Calculation of the Polarization of a Sunlit Sky Composed of Pure Air Molecules

In this paper, an exact solution of the complex and difficult problem of the illumination of the atmosphere and ground by sunlight is discussed in the light of numerical results. Full account is taken of the polarization of radiation by scattering, and allowance is made for the optical anisotropy of the molecules of air. The atmosphere is supposed to be uniformly mixed and stratified in parallel planes.Predictions based on that solution are put to the test of observation. The neutral points are found to occur in the manner they are observed. The incomplete polarization of the light scattered at right angles to the incident solar beam is fully accounted for, assuming a depolarization factor equal to 0.0415 for the molecules of air. Solutions taking no consideration of that factor fail to account for the observed depolarization. The observations of Tichanowsky on the degree of polarization of zenith scattered light are also accounted for when the optical anisotropy of the molecules of air is taken into consideration.