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Theta (uppercase T, lowercase ? or ; ) is the eighth letter of the Greek alphabet
Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
, derived from the Phoenician letter Teth
Teth

is the ninth letter of many Semitic abjads , including Phoenician alphabet, Aramaic alphabet, Hebrew alphabet 'Tet' , Syriac alphabet and Arabic alphabet ; it is 9th in abjadi order and 16th in modern Arabic order....
. In the system of Greek numerals
Greek numerals

Greek numerals are a numeral system using letters of the Greek alphabet. They are also known by the names Milesian numerals, Alexandrian numerals, or alphabetic numerals....
 it has a value of 9. In Classical Greek ? represented an aspirated
Aspiration (phonetics)

In phonetics, aspiration is the strong burst of Earth's atmosphere that accompanies either the release or, in the case of preaspiration, the closure of some obstruents....
 voiceless dental plosive
Voiceless dental plosive

The voiceless dental plosive is a type of consonantal sound, used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is t_d....
 , but in Koiné and later dialects it became a voiceless dental fricative
Voiceless dental fricative

The voiceless dental non-sibilant fricative is a type of consonantal sound used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is T....
 . In American English the name of the letter is commonly . In British English
British English

British English or UK English is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere....
, the name is pronounced .

Letters such as the early Cyrillic letter fita
Fita

Fita is a letter of the early Cyrillic alphabet, descended from the Greek language Theta. It was mainly used to write proper names derived from Greek....
  developed from ?.

In its archaic
Archaic period in Greece

The archaic period in Greece is a period of Ancient Greece history. The term originated in the 18th century and has been standard since. This term arose from the study of Greek art, where it refers to styles mainly of Decorative art and Plastic arts, falling in time between Geometric Art and the art of Classical Greece....
 form, ? was written as:



According to Porphyry of Tyros, the Egyptian
Ancient Egypt

Ancient Egypt was an Ancient history civilization in eastern North Africa, concentrated along the lower reaches of the Nile in what is now the modern nation of Egypt....
s used an X within a circle as a symbol
Symbol

A symbol is something such as an entity, picture, written word, sound, or particular mark that represents something else by association, resemblance, or convention....
 of the soul; having a value of nine, it was used as a symbol for Ennead
Ennead

Ennead , an ancient Greek translation of the Egyptian word, Pesedjet, consists of a grouping of nine deity, most often appearing in the context of Egyptian mythology....
.






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Theta (uppercase T, lowercase ? or ; ) is the eighth letter of the Greek alphabet
Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
, derived from the Phoenician letter Teth
Teth

is the ninth letter of many Semitic abjads , including Phoenician alphabet, Aramaic alphabet, Hebrew alphabet 'Tet' , Syriac alphabet and Arabic alphabet ; it is 9th in abjadi order and 16th in modern Arabic order....
. In the system of Greek numerals
Greek numerals

Greek numerals are a numeral system using letters of the Greek alphabet. They are also known by the names Milesian numerals, Alexandrian numerals, or alphabetic numerals....
 it has a value of 9. In Classical Greek ? represented an aspirated
Aspiration (phonetics)

In phonetics, aspiration is the strong burst of Earth's atmosphere that accompanies either the release or, in the case of preaspiration, the closure of some obstruents....
 voiceless dental plosive
Voiceless dental plosive

The voiceless dental plosive is a type of consonantal sound, used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is t_d....
 , but in Koiné and later dialects it became a voiceless dental fricative
Voiceless dental fricative

The voiceless dental non-sibilant fricative is a type of consonantal sound used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is T....
 . In American English the name of the letter is commonly . In British English
British English

British English or UK English is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere....
, the name is pronounced .

Letters such as the early Cyrillic letter fita
Fita

Fita is a letter of the early Cyrillic alphabet, descended from the Greek language Theta. It was mainly used to write proper names derived from Greek....
  developed from ?.

In its archaic
Archaic period in Greece

The archaic period in Greece is a period of Ancient Greece history. The term originated in the 18th century and has been standard since. This term arose from the study of Greek art, where it refers to styles mainly of Decorative art and Plastic arts, falling in time between Geometric Art and the art of Classical Greece....
 form, ? was written as:
  • a cross within a circle (
    Earth Symbol
    or )


  • and later, as a line or point within a circle ( or
    Sun Symbol
    ).


