Figure 2
The two upper rows show the angular luminance distribution at LakeLab, Germany, for (a) the average over all azimuth angles, (b) the sky segment facing the north (blue area in Fig. 1) (c) the sky segment facing the south (blue area in Fig. 1) and (d) the sky segment facing the west (red area in Fig. 1). Each graph shows clear night (blue diamonds) and overcast night (black circles) data. Note the difference in scale between the two upper rows. The variability near zenith in the clear sky data originates from bright stars. The lower row shows cloud attenuation factors at LakeLab, Germany, for each investigated sky segment derived from the angular luminance distribution shown in (a–d) obtained by dividing the clear sky data by the cloudy sky data. Black squares represent the northern segment, diamonds the southern segment, crosses the average and circles the western segment.
