Tau
166710
223764061
2008-07-05T18:01:04Z
Ishikawa Minoru
1889918
/* Other uses */
:''This article is about the letter of the [[Greek alphabet]]. For other uses, see [[Tau (disambiguation)]].''
{{wiktionarypar2|Τ|τ}}
{{Table_Greekletters|letter=tau}}
'''Tau''' (uppercase '''Τ''', lowercase '''τ'''; {{lang-el|Ταυ}}) is the 19th letter of the [[Greek alphabet]]. In the system of [[Greek numerals]] it has a value of 300. This letter in English is pronounced {{IPA|/taʊ/}}, but in [[Modern Greek]], this letter's name is pronounced {{IPA|/taf/}}. This is because the pronunciation of the combination of Greek letters αυ has changed from ancient to modern times from one of {{IPA|/aʊ/}} to either {{IPA|/av/}} or {{IPA|/af/}} (see [[Greek orthography]]).
The symbolism of the [[cross]] was connected not only to the letter [[chi (letter)|chi]], but also to tau, the equivalent of the last letter in the [[Phoenician alphabet|Phoenician]] and Old Hebrew alphabets, and which was originally cruciform in shape.
==Scientific uses==
The lower-case letter τ is used as a symbol for:
* The perceived motion-gap in [[General Tau Theory]], a psychological principle of perception.
* [[Torque]], the rotational force in [[mechanics]].
* Tuning and Analysis Utilities (TAU) performance evaluation tool, computer science [http://tau.uoregon.edu]
* The elementary [[tau lepton]] particle in [[particle physics]].
* The lifetime of a [[spontaneous emission]] process.
* The [[time constant]] of any device, such as an [[RC circuit]].
* [[Proper time]] in [[Theory of relativity|relativity]].
* The symbol of continuity in electro-flux resonance.
* A [[correlation coefficient|coefficient of correlation]] — see [[Kendall's tau]].
* The [[Golden ratio]] 1.618... (although [[phi (letter)|φ]] (phi) is more common)
* [[Ramanujan's tau function]] in [[number theory]].
* Tau in [[astronomy]] is a measure of [[Opacity (optics)|opacity]], or how much sunlight cannot penetrate the atmosphere.
* [[Tau (protein)|Tau]] in [[biochemistry]] is a [[protein]] associated to [[microtubule]]s.
* [[Shear stress|Shear]] [[Stress (physics)|stress]] in [[continuum mechanics]].
* [[Divisor function]] in number theory.
* [http://www.research.att.com/~njas/sequences/A002183 Number of divisors of highly composite numbers]
* The prefix of many stars, via the [[Bayer designation|Bayer]] stellar designation system. ([[Tau Ceti]] is such a star.)
* The expressed period of the freerunning rhythm of an animal (circadian rhythm terminology). I.e., the length of the daily cycle of an animal when kept in constant light or constant darkness (In humans this is ~24hrs).
==Other uses==
* In ancient times, a symbol for [[life]] and/or [[resurrection]], whereas the 8th letter of the Greek alphabet, [[theta]], was considered the symbol of [[death]].
* In Biblical times, the [[Taw]] was put on men to distinguish those who lamented sin, although newer versions of the Bible have replaced the ancient term “Taw” with "mark" (Ezekiel 9:4) or "signature" (Job 31:35). Its original sound value is a [[voiceless alveolar plosive]], IPA /t/,
* Tau is usually considered as the symbol of [[Franciscan]] orders due to [[Saint Francis of Assisi|St. Francis']] love for it, symbol of the redemption and of the [[Cross]]. Almost all Franciscan churches have painted a tau with two crossing arms, both with [[stigmata]], the one of Jesus and the other of Francis; usually members of the [[Franciscan#The_Third_Order_or_Order_of_Penance.2C_now_known_as_the_Secular_Franciscan_Order|Secular Franciscan Order]] wear a wooden τ in a string with three knots around the neck.
* [[Tau mission]], a proposal to send a space probe to a thousand [[astronomical units]] from the Earth and Sun.
* The [[Tau Empire]], one of the playable races in Warhammer 40K universe.
* In [[Freelancer_(computer_game)#Systems_and_Houses|Freelancer]], the Tau systems make up much of the Border Worlds.
* Surname for Chinese family
* Hyundai Motors uses "Tau" to identify their recently introduced V8 engine.
* In [[Mobile Suit Gundam 00]], fake solar furnaces used to power the three Throne Gundams and later the United Nations' GN-X and Alvatore are referred to as [[List of Mobile Suit Gundam 00 technology#GN Particles|GN Drives Tau]], as opposed to the original drives used by [[List of Mobile Suit Gundam 00 factions#Celestial Being|Celestial Being]].
==Miscellaneous==
An essay written around [[160 AD]], attributed to [[Lucian]], a mock legal prosecution called ''The Consonants at Law — Sigma v. Tau in the Court of Seven Vowels'' contains a reference to the attribution. [[Sigma (letter)|Sigma]] petitions the court to sentence Tau to death by crucifixion, saying:
:''Men weep, and bewail their lot, and curse Cadmus with many curses for introducing ''Tau'' into the family of letters; they say it was his body that tyrants took for a model, his shape that they imitated, when they set up structures on which men are crucified. ''Stauros'' (cross) the vile engine is called, and it derives its vile name from him. Now, with all these crimes upon him, does he not deserve death, nay, many deaths? For my part I know none bad enough but that supplied by his own shape — that shape which he gave to the [[gibbet]] named ''stauros'' after him by men.''
[[Category:Greek letters]]
[[als:Τ]]
[[ar:تاو (حرف إغريقي)]]
[[arc:Τ]]
[[bs:Tau]]
[[br:Tau (lizherenn)]]
[[ca:Tau (lletra grega)]]
[[cy:Tau]]
[[da:Tau]]
[[de:Tau (Buchstabe)]]
[[el:Ταυ]]
[[es:Τ]]
[[eo:Taŭo (litero)]]
[[eu:Τ]]
[[fr:Tau]]
[[ga:Tó]]
[[gd:Tau]]
[[gl:Tau]]
[[ko:Τ]]
[[hr:Tau]]
[[id:Tau]]
[[is:Tá (bókstafur)]]
[[it:Tau (lettera)]]
[[he:טאו (אות)]]
[[ka:ტაუ (ასო)]]
[[ht:Τ]]
[[ku:Tau]]
[[la:Tau]]
[[hu:Tau]]
[[ms:Tau]]
[[nl:Tau (letter)]]
[[ja:Τ]]
[[no:Tau (bokstav)]]
[[nn:Bokstaven Tau]]
[[nds:Tau]]
[[pl:Tau]]
[[pt:Τ]]
[[ru:Тау (буква)]]
[[simple:Tau (letter)]]
[[sk:Tau]]
[[sl:Tau]]
[[sh:Tau]]
[[fi:Tau]]
[[sv:Tau]]
[[th:เทา (อักษรกรีก)]]
[[tr:Τ]]
[[uk:Тау (літера)]]
[[zh:Τ]]