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FrenchStar
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Reged: 07/23/10

Loc: St-Hyacinthe, Quebec, Canada
Research project - Limit for uneven Double Stars
      #5340274 - 07/28/12 03:43 PM

I invite you all to read the September 2012 issue of Sky and Telescope(It's at page 68).

Sissy Haas is asking our help to complete a very interesting project. I invite you all to participate!


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Astrojensen
Post Laureate
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Research project - Limit for uneven Double Stars new [Re: FrenchStar]
      #5340320 - 07/28/12 04:17 PM

Nice, but I don't subscribe to S&T.


Clear skies!
Thomas, Denmark


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FrenchStar
sage
*****

Reged: 07/23/10

Loc: St-Hyacinthe, Quebec, Canada
Re: Research project - Limit for uneven Double Stars new [Re: Astrojensen]
      #5340324 - 07/28/12 04:20 PM

Me neither! When I heard about this project, I bought it at the store...

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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Research project - Limit for uneven Double Stars new [Re: FrenchStar]
      #5340705 - 07/28/12 09:34 PM

Thanks for the notice - despite being an S&T subscriber I hadn't yet seen the September issue. I've now accessed it online.

It's good to see Sissy Haas back, as she's been absent pretty much since the publication of her double star book.
The project is a neat idea, though I suspect it won't lead to anything as definitive as the Dawes Limit, simply because there are too many factors involved.

Even Dawes limited his description to stars of a cetain brightness level, and with telescopes of moderate size. Once you get into pairs where delta-m can be anything at all, and separation ditto, with the two interacting - not to mention telescopes of different sizes (probably by a large amount), a big range of observer experience and visual acuity, magnification used, etc etc - well, we can hope the project can come up with some useful and interesting results but I suspect they'll be more approximate than the Dawes Limit.

Regardless of the above musings, I'll be joining in and recommend others to be part of it as well. We'll see where it goes once there are lots of observers involved.

Haas refers to Chris Lord's work, which is the best attempt I've seen thus far on this vexed question. And she's well aware of various complicating factors involved. So I wish her project well and look forward to seeing the results of it - obviously, given the RA spread of test stars, it'll take at least a year to get them observed and the results collated and analysed.

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.

Now if only the clouds will move away!!


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5340749 - 07/28/12 09:54 PM

A further thought - we might end up with different results according to the size of the central obstruction in telescopes - from zero to around 40%. It's a big factor as pairs become more uneven in magnitude.

Hmmm... an term in an equation, or separate equations based on CO?


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JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5341324 - 07/29/12 09:03 AM

I too am very happy to see Sissy return. I will join up and do my best to help out. It will be a fun project and nice to be working on a double star project. I will, of course, be very interested in the results. The more contributors to the project the better! I hope everyone with an interest in double stars will participate.

best,

JimP


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JimP
Pooh-Bah


Reged: 04/22/03

Loc: South Carolina
Re: Research project - Limit for uneven Double Stars new [Re: FrenchStar]
      #5341332 - 07/29/12 09:07 AM

For those who are interested, but do not have access to S&T, Sissy's e-mail address is <has103@comcast.net>

best,

JimP


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FrenchStar
sage
*****

Reged: 07/23/10

Loc: St-Hyacinthe, Quebec, Canada
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5341401 - 07/29/12 10:05 AM

Quote:

And she's well aware of various complicating factors involved. So I wish her project well and look forward to seeing the results of it - obviously, given the RA spread of test stars, it'll take at least a year to get them observed and the results collated and analysed.

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.




My observing group did contact Sissy Haas and we asked her about the time frame of this Project. It is at least a year of collecting data, if not two.


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Research project - Limit for uneven Double Stars new [Re: FrenchStar]
      #5342343 - 07/29/12 08:42 PM

Did the listed email address for Haas work?
I've had my emails bounce back, undelivered, from the listed email address and from a second attempt at "haas103" instead of "has103".


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FrenchStar
sage
*****

Reged: 07/23/10

Loc: St-Hyacinthe, Quebec, Canada
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5342447 - 07/29/12 09:57 PM

Quote:

Did the listed email address for Haas work?
I've had my emails bounce back, undelivered, from the listed email address and from a second attempt at "haas103" instead of "has103".




Hello,

Here is the email I used: has103@comcast.net No error message, yet.

Frenchstar


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5342627 - 07/30/12 12:05 AM

Quote:

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.

Now if only the clouds will move away!!




Excellent advice Fred. Id say thats more meaningful than selecting endless doublestar combinations [in varying seeing conditions] and such. The stars can be chosen easier and more effectively and the results attained far quicker.

Fact is though, a telescope isnt needed at all if some way of creating artifical stars in a darkened room can be a constructed with the brightness calibrated to match the stellar magnitude scale. In that case it could be done with excedingly accurate and excellent results.

I will say if this is leading up to some contrived "Sissy Limit" or some such Ill stay with Lords and be done with it.

Im still gagging on the Caldwell gaff.

Pete

Edited by azure1961p (07/30/12 12:09 AM)


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Research project - Limit for uneven Double Stars new [Re: azure1961p]
      #5343041 - 07/30/12 09:43 AM

Pete, I don't think the artificial stars viewed naked-eye is a solution - it won't give the same result as real stars viewed through telescopes. Telescope vision differs in a number of ways from naked eye, one being improved visibility of faint stars with magnification, contrast effects, only part of the pupil being used at higher powers thereby reducing astigmatism in the eye as well as reducing other eye aberrations... Others will no doubt think of further differences.

