Rainbow

A rainbow is an optical and meteorological phenomenon that causes a nearly continuous spectrum of light to appear in the sky when the sun shines onto falling rain. It is a multicoloured arc with red on the outside and violet on the inside. The full sequence of colours is most commonly cited as red, orange, yellow, green, blue, indigo, and violet, though it is important to note that this is an inconsistent list; all primary and secondary colors are present in some form, but only one tertiary. It is commonly thought that indigo was included due to the different religious connotations of the numbers six and seven at the time of Isaac Newton's work on light, despite its lack of scientific significance and the poor ability of humans to distinguish colors in the blue portion of the visual spectrum.

Remembering the sequence of colours

A traditional way of recalling each of the seven colours of the rainbow in sequence is by using the mnemonic "Richard Of York Gave Battle In Vain", where the first letter of each word corresponds to the first letter of each colour. The mnemonic alludes to the defeat of Richard III by Henry Tudor at the Battle of Bosworth Field.

Related Topics:
Mnemonic - Richard III - Henry Tudor - Battle of Bosworth Field

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Another, less obvious, though more common way is the use of the meaningless name Roy G. Biv. This method is purely phonetic. A drawback to both of these methods is that they include the colour of indigo between blue and violet, though most modern rainbow definitions do not include that as a distinct colour.

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Since rainbows are composed of a nearly continuous spectrum, different people, most notably across different cultures, identify different numbers of colours in rainbows.

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