# The Luminosity of two stars with same brightness but at different PC away

Stars A and B are both equally bright as seen from Earth, but A is 120 pc away while B is 24 pc away. Which star has the greater luminosity? How many times brighter is it?

The absolute luminosity of A is bigger than B. Like two lamps. $$\frac{120}{24}=5,$$ so A is five times farther B, but as the luminosity decays with the square of the distance, then A is $$5^{2}=25$$ times more luminous.