Menu
Home
People
Places
Arts
History
Plants & Animals
Science
Life & Culture
Technology
Reference.org
Sigma
open-in-new
<h2 id="history">History</h2> <p>The shape (Σς) and alphabetic position of sigma is derived from the <a href="/facts/Phoenician_alphabet/Vr4smuYg">Phoenician</a> letter (<a href="/facts/Shin_(letter)/D8AeI5cw"><i>shin</i></a>). </p><p>Sigma's original name may have been <i>san</i>, but due to the complicated early history of the Greek <a href="/facts/Archaic_Greek_alphabets/hkBDo1WD">epichoric alphabets</a>, <i>san</i> came to be identified as a separate letter in the Greek alphabet, represented as <a href="/facts/San_(letter)/3dTz4Ire">Ϻ</a>.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> <a href="/facts/Herodotus/hTgRSAnv">Herodotus</a> reports that "san" was the name given by the <a href="/facts/Doric_Greek/QeIeRA9C">Dorians</a> to the same letter called "sigma" by the <a href="/facts/Ionic_Greek/5yRPYbuo">Ionians</a>.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a><a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p><p>According to one hypothesis,<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> the name "sigma" may continue that of Phoenician <i><a href="/facts/Samekh/gDVKbXbl">samekh</a></i> (), the letter continued through Greek <i>xi</i>, represented as <a href="/facts/Xi_(letter)/q66nzcM5">Ξ</a>. Alternatively, the name may have been a Greek innovation that simply meant 'hissing', from the root of σίζω (<i>sízō</i>, from <a href="/facts/Proto-Greek_language/0KW6sWxy">Proto-Greek</a> <i>*sig-jō</i> 'I hiss').<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> </p> <h3>Lunate sigma</h3> <p>In handwritten Greek during the <a href="/facts/Hellenistic_period/q6BgQsaF">Hellenistic period</a> (4th–3rd century BC), the <a href="/facts/Epigraphic/E9UbNeDh">epigraphic</a> form of Σ was simplified into a C-like shape,<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> which has also been found on coins from the 4th century BC onward.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> This became the universal standard form of sigma during late antiquity and the Middle Ages. </p><p>Today, it is known as <i>lunate sigma</i> (uppercase Ϲ, lowercase ϲ), because of its <a href="/facts/Crescent/H9oQTpVm">crescent</a>-like shape, and 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. </p><p>A dotted lunate sigma (<i>sigma periestigmenon</i>, Ͼ) was used by <a href="/facts/Aristarchus_of_Samothrace/RsJ3Vedv">Aristarchus of Samothrace</a> (220–143 BC) as an editorial sign indicating that the line marked as such is at an incorrect position. Similarly, a reversed sigma (<i><a href="/facts/Antisigma/HNuURa4C">antisigma</a></i>, Ͻ), may mark a line that is out of place. A dotted antisigma (<i>antisigma periestigmenon</i>, Ͽ) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority. </p><p>In Greek inscriptions from the late first century BC onwards, Ͻ was an abbreviation indicating that a man's father's name is the same as his own name, thus Dionysodoros son of Dionysodoros would be written Διονυσόδωρος Ͻ (<i>Dionysodoros Dionysodorou</i>).