Articles in astronomy give the colors of stars as a number, called color index.
How do you turn this number into a real color?
The color index (CI) is usually
CI = mB - mV
where mB is the blue color magnitude of the star and mV the visible color magnitude. As the magnitude increases with decreasing brightness a star with a smaller index will be more blue and a star with a larger index more red. The following table should help you do the translation:
| Color Index | Spectral Class | Color | |
|---|---|---|---|
| -0.33 | O5 | Blue | |
| -0.17 | B5 | Blue-white | |
| 0.15 | A5 | White with bluish tinge | |
| 0.44 | F5 | Yellow-White | |
| 0.68 | G5 | Yellow | |
| 1.15 | K5 | Orange | |
| 1.64 | M5 | Red |
This table is only valid for the B-V (or Blue minus Visible) color index. Often astronomers use other color indexes such as U-B (Ultraviolet minus Blue) or H-K (H-band minus K-band) indexes.
This page updated on June 27, 2015