The Blue Sun of September 1950

Two causes for a coloured sun are discussed, namely refraction and absorption. The importance of integrating the refraction effects arising from different parts of the sun’s disk as light sources is emphasized. It is shown that by such integration of ring phenomena around the sun, many observed peculiarities may be explained. Important conditions for that some types of coloured suns shall arise are homogeneity of the particles of the scattering medium, and also that the particles shall be large enough to give rise to rings of sufficiently small radius. Transfer of air masses at long distances but without a sideward mixture taking place is in favour of the creation of dust sheets of homogeneous character, as the vertical sedimentation has then time to come into action.