[SQM] a "ground albedo influence" night

Constance Walker cwalker at noao.edu
Sun Dec 20 16:27:26 UTC 2009

Jan, Fabio,

Would you like to make this into a global project (in snowy areas) in  
which students can participate?


On Dec 20, 2009, at 9:16 AM, Jan Hollan wrote:

> Dear friends,
> just a reminder: a bright night with almost all landscape covered with
> cold white snow (here in Brno, just very concentrated salt water could
> thaw it recently) is an ideal opportunity to get the important number:
>            what amount of sky luminance is due
>          to the light disperesed from the ground
> This differs within towns and far from them, of course. But even  
> within
> towns, the amount of sky luminance due to direct emissions from
> luminaires is, fwith no snow, larger, unless the lighting is fully
> shielded.
> Comparison of snowless and snow-rich winter measurements (with the  
> same
> zenith extinction, if possible, or under a known one at least) is  
> our main
> tool in this respect. It can overweight any (wrong) models offered by
> polluters.
> Fabio and I have written about it several times already, but there  
> are not
> many data like that yet. We had a week with snow here in Brno  
> already, but
> this night is the first clear-sky one.
> So, don't miss the opportunity, if it will appear -- tonight or any  
> other
> night this winter.
> best,
>  jenik
> PS. sorry for not responding to darksky issues at all, I'm  
> overwhelmed by
> working on the climate enlightment these months.
> _______________________________________________
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> sqm at unihedron.com
> http://unihedron.com/cgi-bin/mailman/listinfo/sqm

Constance E. Walker, Ph.D.
chair, IYA2009 Dark Skies Awareness Cornerstone Project
director, GLOBE at Night campaign
associate scientist & senior science education specialist

National Optical Astronomy Observatory
950 N. Cherry Avenue
Tucson, AZ 85719 USA
cwalker at noao.edu

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