Fig. 4. Patterns of the degree (d) and angle (; measured from the local mirror meridian) of linear polarization of reflected skylight, and the area detected polarotactically as water versus the solar elevation (_s) for a perfectly black glass (with an index of refraction of 1.5) reflector - which absorbs all penetrating light - calculated for incident single-scattered Rayleigh skylight with the use of the Fresnel formulae. The Brewster angle (56° from the nadir for glass with an index of refraction of 1.5) is represented by a circle within the circular patterns.