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Encyclopedia
Theta is the eighth letter of the Greek alphabet
Greek alphabet
The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

, derived from the Phoenician letter Teth
Teth
' is the ninth letter of many Semitic abjads , including Phoenician, Aramaic, Hebrew Tet , Syriac and Arabic ; it is 9th in abjadi order and 16th in modern Arabic order....

. In the system of Greek numerals
Greek numerals
Greek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...

 it has a value of 9.

Greek



In Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

, θ represented the aspirated
Aspiration (phonetics)
In phonetics, aspiration is the strong burst of air that accompanies either the release or, in the case of preaspiration, the closure of some obstruents. To feel or see the difference between aspirated and unaspirated sounds, one can put a hand or a lit candle in front of one's mouth, and say pin ...

 voiceless dental plosive
Voiceless dental plosive
The voiceless dental plosive is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is t_d...

 /t̪ʰ/, but in Modern Greek
Modern Greek
Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

 it represents the voiceless dental fricative
Voiceless dental fricative
The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

 /θ/.

Forms


In its archaic
Archaic period in Greece
The Archaic period in Greece was a period of ancient Greek history that followed the Greek Dark Ages. This period saw the rise of the polis and the founding of colonies, as well as the first inklings of classical philosophy, theatre in the form of tragedies performed during Dionysia, and written...

 form, θ was written as a cross within a circle (
or
), and later, as a line or point within a circle (
or
).

Latin



In the Latin script used for the Gaulish language
Gaulish language
The Gaulish language is an extinct Celtic language that was spoken by the Gauls, a people who inhabited the region known as Gaul from the Iron Age through the Roman period...

, theta developed into the tau gallicum, conventionally transliterated as Ð, although the bar extends across the centre of the letter. The phonetic value of the tau gallicum is thought to have been [t͡s].

International Phonetic Alphabet


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...

, [θ] represents the voiceless dental fricative
Voiceless dental fricative
The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

, as in thick or thin. It does not represent the consonant 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 spoken languages. The symbol in the International Phonetic Alphabet that represents this sound, eth, is . The symbol was taken from the Old English letter eth, which could stand for either a voiced or unvoiced...

.

Lower case


The lower-case letter θ is used as a symbol for:
  • A plane angle
    Angle
    In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

     in geometry.
  • A special function of several complex variables.
  • One of the Chebyshev function
    Chebyshev function
    [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x ...

    s in prime number theory.
  • The potential temperature in meteorology
    Meteorology
    Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

    .
  • The score of a test taker in item response theory
    Item response theory
    In psychometrics, item response theory also known as latent trait theory, strong true score theory, or modern mental test theory, is a paradigm for the design, analysis, and scoring of tests, questionnaires, and similar instruments measuring abilities, attitudes, or other variables. It is based...

    .
  • Theta Type Replication: a type of bacterial DNA replication
    DNA replication
    DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

     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 letter, followed by the genitive form of its parent constellation's Latin 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.
  • The parameter frequently used in writing the likelihood function
    Likelihood function
    In statistics, a likelihood function is a function of the parameters of a statistical model, defined as follows: the likelihood of a set of parameter values given some observed outcomes is equal to the probability of those observed outcomes given those parameter values...

     (Bayes theorem).
  • The Watterson estimator
    Watterson estimator
    In population genetics, the Watterson estimator is a method for estimating the population mutation rate, \theta = 4N_e\mu, where N_e is the effective population size and \mu is the per-generation mutation rate of the population of interest...

     for the population mutation rate in population genetics
    Population genetics
    Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

    .

Upper case


The upper-case letter Θ is used as a symbol for:
  • Dimensionless temperature in transport phenomena
    Transport Phenomena
    Transport Phenomena is the first textbook that is about transport phenomena. It is specifically designed for chemical engineering students...

    .
  • Big O notation
    Big O notation
    In mathematics, big O notation is used to describe the limiting behavior of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions. It is a member of a larger family of notations that is called Landau notation, Bachmann-Landau notation, or...

    . Denoting an asymptotically tight bound in analysis of algorithms
    Analysis of algorithms
    To analyze an algorithm is to determine the amount of resources necessary to execute it. Most algorithms are designed to work with inputs of arbitrary length...

