The apparent brightness of a star, or other celestial body, expressed in terms of the system of stellar magnitudes. The system had its origins in the classification by brightness of some thousand stars carried out by Hipparchus in the second century B.C., and was standardized by Pogson in 1850. The mean of the twenty brightest stars in the sky is defined to be magnitude 1 (or first magnitude), while the faintest stars normally visible to the unaided eye on a clear dark night are said to be of magnitude 6 (or sixth magnitude); stars which are between these extremes take intermediate values of magnitude. Thus, the brighter the star, the lower its magnitude.
