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{{Short description|Third letter of the Greek alphabet}}
{{distinguish|text=the [[Latin alphabet|Latin]] letter [[Y]], the [[Cyrillic alphabet|Cyrillic]] letter [[У]], or the [[Church Slavonic]] Cyrillic  letter [[Ꙋ|Uk (Ꙋ)]]}}
{{About|the Greek letter Gamma ''Γ'' (and ''γ'') as used in various fields.  For the Latin forms like ''Ɣ'' see {{section link|Gamma|Phonetic transcription}} | other uses|}}
{{pp-semi-indef}}
{{more citations needed|date=March 2016}}
{{Greek Alphabet|letter=gamma}}

'''Gamma''' ({{IPAc-en|'|g|æ|m|ə}};<ref>{{OED|gamma}}</ref> uppercase {{Script|Grek|'''Γ'''}}, lowercase {{Script|Grek|'''γ'''}}; {{langx|el|γάμμα|gámma}}) is the third letter of the [[Greek alphabet]]. In the system of [[Greek numerals]] it has a value of 3. In [[Ancient Greek]], the letter gamma represented a [[voiced velar stop]] {{IPA-el|ɡ|IPA}}. In [[Modern Greek]], this letter normally represents a [[voiced velar fricative]] {{IPA-el|ɣ|IPA}}, except before either of the two [[front vowel]]s (/e/, /i/), where it represents a [[Voiced palatal fricative#Palatal|voiced palatal fricative]] {{IPA-el|ʝ|IPA}}; while /g/ in foreign words is instead commonly transcribed as γκ).

In the [[International Phonetic Alphabet]] and other modern Latin-alphabet based [[phonetic transcription#Alphabetic|phonetic notations]], it represents the voiced velar fricative.

==History==
{{further|History of the Greek alphabet}}
The Greek letter Gamma Γ is a grapheme derived from the [[Phoenician alphabet|Phoenician letter]] {{Script|Phnx|𐤂}} (''gīml'') which was rotated from the [[right-to-left script]] of Canaanite to accommodate the Greek language's writing system of left-to-right. The Canaanite [[grapheme]] represented the /g/ phoneme in the [[Canaanite language]], and as such is cognate with ''[[gimel]]'' ג of the [[Hebrew alphabet]].

Based on its name, the letter has been interpreted as an abstract representation of a [[camel]]'s neck,<ref>{{cite book|last=Russell|first=Bertrand|title=A history of western philosophy|year=1972|publisher=Touchstone book|location=New York|isbn=9780671314002|edition=60th print.|url-access=registration|url=https://archive.org/details/historyofwestern00russ}}</ref> but this has been criticized as contrived,<ref>{{cite book|last=Powell|first=Barry B.|author-link=Barry B. Powell|title=Writing: Theory and History of the Technology of Civilization|url=https://books.google.com/books?id=PZ2Gr3d9X2UC&pg=PA182|year=2012|publisher=John Wiley & Sons|isbn=978-1-118-29349-2|page=182}}</ref> and it is more likely that the letter is derived from an Egyptian hieroglyph representing a club or [[throwing stick]].<ref>{{cite book|last=Hamilton|first=Gordon James|title=The Origins of the West Semitic Alphabet in Egyptian Scripts|url=https://books.google.com/books?id=LdANAAAAYAAJ|year=2006|publisher=Catholic Biblical Association of America|isbn=978-0-915170-40-1|pages=53–6}}</ref>

[[File:NAMA Alphabet grec.jpg|thumb|left|The alphabet on [[black-figure pottery]] with a [[lambda]]-shaped gamma]]
In [[Archaic Greece]], the shape of gamma was closer to a classical [[lambda]] (Λ), while lambda retained the Phoenician [[L]]-shape ({{Script|Phnx|𐌋}}).

