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{{other uses}}
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{{Wiktionary|Σ|σ|ς}}
{{Greek Alphabet|letter=sigma}}
'''Sigma''' (upper-case '''Σ''', lower-case '''σ''', lower-case in word-final position '''ς'''; [[Ancient Greek|Greek]] σίγμα) is the eighteenth letter of the [[Greek alphabet]], and carries the 's' sound. In the system of [[Greek numerals]], it has a value of 200. When used at the end of a word, and the word is not all [[upper case|upper-case]], the final form (ς) is used, e.g. {{unicode|Ὀδυσσεύς}} (Odysseus).  Note the two sigmas in the center of the name, and the word-final sigma at the end.
 
==History==
The shape and alphabetic position of Sigma is derived from [[Phoenician alphabet|Phoenician]] [[Shin (letter)|shin]] {{Unicode|𐤔}} [[Image:Phoenician sin.svg|20px]].
 
===Etymology===
The name of sigma, according to one hypothesis,<ref name="jeffery25">{{cite book|last=Jeffery|first=Lilian H.|title=The local scripts of archaic Greece|place=Oxford|publisher=Clarendon|year=1961|pages=25–27}}</ref> may continue that of Phoenician [[Samekh]]. According to a different theory,<ref name="woodard">{{cite encyclopedia|encyclopedia=Encyclopedia of ancient Greece|editor-first=Nigel Guy|editor-last= Wilson|title=Alphabet|first=Roger D.| last=Woodard|year=2006| publisher=Routldedge| place=London| page=38}}</ref> its original name may have been "''[[San (letter)|San]]''&thinsp;" (the name today associated with another, obsolete letter), while "sigma" was a Greek innovation that simply meant "hissing", based on a nominalization of a verb {{lang|grc|σίζω}} (''sízō'', from earlier *''sig-jō'', meaning 'I hiss').
 
===Uppercase of esh===
The uppercase form of sigma was re-borrowed into the [[Latin alphabet]] to serve as the uppercase of modern [[esh (letter)|esh]] (lowercase: {{unicode|ʃ}}).
 
=== Lunate sigma ===
[[File:Madaba Jerusalem Mosaic.jpg|thumb|left|The [[Madaba Map]], a sixth-century mosaic map of [[Jerusalem]] ("Η ΑΓΙΑ ПОΛΙΣ") uses the lunate sigma.]]
[[File:Metochion Gethsimanis, Jerusalem.jpg|thumb|right|upright|A plaque reading "Μετόχιον Γεθσημανῆς", i.e. [[Metochion]] of [[Gethsemane]], in Jerusalem with a lunate sigma both at the end and in the middle of the word]]
In handwritten Greek during the Hellenistic period (4th and 3rd centuries BC), the epigraphic form of Σ was simplified into a C-like shape.<ref>Edward M. Thompson (1912), ''Introduction to Greek and Latin paleography'', Oxford: Clarendon. p.&nbsp;108, 144</ref> It is also found on coins from the fourth century BC onward.<ref>[http://www.parthia.com/fonts/letterforms_usage.htm Parthia.com]: ''Numismatica Font Projects''.</ref> This became the universal standard form of Sigma during late antiquity and the Middle Ages. It is today known as ''lunate sigma'' (upper-case {{Unicode|Ϲ}}, lower-case {{Unicode|ϲ}}), because of its [[crescent]]-like shape.
 
It is still widely used in decorative typefaces in Greece, especially in religious and church contexts, as well as in some modern print editions of classical Greek texts. The forms of the [[Cyrillic script|Cyrillic letter]] [[Es (Cyrillic)|С]] (representing {{IPA|/s/}}) and [[Coptic alphabet|Coptic letter]] {{coptic|Ⲥ}} ''sima'' are derived from lunate sigma.
 
