The threshold intensity for a human eye to sense the presence of light is 50 photons falling on the retina within a period of 0.1 s. Assume a star radiates with an output of 0.5 ×1026 W in the visible spectrum, with a peak of ?=550 nm. (This star would be similar to the Sun, which radiates with 2.0 ×1026 W). Estimate how far away the star can be away and still be visible to the unaided eye on a dark night. Assume the pupil of the observer's eye has a diameter of 1.0 cm. Give your answer in light years (do not insert a unit). Please show work.