Gamma (uppercase G, lowercase g; Greek: Gamma Gamma) is the third letter of the Greek alphabet. In the system of Greek numerals it has a value of 3. It was derived from the Phoenician letter Gimel . Letters that arose from gamma include the Roman C and G and the Cyrillic letters G and G'.


== Uses ==


=== Greek ===

In Ancient Greek, gamma represented a voiced velar stop /g/. In Modern Greek, it represents a voiced fricative. It is realized either as a palatal /j/ (before a front vowel, /e, i/), or as a velar /g/ (in all other environments).
Both in Ancient and in Modern Greek, before other velars (k, kh, x k, kh, ks), gamma represents a velar nasal /NG/. A double gamma gg represents the sequence /NGg/ (phonetically varying [NGg~g]) or /NGg/.


=== International Phonetic Alphabet ===
In the International Phonetic Alphabet, lowercase gamma (g) represents the voiced velar fricative. A lowercase gamma that lies above the baseline rather than crossing it (u) represents the close-mid back unrounded vowel.


=== Mathematics and science ===


==== Lower case ====
The lower-case letter  is used as a symbol for:
Chromatic number of a graph, sometimes  (Chi) is used, which is also used for the Euler characteristic
Gamma radiation in nuclear physics
The photon, the elementary particle of light
Surface energy in materials science
The Lorentz factor in theory of relativity
The heat capacity ratio Cp/Cv in thermodynamics
The activity coefficient in thermodynamics
The gyromagnetic ratio in electromagnetism
Gamma oscillation in neuroscience
Gamma motoneurons in neuroscience
Gamma is a non-SI metric unit of measure of mass equal to one microgram (1 mg). This always-rare use is currently deprecated.
Gamma is also a non-SI unit of measure of magnetic flux density, sometimes used in geophysics, equal to 1 nanotesla (nT).
The power by which the luminance of an image is increased in gamma correction
The Euler-Mascheroni constant
In mechanical engineering:
Specific weight
The shear rate of a fluid is represented by a lower case gamma with a dot above it: 
Austenite (also known as g-iron), a metallic non-magnetic allotrope or solid solution of iron.

The gamma carbon is the third carbon attached to a functional group in Organic Chemistry and Biochemistry nomenclature; see Alpha and beta carbon


==== Upper case ====
The upper-case letter  is used as a symbol for:
In mathematics, the gamma function (usually written as -function) is an extension of the factorial to complex numbers
In probability theory and statistics, the gamma distribution is a two-parameter family of continuous probability distributions.
Circulation in fluid mechanics
As reflection coefficient in physics and electrical engineering
The tape alphabet of a Turing machine
The Feferman-Schutte ordinal G0


==== Meteorology ====
Gamma was one of the names used in the 2005 Atlantic hurricane season as Tropical Storm Gamma.


== Technical notes ==


=== HTML ===
The HTML entities for uppercase and lowercase gamma are &Gamma; and &gamma;.


=== Unicode ===
Greek Gamma
Coptic Gamma
Latin / phonetic Gamma
CJK Square Gamma
Technical / Mathematical Gamma
These characters are used only as mathematical symbols. Stylized Greek text should be encoded using the normal Greek letters, with markup and formatting to indicate text style.


== See also ==
G, g - Ge (Cyrillic)
G, g - Latin


== References ==