<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p>In <a href="/facts/Unicode/DDu3MfPV">Unicode</a>, the above variations of lunate sigma are encoded as U+03F9 Ϲ GREEK CAPITAL LUNATE SIGMA SYMBOL; U+03FD Ͻ GREEK CAPITAL REVERSED LUNATE SIGMA SYMBOL, U+03FE Ͼ GREEK CAPITAL DOTTED LUNATE SIGMA SYMBOL, and U+03FF Ͽ GREEK CAPITAL REVERSED DOTTED LUNATE SIGMA SYMBOL. </p> <h3>Derived alphabets</h3> <p>Sigma was adopted in the <a href="/facts/Old_Italic_alphabets/4r5FLUvU">Old Italic alphabets</a> beginning in the 8th century BC. At that time a simplified three-stroke version, omitting the lowermost stroke, was already found in Western Greek alphabets, and was incorporated into classical <a href="/facts/Etruscan_alphabet/vSu8y2RQ">Etruscan</a> and <a href="/facts/Old_Italic_scripts/4r5FLUvU">Oscan</a>, as well as in the earliest <a href="/facts/History_of_the_Latin_script/mGT54DaI">Latin</a> <a href="/facts/Epigraphy/E9UbNeDh">epigraphy</a> (early Latin <i><a href="/facts/S/1DcekgEL">S</a></i>), such as the <a href="/facts/Duenos_inscription/V3rXAWSP">Duenos inscription</a>. The alternation between three and four (and occasionally more than four) strokes was also adopted into the <a href="/facts/Elder_Futhark/9KfAExKa">early runic alphabet</a> (early form of the <a href="/facts/Sowil%C5%8D/8pv7mKbo"><i>s</i>-rune</a>). Both the <a href="/facts/Anglo-Saxon_runes/XNUo4zMb">Anglo-Saxon runes</a> and the <a href="/facts/Younger_Futhark/cVcDDaab">Younger Futhark</a> consistently use the simplified three-stroke version. </p><p>The letter <a href="/facts/Es_(Cyrillic)/s4eDGdI2">С</a> of <a href="/facts/Cyrillic_script/0btN3oWC">Cyrillic script</a> originates in the lunate form of Sigma. </p> <h2 id="uses">Uses</h2> <h3>Language and linguistics</h3> <ul><li>In both <a href="/facts/Ancient_Greek/LIK7NlUh">Ancient</a> and <a href="/facts/Modern_Greek/nFsDHrfR">Modern Greek</a>, the sigma represents the <a href="/facts/Voiceless_alveolar_fricative/WLKtEYDe">voiceless alveolar fricative</a> [s]. In Modern Greek, this sound is <a href="/facts/Voice_(phonetics)/VdqrEGQ3">voiced</a> to the <a href="/facts/Voiced_alveolar_fricative/TtHwyzp6">voiced alveolar fricative</a> [z] when occurring before [m], [n], [v], [ð], or [ɣ].</li> <li>The uppercase form of sigma (Σ) was re-borrowed into the <a href="/facts/Latin_alphabet/pqWVHpBz">Latin alphabet</a>—more precisely, the <a href="/facts/Africa_Alphabet/75a1m0D8">International African Alphabet</a>—to serve as the uppercase of modern <a href="/facts/Esh_(letter)/f3QdATn9"><i>esh</i></a> (lowercase: ʃ).</li> <li>In <a href="/facts/Phonology/qWAsvnok">phonology</a>, σ is used to represent <a href="/facts/Syllable/Ylt7pyJe">syllables</a>.</li> <li>In <a href="/facts/Linguistics/oQuamvf2">linguistics</a>, Σ represents the set of symbols that form an alphabet (see also <a href="/facts/Computer_Science/lN3pEyPz">computer science</a>).