[AZ-Observing] Re: Tonight (Friday)
- From: Jeff Hopkins <phxjeff@xxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Sat, 24 Feb 2007 08:02:58 -0700
Hello Frank,
Not only is "Seeing" most subjective, it can vary considerably over a
short distance and time. One nice feature of the AutoStar CCD image
acquisition software is the ability to automatically reject images of
insufficient quality. I have watched that at times and sometimes
dozens of images will be rejected until a clear one comes through.
The same thing with high power observing. By continuously watching an
object at high power, there are usually moments of exceptional
clarity. Also, depending where in the sky you are looking can make a
great difference in how steady the seeing is.
As I have mentioned before, steadiness is the important criteria for
photometry. My main goal for making announcements is to let those who
have regular jobs and watched the 6 o'clock news tell of a stormy
night, that indeed it is not stormy and potentially very good night
to go out and observe. Photometry is a good method of determining the
general quality of the sky.
Last night (Friday) was not as good as Thursday night. It was not as
transparent nor as steady, at least near the zenith from my location.
The following data were taken around 8 PM MST both nights
V Counts B Counts U Counts V SD B SD U SD X
Thursday 99,844 104,660 22,020 0.0022 0.0011 0.0023 1.007
Friday 94,407 98,100 20,407 0.0255 0.0272 0.0477 1.020
Difference 5,437 6,569 1,613
X is the air mass
The counts are per second of a standard comparison star and have been
corrected for dead time and the sky readings subtracted.
Both transparency and steadiness were much better on Thursday night,
but Friday night was still very good for observing.
Jeff
At 01:25 -0700 02/24/2007, Frank Kraljic wrote:
>Jeff,
>
>I haven't been following this thread too closely, but to my knowledge
>seeing and photometry are not related to each other. Transparency
>and photometry, yes, but not seeing. For example, I've experienced
>great seeing (in excess of 500x on Mars and Jupiter with sharp
>results) under cirrus conditions, which should invalidate any
>photometry data. Although many on this list would quantify seeing
>based on observable double star separations (i.e. sub-arcsecond,
>arcsecond seeing), I personally value the seeing based on how high a
>magnification I can put on a stellar or planetary object and attain a
>fine airy disk or observe extreme fine detail on the planets (based
>from experience). In my opinion, the seeing is decent if one maxes
>at 250x. Once you get past 400x with sharp images (assuming one's
>scope is also in proper collimation), then I would classify seeing as
>good. I'll admit this is a subjective approach to the topic.
>
>Hope this may clarify any semantic differences when classifying the
>night as great in terms of seeing, transparency, or both. Perhaps
>Brian can fill us in on the professional definitions and differences
>of photometric, spectroscopic, etc. nights.
>
>-FRANK
--
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
www.hposoft.com
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