There are dramatic and physiologically relevant changes in both skylight color and intensity during evening twilight as the pathlength of direct sunlight through the atmosphere increases, ozone increasingly absorbs long wavelengths and skylight becomes increasingly blue shifted. The moon is above the horizon at sunset during the waxing phase of the lunar cycle, on the horizon at sunset on the n...

We propose a fast approach for photo-realistic rendering of trees under various kinds of daylight, which is particularly useful for the environmental assessment of landscapes. In our approach the 3D tree models are transformed to a quasi-3D tree database registering geometrical and shading information of tree surfaces, i.e. their normal vectors, relative depth, and shadowing of direct sunlight ...

Many insects exploit skylight polarization for visual compass orientation or course control. As found in crickets, the peripheral visual system (optic lobe) contains three types of polarization-sensitive neurons (POL neurons), which are tuned to different (about 60° diverging) e-vector orientations. Thus, each e-vector orientation elicits a specific combination of activities among the POL neuro...

Field observations reveal that night-migrating passerines sometimes fly during early morning hours. Functional consideration of daytime flights have overshadowed proximate questions regarding the sensory basis of daytime orientation. I conducted a series of early morning cage-orientation experiments in spring with four species of migrating warblers (Parulinae) on the north coast of the Gulf of ...