    .
  • Θ (set theory), a certain ordinal number
    Ordinal number
    In set theory, an ordinal number, or just ordinal, is the order type of a well-ordered set. They are usually identified with hereditarily transitive sets. Ordinals are an extension of the natural numbers different from integers and from cardinals...

    .
  • Representing pentaquark
    Pentaquark
    A pentaquark is a hypothetical subatomic particle consisting of four quarks and one antiquark bound together . As quarks have a baryon number of +, and antiquarks of −, it would have a total baryon number of 1, thus being classified as an exotic baryon...

    s, exotic baryon
    Baryon
    A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

    s in particle physics
    Particle physics
    Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

    .
  • Earth Day
    Earth Day
    Earth Day is a day that is intended to inspire awareness and appreciation for the Earth's natural environment. The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. The first Proclamation of Earth Day was by San Francisco, the...

    .
  • Brain Signal Frequency
    Electroencephalography
    Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

     (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 the price of derivatives such as options to a change in underlying parameters on which the value of an instrument or portfolio of financial instruments is dependent. The name is used because the most common of...

     in finance, representing the lost-value rate of an option over time.
  • As a variable indicating Temperature difference in Heat Transfer

In its archaic form

  • In its archaic form (
    ) theta is used as a symbol for Earth.

Greek mathematics


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 scripts used in ancient Crete before Mycenaean Greek Linear B; Cretan hieroglyphs is the second script. In Minoan times, before the Mycenaean Greek dominion, Linear A was the official script for the palaces and religious activities, and hieroglyphs were mainly used on seals....

, Linear B
Linear B
Linear B is a syllabic script that was used for writing Mycenaean Greek, an early form of Greek. It pre-dated the Greek alphabet by several centuries and seems to have died out with the fall of Mycenaean civilization...

, and Egyptian hieroglyphics, the mathematical tensor product
Tensor product
In mathematics, the tensor product, denoted by ⊗, may be applied in different contexts to vectors, matrices, tensors, vector spaces, algebras, topological vector spaces, and modules, among many other structures or objects. In each case the significance of the symbol is the same: the most general...

, exclusive disjunction
Exclusive disjunction
The logical operation exclusive disjunction, also called exclusive or , is a type of logical disjunction on two operands that results in a value of true if exactly one of the operands has a value of true...

, and direct sum
Direct sum
In mathematics, one can often define a direct sum of objectsalready known, giving a new one. This is generally the Cartesian product of the underlying sets , together with a suitably defined structure. More abstractly, the direct sum is often, but not always, the coproduct in the category in question...

 operators, the identification symbol for the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 (as already mentioned), and the Celtic cross
Celtic cross
A Celtic cross is a symbol that combines a cross with a ring surrounding the intersection. In the Celtic Christian world it was combined with the Christian cross and this design was often used for high crosses – a free-standing cross made of stone and often richly decorated...

. The circumpunct, or circled dot, is seen in a wide range of places.

Symbolism


According to Porphyry of Tyros, the Egyptian
Ancient Egypt
Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

s used an X within a circle as a symbol
Symbol
A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

 of the soul; having a value of nine, it was used as a symbol for Ennead
Ennead
The Ennead was a group ofnine deities in Egyptian mythology. The Ennead were worshipped at Heliopolis and consisted of the god Atum, his children Shu and Tefnut, their children Geb and Nut and their children Osiris, Isis, Horus, Set and Nephthys.-Terminology:Egyptian mythology established multiple...

. Johannes Lydus says that the Egyptians
Egyptians
Egyptians are nation an ethnic group made up of Mediterranean North Africans, the indigenous people of Egypt.Egyptian identity is closely tied to geography. The population of Egypt is concentrated in the lower Nile Valley, the small strip of cultivable land stretching from the First Cataract to...

 used a symbol for Kosmos
Cosmos
In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...

 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 (
, 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 word for the practice of adding up the number values of the letters in a word to form a single number. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry....

 as Ηλιος (Helios
Helios
Helios was the personification of the Sun in Greek mythology. 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.

Abbreviation


In classical Athens, it was used as an abbreviation for the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 θάνατος (thanatos, “death”) and as it vaguely resembles a human skull, theta was used as a warning symbol of death
Thanatos
In Greek mythology, Thanatos was the daemon personification of death. He was a minor figure in Greek mythology, often referred to but rarely appearing in person...

