Psi (letter)

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

For other uses, see Psi.

Psi (upper case Ψ, lower case ψ) is the 23rd letter of the Greek alphabet and has a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination /ps/ (like in English "lapse"). In Greek, this consonant cluster can occur in the syllable initial position. However, in most languages of the world this combination is not possible at the beginning of a syllable. In Latin, Greek words beginning with psi are transcribed by ps-, but seem to have been pronounced simply as s-, with a quiescant p. This pronunciation has affected that of Greek words beginning with the letter in most languages of the world (psychology is pronounced with a silent p for example). The name of the letter is pronounced [saɪ] ("sigh") in English. The letter was adopted into the Old Italic alphabet, and its shape is continued into the Algiz rune of the Elder Futhark.

It is also used as a symbol/icon for psychology.

It is perhaps most famous in science for representing a wavefunction in quantum mechanics, particularly with the Schrödinger equation.

Psi is also used as the symbol for the polygamma function, defined by

where Γ(x) is the gamma function.

Psi was also adopted into the early Cyrillic alphabet. See psi (Cyrillic) (Ѱ, ѱ).

A similar character is used to represent Neptune

The content of this page is retrieved from http://en.wikipedia.org/wiki/Psi_%28letter%29 under GFDL