Sigma (upper case Σ, lower case σ; Greek Σιγμα, lower case in word-final position ς) 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, the final form (ς) is used. (e.g. Ὀδυσσεύς (Odysseus) - Note the two sigmas in the center of the name, and the
word-final sigma at the end.) Not to be confused with the cedilla ç.
The letter is ultimately derived from Phoenician Šin 𐤔. However, its name derives from Samekh.
The uppercase form of sigma was borrowed into the Latin alphabet to serve as the uppercase of esh (lowercase: ʃ).
Disigma, or "double sigma", is a non-current term for the character Sampi.
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 can still be seen in inscriptions in Greek Orthodox churches
, and also in certain printed editions of classical authors.
The form of the Cyrillic letter С [s] and Coptic letter sima are derived from lunate sigma.
On coins from the Hellenistic period in India, the script of later coins sometimes use lunate sigma. This sigma continued to be written this way also in Medieval Greek.
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.
Science and mathematics
Upper case Σ is used as a symbol for:
Lower case σ is used for:
During the 1930s, an upper case Σ was in use as the symbol of the Ação Integralista Brasileira
, a radical right-wing party in Brazil
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.
- Mercury-Atlas 8 was called Sigma 7.
- Sigma 2,3,5,6,7,8,9 computers produced by Xerox Data Systems in the 1970s following purchase of SDS, Scientific Data Systems, by it. Successful range of scientific computers similar to IBM 370's.
- Sigma is the name of a system for ontology development and reasoning
- Project Sigma was the name of a proposal for a "spontaneous university" by the Scottish writer Alexander Trocchi.
- Both Lelouch Lamperouge and Schenizel El Britannia, strategists in the Japanese anime Code Geass: Lelouch of the Rebellion, use strategies called "Pattern Sigma", which roughly correspond to the shape of the Greek letter.
- Sigma is the name of an assassin in Eternius, a members only story.