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Theta (UK: /ˈθiːtə/, US: /ˈθeɪtə/; uppercase Θ or ϴ, lowercase θ^{[note 1]} or ϑ; Ancient Greek: θῆτα thē̂ta [tʰɛ̂ːta]; Modern: θήτα thī́ta [ˈθita]) is the eighth letter of the Greek alphabet, derived from the Phoenician letter Teth
In Ancient Greek, θ represented the aspirated voiceless dental plosive /t̪ʰ/, but in Modern Greek it represents the voiceless dental fricative /θ/.
In its archaic form, θ was written as a cross within a circle (as in the Etruscan
The cursive form ϑ was retained by Unicode as U+03D1 ϑ GREEK THETA SYMBOL, separate from U+03B8 θ GREEK SMALL LETTER THETA. For the purpose of writing Greek text, the two can be font variants of a single character, but θ and ϑ are also used as distinct symbols in technical and mathematical contexts. Extensive lists of examples follow below at Mathematics and Science. U+03D1 ϑ GREEK THETA SYMBOL (script theta) is also common in biblical and theological usage e.g. πρόϑεσις instead of πρόθεσις (means placing in public or laying out a corpse).
In Latin script used for the Gaulish language, theta inspired the tau gallicum (
The early Cyrillic letter fita (Ѳ, ѳ) developed from θ. This letter existed in the Russian alphabet until the 1918 Russian orthography reform.
In the International Phonetic Alphabet (IPA), [θ] represents the voiceless dental fricative, as in thick or thin. It does not represent the consonant in the, which is the voiced dental fricative. A similarlooking symbol, [ɵ], which is described as a lowercase barred o, indicates in the IPA a closemid central rounded vowel.
The lowercase letter θ is used as a symbol for:
The uppercase letter Θ is used as a symbol for:
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).^{[3]}
The Egyptians also used the symbol of a point within a circle (
Main article: Theta nigrum 
In classical Athens, it was used as an abbreviation for the Greek θάνατος (thanatos, "death") and as it vaguely resembles a human skull,^{[citation needed]} 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.^{[3]} 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.^{[4]} 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 where a Θ (9) would otherwise be expected.
Greek Life
The names of many American fraternities and sororities are named with Greek letters, including Theta.
Preview  Θ  θ  ϑ  ϴ  ᶿ  

Unicode name  GREEK CAPITAL LETTER THETA  GREEK SMALL LETTER THETA  GREEK THETA SYMBOL  GREEK CAPITAL THETA SYMBOL  MODIFIER LETTER SMALL THETA  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex  dec  hex 
Unicode  920  U+0398  952  U+03B8  977  U+03D1  1012  U+03F4  7615  U+1DBF 
UTF8  206 152  CE 98  206 184  CE B8  207 145  CF 91  207 180  CF B4  225 182 191  E1 B6 BF 
Numeric character reference  Θ 
Θ 
θ 
θ 
ϑ 
ϑ 
ϴ 
ϴ 
ᶿ 
ᶿ 
Named character reference  Θ  θ  ϑ, ϑ, ϑ  
DOS Greek  135  87  159  9F  
DOS Greek2  172  AC  226  E2  
Windows 1253  200  C8  232  E8  
TeX  \Theta  \theta  \vartheta 
Preview  Ⲑ  ⲑ  

Unicode name  COPTIC CAPITAL LETTER THETHE  COPTIC SMALL LETTER THETHE  
Encodings  decimal  hex  dec  hex 
Unicode  11408  U+2C90  11409  U+2C91 
UTF8  226 178 144  E2 B2 90  226 178 145  E2 B2 91 
Numeric character reference  Ⲑ 
Ⲑ 
ⲑ 
ⲑ 
Preview  Ѳ  ѳ  

Unicode name  CYRILLIC CAPITAL LETTER FITA  CYRILLIC SMALL LETTER FITA  
Encodings  decimal  hex  dec  hex 
Unicode  1138  U+0472  1139  U+0473 
UTF8  209 178  D1 B2  209 179  D1 B3 
Numeric character reference  Ѳ 
Ѳ 
ѳ 
ѳ 
Preview  𝚯  𝛉  𝚹  𝛝  

