The letter ω (omega) is the 24th and last letter of the Greek alphabet. It was first introduced in the 7th 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 ith 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).