The Sun appears red when it is on the horizon due to scattering of light by molecules in the atmosphere (Fig. 25.41). The Sun does not appear as reddish in color when it is overhead because the thickness of the atmosphere through which sunlight must travel is smaller when the Sun is overhead than when it is near the horizon.
(a) Take the approximate thickness of the atmosphere to be 2 x 10⁵ m. What distance through the atmosphere must light travel to reach us when the Sun is at the horizon?
(b) Estimate the ratio of the distances that sunlight travels through the atmosphere in these two cases.