always be mentioned; if the quantity is specified while not explicitly discussing a duration, one can assume that "ago" is implied; "mya" includes "ago" explicitly.). In astronomical applications, the year used is the Julian year of precisely 365.25 days.
  • gigaannum, usual symbol Ga, is a unit of time equal to one (short scale) billion (109) years. It is commonly used in scientific disciplines such as cosmology and geology to signify extremely long time periods in the past. For example, the formation of the Earth occurred approximately 4.57 Ga (4.57 billion years) ago.
  • exaannum, usual symbol Ea, is a unit of time equal to (1018) years (one quintillion on the short scale, one trillion on the long scale). It is an extremely long unit of time. The half-life of tungsten-180 is 1.8 Ea.

On hyphenation

The use of the hyphen in SI is reserved for the infrequent practice of combining prefixes, e.g. deca-kiloannum. It is not used in the fashion of kilo-annum.

Deprecated units

  • bya - Formerly used for Ga (ago)
  • byr - Formerly used for Ga (either elapsed or ago)
  • mya - Formerly used for Ma (ago)
  • myr - Formerly used for Ma (either elapsed or ago)
  • tya (sometimes spelled kya) - formerly used for ka (ago)
  • kyr - Formerly used for ka (either elapsed or ago)
These units are deprecated because (except for kyr) they do not use accepted SI prefixes and because the suffixes ya and yr are not accepted SI units.

It has been suggested that tya, kyr, mya (unit), myr, bya, byr be merged into this article or section. ()

See also

References

Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, a "Martian year" is the time in which Mars completes its own orbit.
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The term accusative may be used in the following contexts:
  • A form of morphosyntactic alignment, as found in nominative-accusative languages.
  • The accusative case, which is a grammatical case found in nominative-accusative languages that employ explicit morphology to mark

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grammatical number is grammatical category of nouns, pronouns, and verb agreement that expresses count distinctions (such as "one" or "more than one").[1]
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declension (or declination) is the inflection of nouns, pronouns and adjectives to indicate such features as number (typically singular vs. plural), case (subject, object, and so on), or gender.
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The word masculine can refer to:
  • The property of being biologically male
  • Masculinity, a traditionally male gender role
  • The masculine grammatical gender
The antonym of masculine is feminine.
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Examples
A proper or common noun can co-occur with an article or an attributive adjective. Verbs and adjectives can't. As usual, a `*' in front of an example means that this example is ungrammatical.
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Julian calendar was a reform of the Roman calendar which was introduced by Julius Caesar in 46 BC and came into force in 45 BC (709 ab urbe condita). It was chosen after consultation with the astronomer Sosigenes of Alexandria and was probably designed to approximate the
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International System of Units (abbreviated SI from the French Le Système international d'unités) is the modern form of the metric system.
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An are is a unit of area.

Are or ARE may also refer to:
  • Åre Municipality, a municipality in Sweden
  • Åre (ski area) in Sweden
  • Are language, a language from Papua New Guinea
  • Are languages, a subgroup of the Are-Taupota languages
  • A.R.E.

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The Unified Code for Units of Measure (the UCUM) is a system of codes for unambiguously representing measurement units to both humans and machines.

The code set includes all units defined in ISO 1000, ISO 2955-1983, ANSI X3.
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An are is a unit of area.

Are or ARE may also refer to:
  • Åre Municipality, a municipality in Sweden
  • Åre (ski area) in Sweden
  • Are language, a language from Papua New Guinea
  • Are languages, a subgroup of the Are-Taupota languages
  • A.R.E.

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For the emoticon :D'', see Emoticon. (For technical reasons, :D brings you here.)


Basic Latin alphabet

  Aa Bb Cc Dd  
Ee Ff Gg Hh Ii Jj
Kk Ll Mm Nn Oo Pp
Qq Rr Ss Tt Uu Vv
  Ww Xx Yy Zz  
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A tropical year (also known as a solar year) is the length of time the Sun, as seen from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere) relative to the equinoxes and solstices.
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For the emoticon :D'', see Emoticon. (For technical reasons, :D brings you here.)


Basic Latin alphabet

  Aa Bb Cc Dd  
Ee Ff Gg Hh Ii Jj
Kk Ll Mm Nn Oo Pp
Qq Rr Ss Tt Uu Vv
  Ww Xx Yy Zz  
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A Julian year can refer to:
  • The Julian year (astronomy) is a time interval of exactly 365.25 days, used in astronomy.
  • The Julian year (calendar) is a year in the Julian calendar which has started on different days, at different times, in different countries and is equal

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For the emoticon :D'', see Emoticon. (For technical reasons, :D brings you here.)


Basic Latin alphabet

  Aa Bb Cc Dd  
Ee Ff Gg Hh Ii Jj
Kk Ll Mm Nn Oo Pp
Qq Rr Ss Tt Uu Vv
  Ww Xx Yy Zz  
..... Click the link for more information.
A year (from Old English gēr) is the time between two recurrences of an event related to the orbit of the Earth around the Sun. By extension, this can be applied to any planet: for example, a "Martian year" is the time in which Mars completes its own orbit.
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A millennium (pl. millennia) is a period of time equal to one thousand years (from Latin mille, thousand, and annum, year).
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1000 (one thousand) is the natural number following 999 and preceding 1001. The letter A does not appear in the English spelling of any number lower than "one thousand".
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time.

One view is that time is part of the fundamental structure of the universe, a dimension in which events occur in sequence, and time itself is something that can be measured.
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million (1,000,000), or one thousand thousand, is the natural number following 999,999 and preceding 1,000,001.

In scientific notation, it is written as 106[1]
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Oceanic crust      0-20 Ma
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Palaeontology redirects here. For the scientific journal, see Palaeontology (journal).


Paleontology, palaeontology or palæontology (from Greek: paleo, "ancient"; ontos
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Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data.
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Dinosauria *
Owen, 1842

Orders & Suborders
  • Ornithischia
  • Cerapoda
  • Thyreophora
  • Saurischia

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Tyrannosaurus
Osborn, 1905

Species
  • T. rex (type)
    Osborn, 1905
Synonyms
  • Manospondylus
    Cope, 1892
  • Dynamosaurus
    Osborn, 1905
  • ?Nanotyrannus

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mya or "m.y.a." is an abbreviation for million years ago. This abbreviation is commonly used as a unit of time to denote length of time before the present or "B.P." (before AD 1950). Specifically, one mya is equal to 106 years ago.
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Julian year (symbol: a) is a unit of measurement of time defined as exactly 365.25 days of 86,400 SI seconds each, totalling 31,557,600 seconds. That is the average length of the year in the Julian calendar used in Western societies in previous centuries, and for which the
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1,000,000,000 (alternately known as one thousand million and one billion, see below) is the natural number following 999,999,999 and preceding 1,000,000,001.

In scientific notation, it is written as 109.
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