Letters that arose from the Greek gamma include [[Old Italic script#Etruscan alphabet|Etruscan (Old Italic)]] 𐌂,  [[Latin alphabet|Roman]] [[C]] and [[G]], [[Elder Futhark|Runic]] ''[[kaunan]]'' {{Script|Runr|ᚲ}}, [[Gothic alphabet|Gothic]] ''geuua'' {{Script|Goth|𐌲}}, the [[Coptic alphabet|Coptic]] Ⲅ, and the [[Cyrillic script|Cyrillic]] letters [[Ge (Cyrillic)|Г]] and [[Ge with upturn|Ґ]].<ref name="rapidtables">{{cite web | url=http://www.rapidtables.com/math/symbols/greek_alphabet.htm | title=Greek Alphabet Symbols | publisher=Rapid Tables | access-date=25 August 2014}}</ref>

==Greek phoneme==
{{further|Ancient Greek phonology|Modern Greek phonology}}

The Ancient Greek /g/ phoneme was the voiced velar stop, continuing the reconstructed [[Proto-Indo-European phonology|proto-Indo-European]] ''*g'', ''*ǵ''.

The modern Greek phoneme represented by gamma is realized either as a [[voiced palatal fricative]] ({{IPA|/ʝ/}}) before a [[front vowel]] (/e/, /i/), or as a [[voiced velar fricative]] {{IPA|/ɣ/}} in all other environments. Both in Ancient and in Modern Greek, before other [[velar consonant]]s (κ, χ, ξ – that is, ''k, kh, ks''), gamma represents a [[velar nasal]] {{IPA|/ŋ/}}. A double gamma γγ (e.g., άγγελος, "angel") represents the sequence {{IPA|/ŋɡ/}} (phonetically varying {{IPA|[ŋɡ~ɡ]}}) or {{IPA|/ŋɣ/}}.

==Phonetic transcription==
Lowercase Greek gamma is used in the [[Americanist phonetic notation]] and [[Uralic Phonetic Alphabet]] to indicate voiced consonants.

The gamma was also added to the Latin alphabet, as [[Latin gamma]], in the following forms: majuscule Ɣ, minuscule ɣ, and superscript modifier letter ˠ.

In the [[International Phonetic Alphabet]] the minuscule letter is used to represent a [[voiced velar fricative]] and the superscript modifier letter is used to represent [[velarization]]. It is not to be confused with  the character {{IPA|ɤ}}, which looks like a lowercase Latin gamma that lies above the [[baseline (typography)|baseline]] rather than crossing, and which represents the [[close-mid back unrounded vowel]]. In certain [[Obsolete and nonstandard symbols in the International Phonetic Alphabet|nonstandard variations of the IPA]], the uppercase form is used.{{Citation needed|date=May 2017}}

It is as a full-fledged majuscule and minuscule letter in the alphabets of some of [[languages of Africa]] such as [[Dagbani language|Dagbani]], [[Dinka language|Dinka]], [[Kabye language|Kabye]], and [[Ewe language|Ewe]],<ref>[http://www.bisharat.net/Documents/poal30.htm Practical Orthography of African Languages]</ref> and [[Berber languages]] using the [[Berber Latin alphabet]].

It is sometimes also used in the romanization of [[Pashto]].

