[AZ-Observing] Re: Midwestern Definition of Clear
- From: Russell Chmela~ <rchmela@xxxxxxxxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 10 Jul 2002 09:43:27 -0700
As someone who has observed from many places around the US, I can
echo a lot of what Tom has said. What can really be amazing is how
the sheer quantity of moisture in the air, on even a clear day or night
in the Eastern US can magnify the area of light pollution. I have
had astro visitors come here to Az. and when they see the amount of local
lights they think that it will take 3 hours ride or more to get out
from under some of the light dome. Then I take them to Vekol or
Sentinel and they are dumbfounded to see how dark it can be so "close"
to a mega-city. I tended, when first starting to observe here after
many years of viewing in New England, to think of a "50-percent factor".
So it would go that my 8" SCT would see here the same amount of detail
that a 12" I had used back East. It was fairly linear in that the next
step, my 12" f6 was equivalent to the 18" I had used back in New
England. Thats about where the compare ends , as I had not used any
scope over 20" back East.
What is odd about the skies here is that some nights just do not
appear to be superior by the look of the air in the late afternoon. On
given days, the color blue of the afternoon sky often does not seem
to be a clue. The sky can be a very deep blue and yet the evening
that follows is no different than one preceded by some middle - blue
sky that looked very un - remarkable. Likewise, the appearance of
the night sky to the naked-eye is not always a indicator. I have
been on some nights where the stars seemed to blaze from a black
background and yet the deep sky viewing was average at best. On others
what looks like a gray-ish shaded night sky with average numbers of
visible stars will pour forth spiral arm details, sparkling globulars
and colors in planetaries. Go figure. Of course seeing is a factor
in all of observing and we probably get some of the better nights.
Some of the best seeing I have had is when I observed from home in
Western Florida years back, and often on nights with just magnitude
3 and brighter showing. Seeing in the Northeast was almost consistent
in bad, with just 3 or 4 nights a year allowing 50x per inch.
As Tom has noted, we get a lot of "partial" nights here too, way more
of them than I have seen in the Norteast, Southeast or the Midwest or
out in Calif, where I have viewed.
Less stars for the next few months, but the lightning shows
are a partial consolation.
BTW- where can Osypowski(sp) platforms be found- as in dealers on the
web?
RC
***********************************************************
I have noticed over the years that many amateur astronomers east of the
Mississippi River are not impressed when I tell them that one night in three
is clear in Arizona. Brian Skiff's more than 20 years of data from Lowell
Observatory show an average of 91 photometric nights and 46 partial nights per
year. The numbers aren't much different down here in the deserts, since most
of the clouds are cirrus.
Just some consolation as we look forward to the next couple starless months.
Tom
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