There’s at least one thing in

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Nick James

There’s at least one thing in the descriptive Bortle list that I think sounds very wrong. Bortle 7 (the suburban/urban transition) is probably where I am in Chelmsford most nights but the description says “when it is full moon in a dark location the sky appears like this, but with the difference that the sky appears blue”. This must be rubbish surely? My image processing pipeline produces an estimate of the sky brightness for each image. On a good, dark, transparent night from here I get around 19.2 mag/arcsec^2 near the zenith. A couple of nights ago at full moon I got 16.5 mag/arcsec^2 at the zenith. That sky brightness would be the same even in a normally very dark place since it dominates scattered artificial light so to suggest that my “dark” skies are the same as full moon skies in the countryside seems a bit daft.