Abstract

It is known for about 15 years that the inner edge of refraction halos are strongly polarized¹⁾. This polarization is caused by the birefringence of ice crystals. This causes the halo to consist of two orthogonally polarized components, which are mutually shifted. In case of the 22° halo, this shift is 0.1°. This is five times larger than the resolving power of the human eye. Therefore, the shift of the halo (or the polarization of its inner edge) can be easily observed in Nature. This holds particularly for parhelia: seen through a polarizer, it shifts to and fro as the polarizer rotates.

© 1990 Optical Society of America