Re: Ultra Dark-Adaptation?

On Sun, 21 Jan 2007 15:08:19 -0700, Greg Crinklaw
<theskyhoundyoureye@xxxxxxxxx> wrote:

Hi,

W. H. Greer wrote:
AstroApp wrote:

I tend to fall on the side of arguing against this supposition. I
agree with Greg -- despite Tony Flanders' doubt -- that there are
nights with incredible atmospheric stillness and clarity, above and
beyond the norm.

I still suspect a physiological explanation.

I've been thinking on this, and the more I think about it, the more I'm
convinced that it is extremely unlikely that this is a physiological
effect....

As for how the atmosphere then does this, I'm not certain. This sort of
enhanced viewing is really about contrast, which is why I think that
merely looking at extinction coefficients may miss the mark...
So while I don't have the answer, the questions I'd ask is, "what
atmospheric effects could reduce skyglow while enhancing (or at least
not reducing) transparency?" And, what effect does excellent seeing have
on contrast?

Clear and contrasty skies,
Greg

Years ago here there was a discussion of sky "background" and its
visibility, to which I contributed a comment or two. I notice even
with small aperture scopes that on some occasions there is a very
distinctly visible, palpable irregular background that does not look
to me like an average of the indiscernible light of faint stars, but
rather like a cloudy nebular glow. Of course it is more apparent near
the Milky Way than away from the bulge of our galaxy, so I think that
when THIS phenomenon is visible, we get the best nights for seeing
faint objects. But, when it's visible I can usually detect at least
some of it EVERYWHERE across the whole sky.

Unlike the normal recommendation for deep sky observers usually given
by most experts -- to use low power -- I tend to use the highest power
possible (except, of course, when looking for extremely large angular
diameter objects): so I find myself employing, say, 466x which is
convenient for me with my C-11 with a 6 mm wide field ocular. On
those nights when the "background" is quite noticeable, compared to
the occasions where it is just a bland dark "mush", just about
everything looks really great, and more detail is seen.

I look often at the GOES satellite page before attempting to observe,
and download the 'movie' images of the infrared, visible, and water
vapor detectors.
http://www.goes.noaa.gov/

The distinctness of the sky is probably related to the optimal
conditions of each of these wavebands though the eye is not
necessarily sensitive to them. Moisture will cause much extinction;
high atmospheric winds make the sky seem 'soft' even if the seeing is
apparently steady with little positional displacement of point
sources. The less moisture in the air at various layers near the
observer, the less light scatter.

I am not the sort of person to do a "study" of this and to feel
compelled to record the conditions over time. So I only have a
general feeling about it. This impels me to suspect that there is not
a particularly magical thing about the confluence of weather events
that give us such fabulous nights. Somebody should figure out how to
quantify these things, record them, and compare with visual results in
observing sessions, over time. I'm not the person to do it; I'm too
spontaneous an observer for that.

It also occurred to me that Todd Gross probably knows exactly what is
going on. It has been some time since I've read him here; he has an
elaborate website --
http://www.weatherman.com/
-- and also has written some interesting articles about the
meteorological impact on observing, such as this one about the jet
stream:
http://www.cloudynights.com/item.php?item_id=1482

With regard to the jet stream, it seems to me that when I look at it
using satellite imagery, it's almost ALWAYS bad and flowing right over
my geographical location. Maybe this is one of the most important
mechanisms that affects those good vs. bad vs. average nights.

Meanwhile, I still tend to be surprised by things that I can see when
the weather does not seem remotely cooperative, such as one of my best
views of IC-10 when I struggled to overcome light pollution in some
regions of my local sky, high winds, and the unpleasant and upset
weather conditions near a storm front. Though I've seen the galaxy
better in a darker sky, I can't ever recall detecting more of the
*granularity* of its apparent "surface" -- yet I almost did not bother
to take out my telescope and observe.

AstroApp



.

Relevant Pages

  • Re: Atlas of Light Pollution vs. Experience
    ... sky on moonless nights. ... sites within my greater 'gray' region. ... I almost always observe from locations where either no light ... If it were possible to zoom in on the light pollution charts enough to ...
    (sci.astro.amateur)
  • Re: My First Outing with a Telescope
    ... see familiar, newly learned, sections of sky disappear into the horizon, ... equate the view in my eyepiece with charts and atlases. ... to mentally flip the view and try to figure out which of all those stars ... I would observe stuff that I had previously ...
    (sci.astro.amateur)
  • Re: Whos paranoid now.
    ... The atmosphere, incidentally, is ... :>argon, .038% carbon dioxide, and minute amounts of ... :>The sky! ... :>And I'm going to pretend that I 'win' by posting ...
    (soc.culture.scottish)
  • Quran speaks about the Earths Atmosphere. AMAZING!!!!!!!!!
    ... Modern science has discovered facts about the atmosphere ... "By the sky which returns." ... because of the various phenomena which occur within the layer. ... and ultraviolet radiation. ...
    (uk.religion.islam)
  • Re: Whos paranoid now.
    ... The Phantom Piper wrote: ... :The Phantom Piper: "The sky is a lovely azure colour, ... The atmosphere, incidentally, is ... :And I'm going to pretend that I 'win' by posting ...
    (soc.culture.scottish)