From Wikipedia, the free encyclopedia
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.
In Eastern forms of Greek writing (used in the European Greek colonies) and in the Middle Ages, the lunate sigma (upper case C, lower case ϲ) — which resembles like 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, for example, where, for example, the whole of God's creation may be denoted by the word ΚΟCΜΟC ("cosmos"), which in the modern form of writing Greek would be ΚΟΣΜΟΣ.
Upper case Σ is used as a symbol for ...
Lower case σ is used for ...
- the parametric standard deviation of a population (as opposed to a sample) in statistics
- the divisor function in number theory
- the Stefan-Boltzmann constant
- the "sigma factor" of RNA polymerase
- a measure of electrical conductivity