</li> <li>In <a href="/facts/Historical_linguistics/nj5y6HDR">historical linguistics</a>, Σ is used to represent a <a href="/facts/Common_Brittonic/YnFau4up">Common Brittonic</a> consonant with a sound between [<a href="/facts/Voiceless_alveolar_fricative/WLKtEYDe">s</a>] and [<a href="/facts/Voiceless_glottal_fricative/lfRB7CPW">h</a>]; perhaps an <a href="/facts/Aspirated_consonant/Kat42tA6">aspirated</a> <a href="/facts/Voiceless_postalveolar_fricative/enUwqS2w">[ʃʰ]</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></li></ul> <h3>Science and mathematics</h3> <h4>Mathematics</h4> <ul><li>In general mathematics, lowercase σ is commonly used to represent unknown angles, additionally serving as a shorthand for "<a href="/facts/Countable_set/Wj4DmWPv">countably</a>", whereas Σ is regularly used as the <a href="/facts/Operator_(mathematics)/1VWgEdjS">operator</a> for <a href="/facts/Summation/V2WUxoKn">summation</a>, e.g.:<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a></li></ul> <p> ∑ k = 0 5 k = 0 + 1 + 2 + 3 + 4 + 5 = 15 {\displaystyle \sum _{k=0}^{5}k=0+1+2+3+4+5=15} </p> <ul><li>In <a href="/facts/Mathematical_logic/SaI7Y3wN">mathematical logic</a>, Σ n 0 {\displaystyle \Sigma _{n}^{0}} is used to denote the set of formulae with bounded quantifiers beginning with existential quantifiers, alternating n − 1 {\displaystyle n-1} times between existential and universal quantifiers. This notation reflects an indirect analogy between the relationship of summation and products on one hand, and existential and universal quantifiers on the other. See the article on the <a href="/facts/Arithmetic_hierarchy/rQptcBFK">arithmetic hierarchy</a>.</li> <li>In <a href="/facts/Statistics/DNPsKGYU">statistics</a>, σ represents the <a href="/facts/Standard_deviation/qSug9BRl">standard deviation</a> of population or <a href="/facts/Probability_distribution/EpsKKVRu">probability distribution</a> (where <a href="/facts/Mu_(letter)/j1MMkE2w">mu</a> or μ is used for the mean).<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a></li> <li>In <a href="/facts/Topology/2EqW47cU">topology</a>, σ-compact <a href="/facts/Topological_space/v2ut7CbK">topological space</a> is one that can be written as a countable <a href="/facts/Union_(set_theory)/KVVXKfWl">union</a> of <a href="/facts/Compact_space/d0cgXJH7">compact subsets</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a></li> <li>In <a href="/facts/Mathematical_analysis/XXeR26Ih">mathematical analysis</a> and in <a href="/facts/Probability_theory/mFBn51rE">probability theory</a>, there is a type of <a href="/facts/Field_of_sets/4E3vQl4f">algebra of sets</a> known as <a href="/facts/Sigma-algebra/8LJINLNc">σ-algebra</a> (aka σ-field). Sigma algebra also includes terms such as: <ul><li>σ(<i>A</i>), denoting the <a href="/facts/%CE%A3-algebra/8LJINLNc">generated sigma-algebra</a> of a set <i>A</i></li> <li><a href="/facts/%CE%A3-finite_measure/5PXwoAX7">Σ-finite measure</a> (see <a href="/facts/Measure_(mathematics)/yCq7zlI4">measure theory</a>)</li></ul></li> <li>In <a href="/facts/Number_theory/zhoa7zrc">number theory</a>, σ is included in various <a href="/facts/Divisor_function/rzvm1jw2">divisor functions</a>, especially the sigma function or sum-of-divisors function.</li> <li>In <a href="/facts/Applied_mathematics/qyqklXXm">applied mathematics</a>, σ(<i>T</i>) denotes the spectrum of a <a href="/facts/Linear_map/Q1PBKNVV">linear map</a> <i>T</i>.</li> <li>In <a href="/facts/Complex_analysis/hgCoQlH0">complex analysis</a>, σ is used in the <a href="/facts/Weierstrass_functions/88h4u2hI">Weierstrass sigma-function</a>.