==Mathematics and science==

===Lowercase===
The lowercase letter <math>\gamma</math> is used as a symbol for:
*[[Chromatic number]] of in [[graph theory]]
*[[Gamma ray|Gamma radiation]] in [[nuclear physics]]
*The [[photon]], the elementary particle of light and other [[electromagnetic radiation]]
*The 434&nbsp;nm [[spectral line]] in the [[Balmer series]]
*[[Surface energy]] in [[materials science]]
*The [[Lorentz factor]] in the [[theory of relativity]]
*In mathematics, the [[Incomplete gamma function|lower incomplete gamma function]]
*The [[Euler–Mascheroni constant]] ≈ 0.57721566490153286
*The [[heat capacity ratio]] ''C<sub>p</sub>''&hairsp;&hairsp;/''C<sub>v</sub>'' in [[thermodynamics]]
*The [[activity coefficient]] in [[thermodynamics]]
*The [[gyromagnetic ratio]] in [[electromagnetism]]
*[[Gamma wave]]s in [[neuroscience]]
*[[Gamma motor neuron]]s in [[neuroscience]]
*A non-[[International System of Units|SI]] [[metric system|metric]] [[units of measurement|unit of measure]] of [[mass]] equal to one [[microgram]] (1 μg).<ref>{{cite book |author=François Cardarelli |date=2003 |title=Encyclopaedia of Scientific Units, Weights and Measures |publisher=Springer-Verlag |location=London |isbn=978-1-4471-1122-1}}</ref><ref>{{cite book |date=August 7, 2002 |title=Remembrances of LSD therapy past |author=Betty Grover Eisner, Ph.D. |url=https://maps.org/images/pdf/books/remembrances.pdf |archive-url=https://web.archive.org/web/20141205124722/http://maps.org/images/pdf/books/remembrances.pdf |archive-date=2014-12-05 |url-status=live |page=14 |quote=that fateful 100 gamma, the same dosage I had had at my first LSD session}}</ref> This always-rare use is deprecated.
*A non-[[International System of Units|SI]] [[units of measurement|unit of measure]] of [[magnetic field|magnetic flux density]], sometimes used in [[geophysics]], equal to 10<sup>−5</sup> [[Gauss (unit)|Gauss]] (G), or 1 [[nano-|nano]][[tesla (unit)|tesla]] (nT).<ref>{{Cite web |last=Weisstein |first=Eric W. |date=30 April 2023 |title=Gamma -- from Eric Weisstein's World of Physics |url=https://scienceworld.wolfram.com/physics/Gamma.html |website=scienceworld.wolfram.com}}</ref>
*The power by which the luminance of an image is increased in [[gamma correction]]
*In civil and mechanical engineering:
**[[Specific weight]]
**The [[shear rate]] of a fluid is represented by a lowercase gamma with a dot above it: <math> \dot \gamma </math>
**[[Austenite]] (also known as γ-iron), a metallic non-magnetic allotrope or solid solution of iron.
*The gamma carbon, the third carbon attached to a [[functional group]] in [[organic chemistry]] and [[biochemistry]]; see [[Alpha and beta carbon]]

The lowercase Latin gamma ɣ  can also be used in contexts (such as chemical or molecule nomenclature) where gamma must not be confused with the letter [[y]], which can occur in some computer typefaces.

===Uppercase===
The uppercase letter <math>\Gamma</math> is used as a symbol for:
*In mathematics, the [[gamma function]] (usually written as <math>\Gamma</math>-function) is an extension of the [[factorial]] to [[complex number]]s
*In mathematics, the [[Incomplete gamma function|upper incomplete gamma function]]
*The [[Christoffel symbols]] in differential geometry
*In probability theory and statistics, the [[gamma distribution]] is a two-parameter family of continuous probability distributions.
*In [[solid-state physics]], the center of the [[Brillouin zone]]
*[[circulation (fluid dynamics)|Circulation]] in [[fluid mechanics]]
*As [[reflection coefficient]] in physics and electrical engineering
*The tape alphabet of a [[Turing machine]]
*The [[Feferman–Schütte ordinal]] <math>\Gamma_0</math>
*[[Congruence subgroup]]s of the modular group of other arithmetic groups
*One of the [[Greeks (finance)|Greeks in mathematical finance]]

==Unicode==

* {{unichar|0194|html=}}
* {{unichar|0263|html=}}
* {{unichar|0264|html=}}
* {{unichar|02E0|html=}}
* {{unichar|0393|html=}}
* {{unichar|03B3|html=}}
* {{unichar|1D26|html=}}
* {{unichar|1D5E|html=}}
* {{unichar|1D67|html=}}
* {{unichar|2C84|html=}}
* {{unichar|2C85|html=}}
* {{unichar|330F}}

These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style:

* {{unichar|213D|html=}}
* {{unichar|213E|html=}}
* {{unichar|1D6AA|html=}}
* {{unichar|1D6C4|html=}}
* {{unichar|1D6E4|html=}}
* {{unichar|1D6FE|html=}}
* {{unichar|1D71E|html=}}
* {{unichar|1D738|html=}}
* {{unichar|1D758|html=}}
* {{unichar|1D772|html=}}
* {{unichar|1D792|html=}}
* {{unichar|1D7AC|html=}}

==See also==

{{Wiktionary|Γ|γ}}
{{Wiktionary|Ɣ|ɣ}}
* [[Ge (Cyrillic)|Г, г - Ge (Cyrillic)]]
* [[G|G, g - Latin]]
* [[Gamma correction]]
* [[List of storms named Gamma]]

==References==
{{reflist}}

[[Category:Greek letters]]
[[Category:Phonetic transcription symbols|Gz]]