Unicode name  MATHEMATICAL BOLD CAPITAL THETA 
MATHEMATICAL BOLD SMALL THETA 
MATHEMATICAL BOLD CAPITAL THETA SYMBOL 
MATHEMATICAL BOLD THETA SYMBOL  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex 
Unicode  120495  U+1D6AF  120521  U+1D6C9  120505  U+1D6B9  120541  U+1D6DD 
UTF8  240 157 154 175  F0 9D 9A AF  240 157 155 137  F0 9D 9B 89  240 157 154 185  F0 9D 9A B9  240 157 155 157  F0 9D 9B 9D 
UTF16  55349 57007  D835 DEAF  55349 57033  D835 DEC9  55349 57017  D835 DEB9  55349 57053  D835 DEDD 
Numeric character reference  𝚯 
𝚯 
𝛉 
𝛉 
𝚹 
𝚹 
𝛝 
𝛝 
Preview  𝛩  𝜃  𝛳  𝜗  

Unicode name  MATHEMATICAL ITALIC CAPITAL THETA 
MATHEMATICAL ITALIC SMALL THETA 
MATHEMATICAL ITALIC CAPITAL THETA SYMBOL 
MATHEMATICAL ITALIC THETA SYMBOL  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex 
Unicode  120553  U+1D6E9  120579  U+1D703  120563  U+1D6F3  120599  U+1D717 
UTF8  240 157 155 169  F0 9D 9B A9  240 157 156 131  F0 9D 9C 83  240 157 155 179  F0 9D 9B B3  240 157 156 151  F0 9D 9C 97 
UTF16  55349 57065  D835 DEE9  55349 57091  D835 DF03  55349 57075  D835 DEF3  55349 57111  D835 DF17 
Numeric character reference  𝛩 
𝛩 
𝜃 
𝜃 
𝛳 
𝛳 
𝜗 
𝜗 
Preview  𝜣  𝜽  𝜭  𝝑  

Unicode name  MATHEMATICAL BOLD ITALIC CAPITAL THETA 
MATHEMATICAL BOLD ITALIC SMALL THETA 
MATHEMATICAL BOLD ITALIC CAPITAL THETA SYMBOL 
MATHEMATICAL BOLD ITALIC CAPITAL THETA SYMBOL  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex 
Unicode  120611  U+1D723  120637  U+1D73D  120621  U+1D72D  120657  U+1D751 
UTF8  240 157 156 163  F0 9D 9C A3  240 157 156 189  F0 9D 9C BD  240 157 156 173  F0 9D 9C AD  240 157 157 145  F0 9D 9D 91 
UTF16  55349 57123  D835 DF23  55349 57149  D835 DF3D  55349 57133  D835 DF2D  55349 57169  D835 DF51 
Numeric character reference  𝜣 
𝜣 
𝜽 
𝜽 
𝜭 
𝜭 
𝝑 
𝝑 
Preview  𝝝  𝝷  𝚹  𝞋  

Unicode name  MATHEMATICAL SANSSERIF BOLD CAPITAL THETA 
MATHEMATICAL SANSSERIF BOLD SMALL THETA 
MATHEMATICAL SANSSERIF BOLD CAPITAL THETA SYMBOL 
MATHEMATICAL SANSSERIF BOLD THETA SYMBOL  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex 
Unicode  120669  U+1D75D  120695  U+1D777  120505  U+1D6B9  120715  U+1D78B 
UTF8  240 157 157 157  F0 9D 9D 9D  240 157 157 183  F0 9D 9D B7  240 157 154 185  F0 9D 9A B9  240 157 158 139  F0 9D 9E 8B 
UTF16  55349 57181  D835 DF5D  55349 57207  D835 DF77  55349 57017  D835 DEB9  55349 57227  D835 DF8B 
Numeric character reference  𝝝 
𝝝 
𝝷 
𝝷 
𝚹 
𝚹 
𝞋 
𝞋 
Preview  𝞗  𝞱  𝜭  𝟅  

Unicode name  MATHEMATICAL SANSSERIF BOLD ITALIC CAPITAL THETA 
MATHEMATICAL SANSSERIF BOLD ITALIC SMALL THETA 
MATHEMATICAL SANSSERIF BOLD ITALIC CAPITAL THETA SYMBOL 
MATHEMATICAL SANSSERIF BOLD ITALIC THETA SYMBOL  
Encodings  decimal  hex  dec  hex  dec  hex  dec  hex 
Unicode  120727  U+1D797  120753  U+1D7B1  120621  U+1D72D  120773  U+1D7C5 
UTF8  240 157 158 151  F0 9D 9E 97  240 157 158 177  F0 9D 9E B1  240 157 156 173  F0 9D 9C AD  240 157 159 133  F0 9D 9F 85 
UTF16  55349 57239  D835 DF97  55349 57265  D835 DFB1  55349 57133  D835 DF2D  55349 57285  D835 DFC5 
Numeric character reference  𝞗 
𝞗 
𝞱 
𝞱 
𝜭 
𝜭 
𝟅 
𝟅 
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.