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a></li> <li>In <a href="/facts/Probability_theory/mFBn51rE">probability theory</a> and <a href="/facts/Statistics/DNPsKGYU">statistics</a>, Σ denotes the <a href="/facts/Covariance_matrix/kLhgjHC6">covariance matrix</a> of a set of <a href="/facts/Random_variable/TwTBXnLT">random variables</a>, sometimes in the form | Σ {\displaystyle \;|\!\!\!\Sigma } to distinguish it from the summation operator.</li> <li><a href="/facts/Spectral_theory/8sAEEIMM">Theoretical spectral analysis</a> uses σ as standard deviation opposed to lowercase <a href="/facts/Mu_(letter)/j1MMkE2w">mu</a> as the absolute mean value.</li></ul> <h4>Biology, physiology, and medicine</h4> <ul><li>In <a href="/facts/Biology/1M1ee3pB">biology</a>, the <a href="/facts/Sigma_receptor/JpFeF344">sigma receptor</a> (σ–receptors) is a type of <a href="/facts/Cell_surface_receptor/0YGSjDdL">cell surface receptor</a>.</li> <li>In <a href="/facts/Biochemistry/fa2pWEBp">biochemistry</a>, the <a href="/facts/Sigma_factor/K3WNBB8D">σ factor</a> (or specificity factor) is a protein found in <a href="/facts/RNA_polymerase/gHd0ET9R">RNA polymerase</a>.</li> <li>In <a href="/facts/Bone/kwJaR6IQ">bone physiology</a>, the <a href="/facts/Bone_remodeling_period/tSJ13pC6">bone remodeling period</a>—i.e., the <a href="/facts/Sigma_(bone_remodeling)/tSJ13pC6">life span</a> of a basic multicellular unit—has historically been referred to as the sigma period.</li> <li>In early 20th-century <a href="/facts/Physiology/fh25y2pQ">physiology</a> literature, σ had been used to represent <a href="/facts/Millisecond/xHCyv235">milliseconds</a>.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a></li></ul> <h4>Business, finance, and economics</h4> <ul><li>In <a href="/facts/Finance/fLh1GgN8">finance</a>, σ is the symbol used to represent <a href="/facts/Volatility_(finance)/mCdus1MW">volatility</a> of <a href="/facts/Stock/Qa912YwX">stocks</a>, usually measured by the <a href="/facts/Standard_deviation/qSug9BRl">standard deviation</a> of <a href="/facts/Logarithmic_return/CldGgD1f">logarithmic returns</a>.</li> <li>In <a href="/facts/Accounting/sHznDY3V">accounting</a>, Σ indicates the <a href="/facts/Balance_(accounting)/ls4G17UK">balance</a> of invoice classes and the overall amount of debts and demands.</li> <li>In <a href="/facts/Macroeconomics/4dcQAdCr">macroeconomics</a>, σ is used in equations to represent the <a href="/facts/Elasticity_of_substitution/b1VcdeXC">elasticity of substitution</a> between two inputs.</li> <li>In the <a href="/facts/Machine_industry/TCkq1AP0">machine industry</a>, <a href="/facts/Six_Sigma/ctasMp3w">Six Sigma</a> (6σ) is a quality model based on the <a href="/facts/Standard_deviation/qSug9BRl">standard deviation</a>.</li></ul> <h4>Chemistry</h4> <ul><li><a href="/facts/Sigma_bond/CSyEe5CY">Sigma bonds</a> (σ bonds) are the strongest type of <a href="/facts/Covalent/EzMLf3Pz">covalent</a> <a href="/facts/Chemical_bond/ArNUMnIB">chemical bond</a>.</li> <li>In <a href="/facts/Organic_chemistry/djxhxaNg">organic chemistry</a>, σ symbolizes the sigma constant of <a href="/facts/Hammett_equation/14lHVD7D">Hammett equation</a>.