[AZ-Observing] Re: Pickering Scale
- From: Andrew Cooper <acooper@xxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Thu, 17 Jul 2003 09:30:28 -0700
There are many reasons why different instruments would be affected by
seeing to different degrees, from the way seeing interacts with
smaller/larger apertures, seeing issues in the instrument itself, and
observer quality and bias (how good are your eyes?).
So do you try to compensate the scale for the instrument you are using?
Or, as I often do, just call it as you see it, the effective seeing for
the instrument you are using. I believe this is appropriate because it
records the quality of the observations, and is not meant to be a record
of what any other instrument would see that same night and location. I
want to know why I did or did not see a particular dim central star or
wisp of detail. Pickering or other observer (non instrument) methods
are just a way to standardize the scale. Not perfect, but better than nothing.
If you are doing an observatory site evaluation or making observations
with an instrument this might be different, you would need a more
rigorous and quantitative method. But for us visual observers I would
not worry about calibrating instrument differences. I'll use the same
methods on the 90mm APO or the 18" dob and let the notes stand on their own.
Andrew
William R Wood wrote:
>
> Try this page for a reference as to the Pickering scale:
>
> http://uk.geocities.com/dpeach_78/pickering.htm
>
> I keep a copy of this animation on my laptop to use in the field but a
> static version can be printed out too. After a lot of practice I have
> become pretty good estimating seeing based on this scale. I am working on
> comparing the Pickering scale method to Brian Skiff's equal double star
> method of evaluating seeing.
>
> The Pickering scale is based on a 5" refractor. I haven't been able to do
> side-by-side comparisons but in night-to-night comparisions there is a
> significant difference between my 90mm f/5.6 refractor and my 128mm f/8.1
> refractor. The smaller the scope and/or shorter the f/l, the better the
> seeing looks. I don't know whether aperture or focal length is the more
> important factor. The difference is even more dramatic going from the 5"
> refractor to a 10" f/12 D-K Cassegrain. My ususal rating in the 10" is more
> like 3/10.
>
> Regards,
>
> Bill Wood
> Fountain Hills, AZ
>
> > -----Original Message-----
> > From: az-observing-bounce@xxxxxxxxxxxxx
> > [mailto:az-observing-bounce@xxxxxxxxxxxxx]On Behalf Of Andrew Cooper
> > Sent: Thursday, July 17, 2003 2:29 AM
> > To: AZ-Observing mailing list
> > Subject: [AZ-Observing] Mars-Moon Conjunction
> >
> >
> > The seeing was poor to fair, a pickering 5 perhaps judging from the airy
> > disk. Need to print out a version of the Pickering Scale for the
> > reference section of my observing notebook. My refractor being similar
> > to the instruments he designed the scale for.
> >
> >
> > Good night,
> >
> > Andrew
> >
>
> --
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--
Andrew Cooper
Tucson, AZ
mailto:acooper@xxxxxxxxx
http://www.whitethornhouse.com
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