[AZ-Observing] Re: Happy Jack site

  • From: Brian Skiff <Brian.Skiff@xxxxxxxxxx>
  • To: az-observing@xxxxxxxxxxxxx
  • Date: Fri, 12 Mar 2004 17:00:14 -0700 (MST)

>>  Are there known trends in seeing
>>  quality throughout the year at established sites up your way?

     There are monthly histograms at the bottom of this URL: 


Perhaps more significant is the plot link called "polar plot of wind
direction vs seeing".  Basically the seeing is always good, but is
less good when we get the classic post-frontal northeast wind.  But as
you can see, the seeing goes from ~0".8 for all directions except NE 
up to ~1".2 when it's from the NE.  On Anderson Mesa we typically get
3"-4" or sometimes much worse with that same NE wind.
     From other data that's not on-line, the unnamed Happy Jack hill is 
a bit breezy, but that's why the seeing is as good as it is.  A lot of
sites get decoupled not far above ground level, so that it's calm at the
surface, but producing the various cool-air drainages over the site that
soften the images.  This place sticks up just a bit into the prevailing
westerlies, so stays breezy all night on a typical clear night.  It's not
a strong wind, but a good steady breeze at something like 6-8 mph, if I
remember the mean values correctly.  Most folks will need some sort
of wind buffer to keep a small telescope stable.

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