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Wikipedia / Omega

Omega (, ; uppercase Ω, lowercase ω) is the twenty-fourth and last letter of the Greek alphabet. In the Greek numeric system/isopsephy (gematria), it has a value of 800. The name of the letter was originally ( ), but it was later changed to ( 'big o') in the Middle Ages to distinguish it from omicron , whose name means 'small o', as both letters had come to be pronounced . In modern Greek, its name has fused into ().

In phonetic terms, the Ancient Greek Ω represented a long open-mid back rounded vowel , in contrast to omicron, which represented the close-mid back rounded vowel , and the digraph , which represented the long close back rounded vowel . In modern Greek, both omega and omicron represent the mid back rounded vowel . The letter omega is transliterated into a Latin-script alphabet as or .

As the final letter in the Greek alphabet, omega is often used to denote the last, the end, or the ultimate limit of a set, in contrast to alpha, the first letter of the Greek alphabet, as in the phrase Alpha and Omega.

History

The letter Ω was not part of the early Greek alphabets in the 8th century BC. It was introduced in the late 7th century BC in the Ionian cities of Asia Minor to denote a long open-mid back rounded vowel . It is a variant of omicron (Ο), broken up at the side (), with the edges subsequently turned outward (, , , ). The Dorian city of Knidos as well as a few Aegean islands, namely Paros, Thasos and Melos, chose the exact opposite innovation, using a broken-up circle for the short and a closed circle for the long .

The name Ωμέγα is Byzantine; in Classical Greek, the letter was called ō () (pronounced /ɔ̂ː/), whereas the omicron was called ou () (pronounced /ôː/). The modern lowercase shape goes back to the uncial form , a form that developed during the 3rd century BC in ancient handwriting on papyrus, from a flattened-out form of the letter () that had its edges curved even further upward.

In addition to the Greek alphabet, Omega was also adopted into the early Cyrillic alphabet (see Cyrillic omega (Ѡ, ѡ)). A Raetic variant is conjectured to be at the origin or parallel evolution of the Elder Futhark ᛟ.

Omega was also adopted into the Latin alphabet, as the Latin omega, as a letter of the 1982 revision to the African reference alphabet, and is in sparse use.

The symbol Ω (uppercase letter)

The uppercase letter Ω is used as a symbol:

In chemistry:

  • For oxygen-18, a natural, stable isotope of oxygen.

  • For omega loop, a protein structural motif consisting of a loop of six or more amino acid residues in any sequence, a structure named for its resemblance to the Greek letter.

In physics:

  • For ohm – SI unit of electrical resistance. Unicode has a separate code point (HTML entity ohm;), but it is included only for backward compatibility, and the canonically equivalent code point (Omega;) is preferred. Also formerly also used upside down () to represent mho, the old name for the inverse of an ohm (now siemens with symbol S), the SI unit of electrical conductance.

  • In statistical mechanics, Ω refers to the multiplicity (number of microstates) in a system.

  • The solid angle or the rate of precession in a gyroscope.

  • In particle physics to represent the Omega baryons.

  • In astronomy (cosmology), Ω refers to the average density of the universe, also called the density parameter.

  • In astronomy (orbital mechanics), Ω refers to the longitude of the ascending node of an orbit.

In mathematics and computer science:

As part of a logo or trademark:

Other:

The symbol ω (lowercase letter)

The minuscule letter ω is used as a symbol:

Biology, biochemistry and chemistry:

Physics:

Computer science:

Mathematics:

Finance:

  • In finance, the elasticity of options

  • In analytical investment management, the tracking error of an investment manager

Other:

Unicode

References