ω | omega

The letter ω (omega) is the 24^th and last letter of the Greek alphabet. It was first introduced in the 7^th century BC as a broken-up at the side variant of omicron. This letter was adopted into the early Cyrillic alphabet as Cyrillic omega (Ѡ, ѡ), with both upper- and lower-case letters similar to the Greek lower-case ω.

The lower-case ω has quite a few uses in maths, engineering and sciences, for example

• in astronomy: the argument of periapsis of an orbit
• in biochemistry: to denote the carbon atom furthest from the carboxyl group of a fatty acid. “ω−i fatty acid” is an unsaturated fatty acid with a double bond (C=C) at the i^th carbon atom from the end, as in ω−3 fatty acids, ω−7 fatty acids, etc.
• in electrical circuits: natural frequency ω₀
• in molecular biology: the smallest subunit of RNA polymerase
• in number theory: ω(n), the number of distinct prime factors of n
• in particle physics: omega meson
• in physics: angular frequency and angular velocity
• in protein chemistry: one of three dihedral angles (φ, ψ and ω) in a protein chain. ω is usually restricted to be 180° (trans) or 0° (cis).

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