There is one more complimentary answer, which is that the night sky is not as dark as it seems, but our eyes cannot see all the wavelengths of light that populate the night sky.<p>If we could see deep into the infrared, we might see more faraway stars and galaxies, whose light has been red-shifted by the expansion of space.<p>If we could see wavelengths in the single cm range, we might perceive a dim uniform glow in the night sky: the cosmic background radiation.<p>If we could see radio waves we might see all sorts of light sources in the night sky.