The SQM measurements without lens gave 21.31 mag after the astronomic night began, but one moment it was 21.38 mag -- maybe a result of natural skyglow temporary minimum. With a lens, the readings were 0.50 mag larger, meaning one square second slightly SW from the zenith (to avoid Brno skyglow) being about 21.56 mag.
When we returned at home, I got 19.21 with lens at our garden, Lipova 19, Brno, meaning the zenith sky being about 18.96 mag, for a square second. This is 2.6 mag worse than in Troskotovice -- ten times larger luminance. But this is not the most interesting ratio. Ratios of anthropogenic contributions to the luminance are what should we bother about. One square second of natural zenith sky should have 21.80 mag to 22.00 mag at these years, outside of pronounced solar activity. The natural luminances are therefore 0.17 mcd/m2 to 0.20 mcd/m2. The Troskotovice sky had perhaps 0.26 mcd/m2 near zenith. So the man-made part is 0.09 mcd/m2 at most (and maybe 0.06 mcd/m2 only). This is still one third to one half of the natural amout, quite a lot. But the Brno zenith luminance is about 2.8 mcd/m2, and the anthropogenic component is 2.6 mcd/m2, about fifteen times the natural component. The man-made component, one of the quantities which can characterize light pollution, is thirty to fourty times less above Troskotovice than above Brno residential Masaryk quarter.
jenik hollan