, 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. Petrus de Dacia
Petrus de Dacia (mathematician)
Petrus de Dacia, also called Philomena and Peder nattergal , was a Danish scholar who lived in the 13th century. He worked mainly in Paris and Italy, writing in Latin. He published a calendar of new moon dates for the years 1292 - 1367. In 1292, he published a book on mathematics that contained a...

 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. For this reason, use of the number theta was sometimes avoided where the connotation was felt to be unlucky - the mint marks of some Late Imperial Roman coins famously have the sum ΔΕ or ΕΔ (delta and epsilon, that is 4 and 5) substituted as a euphemism
Euphemism
A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

 where a Θ (9) would otherwise be expected.

Culture


In the science fiction TV series Doctor Who
Doctor Who
Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

, the character of the Doctor was once known as Theta Sigma whilst he lived on Gallifrey
Gallifrey
Gallifrey is a fictional planet in the long-running British science fiction television series Doctor Who and is the homeworld of the Doctor and the Time Lords...

.

See also


  • {{About|the Greek letter}}
    {{Distinguish|Ɵ}}

    {{Wiktionary|Θ|θ}}
    {{Greek Alphabet|letter=theta}}
    Theta (uppercase Θ, lowercase θ or ϑ;
    Ancient Greek
    Ancient Greek
    Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

     {{lang|grc|θῆτα|}} tʰɛ̂ːta; Modern Greek
    Modern Greek
    Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

     {{lang|el|θήτα|}} ˈθita; ˈθiːtə, ˈθeɪtə) is the eighth letter of the Greek alphabet
    Greek alphabet
    The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

    , derived from the Phoenician letter Teth
    Teth
    ' is the ninth letter of many Semitic abjads , including Phoenician, Aramaic, Hebrew Tet , Syriac and Arabic ; it is 9th in abjadi order and 16th in modern Arabic order....

    . In the system of Greek numerals
    Greek numerals
    Greek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...

     it has a value of 9.

    Greek



    In Ancient Greek
    Ancient Greek
    Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

    , θ represented the aspirated
    Aspiration (phonetics)
    In phonetics, aspiration is the strong burst of air that accompanies either the release or, in the case of preaspiration, the closure of some obstruents. To feel or see the difference between aspirated and unaspirated sounds, one can put a hand or a lit candle in front of one's mouth, and say pin ...

     voiceless dental plosive
    Voiceless dental plosive
    The voiceless dental plosive is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is t_d...

     /t̪ʰ/, but in Modern Greek
    Modern Greek
    Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

     it represents the voiceless dental fricative
    Voiceless dental fricative
    The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

     /θ/.

    Forms


    In its archaic
    Archaic period in Greece
    The Archaic period in Greece was a period of ancient Greek history that followed the Greek Dark Ages. This period saw the rise of the polis and the founding of colonies, as well as the first inklings of classical philosophy, theatre in the form of tragedies performed during Dionysia, and written...

     form, θ was written as a cross within a circle (
    or
    ), and later, as a line or point within a circle (
    or
    ).

    Latin



    In the Latin script used for the Gaulish language
    Gaulish language
    The Gaulish language is an extinct Celtic language that was spoken by the Gauls, a people who inhabited the region known as Gaul from the Iron Age through the Roman period...

    , theta developed into the tau gallicum, conventionally transliterated as Ð, although the bar extends across the centre of the letter. The phonetic value of the tau gallicum is thought to have been [t͡s].

    International Phonetic Alphabet


    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...

    , [θ] represents the voiceless dental fricative
    Voiceless dental fricative
    The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

    , as in thick or thin. It does not represent the consonant 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 spoken languages. The symbol in the International Phonetic Alphabet that represents this sound, eth, is . The symbol was taken from the Old English letter eth, which could stand for either a voiced or unvoiced...

    .

