Theta

For other uses, see Theta.

Theta (uppercase Θ / lowercase θ), is a letter in the Greek alphabet. It represents the "th" sound (as in "think") in Ancient and Modern Greek. In the system of Greek numerals, it has a value of 9. The Cyrillic letter Ѳ came from theta.

Greek alphabet
Αα	Alpha	Νν	Nu
Ββ	Beta	Ξξ	Xi
Γγ	Gamma	Οο	Omicron
Δδ	Delta	Ππ	Pi
Εε	Epsilon	Ρρ	Rho
Ζζ	Zeta	Σσ	Sigma
Ηη	Eta	Ττ	Tau
Θθ	Theta	Υυ	Upsilon
Ιι	Iota	Φφ	Phi
Κκ	Kappa	Χχ	Chi
Λλ	Lambda	Ψψ	Psi
Μμ	Mu	Ωω	Omega
Other letters
Ϝϝ	Digamma	Ϟϟ	Koppa
Ϛϛ	Stigma	Ϡϡ	Sampi
Ͱͱ	Heta	Ϸϸ	Sho
Ϻϻ	San
Category•Commons

In mathematics, the lowercase θ is used as a variable to represent an angle, and the uppercase Θ is used in big-theta notation (a variant of big-O notation). The lowercase θ is also used to represent the potential temperature in meteorology.