Why are some stars brighter than others?

Stars vary in brightness because of their intrinsic luminosity and because of their distance from us. More massive stars are larger and hotter and thus brighter than less massive stars. For example, Deneb, the brightest star in the constellation Cygnus, is about 20 times more massive than the Sun and has a luminosity 196,000 times that of the Sun. Proxima Centauri, the nearest star to the Sun, is about seven times smaller than the Sun...