--- Richard Tenney <retenney@yahoo.com> wrote:

. . . One of these days I need to take some time and be first-hand mentored from someone like yourself on how to quickly and accurately assess and document seeing, transparency, etc. . . . Any volunteers or folks with links or references to good tutorials/examples on the subject?

Here's what I do, understanding that there's alot of subjectivity in these scales. But they still give a common nomenclature to describe what you saw to other amateurs - I. To describe the visual limiting magnitude, either zenithal or in the off-zenith naked-eye field-of-view, use one or two sets of standard charts - McBeath's (original 1991 charts) http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1991JBAA..101..213M http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1991JBAA..101..213M&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf or the International Meteor Organization's (McBeath's expanded chart set) http://www.imo.net/visual/major01.html#table2 http://www.imo.net/visual/lm.html which are reproduced in an easier to follow version at The Nine Planets website - http://obs.nineplanets.org/lm/rjm.html II. To describe the overall sky dome in general - Bortle's scale http://skyandtelescope.com/resources/darksky/article_81_1.asp http://www.frostydrew.org/observatory/columns/essays/bortle.htm Bortle's scale is the generally accepted standard. It has one weakness in some skies, e.g. - as can be seen at night travelling east along the Mirror Lake Highway. Some skies might be Bortle "true dark" in one direction and Bortle "suburban-rural transition" in another part of the horizon. With that cavet, it's still a great way to communicate what you saw. III. To describe atmospheric turbulence at the eyepiece as seen in the waveness of a star's image - A) Pickering's 10 point scale http://uk.geocities.com/dpeach_78/pickering http://skyandtelescope.com/howto/scopes/article_569_1.asp B) Antonaidi's 5 point scale http://www.npmas.com/resources/seeingtrans.htm I Perfect steadiness; without a quiver. II Slight undulating, with moments of calm lasting for several seconds. III Moderate seeing, with larger air tremors. IV Poor seeing, with constant troublesome undulations. V Very bad seeing, unsuitable for anything except possibly a very rough sketch. Although less precise than Pickering's scale (which is the generally accepted standard), I tend to use the Antonaidi's scale because it is easier to apply from memory. Pickering's scale is based on doing a Suiter-like star test at extreme magnification and watching the diffraction rings flutter. Antonaidi's scale is more rough but is based on what you normally see in a star field in the eyepiece at ordinary magnifications. E.g. - something simple like - http://uk.geocities.com/dpeach_78/planetseeing.htm C) For astrophotographers - FWHM Both of the Pickering's and Antondaidi's scales have a lot of subjective interpretation built-in. In these days where CCD imaging is widely used, another method used to describe atmospheric turbulence is the Full-Width-Half-Maximum (FWHM) dispersion of a star's image. Your astrophotography software may report this figure. Personally, I'm still in the learning curve stage on this one. For more on FWHM see - http://en.wikipedia.org/wiki/Astronomical_seeing IV. To describe transparency or atmospheric extinction I don't know a good visual scale for describing transparency. Here is an informal, not generally accepted scale from << http://www.backyard-astro.com/Logs/logsreport.html >>. I don't use this scale, but sometimes refer to it for some plain-language descriptions. 01 Use 01 for the clearest possible sky. The atmosphere is perfectly transparent, only a slight amount of haze on the horizon 02 The sky is very clear but not perfectly transparent 03 Haze is noticeable towards the horizon, but the overhead sky is perfectly transparent 04 Very slight haze is noticeable overhead near bright objects 05 Haze appears overhead, but faint stars are visible 06 Obvious haze or thin clouds lie overhead 07 The faintest stars typically visible from the site are not visible 08 Smoke, haze or fog limits visibility significantly and creates glare around objects 09 At the zenith, absorption limits visibility by one magnitude 10 At the zenith, absorption limits visibility by two magnitudes or more V. To describe telescopic limiting magnitude (TLM) I don't do too much of this beyond occassionally checking a chart plotted from Cartes de Ciel or from an AAVSO star field. There are a series of generally accepted star fields for TLM printed in an obscure out-of-print book available at the Marriott Library. "Star Clusters for Finding Your Limiting Magnitude", Appendix B in Clark, R.N., Visual Astronomy of the Deep Sky, Cambridge University Press and Sky Publishing, 355 pages, Cambridge, 1990. << http://www.clarkvision.com/visastro/index.html >> Clarke's star fields are plotted down below between mag 15-16 and are most useful for 10" of aperature and above. They are of less help for small aperatures that might have a telescopic limiting mag between 11-13. They cannot be used with binos. I have Clark's TLM star field charts copied in reference box but don't usually carry them with me. For Items I-III, I have those printed off into a three-ring binder. The binder lives under the back seat of my car or in my "observing box" that gets loaded into the car. Enjoy - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

--- Richard Tenney <retenney@yahoo.com> wrote:

I certainly now have no more excuses... :o) Rich

You can use mine - I'm too lazy to do all that every time I pull a scope out! - Canopus56(Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

--- Chuck Hards <chuckhards@yahoo.com> wrote:

With experience, you can tell when the sky is right and when it's less than ideal pretty quickly. If an individual is compelled to categorize and rate conditions for a scientific or project-related reason, great, if not, it's neurosis or boredom.

One of the attractions of the hobby is it's technical side. Gaining competence in talking about sky conditions is one of those basic astronomy skills, like knowing the relationship between focal length, aperature and magnification, that once mastered, becomes fluid and second-nature. Like anything, if overdone it becomes compulsive and takes away from the simple enjoyment of the hobby.

Unless it's overcast and just hopeless, once at a site I've never packed up and went home because the conditions weren't optimal.

With gas prices making a trip to the dark sky site a $20-$30 proposition and light pollution ever creeping outward, it's nice to have a sense of where the dark holes are at particular sites and if what you want to look at is in one. If it's not in one, so be it, there's always something to look at at any magnitude and level of sky brightness. Like you say, you gotta keep it in perspective. - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

Quoting Chuck Hards <chuckhards@yahoo.com>:

Deer flies.

That's the 'mixed company' terminology. I was actually thinking of it's 10 letter cousin... ;)