Description: The color index of a star or other celestial object is the difference between its brightness or magnitude, as measured in two different color or wavelength bands, such as yellow and blue. The most common color index is (B-V), where B is the magnitude as measured through a standard blue filter, and V is the magnitude as measured through a standard yellow filter. The B filter is similar to the color sensitivity of old-fashioned photographic plates, and the V filter is similar to the color sensitivity of the human eye. For stars, (B-V) is a measure of the temperature, though it can also be affected by the reddening effect of dust between the stars.

Related Terms:

• Color
• Reddening

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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