[Chaos-l] Skywatching canceled

[Robert Nielsen]

John,

Nice article!   So how does one figure out how long each of the 
different "twilights" (civil, nautical, astronomical) last?   I found a 
web site that gives civil twilight times.  Is it roughly the same for 
our latitude?  I'm guessing not ... depending on the season.

Robert  (who should probably just ask Google ... although I'm enjoying 
this discussion on the listserve)

john.6.miller at gsk.com wrote:
>
> I have read that there is a natural luminescense or "airglow" that 
> arises from air molecules being excited by the sun during daylight 
> hours and then slowly decaying with a weak emission of visible light 
> that persists throughout the night.  However, I don't know if the 
> intensity of this phenomenon is sufficient to account for the observed 
> sky brightness you guys are talking about.  See: 
> http://en.wikipedia.org/wiki/Sky_brightness.
>
> John Miller
>
>
>
>
> *"Mark South" <md_south at mac.com>*
> Sent by: chaos-l-bounces at rtpnet.org
>
> 21-Sep-2009 07:48
>
> 	       
> To
> 	"Michael Hrivnak" <mhrivnak at hrivnak.org>
> cc
> 	"CHAOS" <chaos-l at rtpnet.org>
> Subject
> 	Re: [Chaos-l] Skywatching canceled
>
>
>
> 	
>
>
>
>
>
> I suspect that a truly dark place is somerwhere like austrailia or  
> antartica.
> Mark
>
> Sent from my cell phone
>
> On Sep 20, 2009, at 9:46 PM, Michael Hrivnak <mhrivnak at hrivnak.org>  
> wrote:
>
> > You mentioned that the weather wasn't great a lot of the time.  When  
> > the sky
> > was completely clouded over, were the clouds lit up at all, or was  
> > the sky
> > black?  My experience at Almost Heaven was that the sky was actually  
> > a bit
> > brighter when it was completely cloudy.  That tells me that even in  
> > a very
> > dark place, there is some light pollution reflecting off of the  
> > clouds, and thus
> > the same light brightens a clear sky at least a little.
> >
> > Although, I suspect that stars which are too faint for us to resolve
> > individually with the naked eye could collectively cause the whole  
> > sky to seem
> > less-than-black.  It would be interesting to look at a part of the  
> > sky with
> > the least number of stars, and compare its blackness to other parts.
> >
> > Michael
> >
> > On Sunday 20 September 2009 02:32:09 pm Mark South wrote:
> >> I know this is slightly off topic but I had a question
> >>
> >> I noticed at okie Tex one of the darkest star parties in the us that
> >> the sky as never truly black.. sort of how it looks at the
> >> planetarium.  Why is that?  I think it was quite clear but the sky
> >> still was grayish.  Is it possible to find a black sky with stars on
> >> earth with an atmosphere and light adaptation.  Greg Dillon theorized
> >> that it is truly darker than we realize but he thinks the stars light
> >> the sky up some.  Has anyone ever thought of this or been to a truly
> >> black sky?
> >>
> >> Mark
> >>
> >> Sent from my cell phone
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