<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a></li> <li>In <a href="/facts/Alchemy/CEx0U1Em">alchemy</a>, Σ was sometimes used to represent <a href="/facts/Sugar/jb5KXRHT">sugar</a>.</li></ul> <h4>Engineering and computer science</h4> <ul><li>In <a href="/facts/Computer_Science/lN3pEyPz">computer science</a>, Σ represents the set of symbols that form an alphabet (see also <a href="/facts/Linguistics/oQuamvf2">linguistics</a>)</li> <li><a href="/facts/Relational_algebra/7tjTFXdf">Relational algebra</a> uses the values σ a θ b ( R ) {\displaystyle \sigma _{a\theta b}(R)} and σ a θ v ( R ) {\displaystyle \sigma _{a\theta v}(R)} to denote <a href="/facts/Selection_(relational_algebra)/vHT4UCT1">selections</a>, which are a type of <a href="/facts/Unary_operation/kb6CkgsX">unary operation</a>.</li> <li>In <a href="/facts/Machine_learning/e0w0XJTu">machine learning</a>, σ is used in the formula that derives the <a href="/facts/Sigmoid_function/lAXu3AwW">Sigmoid function</a>.</li> <li>In <a href="/facts/Radar_jamming/sGoEJ6Bv">radar jamming</a> or <a href="/facts/Electronic_warfare/c6XGz9y0">electronic warfare</a>, <a href="/facts/Radar_cross-section/XdgINtML">radar cross-sections</a> (RCS) are commonly represented as σ when measuring the size of a target's image on radar.</li> <li>In <a href="/facts/Signal_processing/Npaja6zb">signal processing</a>, σ denotes the <a href="/facts/Damping_ratio/UW3RsjEd">damping ratio</a> of a system parameter.</li> <li>In <a href="/facts/Theoretical_computer_science/jSkGGuvy">theoretical computer science</a>, Σ serves as the <a href="/facts/Busy_beaver/qfdJPkVu">busy beaver</a> function.</li> <li>In <a href="/facts/Civil_engineering/avh5kEq2">civil engineering</a>, σ refers to the normal stress applied on a material or structure.</li></ul> <h4>Physics</h4> <ul><li>In <a href="/facts/Nuclear_physics/fzQbt1aF">nuclear</a> and <a href="/facts/Particle_physics/YgIuyj2t">particle physics</a>, σ is used to denote <a href="/facts/Cross_section_(physics)/lo014h2D">cross sections</a> in general (see also <a href="/facts/Radar_cross-section/XdgINtML">RCS</a>), while Σ represents macroscopic <a href="/facts/Cross_section_(physics)/lo014h2D">cross sections</a> [1/length].</li> <li>The symbol is to denote the <a href="/facts/Stefan%E2%80%93Boltzmann_constant/A0FvPHIh">Stefan–Boltzmann constant</a>.<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a></li> <li>In relation to fundamental properties of material, σ is often used to signify <a href="/facts/Electrical_conductivity/akyCKvMy">electrical conductivity</a>.</li> <li>In <a href="/facts/Electrostatics/bxkuW6s4">electrostatics</a>, σ represents <a href="/facts/Surface_charge/p067lYHS">surface charge</a> density.</li> <li>In <a href="/facts/Continuum_mechanics/vI7LpFDk">continuum mechanics</a>, σ is used to signify normal <a href="/facts/Stress_(physics)/ErAXDbbd">stress</a>.<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a></li> <li>In <a href="/facts/Condensed_matter_physics/EBVI5nmL">condensed matter physics</a>, Σ denotes <a href="/facts/Self-energy/qhFMapN6">self-energy</a>.</li> <li>The symbol can be used to signify <a href="/facts/Surface_tension/EuluYmSM">surface tension</a> (alternatively, <i><a href="/facts/Gamma/RkmPeRj3">γ</a></i> or <i><a href="/facts/T/1GaDe2Vy">T</a></i> are also used instead).