The stars Procyon and Betelgeuse both appear equally bright to Earthbound viewers. Yet Betelgeuse emits 5000 times more light than Procyon. Why do they appear to be equally bright?

Question

Quizplus · Accepted Answer

The apparent brightness of a star depends not only on its intrinsic luminosity (how much energy it emits) but also on its distance from the observer. Betelgeuse is much farther away from Earth than Procyon, so even though it emits much more light, it appears equally bright to us because that light is spread out over a larger distance.

The Stars Procyon and Betelgeuse Both Appear Equally Bright to Earthbound