Μ

My in a capital letter Etymologicum Magnum (1499).

My (according to the RAE since 2001) or my (in capital letters Μ, lowercase μ; call in ancient Greek μῦ mû /mŷː/, in Modern Greek μι/μυ mi/my /mi/) is the twelfth letter of the Greek alphabet. Called mu, in an extraordinary way, in the scientific field.^{[citation required]} Its phoneme corresponds to that of the Spanish em.

In the Greek numeral system it has a value of 40 (Μʹ).

History

Epigraphic variants

In archaic epigraphic sources the following variants appear:

Use

The lowercase letter μ is used as a symbol in many different disciplines. Its capital form, on the other hand, is rarely used, since it is indistinguishable from the Latin letter M or the Cyrillic М. Among its uses we can highlight:

• Measurement units
  • The micro prefix, micro character or micro symbol of the SI, which represents a millionth, or 10th^-6 part of another unit. Unicode assigns for this use a separate symbol, but it is usually indistinguishable from the assigned to the Greek letter; however, it is a different character. The HTML representation of the micro symbol is µ.
  • The micron, an old unit corresponding to the micrometer (μm).

• Physics
  • In dynamics, the friction coefficient
  • In electromagnetism, magnetic permeability
  • In fluid mechanics, dynamic viscosity.
  • In particle physics, the elemental particle muon.
  • The mass reduced in the problem of two bodies.
  • In astrophysics, the standard gravitational parameter of astronomical objects.
  • In radiophysics, the linear attenuation coefficient.

• Thermodynamics
  • The chemical potential of a system.

• Maths
  • In Number Theory, the Function of Möbius
  • In probability and statistics, the average or expected value of a distribution.
  • In theory of measure, a measurement.

• Medicine
  • In virology, in the context of the COVID-19 pandemic, the World Health Organization (WHO) designated Mu as an enhanced monitoring variant, a mutation of the SARS-CoV-2, virus that produces COVID-19 disease, found in January 2021 in Colombia.

It is rarely used to distinguish between an object represented by the letter m and another of the same nature.

Unicode

• Greek and Coptic

• Maths