Color Index

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Color Index

(symbol C) 

Of a star, the numerical difference between the apparent photographic magnitude <math>m_pg</math> and the apparent photovisual magnitude m_pv or

C = m_pg - m_pv

The color index is zero for class A0 stars of magnitudes between 5.5 and 6.5; it is positive for red stars and negative for bluish stars. Various other color indices can be formed by using apparent magnitudes measured in other systems. Thus, the intrinsic color index is apparent photographic magnitude minus apparent ultraviolet magnitude.

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use