</li> <li>In <a href="/facts/Quantum_mechanics/BRc3Mzgr">quantum mechanics</a>, σ is used to indicate <a href="/facts/Pauli_matrices/BdeC2wos">Pauli matrices</a>.</li> <li>In <a href="/facts/Astronomy/0ArJVM1p">astronomy</a>, σ represents <a href="/facts/Velocity_dispersion/9FYB7pb9">velocity dispersion</a>.</li> <li>In astronomy, the prefix Σ is used to designate double stars of the Catalogus Novus Stellarum Duplicium by <a href="/facts/Friedrich_Georg_Wilhelm_von_Struve/ajPxYc1q">Friedrich Georg Wilhelm von Struve</a>.</li> <li>In particle physics, Σ represents a class of <a href="/facts/Baryon/QFwAUWK2">baryons</a>.</li></ul> <h3>Organizations</h3> <ul><li>During the 1930s, an uppercase Σ was in use as the symbol of the <a href="/facts/Brazilian_Integralism/YlbPuN7Y">Ação Integralista Brasileira</a>, a fascist political party in <a href="/facts/Brazil/QHkG46GL">Brazil</a>.</li> <li><a href="/facts/Sigma_Corporation/C3ys00xs">Sigma Corporation</a> uses the name of the letter but not the letter itself, but in many Internet forums, photographers refer to the company or its lenses using the letter.</li> <li><a href="/facts/Sigma_Aldrich/zD2jRqQp">Sigma Aldrich</a> incorporate both the name and the character in their logo.</li></ul> <h2 id="unicode">Unicode</h2> <ul><li>U+037B ͻ GREEK SMALL REVERSED LUNATE SIGMA SYMBOL</li> <li>U+037C ͼ GREEK SMALL DOTTED LUNATE SIGMA SYMBOL</li> <li>U+037D ͽ GREEK SMALL REVERSED DOTTED LUNATE SIGMA SYMBOL</li> <li>U+03A3 Σ GREEK CAPITAL LETTER SIGMA (Σ)</li> <li>U+03C2 ς GREEK SMALL LETTER FINAL SIGMA (ς, ς, ς)</li> <li>U+03C3 σ GREEK SMALL LETTER SIGMA (σ)</li> <li>U+03F2 ϲ GREEK LUNATE SIGMA SYMBOL</li> <li>U+03F9 Ϲ GREEK CAPITAL LUNATE SIGMA SYMBOL</li> <li>U+03FD Ͻ GREEK CAPITAL REVERSED LUNATE SIGMA SYMBOL</li> <li>U+03FE Ͼ GREEK CAPITAL DOTTED LUNATE SIGMA SYMBOL</li> <li>U+03FF Ͽ GREEK CAPITAL REVERSED DOTTED LUNATE SIGMA SYMBOL</li> <li>U+2140 ⅀ DOUBLE-STRUCK N-ARY SUMMATION</li> <li>U+2211 ∑ N-ARY SUMMATION (∑, ∑)</li> <li>U+23B2 ⎲ SUMMATION TOP<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a></li> <li>U+23B3 ⎳ SUMMATION BOTTOM</li> <li>U+2CA4 Ⲥ COPTIC CAPITAL LETTER SIMA</li> <li>U+2CA5 ⲥ COPTIC SMALL LETTER SIMA</li> <li>U+2CEA ⳪ COPTIC SYMBOL SHIMA SIMA</li> <li>U+1D6BA 𝚺 MATHEMATICAL BOLD CAPITAL SIGMA<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a></li> <li>U+1D6D3 𝛓 MATHEMATICAL BOLD SMALL FINAL SIGMA</li> <li>U+1D6D4 𝛔 MATHEMATICAL BOLD SMALL SIGMA</li> <li>U+1D6F4 𝛴 MATHEMATICAL ITALIC CAPITAL SIGMA</li> <li>U+1D70D 𝜍 MATHEMATICAL ITALIC SMALL FINAL SIGMA</li> <li>U+1D70E 𝜎 MATHEMATICAL ITALIC SMALL SIGMA</li> <li>U+1D72E 𝜮 MATHEMATICAL BOLD ITALIC CAPITAL SIGMA</li> <li>U+1D747 𝝇 MATHEMATICAL BOLD ITALIC SMALL FINAL SIGMA</li> <li>U+1D748 𝝈 MATHEMATICAL BOLD ITALIC SMALL SIGMA</li> <li>U+1D768 𝝨 MATHEMATICAL SANS-SERIF BOLD CAPITAL SIGMA</li> <li>U+1D781 𝞁 MATHEMATICAL SANS-SERIF BOLD SMALL FINAL SIGMA</li> <li>U+1D782 𝞂 MATHEMATICAL SANS-SERIF BOLD SMALL SIGMA</li> <li>U+1D7A2 𝞢 MATHEMATICAL SANS-SERIF BOLD ITALIC CAPITAL SIGMA</li> <li>U+1D7BB 𝞻 MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL FINAL SIGMA</li> <li>U+1D7BC 𝞼 MATHEMATICAL SANS-SERIF