A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines onto droplets of moisture in the Earth’s atmosphere. They take the form of a multicoloured arc, with red on the outer part of the arch and violet on the inner section of the arch.
A rainbow spans a continuous spectrum of colours. Traditionally, however, the sequence is quantised. The most commonly cited and remembered sequence, in English, is Newton’s sevenfold red, orange, yellow, green, blue, indigo and violet. “Roy G. Biv” and “Richard of York Gave/Gained Battle in Vain” are popular mnemonics. Another one is “Read Out Your Green Book In Verse”.
Rainbows can be caused by other forms of water than rain, including mist, spray, and dew.
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