    Lower case


    The lower-case letter θ is used as a symbol for:
    • A plane angle
      Angle
      In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

       in geometry.
    • A special function of several complex variables.
    • One of the Chebyshev function
      Chebyshev function
      [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x ...

      s in prime number theory.
    • The potential temperature in meteorology
      Meteorology
      Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

      .
    • The score of a test taker in item response theory
      Item response theory
      In psychometrics, item response theory also known as latent trait theory, strong true score theory, or modern mental test theory, is a paradigm for the design, analysis, and scoring of tests, questionnaires, and similar instruments measuring abilities, attitudes, or other variables. It is based...

      .
    • Theta Type Replication: a type of bacterial DNA replication
      DNA replication
      DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

       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 letter, followed by the genitive form of its parent constellation's Latin 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.
    • The parameter frequently used in writing the likelihood function
      Likelihood function
      In statistics, a likelihood function is a function of the parameters of a statistical model, defined as follows: the likelihood of a set of parameter values given some observed outcomes is equal to the probability of those observed outcomes given those parameter values...

       (Bayes theorem).
    • The Watterson estimator
      Watterson estimator
      In population genetics, the Watterson estimator is a method for estimating the population mutation rate, \theta = 4N_e\mu, where N_e is the effective population size and \mu is the per-generation mutation rate of the population of interest...

       for the population mutation rate in population genetics
      Population genetics
      Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

      .

    Upper case


    The upper-case letter Θ is used as a symbol for:
    • Dimensionless temperature in transport phenomena
      Transport Phenomena
      Transport Phenomena is the first textbook that is about transport phenomena. It is specifically designed for chemical engineering students...

      .
    • Big O notation
      Big O notation
      In mathematics, big O notation is used to describe the limiting behavior of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions. It is a member of a larger family of notations that is called Landau notation, Bachmann-Landau notation, or...

      . Denoting an asymptotically tight bound in analysis of algorithms
      Analysis of algorithms
      To analyze an algorithm is to determine the amount of resources necessary to execute it. Most algorithms are designed to work with inputs of arbitrary length...

      .
    • Θ (set theory), a certain ordinal number
      Ordinal number
      In set theory, an ordinal number, or just ordinal, is the order type of a well-ordered set. They are usually identified with hereditarily transitive sets. Ordinals are an extension of the natural numbers different from integers and from cardinals...

      .
    • Representing pentaquark
      Pentaquark
      A pentaquark is a hypothetical subatomic particle consisting of four quarks and one antiquark bound together . As quarks have a baryon number of +, and antiquarks of −, it would have a total baryon number of 1, thus being classified as an exotic baryon...

      s, exotic baryon
      Baryon
      A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

      s in particle physics
      Particle physics
      Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

      .
    • Earth Day
      Earth Day
      Earth Day is a day that is intended to inspire awareness and appreciation for the Earth's natural environment. The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. The first Proclamation of Earth Day was by San Francisco, the...

      .
    • Brain Signal Frequency
      Electroencephalography
      Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

       (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 the price of derivatives such as options to a change in underlying parameters on which the value of an instrument or portfolio of financial instruments is dependent. The name is used because the most common of...

       in finance, representing the lost-value rate of an option over time.
    • As a variable indicating Temperature difference in Heat Transfer

    In its archaic form

    • In its archaic form (
      ) theta is used as a symbol for Earth.

    Greek mathematics


    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 scripts used in ancient Crete before Mycenaean Greek Linear B; Cretan hieroglyphs is the second script. In Minoan times, before the Mycenaean Greek dominion, Linear A was the official script for the palaces and religious activities, and hieroglyphs were mainly used on seals....

    , Linear B
    Linear B
    Linear B is a syllabic script that was used for writing Mycenaean Greek, an early form of Greek. It pre-dated the Greek alphabet by several centuries and seems to have died out with the fall of Mycenaean civilization...

    , and Egyptian hieroglyphics, the mathematical tensor product
    Tensor product
    In mathematics, the tensor product, denoted by ⊗, may be applied in different contexts to vectors, matrices, tensors, vector spaces, algebras, topological vector spaces, and modules, among many other structures or objects. In each case the significance of the symbol is the same: the most general...

    , exclusive disjunction
    Exclusive disjunction
    The logical operation exclusive disjunction, also called exclusive or , is a type of logical disjunction on two operands that results in a value of true if exactly one of the operands has a value of true...

