2007 Schools Wikipedia Selection. Related subjects: Linguistics

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

Theta (uppercase Θ, lowercase θ) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth. In the system of Greek numerals it has a value of 9. In Classical Greek θ represented an aspirated voiceless dental plosive (/tʰ/), but in Koiné and later dialects it became a voiceless dental fricative /θ/. In American English, the name of the letter is commonly pronounced [θeɪɾə]. In Modern Greek and British English, the name is pronounced [θiːtə].

Letters such as the early Cyrillic letter fita (Ѳ, ѳ) developed from θ.

In its archaic form, θ was written as:

  • a cross within a circle (A symbol of a cross within a circle or Another symbol of a cross within a circle)
  • and later, as a line or point within a circle (The symbol of a line within a circle or The symbol of a point within a circle).

According to Porphyry of Tyros, the Egyptians used an X within a circle as a symbol of the soul; having a value of nine, it was used as a symbol for Ennead. Johannes Lydus says that the Egyptians used a symbol for Kosmos in the form of theta, with a fiery circle representing the world, and a snake spanning the middle representing Agathos Daimon.

The Egyptians also used the symbol of a point within a circle (The symbol of a point within a circle, the sun disc) to represent the sun, which might be a possible origin of its use as the Sun's astrological glyph. It is worthwhile to note that θῆτα (theta) has the same numerical value in isopsephy as Ηλιος ( Helios): 318.

In classical Athens, it was used as an abbreviation for the Greek θάνατος (thanatos, "death") and as it vaguely resembles a human skull, theta was used as a warning symbol of death, in the same way that skull and crossbones are used in modern times. It survives on potsherds used by Athenians when voting for the death penalty.


The lower-case letter θ is used as a symbol for:

  • A plane angle in geometry.
  • The voiceless dental fricative in the International Phonetic Alphabet, such as in the words thick or thin (but not as in the, which is the voiced dental fricative).
  • The Potential temperature in meteorology.

The upper-case letter Θ is used as a symbol for:

  • Dimensionless temperature in transport phenomena.
  • Big O notation. Denoting an asymptotically tight bound in analysis of algorithms.
  • Θ (set theory), a certain ordinal number.
  • Representing pentaquarks, exotic baryons in particle physics.
  • Earth Day.
  • Brainwave Frequency (Beta, Alpha, Theta, Delta) ranging from 4-8 Hz

Use in Options Investing

  • Theta is known as an option greek measuring the rate of time decay on a daily basis. One can look as this as an ice cube melting in your hand. A Theta of -.05 means that the option is losing a nickle of time value each day. Other option greeks include Delta, Vega, Rho and Gamma.

Uses as names

  • Theta Sigma is the nickname of the Doctor of the television series Doctor Who
Retrieved from ""