What makes some stars brighter than others? Interestingly, there is a relationship between the color of a star, its temperature, and its brightness. The temperature of a star determines its surface color and luminosity (the star’s actual output of energy, which we see as how bright it appears). In general, cool stars such as Betelgeuse are reddish; medium temperature stars such as our Sun are yellow-orange; and hotter stars, such as Sirius and Rigel, are blue or blue-white). The hottest stars, logically, are also the brightest stars. However, the size of the star and its distance from the Earth play important roles in how bright the star appears.