According to Porphyry of Tyros, the Egyptian
Ancient Egypt

Ancient Egypt was an Ancient history civilization in eastern North Africa, concentrated along the lower reaches of the Nile in what is now the modern nation of Egypt....
s used an X within a circle as a symbol
Symbol

A symbol is something such as an entity, picture, written word, sound, or particular mark that represents something else by association, resemblance, or convention....
 of the soul; having a value of nine, it was used as a symbol for Ennead
Ennead

Ennead , an ancient Greek translation of the Egyptian word, Pesedjet, consists of a grouping of nine deity, most often appearing in the context of Egyptian mythology....
. Johannes Lydus says that the Egyptians
Egyptians

Egyptians is the name of the nationality and Mediterranean North African ethnic group native to Egypt.Egyptian identity is closely tied to the Geography of Egypt, dominated by the lower Nile Valley, the small strip of cultivable land stretching from the Cataracts of the Nile to the Mediterranean Sea and enclosed by desert both to the Easte...
 used a symbol for Kosmos
Cosmos

In its most general sense, a cosmos is an orderly or harmonious system. It originates from a Greek language term ??s??? meaning "order, orderly arrangement, ornaments," and is the antithetical concept of chaos....
 in the form of theta, with a fiery circle representing the world, and a snake spanning the middle representing Agathos Daimon (literally: good spirit).

The Egyptians also used the symbol of a point within a circle (
Sun Symbol
, 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 (theta) has the same numerical value in isopsephy
Isopsephy

Isopsephy is the Greek language word for the practice of adding up the Greek numerals in a word to form a single number. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry....
 as ????? (Helios
Helios

Helios is the god of sun.In Greek mythology the sun was personified as Helios . Homer often calls him simply Titan or Hyperion , while Hesiod and the Homeric Hymn separate him as a son of the Titans Hyperion and Theia or Euryphaessa and brother of the goddesses Selene, the moon, and Eos, the dawn....
): 318.

In classical Athens, it was used as an abbreviation for the Greek
Greek language

Greek is an Indo-European languages native to the southern Balkan peninsula, the language of the Greek people. It forms an independent branch within Indo-European....
 ???at?? (thanatos, “death”) and as it vaguely resembles a human skull, theta was used as a warning symbol of death
Thanatos

In Greek religion, Th?natos was the Daemon personification of Death and Mortality. He was a minor figure in Greek mythology, often referred to but rarely appearing in person....
, in the same way that skull and crossbones
Skull and crossbones

A skull and crossbones is a symbol consisting of a human skull and two bones crossed together under the skull. Today, it is generally used as a warning of danger ....
 are used in modern times. It survives on potsherds used by Athenians when voting for the death penalty. Petrus de Dacia
Petrus de Dacia

Petrus de Dacia was a Swedish_ethnic_group monk of the Dominican order who lived in Gotland from the 1230s to 1289. Though he wrote in Latin, he is often credited as the first author in Sweden....
 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.

Symbol

The lower-case letter ? is used as a symbol for:
  • A plane angle
    Angle

    In geometry and trigonometry, an angle is the figure formed by two Ray sharing a common endpoint, called the vertex of the angle . The magnitude of the angle is the "amount of rotation" that separates the two rays, and can be measured by considering the length of circular arc swept out when one ray is rotated about the vertex to coincide...
     in geometry.
  • A special function
    Theta function

    In mathematics, theta functions are special functions of several complex variables. They are important in several areas, including the theories of abelian variety and moduli spaces, and of quadratic forms....
     of several complex variables.
  • The voiceless dental fricative
    Voiceless dental fricative

    The voiceless dental non-sibilant fricative is a type of consonantal sound used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is T....
     in the International Phonetic Alphabet
    International Phonetic Alphabet

    The International Phonetic Alphabet "The acronym 'IPA' strictly refers [...] to the 'International Phonetic Association'. But it is now such a common practice to use the acronym also to refer to the alphabet itself that resistance seems pedantic....
    , such as in the words thick or thin (but not as in the, which is the voiced dental fricative
    Voiced dental fricative

    The voiced dental non-sibilant fricative is a type of consonantal sound, used in some Speech communication languages. The symbol in the International Phonetic Alphabet that represents this sound, eth, is , and the equivalent X-SAMPA symbol is D....
    ).
  • The Potential temperature
    Potential temperature

