Theta

Theta uc lc.svg
Greek alphabet
Αα Alpha Νν Nu
Ββ Beta Ξξ Xi
Γγ Gamma Οο Omicron
Δδ Delta Ππ Pi
Εε Epsilon Ρρ Rho
Ζζ Zeta Σσς 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 characters
Digamma uc lc.svg Digamma Greek Stigma.svg Stigma
Greek Heta.svg Heta Greek San.svg San
Qoppa Q-and-Z-shaped.svg Qoppa Greek Sampi 2 shapes.svg Sampi
Greek diacritics

Theta (uppercase Θ, lowercase θ or ϑ;[1] Greek: Θήτα) 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 (/t̪ʰ/), but in Koiné and later dialects it became a voiceless dental fricative /θ/. In American English the name of the letter is commonly pronounced /ˈθeɪtə/. In British English, it is pronounced /ˈθiːtə/.

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

In its archaic form, θ was written as:

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 (literally: good spirit).[2]

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.[2] Petrus de Dacia in a document from 1291 relates the idea that theta was used to brand criminals as empty ciphers, and the branding rod was affixed to the crossbar spanning the circle.[3]

Contents

Symbol

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

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

The common usage of theta in mathematical problems began with the Greeks. They logically chose this Greek symbol since it was the next in their alphabet not yet used and was easily legible when recreating for multiple uses. Archaic crossed forms of theta are seen in the wheel letters of Linear A, Linear B, and Egyptian hieroglyphics, the mathematical tensor product, exclusive disjunction, and direct sum operators, the identification symbol for the Earth (as already mentioned), and the Celtic cross. The circumpunct, or circled dot, is seen in a wide range of places.

In Popular Culture

In the science fiction TV series Doctor Who, the character of the Doctor was once known as Theta Sigma whilst he lived on Gallifrey.

Notes

  1. ↑ Unicode keeps U+03D1 ϑ "GREEK THETA SYMBOL" ("=script theta") separate from U+03B8 θ "GREEK SMALL LETTER THETA"; while for the purpose of writing Greek text the two can be considered font variants, θ and ϑ can be distinct as symbols in technical or mathematical use.
  2. ↑ 2.0 2.1 Barry, Kieren (1999), The Greek Qabalah: Alphabetic Mysticism and Numerology in the Ancient World, Samuel Weiser, p. 73, ISBN 1-57863-110-6 .
  3. ↑ Kaplan, Robert (2000), The Nothing that Is: A Natural History of Zero, Oxford University Press, pp. 66, ISBN 0-1951-4237-3 .

See also