Even the smallest amount of the Sun’s disk is bright enough to hurt your eyes if you stare at it. But the Sun is bright because it’s so close to us. If you stand farther away from a light, it looks dimmer. Astronomers know the phenomenon as the difference between absolute magnitude and apparent magnitude. The former is a measure of intrinsic brightness, and the latter is how bright we perceive something to be from Earth.
Mathematically, it’s the distinction between luminosity, which is how much energy an object produces per unit time, and flux, which is how much of that reaches us per unit area. If you have two objects with the same luminosity L, the one with a smaller distance D will have a higher observed brightness F. Alternately, if two objects have the same brightness, the one at greater distance is more luminous:
