FreeLists / az-observing / [AZ-Observing] Re: Cherry Rd last night - WOW!

[Tom Polakis <tpolakis@xxxxxxx>]

Brian Skiff wrote:

>      Tom's (and my) more general complaint would be that the x-out-of-ten 
> ratings are not only highly subjective, but also inconsistent both for 
> specific sites, but interpersonally, and also in grosser sense that a "10" at 
> the Muskegon wastewater plant is a lot different than "10" at 7000 feet in 
> Arizona on a dry spring night. 


Well, probably anything is better than what I do in my notes, which is to not 
assign any rating at all to the sky.  My experience is that on nights that I'd 
actually drive to a dark site to observe, the sky transparency isn't 
significantly different at the eyepiece from night to night.  I generally try 
to keep the scope pointed near the meridian, when objects are highest, and 
affected the least by lesser transparency.  I think the amount of variation in 
extinction on "photometric" nights is only on the order of a tenth of a 
magnitude or so.  If it's worse than that, then it's too humid or smoky, and I 
won't bother taking notes.

Back to dependency on the site, when I used to give such a rating, it was 
completely independent of the site.  Buckeye (or Muskegon Wastewater) could get 
a 10 out of 10 for transparency as often as Five Mile Meadow.  This isn't the 
correct way or anything; it's just how some people do it.

One thing I have noticed about the transparency ratings is that they don't seem 
to use the full scale.  Ratings below 6 or above 8 are very uncommon.  It's 
sort of like figure skating scores in the Olympics.  Perform the routine to 
perfection like a programmed robot, and receive a 9.92 out of 10; fall on your 
butt several times and stumble through the routine, and receive a 9.78.

Tom

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