Top images show the Arctic sky on day of (a) fog, (b) sun, and (c) clouds. Images d-f show patterns of the degree of linear polarization. The faint gray line delineates between the sun and the anti-sun. The direction of polarization is perpendicular to the plane of scattering determined by the sun, the observer and the celestial point observed. Readings from two different points in the sky allow one to draw circles passing through these points perpendicularly to the direction of sky light polarization, and the circles intersect at the sun and anti-sun. The angle of polarization can be seen in images g-i. Credit: G. Horvath/Proceedings of the Royal Society A