[SQM] maps for Globe at Night

Jan Hollan jhollan at amper.ped.muni.cz
Sun Feb 28 22:58:05 UTC 2010

Dear Connie,

your Feb 20 letter to the SQM list was nice, not repeating the 
embarrassing advice to investigate the artificial contribution to the sky 
luminance during nautical twilight (one hour after sunset...), advising us 
to observe 8 p.m. or later. But the globeatnight site is no better than 
2009 unfortunately. Even the maps are the same, VERY bad ones over 5 mag.

I'm sorry I did not offer my help for this year campaign explicitly, being 
too busy and assuming somehow that my letters from March 2009 will do.

Would it be still possible to offer good maps instead, including 
Sirius, computed for some defined zenith extinction etc.?
I'd make them tomorrow, for a set of latitudes and times. 
Perhaps for ZE = 30 cmag (rather than for 20 cmag), as
just with Sirius included in each map.

cheers, jenik

---------- Forwarded message ----------
Date: Sun, 15 Mar 2009 21:04:54 -0700
From: Constance Walker <cwalker at noao.edu>
To: Jan Hollan <jhollan at amper.ped.muni.cz>
Cc: ida at amper.ped.muni.cz, Jan Kondziolka <KondziolkaJan at seznam.cz>,
     "[ISO-8859-1] Petr Horálek" <Horalek.Petr at seznam.cz>
Subject: Re: maps for Globe at Night


Your maps are VERY well done. And I agree with you about being careful
in specifying when to start observing.

At this point I work with the GLOBE project at UCAR on GLOBE at Night.
They are in charge of putting things onto the GLOBE at Night website.
They are saturated with work from other projects and at this point
they would be reluctant to make any changes to the webpages.

However, next year, I will have control over the webpages and can make
the kinds of changes you are suggesting. I will be putting together a
working group for the GLOBE at Night project and I would like it if
you could be on that group and help me make these kinds of changes.
Would that be alright?


On Mar 15, 2009, at 1:28 PM, Jan Hollan wrote:

> Connie, an improved set of four maps is
> http://amper.ped.muni.cz/jenik/astro/maps/GaN-Orion/45-75.pdf
> including an explanatory caption replacing the maps for even poorer
> skies - for EU mid latitudes or northern US ones. I've included
> Sirius somehow, as it is the only way to find Betelgeuse and Rigel
> reliably under 1 mag limit skies, when no Orion asterism is
> apparent. I believe it's ready to be published at GaN pages -- even
> if OK just for our middle latitudes. Alternatively, those bad noisy
> black maps for 5 to 7 mag on GaN pages might be hyperlinked to my
> pdfs.
> I was a bit angry that Petr recommended observing just an hour after
> sunset -- as it is a nonsense to investigate man-made skyglow during
> nautical twilight. But he took it from the "For Parents" page of
> GaN... One hour+ may be OK for equator, but not for mid latitudes!
> At 50 degrees, twilight (astronomical) ends 2 h after sunset these
> days. In London or New York, no change at all between 1 h and 2 h
> after sunset may be apparent, but a tremendous change continues in
> nature: the glory of the Heavens becomes revealed.
> A good advice might be to observe several times, starting 1 h after
> sunset (when Evening Star with its narrow crescent is still visible
> in our latitude, through its conjunction with the Sun on Mar 27) and
> finishing when the astronomical night begins. It lasts whole two
> another hours at Polar Circle... a good way to become fully adapted
> to night light levels.
> cheers,
> jenik

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