polarization pattern: light scattered in a blue sky forms a pattern of partially polarized ultraviolet light. this depends on the position of the sun, and is invisible to human eyes. each lens unit of a compound eye has a uv receptor, and a uv filter oriented differently in each of these units, so a bee is able to detect this polarization pattern. a small piece of blue sky is enough for a bee to recognize the pattern changes occurring over the course of a day. this provides not only directional but also information on the time of day.