Sigma

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For other uses, see Sigma (disambiguation).

Look up Σ, σ, ς in Wiktionary, the free dictionary.

Greek alphabet

Α α Alpha	Ν ν Nu
Β β Beta	Ξ ξ Xi
Γ γ Gamma	Ο ο Omicron
Δ δ Delta	Π π Pi
Ε ε Epsilon	Ρ ρ Rho
Ζ ζ Zeta	Σ σ ς Sigma
Η η Eta	Τ τ Tau
Θ θ Theta	Υ υ Upsilon
Ι ι Iota	Φ φ Phi
Κ κ Kappa	Χ χ Chi
Λ λ Lambda	Ψ ψ Psi
Μ μ Mu	Ω ω Omega
Obsolete letters
Ϝ ϝ Digamma	Ϻ ϻ San
Ϙ ϙ Qoppa	Ϡ ϡ Sampi
Ϛ ϛ Stigma	Ϸ ϸ Sho

Sigma (upper case Σ, lower case σ, lowercase in word-final position ς) is the 18th letter of the Greek alphabet. 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 upper case, the final form (ς) is used.

The letter is ultimately derived from Phoenician Sin . However, its name derives from Samekh.

In Eastern forms of Greek writing (as opposed to the Western Greek alphabet used in the European Greek colonies) and in the Middle Ages, the lunate sigma (upper case Ϲ, lower case ϲ) — which resembles, but which is not at all related to, the Latin letter C — was often used. Lunate sigma was frequently used for writing Medieval Greek, and it can still sometimes be seen in inscriptions in Greek Orthodox churches, but also in certain printed editions of classical authors. The form of the Cyrillic letter С [s] derives from lunate sigma.

A dotted lunate sigma (sigma periestigmenon, encoded at U+03FE Ͼ) is used by Aristarchus of Samothrace as an editorial sign indicating that the line so marked is at an incorrect position. Similarly, an antisigma (encoded at U+03FD Ͻ) may mark a line that is out of place. A dotted antisigma (antisigma periestigmenon, encoded at U+03FF Ͽ) may indicate a line after which rearrangements should be made, or to variant readings of uncertain priority.

The uppercase form of sigma was borrowed into the Latin alphabet to serve as the uppercase of esh (lowercase: ʃ).

1 Science
2 Politics
3 Popular culture and use in fiction
4 See also

[edit] Science

Upper case Σ is used as a symbol for:

the summation operator
a class of baryons in particle physics

Lower case σ is used for:

sigma bonds in chemistry
the parametric standard deviation of a population (as opposed to a sample) in statistics
a quality model for business, Six Sigma, based on the standard deviation, often referred to as "6σ"
sigma-algebras, sigma-fields and sigma-finiteness in measure theory
the sum-of-divisors function in number theory
the Stefan-Boltzmann constant
the "sigma factor" of RNA polymerase
a measure of electrical conductivity
Normal stress in continuum mechanics

[edit] Politics

During the 1930s, an upper case Σ was in use as the symbol of the Ação Integralista Brasileira, a fascist party in Brazil.

[edit] Popular culture and use in fiction

In a practice similar to faux Cyrillic, capital sigmas are sometimes used in place of Roman E to give a Greek flavour to titles or text (for example, the film My Big Fat GRΣΣK Wedding).