FreeLists / az-observing / [AZ-Observing] Re: Alt Extinction was: Mag sequence

[Russell Chmela~ <rchmela@xxxxxxxxxxxxxxxxxxx>]

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Transparency of course gets better as you go up, but the diminishing
returns from physiological effects still has to be examined.  But this 5000-
foot figure sets a fair lower limit to optimal observing sites for visual
astronomy.  For imaging of course, you want to go as high as possible.

All for now.

\Brian
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  Glad you did qualify that about high - altitude sites. It does
vary between individuals. For me - middle aged couch potato who
lives at 1000' I tried sites from 3000' to 12000' (Pikes Peak)
and found that about 7000' is where the law of diminishing visual
sets in. The big difference was the horizons, those lower parts
of the sky were much better at the high site than lower sites, but
looking at the zenith was not much better for me than at 3000'.
 Acclimating is a good idea, but
if you don't live where you observe...
 
  That brings up another tangible ... If building a professional obs.
site or taking a once in a while amateur trip than yes, the high
ground is a good place. But for repeated trips for the city dweller
it is a different story sometimes. I was very put out when I tried 
living in the SF Bay area a few years ago and most of the regular 
sites anywhere in a sane driving time (3 hours max IMHO) were peaks
or high valleys. Just about all the roads to these were of the same
breed- narrow, winding and in that area of the country- CROWDED!
Usually well stocked with young adreno-heads going way too fast and
being inconsiderate at best and downright suicidal in some areas.
Roads were bad to drive by day, dangerous at night. I went to Lick Obs.
once for an evening program and after getting back was convinced that
it has the worst road I had ever traveled, despite the awesome scenic
beauty. 
   Now if you are a mountain racer... its all good , then.
  KPNO, Mars hill, McDonald Obs and Prude ranch are all easy drives, BTW.
I thought that Mauna Kea was easier than that road to Lick.
  
 I was surprised from the table in your post that the numbers for
the extinction were so low, but as you pointed out, that is just one
part of the mix. 
   
 RC
 

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