    The potential temperature of a Air parcel of fluid at pressure is the temperature that the parcel would acquire if Adiabatic process brought to a standard reference pressure , usually 1000 millibars....
     in meteorology
    Meteorology

    Meteorology is the interdisciplinary scientific study of the Earth's atmosphere that focuses on weather processes and forecasting . Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the eighteenth century....
    .
  • The score of a test taker in item response theory
    Item response theory

    In psychometrics, item response theory is a body of theory describing the application of mathematical models to data from questionnaires and Test as a basis for measurement abilities, attitudes, or other variables....
    .
  • Theta Type Replication: a type of bacterial DNA replication
    DNA replication

    DNA replication, the basis for heredity, is a fundamental process occurring in all living organisms to copy their DNA. This process is "semiconservative replication" in that each strand of the original double-stranded DNA molecule serves as template for the reproduction of the complementary strand....
     specific to circular chromosomes.
  • Threshold value of an artificial neuron.
  • A Bayer designation
    Bayer designation

    A Bayer designation is a stellar designation in which a specific star is identified by a Greek alphabet, followed by the genitive case form of its parent constellation's Latin language name....
     letter applied to a star in a constellation; usually the eighth star so labelled but not necessarily the eighth brightest as viewed from Earth.
  • Theta has also gained a new significance in the north-eastern region of the United States as a symbol for affection, in a similar capacity to the “heart” symbol.
  • The parameter frequently used in writing the likelihood function
    Likelihood function

    In statistics, the likelihood function is a function of the parameters of a statistical model that plays a key role in statistical inference. In non-technical usage, "likelihood" is a synonym for "probability", but throughout this article only the technical definition is used....
    .


The upper-case letter T is used as a symbol for:
  • Dimensionless temperature in transport phenomena
    Transport phenomena

    In physics, chemistry, biology and engineering, a transport phenomenon is any of various mechanisms by which particles or physical quantity move from one place to another....
    .
  • Big O notation
    Big O notation

    In mathematics, big O notation describes the asymptotic analysis of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions....
    . Denoting an asymptotically tight bound in analysis of algorithms.
  • T (set theory)
    T (set theory)

    In set theory, Θ is the least ordinal α such that there is no surjection from the reals onto α.If the axiom of choice holds then Θ is simply , the cardinal successor of the cardinality of the continuum....
    , a certain ordinal number
    Ordinal number

    In set theory, an ordinal number, or just ordinal, is the order type of a well-order. They are usually identified with hereditarily transitive sets....
    .
  • Representing pentaquark
    Pentaquark

    A pentaquark is an hypothetical subatomic particle consisting of a group of five quarks , or more specifically four quarks and one anti-quark and is represented by T....
    s, exotic baryon
    Baryon

    Baryons are the family of composite particle subatomic particle made of three quarks, as opposed to the mesons which are the family of composite particles made of one quark and one antiquark....
    s in particle physics
    Particle physics

    Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
    .
  • Earth Day
    Earth Day

    Earth Day is one of two observances, both held annually during spring in the northern hemisphere, and autumn in the southern hemisphere. These are intended to inspire awareness of and appreciation for the Earth's environment....
    .
  • Brain Signal Frequency
    Electroencephalography

    Electroencephalography is the recording of electrical activity along the scalp produced by the firing of neurons within the brain. In clinical contexts, EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20-40 minutes, as recorded from multiple electrodes placed on the scalp....
     (Beta, Alpha, Theta, Delta) ranging from 4–8 Hz.
  • One of the variables known as "Greeks"
    Greeks (finance)

    In mathematical finance, the Greeks are the quantities representing the sensitivities of derivative such as option to a change in underlying parameters on which the value of an instrument or Portfolio of financial instruments is dependent....
     in finance, representing the lost-value rate of an option over time.


