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color index

noun Astronomy.
  1. the difference between the apparent photographic magnitude and the apparent visual magnitude of a star.
  2. the difference between the magnitudes of a star in any two spectral regions.
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Origin of color index

First recorded in 1920–25
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for color index

Historical Examples

  • The color-index is thus almost invariably low, the average being about 0.5.

    A Manual of Clinical Diagnosis

    James Campbell Todd