Re: Sky Quality Meter - Light Pollution Map Correlation

[Jan Hollan <jhollan@amper....muni.cz>]

Robert, it reads sound, if mcd be changed to ucd (I mean microcandela).
It's true that one microcandela per square metre is not much different
from one S10 unit (that one fifth difference is 0.2 mag, what can be
neglected mostly).

The measurements in little polluted areas don't depend on humidity
or air transparency, but rather on the aiglow produced in the height over
80 km, this is the variable component.

Considerably polluted sites far from the pollution sources are darker with
very turbid air (the pollution does not propagate to them}, the opposite
is true for sites close to the light sources.

An accurate assesment of the amount of pollution can be obtained any clear
night, when the readings are taken at two sites, at an almost natural site
and at the investigated site, if they are not more than some 50 km apart.
This is because of the natural airglow being produced so high in the
atmosphere, affecting both sites similarly.

To get a 0.1 mag accuracy (that's the difference between the 20 % and 30 %
limit) is not easy in reality. But using a reference almost non-polluted
site for simultaneous readings, it is achievable.

so much for now,
 jenik