asaint
Carpal Tunnel
Reged: 04/25/03
Posts: 2021
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Seeing and Transparency
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John Kocijanski
Pooh-Bah
Reged: 08/22/03
Posts: 1488
Loc: Monticello, NY
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Excellent information. Well done. Thanks.
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John
Deep Space Observer 10 * SPC-8 * C102 HD f/10 * XT 4.5 * AT1010N * PST *
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David Pavlich
Postmaster
Reged: 05/18/05
Posts: 6542
Loc: Mandeville, LA USA 30.38 X 90....
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Terrific article, Don! This should go in the must read list for beginners.
David
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A few scopes and mounts.
Proud Member; PAS NOLA,
Life expectancies would go WAY up if green vegetables smelled like bacon...
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cildarith
Carpal Tunnel
Reged: 08/26/04
Posts: 2122
Loc: San Diego, CA
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Excellent article, Don. Thank you!
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Eric
6" f/6 Parks Newtonian
10x50 Bushnell Binocs
CN Sketch Gallery
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mistyridge
Carpal Tunnel
Reged: 10/28/05
Posts: 2268
Loc: Loomis, CA -26Mi E of Sacto.
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Great article,Don. The attached websites are really useful. Thanks.
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Mike F
Misty Ridge Observatory
Stellarvue SV115T "WOW"! What a view.
Stellarvue SV70ED
Stellarvue Nighthawk
18" f/4.5 Teeter's, Swayze mirror
12.5" f/5 Astrosky, OWL mirror
15X70 Binos
Mounts: DM-6,M-1,CG-5(ASGT)
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go_ahead_ed
professor emeritus
Reged: 05/11/03
Posts: 535
Loc: Anaheim, CA 117.55W, 33.49N
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Very good artice Don!
Clear and concise descriptions and explanations of the varying conditions we find ourselves observing under. I would only add one additional component... your comments about how spot-on collimation seems to increase the frequency of nights with good "seeing" 
It's like the Gods of Good Seeing reward the sacrifices of those who put extra time and effort into careful collimation...
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Ed
12.5" Discovery PDHQ
Orion XT8
90mm C90
80mm Konus f/5
50mm Stellarvue F50W2
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Kevin201
super member
Reged: 07/06/04
Posts: 189
Loc: North of Boston
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Very good article. Seeing and Transparency are little hard to understand for beginners.
Is there a scale of 1 to 10 to Transparency?
What magnification do you need to see the airy disk?
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Mark
Orion XT10i, Moonlite CR2
Dewbuster
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10959
Loc: Los Angeles
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Yes, the Bortle Scale: here.
It's very approximate, but seems to correspond to what's seen fairly well. What I think I disagree with is the limiting magnitude that accompanies each class.
The Airy disc is easily seen with 1X per millimeter of aperture (1mm exit pupil), and can usually be seen at lower powers (say, .5X per mm of aperture) if the seeing is very steady.
Since the Airy disc is larger in smaller scopes, correspondingly less magnification is required to see the Airy disc. Want to see the Airy disc easily? Put a cardboard mask in front of your scope with a 1" diameter hole in it and look at Vega or Deneb. That's an Airy disc.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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Anonymous
Unregistered
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very well done, Don.
I must read for newbies (and others). Explains alot; when I first started I had constant misgivings: my scope "worked" one night but did not the next. It was not intuative at the time as to the cause. Although shipping companies may sue you for interference with business practices in the lack of returning perfectly good scopes due to a night or two of bad conditions.
Bill
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johnmkanz
super member
Reged: 11/03/05
Posts: 163
Loc: Greenfield, MA
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I never saw the Bortle scale before—depressingly, my "rural" sky now seems t be a "bright suburban" sky (mag 5.5 limit naked eye).
What I record for transparency is the naked eye limiting magnitude for stars. I use the little dipper for a start, which goes fainter than mag 5.
John Kanzler
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www.johnkanzler.com
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Anonymous
Unregistered
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Quote:
I never saw the Bortle scale before—depressingly, my "rural" sky now seems t be a "bright suburban" sky (mag 5.5 limit naked eye).
What I record for transparency is the naked eye limiting magnitude for stars. I use the little dipper for a start, which goes fainter than mag 5.
John Kanzler
Your sky did not change; just the description 
I do not find the Bortle scale absolute or internally consistant. M33, for example(naked eye,) is at times easy; at other times difficult at best despite *seemingly* similar conditions (same dark adaptation time and such). I did not change location but conditions are ever-changing.
Be well,
Bill
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10959
Loc: Los Angeles
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Bill is right.
As I said in the article, clarity of the sky, COUPLED with a dark sky will produce wonders in any scope. M33 is one of those objects where a very slight change in clarity of the air makes a huge difference in the ability to see it and/or details within it. I've seen a few nights in 42 years (yes, only a few), where seeing, clarity, and darkness were all perfect at the same time.
One of those times I saw Saturn on a 7" f/12 refractor with a Parks 3.8mm Plossl in a 2X barlow lens, and the image was sharp and stationary!. That's 1123X, and we could have used more. Unfortunately, that was before the advent of quality 2-3mm focal length eyepieces. Titan had a visible disc.
On the same night, I first saw the Horsehead Nebula in a friend's 10" dob--no filter--and it was easy.
M42 displayed color in an acquaintance's C90.
I spotted stars E and F in the Trapezium in my 5" that night.
You remember nights like that. They just don't happen that often.
The Bortle scale has flaws, but, unlike most other scales, it has a lot of classes that would be called "clear", yet which differ appreciably. I find that more useful than scales that only have one or two classes of clear skies.
One complaint: I observed at one mountain site in AZ for 3 nights: the first two were Bortle Class 1--Fantastic. The third night was so much clearer, it was if I'd observed the first 2 nights through tranlucent film. What the heck was the third night? Bortle Class 0? 
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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Anonymous
Unregistered
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Agreed that the Bortle scale has flaws; probably needs subdivisions in the "dark sky" realm. I would have never have thought so in my previous "rural" location.
M33 is sort of my litmous test for conditions when it is above the horizon. It is fickle to the un-aided eye. I am sure other objects are as good or better as an indicator.
I had three nights this year that I considered very good. Such is the fleeting moments one cherishes.
It was enough, one night, to prod my spouse and son out of bed and outside just to look up sans scope. They were impressed and trust me, that is a rare circumstance.
As for your "third night" on the mountain; call it a -1 Bortle and hope you have many many more!
Thanks again for your article.
Be well,
Bill
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CreationAstroGuy
professor emeritus
Reged: 05/18/07
Posts: 524
Loc: NW WA
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Great artical! Thanks!
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Ryan Nelson
8" LX90 GPS UHTC
DSI with a 3.3 reducer
Eyepieces; 22mm Nagler, 16mm Meade Seires 5000, 26mm Meade Seires 4000, and a 9mm Burgess/TMB planitary!
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Glassthrower
Vendor - Galactic Stone & Ironworks
Reged: 04/07/05
Posts: 14687
Loc: Hurricane Alley
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Here is a related article written by CN's Phil Creed -
http://www.glassthrower.com/haze.html
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Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.
Galactic Stone & Ironworks - Buy/Sell/Trade Meteorites, Moon Rocks, Mars Rocks, & 35 different falls and types!
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