color index: meaning, definition, pronunciation and examples
C1/C2Technical/Scientific
Quick answer
What does “color index” mean?
A numerical value expressing the color of an object, calculated as the difference in magnitudes (brightness) measured in two specific wavelength bands, used especially in astronomy to estimate temperature.
Audio
Pronunciation
Definition
Meaning and Definition
A numerical value expressing the color of an object, calculated as the difference in magnitudes (brightness) measured in two specific wavelength bands, used especially in astronomy to estimate temperature.
In broader contexts, any systematic scale or numerical identifier used to specify a color precisely, such as in printing, painting, or digital design. In economics, sometimes used informally for indices tracking commodity prices (e.g., color pigments).
Dialectal Variation
British vs American Usage
Differences
Spelling: 'colour index' (UK) vs. 'color index' (US). The term is equally common in scientific writing in both varieties.
Connotations
Identical technical meaning. No difference in connotation.
Frequency
Slightly more frequent in American English due to the dominance of US institutions in astronomical research, but the difference is negligible in academic texts.
Grammar
How to Use “color index” in a Sentence
The color index of [celestial object] is [value]to calculate/measure/determine the color index[Object] has a color index of [value]Vocabulary
Collocations
Usage
Meaning in Context
Business
Virtually unused, except in very niche industries like art supplies or printing ink manufacturing.
Academic
Primarily used in astronomy, astrophysics, and photometry research papers and textbooks.
Everyday
Extremely rare. Would only be used by amateur astronomers or in very specific technical hobbies.
Technical
The primary domain. Used in observational astronomy, telescope data analysis, and stellar classification.
Vocabulary
Synonyms of “color index”
Strong
Neutral
Weak
Vocabulary
Antonyms of “color index”
Watch out
Common Mistakes When Using “color index”
- Using 'color index' to refer to a Pantone number or RAL code without clear technical context. In strict usage, it's an astronomical term.
- Saying 'the color index is blue' instead of 'the color index is low (negative), indicating a blue star.'
- Treating it as a countable noun without an article: 'We measured color index' instead of 'We measured *the* color index' or 'We measured color indices.'
FAQ
Frequently Asked Questions
No. In technical usage, a 'color index' is a specific astrophysical measurement. Systems like hex codes, Pantone, or RAL are color *models* or *catalogs* for design and industry, not 'indices' in the scientific sense.
Yes, absolutely. For very hot, blue stars (like O-type stars), the magnitude in the blue filter is brighter (a smaller number) than in the visual filter, making the difference (B-V) negative.
The B (blue) and V (visual, centered on green-yellow) filters correspond to wavelengths where the human eye and many standard detectors are sensitive, and they effectively bracket the peak of a star's blackbody radiation, providing a sensitive temperature gauge.
Yes. 'U-B' (Ultraviolet minus Blue) is another standard color index. Different combinations of filters (U-B, B-V, V-R, etc.) probe different parts of a star's spectrum and are used to study various properties, including temperature and chemical composition.
A numerical value expressing the color of an object, calculated as the difference in magnitudes (brightness) measured in two specific wavelength bands, used especially in astronomy to estimate temperature.
Color index is usually technical/scientific in register.
Color index: in British English it is pronounced /ˈkʌlə ˈɪndɛks/, and in American English it is pronounced /ˈkʌlɚ ˈɪndɛks/. Tap the audio buttons above to hear it.
Learning
Memory Aids
Mnemonic
Think 'Color Index = Cosmic Indicator'. Just as an index in a book points to information, a star's color index points to its temperature (blue = hot, red = cool).
Conceptual Metaphor
A color index is a **stellar thermometer** or a **cosmic barcode** that encodes physical properties through simple numbers.
Practice
Quiz
What does a more negative B-V color index typically indicate about a star?