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Abstract

A term used to denote the well-known coloured arc sometimes seen against a sunlit background of falling water drops. Rainbows are typically seen when the Sun is low in the sky, and the observer is facing a raincloud on the horizon opposite the Sun (i.e. at the antisolar point). When more than one rainbow is visible (i.e. a double rainbow), the inner, brighter one is called the primary bow and the outer, fainter one the secondary bow. Primary rainbows are coloured blue to red outwards from the antisolar point, whereas the colours of secondary rainbows are reversed, i.e. red to blue outwards from the antisolar point. The relatively dark area in between the primary and secondary bows is called Alexander’s band or Alexander’s dark band, after the Greek philosopher Alexander of Aphrodisias (c. ad 200).