- Eta (letter)
Eta (uppercase Η, lowercase η; _el. Ήτα) is the seventh letter of the
Greek alphabet . In the system ofGreek numerals it has a value of 8. Letters that arose from Eta include the LatinH and the Cyrillic letter И.In
Modern Greek the letter, pronounced IPA| [ˈita] , represents aclose front unrounded vowel , IPA|/i/. InClassical Greek , it represented a longopen-mid front unrounded vowel , IPA|/ɛː/.History
The letter shape H was originally used in most Greek dialects to represent the sound /h/, a
voiceless glottal fricative . In this function, it was borrowed in the 8th century BC by the Etruscan and other Old Italic alphabets, which were based on the Euboean form of the Greek alphabet. This ultimately gave rise to the Latin alphabet with its letterH .In the
Ionic dialect , however, the sound /h/ disappeared by the sixth century BC, and the letter was re-used to represent the long vowel IPA|/ɛː/ instead. In 403 BC,Athens took over the Ionian spelling system and with it the vocalic use of H (even though it still also had the /h/ sound itself at that time). This later became the standard orthography in all of Greece.Other regional variants of the Greek alphabet (
epichoric alphabets ), in dialects that still preserved the sound /h/, employed various glyph shapes for consonantal Heta side by side with the new vocalic Eta for some time. One of them was a tack-like shape, looking like the left half of an H. This system was first used in the southern Italian colonies of Heracleia and Tarentum. When Greek orthography was codified by grammarians in the Hellenistic era, they used adiacritic symbol derived from this half-H shape to signal the presence of /h/, and added as its counterpart a reverse-shaped diacritic to denote absence of /h/. These symbols were the origin of therough breathing andsmooth breathing diacritics that became part of classical Greek orthography.Nick Nicholas (2003), "Greek /h/" [http://www.tlg.uci.edu/~opoudjis/unicode/unicode_aitch.html] ]In the typographic conventions of modern
epigraphy , the archaic consonantal Heta (Ͱ, ͱ) in ancient inscriptions is usually rendered by means of a lowercase Latin letter "h". Sometimes, symbols directly representing the old half-H glyph shape are also used. TheUnicode standard of computer encoding, as of 2007, is expected to introduce code points designed for this usage in its version 5.1. Like other archaic letters, they come in a lowercase and uppercase variant (U+0370 and U+0371), to cater for the needs of modern typography. [Summary of repertoire for FDAM 3 of ISO/IEC 10646 [http://std.dkuug.dk/jtc1/sc2/wg2/docs/n3263.pdf] ]During the time of post-classical
Koiné Greek , the IPA|/ɛː/ sound represented by Eta was raised and merged with several other formerly distinct vowels. Thus inModern Greek , Eta is pronounced IPA| [ˈita] and represents the sound /i/ (aclose front unrounded vowel ). It shares this function with several other letters (ι, υ) anddigraph s (ει, οι), which are all pronounced alike (ioticism).Eta was also borrowed with the sound value of [i] into the
Cyrillic alphabet , where it gave rise to the Cyrillic letter И.ymbol
Small eta is sometimes used in place of eng (ŋ) when eng is not available, because of their similar appearance.
The upper-case letter Η is used as a symbol in:
*Textual criticism , theAlexandrian text-type (from "Hesychius", its once-supposed editor).
*Chemistry ,enthalpy . H as symbol of enthalpy sometimes is said to be a Greek eta, but since enthalpy comes from ἐνθάλπος (smooth breathing and epsilon), it is more likely a Latin H for 'heat'.The lower-case letter η is used as a symbol in:
*Thermodynamics , the efficiency of aCarnot heat engine .
*Chemistry , thehapticity , or the number ofelectron s shared between ametal center and a ligand in acoordination compound . For example, anallyl group can coordinate topalladium in the η¹ mode or the η³ mode.
*Optics , therefractive index of an optical medium (although the letter "n" is more common). It may also refer to theelectromagnetic impedance of a medium.
*Particle physics , to represent the ηmeson s.
*Quantum Field Theory (physics), to represent themetric tensor .
*Statistics , "η"2 is the "partial regression coefficient". "η" is the symbol for the linear predictor of ageneralized linear model , and can also be used to denote the median of a population.
*Economics , "η" is the elasticity.
*Astronomy , the seventh brightest (usually) star in aconstellation . "See"Bayer designation .
*Experimental particle physics , η stands forpseudorapidity .
*Mathematics, η-conversion, see lambda calculus
*Fluid dynamics , η stands forviscosity .
*Mathematics, theDirichlet eta function ,Dedekind eta function , andWeierstrass eta function .
*Biology , aDNA polymerase found in highereukaryotes and implicated in Translesion Synthesis.
*Neural network backpropagation , η stands for the learning rate.
*Telecommunications Eta stands for efficiency
*Electronics , η stands for the ideality factor of abipolar transistor , and has a value close to 1.000. It appears in contexts where the transistor is used as a temperature sensing device, e.g. the thermal "diode" transistor that is embedded within a computer's microprocessor.References
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