The brightness of a star depends on its

The brightness of a star as observed from Earth (apparent brightness) is determined by three primary factors: its size (radius), its surface temperature, and its distance from the observer. According to the Stefan-Boltzmann Law, a star's intrinsic luminosity is directly proportional to its surface area (related to the square of its radius) and the fourth power of its absolute temperature. While luminosity represents the total power output, the brightness perceived on Earth follows the inverse square law, meaning it decreases as the square of the distance increases. Therefore, two stars with identical intrinsic luminosity will appear to have different brightnesses if they are at different distances. While mass influences a star's lifecycle and luminosity on the main sequence, it is not a direct parameter in the observational calculation of apparent brightness compared to the immediate physical variables of size, temperature, and distance.