solid angle, Ω, ω 

https://doi.org/10.1351/goldbook.S05732
Of a cone, the ratio of the area cut out on a spherical surface (with its centre at the apex of that cone) to the square of the radius of the sphere. It is a quantity of dimension one (dimensionless quantity) with unit steradian (sr=1).
Sources:
Green Book, 2nd ed., p. 11 [Terms] [Book]
PAC, 1996, 68, 957. (Glossary of terms in quantities and units in Clinical Chemistry (IUPAC-IFCC Recommendations 1996)) on page 992 [Terms] [Paper]
Citation: 'solid angle' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.S05732 RIS BibTex EndNote
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Last revised: February 24, 2014