[AZ-Observing] Re: Trip to NM -- and sky brightness

  • From: Robert Ayers <astroayers@xxxxxxxxx>
  • To: stanlep@xxxxxxxxxxxxx
  • Date: Sun, 7 Jun 2009 11:12:03 -0700

I read your article with interest since I'm looking for a dark sky
site in AZ-NM and have looked at locations around Pie Town / Quemado.

I agree that your SQM reading are un-good.   "Far away from lights"
one should see 21.8 or better.   But I note that SQMs do differ.   And
Brian Skiff notes that when the summer Milky Way is overhead a zenith
SQM reading at a dark site will be affected by the Milky Way.   Might
your varying readings from Sept 2007 be partly explained by when at
night you made the readings?  Milky Way moves ...

I find that the major contribution to **perceived** sky brightness is
atmospheric haze and "extinction".   The "bowl of the sky" looks much
much better when there is little or no horizon-fading.

My absolutely best sky was observing from north Chile, in the Atacama
desert at over 13000 feet.  Retinal oxygen starvation did darken the
sky, but what was scary-good was that the "color" of the sky was the
same at the horizon as at the zenith.  A setting star did not fade
out.  It just set, winking out past distant hills.

Bob Ayers
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