BOLD ITALIC SMALL SIGMA</li></ul> <h2 id="see-also">See also</h2> Wikimedia Commons has media related to the letter sigma. Look up <i>Σ</i>, <i>σ</i>, or <i>ς</i> in Wiktionary, the free dictionary. <ul><li><a href="/facts/Antisigma/HNuURa4C">Antisigma</a></li> <li><a href="/facts/Greek_letters_used_in_mathematics,_science,_and_engineering/n3m8WSWw">Greek letters used in mathematics, science, and engineering</a></li> <li><a href="/facts/Sampi/9DFP42GB">Sampi</a></li> <li><a href="/facts/Sho_(letter)/XeaTJQIE">Sho (letter)</a></li> <li><a href="/facts/Stigma_(letter)/kjCdlnew">Stigma (letter)</a></li> <li><a href="/facts/Sibilant_consonant/5ejwC21e">Sibilant consonant</a></li> <li><a href="/facts/Summation/V2WUxoKn">Summation</a> (Σ)</li> <li>Combining form "<i>sigm-</i>" (e.g. <a href="/facts/Sigmodon/8aTWjwpj"><i>sigmodon</i></a>, <a href="/facts/Sigmurethra/Multl9vx"><i>sigmurethra</i></a>, etc.)</li> <li>Derivative "<i><a href="/facts/Sigmoid_(disambiguation)/YRmCPpw8">sigmoid</a></i>" (e.g. <a href="/facts/Sigmoid_sinus/yo28ydzt">sigmoid sinus</a>, <a href="/facts/Sigmoid_colon/vdrXYrG4">sigmoid colon</a>, <a href="/facts/Sigmoidoscopy/ApwcMKWD">sigmoidoscopy</a>, etc.)</li></ul> <h3>Notes</h3> <h3>Citations</h3> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>"sigma". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.) <a href="https://www.oed.com/search/dictionary/?q=sigma" target="_blank">https://www.oed.com/search/dictionary/?q=sigma</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Woodard, Roger D. (2006). "Alphabet". In Wilson, Nigel Guy (ed.). Encyclopedia of Ancient Greece. London: Routledge. p. 38. <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>"the same letter, which the Dorians call "san", but the Ionians 'sigma'..." [translated from Ancient Greek: "τὠυτὸ γράμμα, τὸ Δωριέες μὲν σὰν καλέουσι ,Ἴωνες δὲ σίγμα"] (Herodotus 1.139) <a href="/wiki/Ancient_Greek" target="_blank">/wiki/Ancient_Greek</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Herodotus, Histories 1.139 — Everson, Michael and Nicholas Sims-Williams. 2002. "Non-Attic letters," transcribed by N. Nicholas. Archived from the original 2020-06-28. <a href="/wiki/Herodotus" target="_blank">/wiki/Herodotus</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Jeffery, Lilian H. (1961). The Local Scripts of Archaic Greece. Oxford: Clarendon. pp. 25–7. <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Woodard, Roger D. (2006). "Alphabet". In Wilson, Nigel Guy (ed.). Encyclopedia of Ancient Greece. London: Routledge. p. 38. <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Thompson, Edward M. (1912). Introduction to Greek and Latin Paleography. Oxford: Clarendon. p. 108, 144. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Hopkins, Edward C. D. (2004). "Letterform Usage | Numismatica Font Projects" Parthia. <a href="http://www.parthia.com/fonts/letterforms_usage.htm" target="_blank">http://www.parthia.com/fonts/letterforms_usage.htm</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>de Lisle, Christopher (2020). "Attic Inscriptions in UK Collections: Ashmolean Museum, Oxford". AIUK. 11: 11. ISSN 2054-6769. Retrieved 2 June 2022. <a href="https://www.atticinscriptions.com/papers/aiuk-11/" target="_blank">https://www.atticinscriptions.com/papers/aiuk-11/</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Follet, Simone (2000). "Les deux archontes Pamménès du Ier siècle a.c. à Athènes". Revue des Études Grecques. 