Mu (letter)

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
Digamma	San
Qoppa	Sampi
Ϛ ϛ Stigma	Sho

For other uses, see Mu.

Mu, pronounced "Mew", (upper case Μ, lower case μ) is the 12th letter of the Greek alphabet. In the system of Greek numerals it has a value of 40.

The word mu is written μῦ in traditional Greek polytonic orthography. In Modern Greek it is sometimes written μι (mi).

Mu was derived from the Egyptian hieroglyphic symbol for water () which had been simplified by the Phoenicians and named after their word for water, mem. The sound "M" is still connected with the sea in many languages, as in Hebrew ma'im, Latin mare, Portuguese mar, German Meer, and French mer.

The letter mu appears in conjunction with alpha and omega to signify the "beginning, middle (meson) and end," a phrase found in an Orphic verse describing Zeus, and later adopted to describe both Jehovah and Jesus.

In Aeschylus' Eumenides, the repeated moaning of the letter mu is the sound made by the sleeping Furies as the ghost of Clytemnestra begins to invoke them. It again appears as an ominous mantra in a 10th century Coptic papyrus, containing a Christian curse against perjurers that invokes the angel Temeluchos:

I adjure you by the seven perfect letters, ΜΜΜΜΜΜΜ. You must appear to him, you must appear to him. I adjure you by the seven angels around the throne of the father.

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

• In mathematics:
  • the Möbius function in number theory
  • the population mean or expected value in probability and statistics
  • a measure in measure theory
• In measurement:
  • the SI prefix micro-, which represents one millionth, or 10⁻⁶. Unicode actually encodes the micro sign separately from the greek letter though they look identical in most fonts.
  • the micron, an old unit which corresponds to the micrometre (which is now denoted "µm")
• In classical physics and engineering:
  • the coefficient of friction
  • reduced mass in the two-body problem
  • permeability in electromagnetism
• In particle physics:
  • the elementary particle called the muon

Rarely, the letter μ may be used to distinguish one item represented by "m" from another (but a better option might be to use "m", "m", "m", etc.).

Letters that arose from the Greek Μ include the Latin M and Cyrillic М.

In 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 is considered a distinct character by unicode for historical reasons and is found at U+00B5 as well as position B5_HEX in ISO 8859-1, 3, 8, 9, 13 and 15. 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.

A BitTorrent client has been named µTorrent because of its tiny size.

References

• Moralia, by Plutarch
• Ancient Christian Magic, by M. Meyer and R. Smith (ed.), Princeton University Press, ISBN 0691004587

The content of this page is retrieved from http://en.wikipedia.org/wiki/Mu_%28letter%29 under GFDL