    , and direct sum
    Direct sum
    In mathematics, one can often define a direct sum of objectsalready known, giving a new one. This is generally the Cartesian product of the underlying sets , together with a suitably defined structure. More abstractly, the direct sum is often, but not always, the coproduct in the category in question...

     operators, the identification symbol for the Earth
    Earth
    Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

     (as already mentioned), and the Celtic cross
    Celtic cross
    A Celtic cross is a symbol that combines a cross with a ring surrounding the intersection. In the Celtic Christian world it was combined with the Christian cross and this design was often used for high crosses – a free-standing cross made of stone and often richly decorated...

    . The circumpunct, or circled dot, is seen in a wide range of places.

    Symbolism


    According to Porphyry of Tyros, the Egyptian
    Ancient Egypt
    Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

    s used an X within a circle as a symbol
    Symbol
    A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

     of the soul; having a value of nine, it was used as a symbol for Ennead
    Ennead
    The Ennead was a group ofnine deities in Egyptian mythology. The Ennead were worshipped at Heliopolis and consisted of the god Atum, his children Shu and Tefnut, their children Geb and Nut and their children Osiris, Isis, Horus, Set and Nephthys.-Terminology:Egyptian mythology established multiple...

    . Johannes Lydus says that the Egyptians
    Egyptians
    Egyptians are nation an ethnic group made up of Mediterranean North Africans, the indigenous people of Egypt.Egyptian identity is closely tied to geography. The population of Egypt is concentrated in the lower Nile Valley, the small strip of cultivable land stretching from the First Cataract to...

     used a symbol for Kosmos
    Cosmos
    In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...

     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 (
    , 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 {{Polytonic|θῆτα}} (theta) has the same numerical value in isopsephy
    Isopsephy
    Isopsephy is the Greek word for the practice of adding up the number values of the letters in a word to form a single number. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry....

     as Ηλιος (Helios
    Helios
    Helios was the personification of the Sun in Greek mythology. 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.

    Abbreviation


    In classical Athens, it was used as an abbreviation for the Greek
    Greek language
    Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

     θάνατος (thanatos, “death”) and as it vaguely resembles a human skull, theta was used as a warning symbol of death
    Thanatos
    In Greek mythology, Thanatos was the daemon personification of death. He was a minor figure in Greek mythology, often referred to but rarely appearing in person...

    , 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. Petrus de Dacia
    Petrus de Dacia (mathematician)
    Petrus de Dacia, also called Philomena and Peder nattergal , was a Danish scholar who lived in the 13th century. He worked mainly in Paris and Italy, writing in Latin. He published a calendar of new moon dates for the years 1292 - 1367. In 1292, he published a book on mathematics that contained a...

     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. For this reason, use of the number theta was sometimes avoided where the connotation was felt to be unlucky - the mint marks of some Late Imperial Roman coins famously have the sum ΔΕ or ΕΔ (delta and epsilon, that is 4 and 5) substituted as a euphemism
    Euphemism
    A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

     where a Θ (9) would otherwise be expected.

    Culture


    In the science fiction TV series Doctor Who
    Doctor Who
    Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

    , the character of the Doctor was once known as Theta Sigma whilst he lived on Gallifrey
    Gallifrey
    Gallifrey is a fictional planet in the long-running British science fiction television series Doctor Who and is the homeworld of the Doctor and the Time Lords...

    .

    See also


    • {{About|the Greek letter}}
      {{Distinguish|Ɵ}}

      {{Wiktionary|Θ|θ}}
      {{Greek Alphabet|letter=theta}}
      Theta (uppercase Θ, lowercase θ or ϑ;
      Ancient Greek
      Ancient Greek
      Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

       {{lang|grc|θῆτα|}} tʰɛ̂ːta; Modern Greek
      Modern Greek
      Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

       {{lang|el|θήτα|}} ˈθita; ˈθiːtə, ˈθeɪtə) is the eighth letter of the Greek alphabet
      Greek alphabet
      The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

      , derived from the Phoenician letter Teth
      Teth
      ' is the ninth letter of many Semitic abjads , including Phoenician, Aramaic, Hebrew Tet , Syriac and Arabic ; it is 9th in abjadi order and 16th in modern Arabic order....

      . In the system of Greek numerals
      Greek numerals
      Greek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...

       it has a value of 9.