113: 188–192. doi:10.3406/reg.2000.4402. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Conroy, Kevin M. (21 February 2008). "Celtic initial consonant mutations - nghath and bhfuil?" – via dlib.bc.edu. <a href="http://dlib.bc.edu/islandora/object/bc-ir:102094" target="_blank">http://dlib.bc.edu/islandora/object/bc-ir:102094</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>Weisstein, Eric W. "Sigma". mathworld.wolfram.com. Retrieved 2025-01-25. <a href="https://mathworld.wolfram.com/Sigma.html" target="_blank">https://mathworld.wolfram.com/Sigma.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>Weisstein, Eric W. "Sigma". mathworld.wolfram.com. Retrieved 2025-01-25. <a href="https://mathworld.wolfram.com/Sigma.html" target="_blank">https://mathworld.wolfram.com/Sigma.html</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>Weisstein, Eric W. "Sigma-Compact Topological Space". mathworld.wolfram.com. Retrieved 2025-01-25. <a href="https://mathworld.wolfram.com/Sigma-CompactTopologicalSpace.html" target="_blank">https://mathworld.wolfram.com/Sigma-CompactTopologicalSpace.html</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>Weisstein, Eric W. "Weierstrass Sigma Function". mathworld.wolfram.com. Retrieved 2025-01-25. <a href="https://mathworld.wolfram.com/WeierstrassSigmaFunction.html" target="_blank">https://mathworld.wolfram.com/WeierstrassSigmaFunction.html</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>Hill, A. V. (1935). "Units and Symbols". Nature. 136 (3432): 222. Bibcode:1935Natur.136..222H. doi:10.1038/136222a0. S2CID 4087300. <a href="https://doi.org/10.1038%2F136222a0" target="_blank">https://doi.org/10.1038%2F136222a0</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> <li id="fn:17"><p>Chemistry (IUPAC), The International Union of Pure and Applied. "IUPAC - σ-constant (C05438)". goldbook.iupac.org. Retrieved 2025-01-25. <a href="https://goldbook.iupac.org/terms/view/C05438" target="_blank">https://goldbook.iupac.org/terms/view/C05438</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></p></li> <li id="fn:18"><p>"CODATA Value: Stefan-Boltzmann constant". physics.nist.gov. Retrieved 2025-01-25. <a href="https://physics.nist.gov/cgi-bin/cuu/Value?sigma" target="_blank">https://physics.nist.gov/cgi-bin/cuu/Value?sigma</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></p></li> <li id="fn:19"><p>Elert, Glenn (2023), "Special Symbols", The Physics Hypertextbook, hypertextbook, retrieved 2025-02-01, σ normal stress <a href="https://physics.info/symbols/" target="_blank">https://physics.info/symbols/</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></p></li> <li id="fn:20"><p>Combined with U+23B3 to make a double-high sigma <a href="#fnref:20" class="footnote-back-ref">↩</a></p></li> <li id="fn:21"><p>The MATHEMATICAL characters should only be used for math. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style. <a href="#fnref:21" class="footnote-back-ref">↩</a></p></li> </ol>