UBV three-color star system of UBV system

The UBV system is also called the Johnson system, which is a classification only used in photometric measurements of stars. According to the luminosity of stars at three different wavelengths: ultraviolet (U), blue (B) and visual (V), stars are classified by UBV photometry. This classification was proposed by American astronomers Harold Lester Johnson and William Wilson Morgan in 1953. The blue light at the end of the visible light range was originally chosen because it was Colors that can also be observed through photography.

In practical applications, astronomers will compare the luminosity differences between U, B, and V colors, called the color index, to compare the differences between different stars. The UBV star catalog usually gives V, (B-V) and (U-B), where V is the V magnitude; (B-V) and (U-B) represent the color index of the celestial body.