      Greek



      In Ancient Greek
      Ancient Greek
      Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...

      , θ represented the aspirated
      Aspiration (phonetics)
      In phonetics, aspiration is the strong burst of air that accompanies either the release or, in the case of preaspiration, the closure of some obstruents. To feel or see the difference between aspirated and unaspirated sounds, one can put a hand or a lit candle in front of one's mouth, and say pin ...

       voiceless dental plosive
      Voiceless dental plosive
      The voiceless dental plosive is a type of consonantal sound, used in some spoken languages. The symbol in the International Phonetic Alphabet that represents this sound is , and the equivalent X-SAMPA symbol is t_d...

       /t̪ʰ/, but in Modern Greek
      Modern Greek
      Modern Greek refers to the varieties of the Greek language spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic...

       it represents the voiceless dental fricative
      Voiceless dental fricative
      The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

       /θ/.

      Forms


      In its archaic
      Archaic period in Greece
      The Archaic period in Greece was a period of ancient Greek history that followed the Greek Dark Ages. This period saw the rise of the polis and the founding of colonies, as well as the first inklings of classical philosophy, theatre in the form of tragedies performed during Dionysia, and written...

       form, θ was written as a cross within a circle (
      or
      ), and later, as a line or point within a circle (
      or
      ).

      Latin



      In the Latin script used for the Gaulish language
      Gaulish language
      The Gaulish language is an extinct Celtic language that was spoken by the Gauls, a people who inhabited the region known as Gaul from the Iron Age through the Roman period...

      , theta developed into the tau gallicum, conventionally transliterated as Ð, although the bar extends across the centre of the letter. The phonetic value of the tau gallicum is thought to have been [t͡s].

      International Phonetic Alphabet


      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...

      , [θ] represents the voiceless dental fricative
      Voiceless dental fricative
      The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...

      , as in thick or thin. It does not represent the consonant 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 spoken languages. The symbol in the International Phonetic Alphabet that represents this sound, eth, is . The symbol was taken from the Old English letter eth, which could stand for either a voiced or unvoiced...

      .

      Lower case


      The lower-case letter θ is used as a symbol for:
      • A plane angle
        Angle
        In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...

         in geometry.
      • A special function of several complex variables.
      • One of the Chebyshev function
        Chebyshev function
        [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x [Image:ChebyshevPsi.png|thumb|right|The Chebyshev function ψ, with x ...

        s in prime number theory.
      • The potential temperature in meteorology
        Meteorology
        Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...

        .
      • The score of a test taker in item response theory
        Item response theory
        In psychometrics, item response theory also known as latent trait theory, strong true score theory, or modern mental test theory, is a paradigm for the design, analysis, and scoring of tests, questionnaires, and similar instruments measuring abilities, attitudes, or other variables. It is based...

        .
      • Theta Type Replication: a type of bacterial DNA replication
        DNA replication
        DNA replication is a biological process that occurs in all living organisms and copies their DNA; it is the basis for biological inheritance. The process starts with one double-stranded DNA molecule and produces two identical copies of the molecule...

         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 letter, followed by the genitive form of its parent constellation's Latin 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.
      • The parameter frequently used in writing the likelihood function
        Likelihood function
        In statistics, a likelihood function is a function of the parameters of a statistical model, defined as follows: the likelihood of a set of parameter values given some observed outcomes is equal to the probability of those observed outcomes given those parameter values...

         (Bayes theorem).
      • The Watterson estimator
        Watterson estimator
        In population genetics, the Watterson estimator is a method for estimating the population mutation rate, \theta = 4N_e\mu, where N_e is the effective population size and \mu is the per-generation mutation rate of the population of interest...

         for the population mutation rate in population genetics
        Population genetics
        Population genetics is the study of allele frequency distribution and change under the influence of the four main evolutionary processes: natural selection, genetic drift, mutation and gene flow. It also takes into account the factors of recombination, population subdivision and population...

        .

      Upper case


      The upper-case letter Θ is used as a symbol for:
      • Dimensionless temperature in transport phenomena
        Transport Phenomena
        Transport Phenomena is the first textbook that is about transport phenomena. It is specifically designed for chemical engineering students...