A dotted lunate sigma (''sigma periestigmenon'', encoded at U+03FE {{unicode|Ͼ}}) was used by [[Aristarchus of Samothrace]] as an editorial sign indicating that the line so marked is at an incorrect position. Similarly, an [[antisigma]] or reversed sigma ({{unicode|Ͻ}}) may mark a line that is out of place. A dotted [[antisigma]] or dotted reversed sigma (''antisigma periestigmenon'': {{unicode|Ͽ}}) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority.
 
==Uses==
 
===Greek===
In both [[Ancient Greek|Ancient]] and [[Modern Greek]], the sigma represents the [[voiceless alveolar fricative]] {{IPA|/s/}}. Both in Ancient and Modern Greek, this sound is [[voice (phonetics)|voiced]] to {{IPA|/z/}} before {{IPA|/m/}} or {{IPA|/n/}}.
 
===Berber===
Upper-case Σ may be used in the [[Berber Latin alphabet]] for <nowiki>[</nowiki>[[ʕ]]<nowiki>]</nowiki>, though the [[INALCO]] standard uses [[Ɛ]] instead.
 
===Science and mathematics===
 
====Upper-case====
Upper-case Σ is used as a symbol for:
* the [[summation]] operator
* a class of [[baryon]]s in [[particle physics]]
* macroscopic [[Cross section (physics)|cross section]]s in [[nuclear physics|nuclear]] and particle physics
* [[self-energy]] in [[condensed matter physics]]
* the [[Balance (accounting)|balance]] of the invoice classes and the overall amount of the debts and demands in [[economics]]
* the set of symbols that form an alphabet in [[linguistics]] and [[Computer Science|computer science]]
* the [[covariance matrix]] of a set of random variables in [[probability theory]] and [[statistics]], sometimes in the form <math>|\!\!\!\Sigma</math> to distinguish it from the summation operator.
 
====Lower-case====
Lower-case σ is used for:
* [[sigma bond]]s in [[chemistry]]
* to represent an unknown angle in mathematics
* [[Velocity dispersion]] in [[astronomy]]
* [[Sigma constant]] in science
* the [[sigma receptor]] in [[biology]]
* the [[standard deviation]] of a [[Standard deviation#Estimating_population_standard_deviation|population]] or [[probability distribution]] in [[statistics]]
* a quality model for business, [[Six Sigma]], based on the [[standard deviation]], often referred to as "'''6σ'''"
* [[sigma-algebra]]s, sigma-fields, and [[Sigma-finite measure|sigma-finiteness]] in [[Measure (mathematics)|measure theory]]; in general terms, the symbol ''σ'' serves as a shorthand for "[[countable set|countably]]", e.g. a ''σ''-compact [[topological space]] is one that can be written as a countable [[union (set theory)|union]] of [[compact space|compact subsets]].
* the [[Sigma-algebra#Generated_.CF.83-algebra|generated sigma-algebra]] of a set <math>A</math> is denoted <math>\sigma(A)</math>
* the [[divisor function|sum-of-divisors function]] in [[number theory]]
* the [[Stefan–Boltzmann constant]]
* the "[[sigma factor]]" of [[RNA polymerase]]
* a measure of [[electrical conductivity]]
* the [[Surface charge]] density in electrostatics
* [[Normal stress|Normal]] [[Stress (physics)|stress]] in [[continuum mechanics]]
* volatility of a [[stock]] generally needed for [[options pricing]]
* a [[syllable]] in [[phonology]]
* the [[spectrum of a matrix]] <math>A</math>, denoted as <math>\sigma(A)</math>, in [[applied mathematics]]
* [[surface tension]]
* the [[unary operation]] of [[Selection (relational algebra)|selection]] on a database relation in [[relational algebra]]
* the [[Pauli matrices]] in [[quantum mechanics]]
* a target's [[radar cross-section]] (RCS) in [[radar jamming]] or [[Electronic warfare|Electronic Warfare]] (EW)
* the [[Sigma (bone remodeling)|life span]] of a basic multicellular unit (BMU) in [[bone remodeling]]
* the Damping Parameter in Signal processing
* a millisecond in early 20th-century physiology literature.<ref name=Hill1935>{{cite doi|10.1038/136222a0}}</ref>
 
===Politics===
During the 1930s, an upper-case Σ was in use as the symbol of the [[Brazilian Integralism|Ação Integralista Brasileira]], a political party in [[Brazil]].
 
