[AZ-Observing] Re: Sunglow (was: Tucson Observing Sites)

  • From: Wil Milan <wmilan@xxxxxxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Sat, 22 Dec 2001 22:31:53 -0700

At 09:13 PM 12/22/2001, you wrote:

>Sad to admit, my enthusiasm for Sunglow has waned over the past year.  I
>suppose cloudy nights add to my disappointment, but as Tom mentioned,
>consistent poor seeing is painful to observe through.  I can only recall
>three maybe four nights of quality (400-500x plus) seeing; however, three of
>those four nights lasting just more than an hour's time.
>
>Perhaps I'm spoiled, taking our skies and weather for granted--by God, I'd
>probably quit the hobby if I lived out east--yet, I take pride in saying,
>seeing below 250x is worth very little of my serious time, regardless of
>transparency.

I think much of the "disagreement" about Sunglow, or probably anyplace 
else, is our varying aims and expectations. To me a night where one can 
use > 500x magnification is truly exceptional anywhere, and I know of no 
place readily accessible where that kind of seeing is the norm. Gainfully 
using 500x implies seeing well under one arcsecond -- very rare conditions 
indeed.

I routinely make numerical measurements of seeing-related motion as part of 
the autoguiding process for astrophotography, and it's a rare night 
anywhere where sub-arcsecond seeing prevails for an extended period. More 
typical at the better sites is 1 to 2 arcseconds, a level of seeing that 
can be fully exploited with less than 300x.

If you know of an accessible place where sub-arcsecond seeing is the norm, 
please pass it on, because I've not heard of it. Barring that, I think that 
calling anything below that level as "poor" (or "ugh" :-) ) is not a very 
useful standard. If we use near-perfection as the standard the almost every 
place on Earth is terrible and we should all just queue up to climb Mauna 
Kea. In Arizona, part (but not all) of the KPNO site regular offer that 
kind of seeing, but I don't know of any other.

Also, seeing is only half the story. Because of their local climate, urban 
Houston, Texas, and Tampa, Florida often have superb seeing, some of the 
best planetary viewing to be had anywhere in North America, but for 
deep-sky viewing they're nearly useless. Dark, clear skies matter a great 
deal, and in that regard a number of places in Arizona that may not offer 
regular sub-arcsecond seeing nevertheless rate as excellent sites because 
they allow viewing of dim objects that cannot be seen as well (or at all) 
from sites not as dark and/or transparent.

Aside: The absolute best seeing I've ever experienced occurred a year ago 
November, coincidentally at Sunglow when a large group was there, including 
quite a few AZ observers. By 2:30am almost everyone had gone off to bed and 
the only ones still up were Frank Martin and me, and we were putting away 
equipment. Just before putting away his 11" scope Frank decided to take a 
quick look at Jupiter and was surprised how steady the view was. He asked 
me if I had a Barlow, and to make a long story short, for the next hour 
Frank and I reveled in views that were rock-steady even at nearly 800x. (We 
had no ocular combinations to go higher than that, else we would have tried 
it.) Band details and festoons were crisp and clear, and most memorable to 
me is that it was the only time I've ever seen clear detail on the face of 
Jupiter's moon Io.

It seemed almost magical, something that Frank and I still talk about and 
I'm sure will never forget. But that kind of thing is very rare anywhere, 
and I wouldn't consider a site poor because that kind of seeing is not an 
every-night occurrence there.

Interesting, the next-best seeing I've ever experienced was at the old SAC 
Buckeye Hills site in December 1996, a mediocre site even then, but for a 
few hours that cold night it was terrific. Once in a while almost anyplace 
can get lucky, I guess.

Wil Milan
http://www.astrophotographer.com/
"The heavens declare the glory of God
And the firmament proclaims His handiwork."
   -- Psalm 19:1



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