        .
      • Big O notation
        Big O notation
        In mathematics, big O notation is used to describe the limiting behavior of a function when the argument tends towards a particular value or infinity, usually in terms of simpler functions. It is a member of a larger family of notations that is called Landau notation, Bachmann-Landau notation, or...

        . Denoting an asymptotically tight bound in analysis of algorithms
        Analysis of algorithms
        To analyze an algorithm is to determine the amount of resources necessary to execute it. Most algorithms are designed to work with inputs of arbitrary length...

        .
      • Θ (set theory), a certain ordinal number
        Ordinal number
        In set theory, an ordinal number, or just ordinal, is the order type of a well-ordered set. They are usually identified with hereditarily transitive sets. Ordinals are an extension of the natural numbers different from integers and from cardinals...

        .
      • Representing pentaquark
        Pentaquark
        A pentaquark is a hypothetical subatomic particle consisting of four quarks and one antiquark bound together . As quarks have a baryon number of +, and antiquarks of −, it would have a total baryon number of 1, thus being classified as an exotic baryon...

        s, exotic baryon
        Baryon
        A baryon is a composite particle made up of three quarks . Baryons and mesons belong to the hadron family, which are the quark-based particles...

        s in particle physics
        Particle physics
        Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...

        .
      • Earth Day
        Earth Day
        Earth Day is a day that is intended to inspire awareness and appreciation for the Earth's natural environment. The name and concept of Earth Day was allegedly pioneered by John McConnell in 1969 at a UNESCO Conference in San Francisco. The first Proclamation of Earth Day was by San Francisco, the...

        .
      • Brain Signal Frequency
        Electroencephalography
        Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

         (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 the price of derivatives such as options to a change in underlying parameters on which the value of an instrument or portfolio of financial instruments is dependent. The name is used because the most common of...

         in finance, representing the lost-value rate of an option over time.
      • As a variable indicating Temperature difference in Heat Transfer

      In its archaic form

      • In its archaic form (
        ) theta is used as a symbol for Earth.

      Greek mathematics


      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 scripts used in ancient Crete before Mycenaean Greek Linear B; Cretan hieroglyphs is the second script. In Minoan times, before the Mycenaean Greek dominion, Linear A was the official script for the palaces and religious activities, and hieroglyphs were mainly used on seals....

      , Linear B
      Linear B
      Linear B is a syllabic script that was used for writing Mycenaean Greek, an early form of Greek. It pre-dated the Greek alphabet by several centuries and seems to have died out with the fall of Mycenaean civilization...

      , and Egyptian hieroglyphics, the mathematical tensor product
      Tensor product
      In mathematics, the tensor product, denoted by ⊗, may be applied in different contexts to vectors, matrices, tensors, vector spaces, algebras, topological vector spaces, and modules, among many other structures or objects. In each case the significance of the symbol is the same: the most general...

      , exclusive disjunction
      Exclusive disjunction
      The logical operation exclusive disjunction, also called exclusive or , is a type of logical disjunction on two operands that results in a value of true if exactly one of the operands has a value of true...

      , and direct sum
      Direct sum
      In mathematics, one can often define a direct sum of objectsalready known, giving a new one. This is generally the Cartesian product of the underlying sets , together with a suitably defined structure. More abstractly, the direct sum is often, but not always, the coproduct in the category in question...

       operators, the identification symbol for the Earth
      Earth
      Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

       (as already mentioned), and the Celtic cross
      Celtic cross
      A Celtic cross is a symbol that combines a cross with a ring surrounding the intersection. In the Celtic Christian world it was combined with the Christian cross and this design was often used for high crosses – a free-standing cross made of stone and often richly decorated...

      . The circumpunct, or circled dot, is seen in a wide range of places.