==Companies==
[[Sigma Corporation]] uses the name of the letter but not the letter itself, however in many Internet forums photographers refer to the company or its lenses using the sigma letter.
 
==Character encodings==
 
* Greek Sigma
 
{{charmap
|03A3|name1=Greek Capital Letter Sigma
|03C3|name2=Greek Small Letter Sigma
|03C2|name3=Greek Small Letter Final Sigma
|03F9|name4=Greek Capital Lunate Sigma Symbol
|03F2|name5=Greek Lunate Sigma Symbol
|map2=DOS Greek|map2char1=91|map2char2=A9|map2char3=AA
|map3=DOS Greek-2|map3char1=CF|map3char2=EC|map3char3=ED
|map4=Windows 1253|map4char1=D3|map4char2=F3|map4char3=F2
|namedref1=[[TeX]]|ref1char1=\Sigma|ref1char2=\sigma|ref1char3=\varsigma
}}
<ref>Unicode Code Charts: [http://www.unicode.org/charts/PDF/U0370.pdf Greek and Coptic (Range: 0370-03FF)]</ref>
 
{{charmap
|03FD|name1=Greek Capital Reversed Lunate Sigma Symbol
|037B|name2=Greek Small Reversed Lunate Sigma Symbol
|03FE|name3=Greek Capital Dotted Lunate Sigma Symbol
|037C|name4=Greek Small Dotted Lunate Sigma Symbol
|03FF|name5=Greek Capital Reversed Dotted Lunate Sigma Symbol
|037D|name6=Greek Small Reversed Dotted Lunate Sigma Symbol
}}
 
* Coptic Sima
 
{{charmap
|2CA4|name1=Coptic Capital Letter Sima
|2CA5|name2=Coptic Small Letter Sima
}}
 
* Mathematical Sigma
 
{{charmap
|2211|name1=N-ary Summation
|1D6BA|name2=Mathematical Bold<br />Capital Sigma
|1D6D4|name3=Mathematical Bold<br />Small Sigma
|1D6D3|name4=Mathematical Bold<br />Small Final Sigma
|1D6F4|name5=Mathematical Italic<br />Capital Sigma
|1D70E|name6=Mathematical Italic<br />Small Sigma
}}
 
{{charmap
|1D70D|name1=Mathematical Italic<br />Small Final Sigma
|1D72E|name2=Mathematical Bold Italic<br />Capital Sigma
|1D748|name3=Mathematical Bold Italic<br />Small Sigma
|1D747|name4=Mathematical Bold Italic<br />Small Final Sigma
|1D768|name5=Mathematical Sans-Serif<br />Bold Capital Sigma
}}
 
{{charmap
|1D782|name1=Mathematical Sans-Serif<br />Bold Small Sigma
|1D781|name2=Mathematical Sans-Serif<br />Bold Small Final Sigma
|1D7A2|name3=Mathematical Sans-Serif<br />Bold Italic Capital Sigma
|1D7BC|name4=Mathematical Sans-Serif<br />Bold Italic Small Sigma
|1D7BB|name5=Mathematical Sans-Serif<br />Bold Italic Small Final Sigma
}}
 
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.
 
==See also==
*[[Antisigma]]
*[[Greek letters used in mathematics, science, and engineering]]
*[[Sampi]]
*[[Sibilant consonant]]
*[[∑]], or [[summation]]
*"Sigm-" as a combining form, as in [[sigmodon|''sigm''odon]], [[sigmurethra|''sigm''urethra]], or in the derivative "sigmoid", as in [[sigmoid sinus]], [[sigmoid colon]], [[sigmoidoscopy]], etc.
 
==References==
{{Reflist}}
 
[[Category:Greek letters]]

Revision as of 17:21, 4 February 2014

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