[AZ-Observing] Re: Cherry Rd last night - WOW!
- From: Brian Skiff <Brian.Skiff@xxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Sun, 10 Jul 2005 21:03:05 -0700 (MST)
>> The last night I was out was to observe Deep Impact last week, at
>> Stan Gorodinski's, from Dewey, AZ. I thought the night was good for
>> observing, but not as good as last night. For the record I gave it 7's for
>> both seeing and transparency.
With some prodding of certain people to reduce data in a certain way,
I could probably provide numbers that would indicate the two nights were
nearly identical, with a slight edge ot the comet-impact night.
overall extinction has been ramping up as we get a bit warmer and also
closer to monsoon season, so this weekend was less transparent than
last weekend. Not by much, but the blueness of the daytime sky has been
gradually weakening.
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. I've noticed also that
seeing tends to be rated by the amount of naked-eye scintillation, which
is only moderately correlated with image-blur size viewed through the
telescope. I know you guys have been at Cherry Road on other perfectly
acceptable 'photometric' nights, and at least if we assume that general
lower-troposphere transparency is not a lot different in Flagstaff, then
all those nights are pretty much identical, despite their ratings all over
the scale. Seeing might well be different due to local topographic
effects, cold-air drainage, etc., but the transparency is pretty uniform.
I don't know that there's much need for an absolute calibration,
since we'd want things done without instrumentation, but I would argue
(and have in the past on this list) that it's not that big a deal to
actually find limiting stellar magnitudes (I would do them telescopically,
not naked-eye), and also to get a fair estimate of the seeing in arcseconds
using close, equal double stars. For a specific observer/telescope/site
combination, such numbers would provide a more consistent estimate of
the quality of a night. An added benefit, and perhaps the main one in fact,
is that by doing this sort of estimating, you will gain some very useful
visual skills, and thus see more stuff when you're doing oridnary sorts
of observing. And that's what it's all about, que no?
\Brian
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