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 A

Linear A is one of two linear scripts used in ancient Crete before Mycenaean Greek language Linear B. In Minoan Civilization times, before the Greek Mycenaean dominion, Linear A was the official script for the palaces and the cult and Cretan Hieroglyphs were mainly used on seals....
, Linear B
Linear B

Linear B is a script that was used for writing Mycenaean language, an early form of Greek language. It predated the Greek alphabet by several centuries and seems to have died out with the fall of Mycenaean Greece civilization....
, and Egyptian hieroglyphics, the mathematical tensor product
Tensor product

In mathematics, the tensor product, denoted by , may be applied in different contexts to vector spaces, matrix , tensors, vector spaces, algebra over a field, topological vector spaces, and module s....
, exclusive disjunction
Exclusive disjunction

The Logical connective exclusive disjunction, also called exclusive or , is a type of logical disjunction on two operands that results in a value of true if and only if exactly one of the operands has a value of true....
, and direct sum operators, the astrological symbol for the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 (as already mentioned), and the Celtic cross
Celtic cross

File:Celtic-style crossed circle.svgFile:CelticCross.svgA Celtic cross is a symbol that combines a cross with a ring surrounding the intersection....
. The circumpunct, or circled dot, is seen in a wide range of places.

Usage in names

  • Kappa Alpha Theta
    Kappa Alpha Theta

    Kappa Alpha Theta is an international women's fraternities and sororities founded on January 27, 1870 at DePauw University. Kappa Alpha Theta was the first Greek-letter women's fraternity....
     is a women's fraternity whose members are designated “Thetas”.
  • Theta refers to a member of Sigma Phi Theta, a local fraternity at Texas Lutheran University
    Texas Lutheran University

    Texas Lutheran University is an undergraduate, private, coeducational university affiliated with the Evangelical Lutheran Church in America. The University was founded in 1891, and currently serves roughly 1,400 students each Academic term....
    .
  • Theta is also the name of a melodic death metal
    Melodic death metal

    Melodic death metal is a subgenre of death metal which combines the melody of the New Wave of British Heavy Metal with the intensity of death metal....
     band based in Plattsburgh, New York.
  • Theta is the name of a biological weapon and boss featured in the Atari video game Area 51.
  • Thetamen is a nickname also used by the fraternity Iota Phi Theta.
  • Theta Phi Alpha is a sorority.
  • Theta Chi
    Theta Chi

    Theta Chi Fraternity is an international Fraternities and sororities. It was founded on April 10, 1856 as the Theta Chi Society, at Norwich University, Norwich, Vermont, United States, and was the 21st of the 71 North-American Interfraternity Conference men's fraternities ....
     is a Fraternity.
  • Theta refers to a member of the Alpha Pi Theta Brotherhood of Emerson College
    Emerson College

    Emerson College is a private university in Boston, Massachusetts, Massachusetts that focuses on the communication arts. Founded in 1880 by Charles Wesley Emerson as a "school of oratory," in Boston, Emerson's main campus is located on the Southeast corner of the Boston Common , in the Boston Theatre District....
    .
  • In generative grammar
    Generative grammar

    In theoretical linguistics, generative grammar refers to a particular approach to the study of syntax. A generative grammar of a language attempts to give a set of rules that will correctly predict which combinations of words will form grammatical sentences....
    , theta role
    Theta role

    In Generative grammar, a theta role or ?-role is the formal device for representing syntactic verb argument required syntactically by a particular verb....
    s are representations of a constituent
    Constituent (linguistics)

    In syntax analysis, a constituent is a word or a group of words that functions as a single unit within a hierarchical structure.Phrases are usually constituents of a clause, but clauses may also be embedded into a bigger structure....
    's syntactic and semantic contributions to a sentence.
  • In Scientology
    Scientology

    Scientology is a Scientology beliefs and practices created by American science fiction author L. Ron Hubbard in 1952 as a successor to his earlier self-help system, Dianetics....
    , the word "theta" is often used as an adjective to express or convey a sense of spirituality or uplifting feeling. See also thetan
    Thetan

    In Scientology, the concept of thetan is similar to the concept of spirit or soul found in other Religion. The term is derived from the Greek letter theta, which in Scientology beliefs and practices represents "the source of life, or life itself."...
    , the Scientology term for "spirit".
  • In the machinima Red vs Blue, Theta is the AI of the Freelancer North Dakota.


See also


  • Fita
    Fita

    Fita is a letter of the early Cyrillic alphabet, descended from the Greek language Theta. It was mainly used to write proper names derived from Greek....
    , a letter of the early Cyrillic alphabet
    Early Cyrillic alphabet

    The old Cyrillic alphabet was a writing system developed in the First Bulgarian Empire in the tenth century to write the Old Church Slavonic liturgical language....
     derived from the Greek theta.