Prof. Mark Dennis: Blue sky research: the polarization of sky light
Source: Monday physics colloquium
Blue sky research: the polarization of sky light
Prof. Mark Dennis: H. H. Wills Physics Laboratory, University of Bristol, UK
A little-known fact is that the polarization of the natural blue sky of daylight contains polarization singularities (polarization vortices), where the degree of polarization vanishes. They were discovered by observation in the 1800s, explained approximately by Rayleigh scattering, and their detailed prediction was one of the successes of Chandrasekhar's radiative transfer theory in the 1950s. Here, I will discuss their topological properties: as simple examples of polarization singularities, they organize the pattern of polarization in skylight. A simple mathematical ansatz is consistent both with observations and Chandrasekhar's theory, and justified in terms of an analytic approximation of radiative transfer. The ansatz is closely related to polarization patterns in crystal optics, and is related to the polarization of the cosmic microwave background radiation.