Re: [SQM] Need some measurement guidelines

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

> 1. Location (lat & long)
> 2. time in UT
> 3. Date
> 4.Weather conditions (cloud, temp, etc)

These should do (some other ones can be easily computed from them). Just
the weather conditions are to be defined in more detail. Cloud kind and
cloud cover proportion are of interest. In fact, two situations are most
interesting, clear and overcast. Cloud height and transparency, i.e.
cloud type (Ns, St or Sc, Ac or As, Ci or Cs) is relevant.

For clear sky, the only important weather parameter is air transparency.
Horizontal visibility is a possible measure, another one is extinction of
direct light in zenith. I wrote already to this forum about some ways how
to measure it by SQM, using Sun or Moon, mentioning the first one of these
two postings:

Dark Sky Meter for research
        URL: http://amper.ped.muni.cz/jenik/letters/public/msg00188.html

Re: sky brightness measures
        URL: http://amper.ped.muni.cz/jenik/letters/public/msg00191.html

Even a visual method could be satisfactory: try to find two stars which
appear equally bright, but are in very different angular heights. One at
or below 15 degrees, the other above 50 degrees. Just note their
designations. Using e.g. my star_pos programme (I could make it available
online, if needed), the zenith extinction can be computed from such simple
observation.

jenik