Eta (letter)
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| [[Image:Greek alphabet {{{letter|alpha-omega}}}.png| 200px|center]] | |
| Greek alphabet | |
|---|---|
| Α α Alpha | Β β Beta |
| Γ γ Gamma | Δ δ Delta |
| Ε ε Epsilon | Ζ ζ Zeta |
| Η η Eta | Θ θ Theta |
| Ι ι Iota | Κ κ Kappa |
| Λ λ Lambda | Μ μ Mu |
| Ν ν Nu | Ξ ξ Xi |
| Ο ο Omicron | Π π Pi |
| Ρ ρ Rho | Σ σ ς Sigma |
| Τ τ Tau | Υ υ Upsilon |
| Φ φ Phi | Χ χ Chi |
| Ψ ψ Psi | Ω ω Omega |
| obsolete letters | |
| Image:Greek alphabet digamma2.png Digamma | Image:Greek alphabet san.png San |
| Image:Greek alphabet qoppa.png Qoppa | Image:Greek alphabet sampi.png Sampi |
| Image:Greek alphabet stigma.png Stigma | Image:Greek alphabet sho.png Sho |
- For other uses, see Eta.
In Modern Greek the letter is pronounced [[Close front unrounded vowel|Template:IPA]]. In the Classical version of the Ancient Greek language, it was pronounced as a long Template:IPA. The symbol was initially used to denote the rough breathing, [[Voiceless glottal fricative|Template:IPA]]. In the Ionic dialect, where this sound had disappeared by the sixth century BC, the letter was used to represent the long [[[Template:IPA]]]. When the Ionic alphabet was adopted in Athens in 403 BC, [[[Template:IPA]]] (previously written as Ε) was also written as Η there too, hence the modern usage.
Symbol
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 for:
- In textual criticism, the Alexandrian text-type (from Hesychius, its once-supposed editor).
- In chemistry, enthalpy.
The lower-case letter η is used as a symbol for:
- In thermodynamics, the efficiency of a Carnot heat engine.
- In chemistry, the number of electrons shared between a metal center and a ligand in a coordination compound. For example, an allyl group can coordinate to palladium in the η¹ mode or the η³ mode.
- In optics, the refractive index of an optical medium (although the letter n is more common).
- In particle physics, to represent the η baryons.
- In statistics, η2 is the "partial regression coefficient".
- In astronomy, the seventh brightest (usually) star in a constellation. See Bayer designation.
- In experimental particle physics, η stands for pseudorapidity.
- In mathematics, η-conversion, see lambda calculus
- In fluid dynamics, η stands for viscosity.als:Η
bg:Ета ca:Eta da:Eta de:Eta el:Ήτα es:Η fr:Êta ga:Éite ko:Η he:אטא nl:Èta nds:Eta ja:Η no:Eta (bokstav) pl:Eta pt:Η fi:Eeta sv:Eta zh:Η