Theta 166758 224343930 2008-07-08T13:00:20Z 212.93.232.206 /* Usage in names */ {{wiktionarypar2|Θ|θ}} {{Table Greekletters|letter=theta}} {{dablink|For other senses of this word, see [[theta (disambiguation)]].}} '''Theta''' (uppercase '''Θ''', lowercase '''θ''' or '''{{IPA|ϑ}}'''; {{lang-el|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 [[aspiration (phonetics)|aspirated]] [[voiceless dental plosive]] ({{IPA|/t̪ʰ/}}), but in [[Koiné]] and later dialects it became a [[voiceless dental fricative]] {{IPA|/θ/}}. In American English the name of the letter is commonly {{pronEng|ˈθeɪtʌ}}. In [[British English]], the name is pronounced {{IPA|/ˈθiːtə/}}. Letters such as the early [[Cyrillic]] letter ''[[fita]]'' ({{Unicode|Ѳ, ѳ}}) developed from θ. In its [[Archaic period in Greece|archaic]] form, θ was written as: * a cross within a circle ([[Image:Earth symbol.svg|16px|A symbol of a cross within a circle]] or [[Image:Cross within circle 2.png|16px|Another symbol of a cross within a circle]]) * and later, as a line or point within a circle ([[Image:Line within circle.png|16px|The symbol of a line within a circle]] or [[Image:Sun symbol.svg|16px|The symbol of a point within a circle]]). According to [[Porphyry of Tyros]], the [[Ancient Egypt|Egyptian]]s 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'').<ref name="Barry_1">{{Harvard reference| Author=Barry, Kieren | Last=Barry | First=Kieren | Title=The Greek Qabalah: Alphabetic Mysticism and Numerology in the Ancient World | Publisher=[[Samuel Weiser]] | page=p. 73 | Year=1999 | ID=ISBN 1-57863-110-6 }}.</ref> The Egyptians also used the symbol of a point within a circle ([[Image:Sun symbol.svg|15px|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]] as Ηλιος (''[[Helios]]''): 318. In classical Athens, it was used as an abbreviation for the [[Greek language|Greek]] θάνατος (''thanatos'', “death”) and as it vaguely resembles a human skull, theta was used as a warning symbol of [[Thanatos|death]], in the same way that [[skull and crossbones]] are used in modern times. It survives on [[potsherd]]s used by Athenians when voting for the [[death penalty]].<ref name="Barry_1"/> [[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.<ref>{{Harvard reference | last = Kaplan | first = Robert | title = The Nothing that Is: A Natural History of Zero | publisher = [[Oxford University Press]] | date = 2000 | pages = p. 66 | isbn = 0-1951-4237-3 }}.</ref> ==Symbol== The lower-case letter θ is used as a symbol for: * A [[angle|plane angle]] in geometry. * The [[voiceless dental fricative]] in the [[International Phonetic Alphabet]], such as in the words ''<u>th</u>ick'' or ''<u>th</u>in'' (but not as in ''<u>th</u>e'', which is the [[voiced dental fricative]]). * The [[Potential temperature]] in [[meteorology]]. * The score of a test taker in [[item response theory]]. * Theta Type Replication: a type of bacterial [[DNA replication]] specific to circular [[chromosomes]] * Threshold value of an artificial neuron. * 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.{{Fact|date=October 2007}} * The parameter in the [[likelihood function]] The upper-case letter Θ is used as a symbol for: * Dimensionless temperature in [[transport phenomena]]. * [[Big O notation]]. Denoting an asymptotically tight bound in analysis of algorithms. * [[Θ (set theory)]], a certain [[ordinal number]]. * Representing [[pentaquark]]s, exotic [[baryon]]s in [[particle physics]]. * [[Earth Day]]. * [[Electroencephalography|Brain Signal Frequency]] (Beta, Alpha, Theta, Delta) ranging from 4–8 Hz * One of the variables known as [[Greeks (finance)]], representing the lost-value rate of an option over time. ==Usage in names== * [[Kappa Alpha Theta]] is a [[sorority]] whose members are designated “Thetas”. * Theta refers to a member of [[Sigma Phi Theta]], a local fraternity at [[Texas Lutheran University]]. * Theta is also the name of a [[melodic death metal]] band based in [[Plattsburgh, New York]].<!-- Name of band? --> * Theta is the name of a biological weapon and boss featured in the Atari video game [[Area 51 (2005 video game)|Area 51]]. * Thetamen is a nickname also used by the [[Fraternities and sororities|fraternity]] [[Iota Phi Theta]]. * Theta Phi Alpha is a sorority. * Theta refers to a member of the Alpha Pi Theta Brotherhood of [[Emerson College]] * [http://www.thetahealing.com/ Theta healing] is a name for healing procedure where practitioner and client enter theta brainwawe frequency. ==References== <references/> [[Category:Greek letters]] [[Category:Phonetic transcription symbols]] [[als:Θ]] [[ar:ثيتا (حرف إغريقي)]] [[arc:Θ]] [[ast:Theta]] [[br:Theta (lizherenn)]] [[ca:Theta]] [[cy:Theta]] [[da:Theta]] [[de:Theta]] [[el:Θήτα]] [[es:Θ]] [[eo:Teto]] [[ext:Teta]] [[eu:Thita]] [[fr:Thêta]] [[ga:Téite]] [[gd:Theta]] [[gl:Theta]] [[ko:Θ]] [[hr:Theta]] [[is:Þeta]] [[it:Theta (lettera)]] [[he:תטא]] [[ka:თეტა (ასო)]] [[ht:Θ]] [[la:Theta]] [[hu:Théta]] [[ms:Teta]] [[nah:Θ]] [[nl:Thèta]] [[ja:Θ]] [[no:Theta]] [[nn:Theta]] [[nds:Theta]] [[pl:Theta]] [[pt:Θ]] [[ru:Тета (буква)]] [[simple:Theta]] [[sk:Théta]] [[sl:Theta]] [[sh:Theta]] [[fi:Theeta]] [[sv:Theta]] [[th:ทีตา]] [[tr:Θ]] [[uk:Тета (літера)]] [[zh:Θ]]