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Lists of doubles for seeing quality estimates

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#1 WeltevredenKaroo

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Posted 01 March 2013 - 03:16 PM

I want to switch my seeing quality estimates from the subjective 1 - 10 scale to the arsec scale. Is there a list of doubles by separations from 1.0 to 4.0 secs arranged by sky region or constellation that I can use for quick seeing checks? I'm in the southern hemisphere at -36° and don't have go-to capability, electricity, or cell reception. The skies are very dark, though, lim vis mag 7.5-plus. Finding by chart and starhop works quite well for DSOs to vm13.0, using a 150mm Mak at 60x as a finder. I wouldn't think it too difficult to starhop doubles to m9.0. Suggestions?

#2 WRAK

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Posted 01 March 2013 - 04:56 PM

Name the constellation you want and I can select the doubles you want from the WDS catalogue - but I do not really understand your intention. To my understanding there is only one "objective" criterium for seeing quality and this is the stability of the diffraction pattern of a single star of reasonable brightness.
Wilfried

#3 Tom and Beth

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Posted 01 March 2013 - 06:17 PM

Just as a FWIW.

I can see where the OP is coming from, have also used close double stars to ascertain the seeing, For example, If I can clearly split an equal brightness pair at 1 arc second separation...yada yada yada.

Both methods rely in PART of a subject evaluation of the stability of their respective image. Over the years, I have gravitated to using the diffraction pattern.

To the OP,

#4 fred1871

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Posted 01 March 2013 - 07:31 PM

A few matters here - I'll assume you're at the latitude given in your identity (-24 etc) rather than -36 (in the ocean, I suspect, south of the South African coast - or are you on an island?).

I'll say the same as Wilfried and Tom and Beth - the diffraction pattern of a single star is your best way of evaluating seeing. That's why the standard scales, developed over the years, are based on a single star. Single star or double, there's a subjective element in it.

Star-hopping? Works fine, if your charts go deep enough. The First edition Uranometria is good for that (more stars than 2nd edition, and printed with better visibility under a red light).

You could also download the Tri-Atlas -
www.uv.es/jtorres/triatlas.html

The B and C charts series go plenty faint enough for finding 9th mag stars, and at a sufficient scale. B goes to mag 11, C to 13, for stars. And plenty of doubles are identified, not just marked, so you can look up current data in the WDS.

You could print off the B charts, for example, to have hard copy for use under the stars. My own preference is the C charts, mostly used at 200-400% to make reading easy.

#5 WeltevredenKaroo

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Posted 02 March 2013 - 06:15 PM

Thanks, fred1871, for the Torres B or C suggestion. I went to the local printer today and had the whole B atlas done in A3 size and coil bound. It sure makes an impressive sheaf on the observing table—too bad I can't use the northern third of it. Yes, I'm at -32° not -36° (typo)—it's already dewy enough around here surrounded by semi-desert; the last thing I need is water on all sides.

To WRAK, Tom & Beth, the problem with using diff rings when citing seeing conditions in an observing report is that the brightness and width of the rings differ by aperture and individual scope optical quality. Additionally, the air column gets more turbulent as aperture goes up and exit pupil goes down, so tolerable seeing in a 80mm can be just awful in a 200mm. Citing the Pickering or other Airy disk scale is subjective. My optical image at Pick 5 may not be your mental image of Pick 5. If one cites "seeing Pickering 6 to 7", readers can't get a solid handle on how that relates to magnitude depth on a globular or what H2 knots on a galaxy arm look like. I want to cite arcsecs because a GC in 2.5" seeing shows noticeably fewer faint stars than the same GC in 1.5" seeing. The ephemeral contrasts that make galaxies so exciting on a good night are the first thing to vanish if upper altitude seeing goes to hooey.

I'll annotate the doubles on the atlas as I go, so eventually there's be a useful selection on the pages most often used.

#6 WRAK

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Posted 03 March 2013 - 04:22 AM

...the problem with using diff rings when citing seeing conditions in an observing report is that the brightness and width of the rings differ by aperture and individual scope optical quality. Additionally, the air column gets more turbulent as aperture goes up and exit pupil goes down, so tolerable seeing in a 80mm can be just awful in a 200mm...


Certainly true, another factor is also the altitude - near zenith the seeing can be quite good and at 30° altitude awful. But what you are looking for is the given seeing for your given conditions and therefore it is no longer this subjective.
Nice description of the Pickering seeing scale with relation to double stars: http://www.carbonar....ting-seeing.htm
Really good pictures for the Pickering seeing scale: http://www.damianpea...m/pickering.htm
Clear skies
Wilfried

#7 Dan Williams

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Posted 04 March 2013 - 08:58 PM

You will find what you are looking for here: http://www.alpo-astr...ing_Mars_8.html (table 7-1). It will allow you to estimate seeing in arc-seconds by the resolution of your telescope and the diffraction pattern. True, a one arc-second may work well in my small refractor but a larger scope will be limited to one arc-second and would need maybe a half arc-second seeing to be able to use the full resolution of that scope. As for tube currents, you won't want to be splitting doubles until that has died down. The position in the sky doesn't matter either, because you will want to know the seeing at the location of the double you are observing. I know I'm not explaining this well, but once you read the article you will be able to follow what I'm saying.

~ Dan

#8 fred1871

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Posted 08 March 2013 - 10:15 PM

A follow-up on my suggestion about the Tri-Atlas - today I did a comparison of an area in Gemini, on B and C charts.

The C chart showed more doubles marked, and more doubles labelled, without going fainter than 10th magnitude, even though both charts show stars below 10th magnitude. The difference in scale between B and C is certainly one factor in this, as there's less space for labels on B charts.

So for the "find every double you can" observer (and some others of us :grin:) there's a benefit to using C charts.

#9 inZet

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Posted 07 May 2013 - 05:50 PM

Use my site, stelledoppie.goaction.it to create your own list, selecting by constellation and other criteria.
You can export in excel or print the list.






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