Published in Appl. Opt. 47, H167-170, doi:10.1364/AO.47.00H167 in 2008
G. P. Können, M. Bodó and Á. Kiricsi
An isolated colourless spot of 1° diameter located at the antisolar point was observed from a plane on the clouds beneath it. The spot can be explained by light scattering on randomly oriented ice crystals, via light paths similar to those responsible for the subparhelic circle. Its peculiar polarization properties potentially enable its detecting in cases where the spot is embedded in a glory.