Mu (letter)

Greek alphabet
Αα	Alpha	Νν	Nu
Ββ	Beta	Ξξ	Xi
Γγ	Gamma	Οο	Omicron
Δδ	Delta	Ππ	Pi
Εε	Epsilon	Ρρ	Rho
Ζζ	Zeta	Σσς	Sigma
Ηη	Eta	Ττ	Tau
Θθ	Theta	Υυ	Upsilon
Ιι	Iota	Φφ	Phi
Κκ	Kappa	Χχ	Chi
Λλ	Lambda	Ψψ	Psi
Μμ	Mu	Ωω	Omega
Other characters
	Digamma		Stigma
	Heta		San
	Qoppa		Sampi
Greek diacritics

Mu (uppercase Μ, lowercase μ; Ancient Greek μῦ [myː]), Modern Greek Μι or Μυ [mi]) is the 12th letter of the Greek alphabet. In the system of Greek numerals it has a value of 40. Mu was derived from the Egyptian hieroglyphic symbol for water (𓈖) which had been simplified by the Phoenicians and named after their word for water, to become 𐤌. Letters that arose from Mu include the Roman M and the Cyrillic letter М. Sounds like 'mee'.

Names

Ancient Greek

The name of the letter is written μῦ in traditional Greek polytonic orthography. In Modern Greek the ancient version is sometimes written μύ.

Modern Greek

In Modern Greek, the name of the letter is spelled μι and is pronounced [mi].

Academia

The lower-case letter mu is used as a special symbol in many academic fields. The upper case Mu is not generally used in this way because it is normally indistinguishable from the Latin M.

• In mathematics:
  • the µ-roots of a complex number z = a + bi
  • the Möbius function in number theory
  • the integrating factor in ordinary differential equations
  • the population mean or expected value in probability and statistics
  • a measure in measure theory
  • minimalization in computability theory and Recursion theory
  • the learning rate as used in artificial neural networks
• In measurement:
  • the SI prefix micro-, which represents one millionth, or 10⁻⁶.
  • the micron, an old unit which corresponds to the micrometre (which is now denoted "µm")
• In classical physics and engineering:
  • the coefficient of friction (also used in aviation as braking coefficient)
  • reduced mass in the two-body problem
  • linear density or mass per unit length in strings and other one-dimensional objects.
  • permeability in electromagnetism
  • the magnetic dipole moment of a current-carrying coil
  • dynamic viscosity in fluid mechanics
  • the amplification factor of a triode vacuum tube
  • the electrical mobility of a charged particle
  • the airspeed relative to rotor tip speed, in rotorcraft
• In inorganic chemistry:
  • the prefix given in IUPAC nomenclature for a bridging ligand.
• In particle physics:
  • the elementary particles called the muon and antimuon
• In Pharmacology:
  • an important opiate receptor
• In thermodynamics:
  • the chemical potential of a system or component of a system.
• In orbital mechanics:
  • Standard gravitational parameter of a celestial body, the product of the gravitational constant G and the mass M.
• In music:
  • Mu major chord

Computing

In Unicode, the upper and lower case mu are encoded at U+039C and U+03BC respectively. In ISO 8859-7 they are encoded at CC_HEX and EC_HEX. The micro sign or micron is considered a distinct character from the Greek alphabet letter by Unicode for historical reasons (although it is a homoglyph) and is found at U+00B5 as well as position B5_HEX in ISO 8859-1, 3, 8, 9, 13 and 15, and thus in the corresponding Windows code pages Windows-1252 etc. ISO-8859-5 also has a character that looks somewhat like lower case mu at E6_HEX but this is actually supposed to be the Cyrillic small letter tse (ц). In HTML code, the μ symbol is represented by "μ", "μ" and the entity "μ".

When Alt-0181 or the DOS legacy Alt+230 is typed into an editable field using the numeric keypad in Microsoft Windows, the µ symbol appears. Also pressing AltGr + M results in a µ on some keyboard layouts. In HTML code, the µ symbol is represented by "µ", "µ" and the entity "µ".

Because µ is the abbreviation for the metric system prefix micro-, the symbol is used in many word plays about the field of micro-computing. For example, the symbol is used in the name and logo of the popular bittorrent client, µTorrent. Also, the microcontrollers are commonly represented in schematics as µC. It is sometimes simply substituted with a u, the most similar-looking ASCII glyph, eg. uTorrent.