Eta (letter)
For other uses, see Eta. |
Handwritten variant of lowercase eta, from the Byzantine period |
In
Modern Greek the letter is pronounced
. In
Classical Greek, it was pronounced as a long . The symbol was initially used to denote the
rough breathing,
. In the
Ionic dialect, where this sound had disappeared by the sixth century BC, the letter was used to represent the long []. When the Ionic alphabet was adopted in
Athens in
403 BC, [] (previously written as Ε) was also written as Η there too, hence the modern usage.
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.
