Why the Sky is Blue: The Role of Ozone

Abstract

The only planets in our solar system having distinct ozone layers in their atmospheres are the earth and Mars, both of which have a characteristic blue sky. The earth's sky appears deeper blue after heavy rains eliminate the majority of the dust and various amounts of gases; this finding contradicts the theory that Rayleigh's scattering is the cause of the sky's blue colour. Additionally, we argue in this work that Rayleigh scattering should make the sky closer to the earth appear deeper blue and the sky overhead lighter because at least 50% of the earth's atmospheric molecules are held near to the surface of the earth; however, the opposite is true. In comparison, the true splitting of the rising and setting sun's rays causes the light and sky to turn orange-red, but in this situation, the clouds and objects in the rays' path also turn yellow-orange, as expected. The absence of blue sky in other planets' and our moon's skies, despite having differing mixtures of gases but no clearly delineated ozone layer, and the presence of black "sky" away from the lower parts of the earth's atmosphere beyond the stratosphere, and especially the appearance of a sharp demarcation about the lower part of the stratosphere where the blue stops and black sky appears, all argue in favour of ozone as the cause of the blue colour of sky. In this paper, we propose that the proper colour of the sky is dark blue, as seen in pristine areas and in photographs of the earth taken from space, but that the sky over populated areas and other dusty areas becomes lighter blue; the almost-white colour of the sky at the horizon is caused by the concentration of dust in the atmosphere closest to the ground.