RE: Data Volume

[Tom Droege <tdroege2@earthlink.net>]

I am doing my best to cool to constant temperature the year around.  I 
think this is best for the calibration.  We shall see how well we do when 
someone writes software that monitors such things.  Note that this is what 
the chiller posts are all about.

Tom Droege

At 09:48 AM 7/3/02 -0500, you wrote:
>I haven't looked at any of the data recently--working on the perls version
>of the STAMP SW-- but how cold is the camera?  If your minimum temperature
>is determined 'from ambient' you are perhaps 25 C warmer than before.  If
>you cool to a constant temperature, I'll crawl back under my rock.
>
>
>Rich
>
>
> > -----Original Message-----
> > From: owner-tass@listserv.wwa.com [mailto:owner-tass@listserv.wwa.com]On
> > Behalf Of jg
> > Sent: Tuesday, July 02, 2002 15:19
> > To: Tom Droege
> > Cc: tass@listserv.wwa.com
> > Subject: Re: Data Volume
> >
> >
> > Tom Droege wrote:
> > >
> > > I am getting fewer measurements this summer than last winter.
> > Expected, of
> > > course.  But I notice that I do not measure as faint as in the
> > winter, and
> > > this has a big effect on the number of stars seen.  Some of the
> > scans are
> > > now in the Summer Milky Way.  So far I see about 1/3 the star
> > detections as
> > > in the winter Milkey Way.  Either the stars are less dense, or there is
> > > something else going on.
> > >
> > > I mostly suspect that the hazy conditions in the summer cut down just
> > > enough light that I get a mag or so less sensitivity.  Anyone with
> > > experience on this want to comment.  I suppose all surveys have this
> > > problem.  Some areas of the sky just get better coverage.
> > >
> > > Tom Droege
> >
> > Okay, some of this you might know as obvious anyway, but just in case.
> >
> > There's civil twilight (sun only down to six degrees below horizon),
> > nautical [I think called "military" in USA] twilight, 6 to 12 degrees,
> > and astronomical twilight, 12 to 18 degrees.  Lower than 18 degrees it's
> > "night".
> >
> > At my latitude, +52 degrees, we never really get long at much darker
> > than astronomical twilight all night long during June, July and August.
> > For a short while around June we don't even manage astronomical
> > twilight.  Things'll be better at +41.5 degrees lat, but still, it just
> > isn't as dark.
> >
> > On the other hand, I dunno how your camera setup works, but star
> > brightness is a limiting factor to the eyeball.  I've been less dark
> > adapted at the end of some observing runs than I was to start with due
> > to too much Milky Way in the sky.  This too increases the brightness of
> > the background sky, reducing limiting magnitude.  There are a lot more
> > faint on the edge of detection stars in these Milky Way fields.
> >
> > Winter Milky Way fields are towards outer spiral arms from your
> > latitude, on the whole, whereas Summer ones are towards inner spiral
> > arms and the Galactic Centre, usually far more dense in both stars and
> > extinction-causing dust (reddens stars as well as making 'em fainter).
> >
> > I don't know if "airglow" is more prominent in Northern Summer months,
> > I'd have thought that was more connected to the seasons of the sun than
> > the earth though.  This is generally due to flourescence and
> > recombination in the upper atmosphere due to incident solar radiation.
> > I suppose there's more radiation for longer in Northern Summer during
> > the day, but I can't remember if recombination is "realtime" or occurs
> > more at night when the upper atmosphere is cooling off, ie less
> > "energized". Basically, I can't barely remember how airglow works.
> >
> > The latter few are fairly small in effect, but they add up to a brighter
> > sky background.  Some, all, or none of the above may be at play here,
> > but the twilight one for definite I feel.
> >
> > Hopefully someone'll be able to elaborate on this more jargony like ;)
> >
> > Maybes you're more likely to find airglow and starglow mentioned in
> > weather books than astro books.  All pale into insignificance relative
> > to light pollution nowadays, so don't get mentioned much.
> >
> > Cheers
> >
> > John G.
> >
> >
> >