colour index

noun

astronomy the difference between the apparent magnitude of a star measured in one standard waveband and in a longer standard waveband, indicating its colour and temperature
geology the sum of the dark or coloured minerals of a rock, expressed as a percentage of the total minerals
chem physics a systematic arrangement of colours according to their hue, saturation, and brightness

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Instead of s there may also be used another expression for the colour, called the colour-index.

The difference between the photographic and the visual magnitudes is called the colour-index (c).

From each catalogue of visual magnitudes of the stars we may obtain their photographic magnitude through adding the colour-index.

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