      Symbolism


      According to Porphyry of Tyros, the Egyptian
      Ancient Egypt
      Ancient Egypt was an ancient civilization of Northeastern Africa, concentrated along the lower reaches of the Nile River in what is now the modern country of Egypt. Egyptian civilization coalesced around 3150 BC with the political unification of Upper and Lower Egypt under the first pharaoh...

      s used an X within a circle as a symbol
      Symbol
      A symbol is something which represents an idea, a physical entity or a process but is distinct from it. The purpose of a symbol is to communicate meaning. For example, a red octagon may be a symbol for "STOP". On a map, a picture of a tent might represent a campsite. Numerals are symbols for...

       of the soul; having a value of nine, it was used as a symbol for Ennead
      Ennead
      The Ennead was a group ofnine deities in Egyptian mythology. The Ennead were worshipped at Heliopolis and consisted of the god Atum, his children Shu and Tefnut, their children Geb and Nut and their children Osiris, Isis, Horus, Set and Nephthys.-Terminology:Egyptian mythology established multiple...

      . Johannes Lydus says that the Egyptians
      Egyptians
      Egyptians are nation an ethnic group made up of Mediterranean North Africans, the indigenous people of Egypt.Egyptian identity is closely tied to geography. The population of Egypt is concentrated in the lower Nile Valley, the small strip of cultivable land stretching from the First Cataract to...

       used a symbol for Kosmos
      Cosmos
      In the general sense, a cosmos is an orderly or harmonious system. It originates from the Greek term κόσμος , meaning "order" or "ornament" and is antithetical to the concept of chaos. Today, the word is generally used as a synonym of the word Universe . The word cosmos originates from the same root...

       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 (
      , 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 {{Polytonic|θῆτα}} (theta) has the same numerical value in isopsephy
      Isopsephy
      Isopsephy is the Greek word for the practice of adding up the number values of the letters in a word to form a single number. The early Greeks used pebbles arranged in patterns to learn arithmetic and geometry....

       as Ηλιος (Helios
      Helios
      Helios was the personification of the Sun in Greek mythology. 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.

      Abbreviation


      In classical Athens, it was used as an abbreviation for the Greek
      Greek language
      Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

       θάνατος (thanatos, “death”) and as it vaguely resembles a human skull, theta was used as a warning symbol of death
      Thanatos
      In Greek mythology, Thanatos was the daemon personification of death. He was a minor figure in Greek mythology, often referred to but rarely appearing in person...

      , 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. Petrus de Dacia
      Petrus de Dacia (mathematician)
      Petrus de Dacia, also called Philomena and Peder nattergal , was a Danish scholar who lived in the 13th century. He worked mainly in Paris and Italy, writing in Latin. He published a calendar of new moon dates for the years 1292 - 1367. In 1292, he published a book on mathematics that contained a...

       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. For this reason, use of the number theta was sometimes avoided where the connotation was felt to be unlucky - the mint marks of some Late Imperial Roman coins famously have the sum ΔΕ or ΕΔ (delta and epsilon, that is 4 and 5) substituted as a euphemism
      Euphemism
      A euphemism is the substitution of a mild, inoffensive, relatively uncontroversial phrase for another more frank expression that might offend or otherwise suggest something unpleasant to the audience...

       where a Θ (9) would otherwise be expected.

      Culture


      In the science fiction TV series Doctor Who
      Doctor Who
      Doctor Who is a British science fiction television programme produced by the BBC. The programme depicts the adventures of a time-travelling humanoid alien known as the Doctor who explores the universe in a sentient time machine called the TARDIS that flies through time and space, whose exterior...

      , the character of the Doctor was once known as Theta Sigma whilst he lived on Gallifrey
      Gallifrey
      Gallifrey is a fictional planet in the long-running British science fiction television series Doctor Who and is the homeworld of the Doctor and the Time Lords...

      .

      See also

      • {{unicode
        Fita
        Fita is a letter of the Early Cyrillic alphabet. The shape and the name of the letter are derived from the Greek letter Theta .In the Cyrillic numeral system, Fita has a value of 9.- Shape :...

        , a letter of the early Cyrillic alphabet
        Early Cyrillic alphabet
        The Early Cyrillic alphabet is a writing system developed in the First Bulgarian Empire in the 9th or 10th century to write the Old Church Slavonic liturgical language...

         derived from the Greek theta
      • ʘ - Bilabial click
      • Voiceless dental fricative
        Voiceless dental fricative
        The voiceless dental non-sibilant fricative is a type of consonantal sound used in some spoken languages. It is familiar to English speakers as the 'th' in thing. Though rather rare as a phoneme in the world's inventory of languages, it is encountered in some of the most widespread and influential...