Besides, anything derived by such an experiment would immediately get lots of complaints just because it's an artificial arrangement.


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Simoes Pedro
sage
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Reged: 02/03/09

Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5343560 - 07/30/12 02:45 PM

What's the project?

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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: Research project - Limit for uneven Double Stars new [Re: Simoes Pedro]
      #5343614 - 07/30/12 03:12 PM Attachment (38 downloads)

Quote:

Here is the email I used: has103@comcast.net No error message, yet.

Frenchstar




That is the email address that is given in the article.

Quote:

What's the project?




It is in an article by Sissy Haas in the Sept. issue of S&T, Page 68-71, titled Finding the Limit for Uneven Double Stars. Anyone interested in double stars should participate in helping determine this. This information will be used to refine or make a new chart like this one found on page 5 of her book Double Stars for small telescopes


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Astrojensen
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Reged: 10/05/08

Loc: Bornholm, Denmark
Re: Research project - Limit for uneven Double Stars new [Re: blb]
      #5343651 - 07/30/12 03:34 PM

Haven't read the article, but I have one immediate question: Does the unequal doubles need to be truly split (difficult to judge) or merely detected as doubles? (IE one component is technically behind the other a little, but it betrays itself by putting up a slight bulge in the first diffraction ring of the main star).


Clear skies!
Thomas, Denmark


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FrenchStar
sage
*****

Reged: 07/23/10

Loc: St-Hyacinthe, Quebec, Canada
Re: Research project - Limit for uneven Double Stars new [Re: Astrojensen]
      #5343755 - 07/30/12 04:23 PM

Quote:

Haven't read the article, but I have one immediate question: Does the unequal doubles need to be truly split (difficult to judge) or merely detected as doubles? (IE one component is technically behind the other a little, but it betrays itself by putting up a slight bulge in the first diffraction ring of the main star).





Hello!

Here is what Sissy Haas has to say about it (from an email exchange with her) :

"It needn't be split by any space, or even a one hundred percent ball. But so long as you've UNQUESTIONABLY seen a second body next to the main star, then I think we can call it resolved. The thing that's most important is that the observation be honest.

Don't claim to have seen the companion if you suspect but don't feel certain. And as you don't need me to tell you, a companion you ALMOST think you saw might show up on a better night."


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blb
Post Laureate


Reged: 11/25/05

Loc: Piedmont NC
Re: Research project - Limit for uneven Double Stars new [Re: FrenchStar]
      #5343914 - 07/30/12 06:06 PM

I really wish that this project went beyond a magnitude difference of 4.0 to at least 5.0 or 6.0. There are many challenge objects that we look at that have a greater difference in magnitude. For example I looked at Sirius, the Dog Star and the Pup last winter with my 4" TV102 refractor. Those stars have a magnitude difference of 10.0 and I could see the companion (Pup). Limiting this to a magnitude difference of only 4.0 is to limit the chart to only the brighter pairs. I personaly would like to have information on seeing those pairs with a greater difference magnitude.

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Fuzzyguy
professor emeritus


Reged: 12/21/11

Loc: Colorado/Kansas
Re: Research project - Limit for uneven Double Stars new [Re: fred1871]
      #5344259 - 07/30/12 09:51 PM

Quote:

It occurs to me that a useful approach is to use aperture stops or a diaphragm on a telescope - so a pair might be easy at full aperture, difficult at 3/4 aperture, not seen at 1/2 aperture. That way the same observer can give results for multiple apertures.




I'm not a scientist, optical engineer or astro physicist nor do I play any of these on TV, but if you put field stops on reflectors wouldn't that increase the percentage of CO? And wouldn't this affect results and skew the data? Or does CO only affect lunar, planetary and DSO viewing? I'm kinda new to this, so just thought I'd ask.


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drollere
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Reged: 02/02/10

Loc: sebastopol, california
Re: Research project - Limit for uneven Double Stars new [Re: blb]
      #5344265 - 07/30/12 09:55 PM

i'm not much interested in the "rules" that float around among astronomers about seeing, magnification, resolution, and so on. and i agree with some of the previous posts that this particular objective -- resolution as a function of aperture and magnitude difference -- is likely to yield disappointing results.

the analogous problem is magnitude limit by aperture. bradley schaefer took a thwack at it with a dataset of observer reports; then nils carlin and chris lord tried to improve on it with more complicated formulations. in schaefer's case, his predictions are inaccurate by about one to one half magnitude, equivalent to the difference between a 6" and 8" telescope.

the problem is that these are all attempts at what is called predictive psychophysics. and those have always come to grief. the simple problem of color matching (color discrimination), which has had several large industrial and academic research projects thrown at it, discovered in the end that human visual response is not at all easy to predict with any accuracy. there is simply too much variation across individuals. and with a target task like double star observing that depends quite a lot on experience and skill and instrument, and the terrifically weak criterion in play (what does "resolve" or "recognize" or "separate" mean, exactly?), well ...

i recently completed a campaign of observing every double star listed in Haas and the Cambridge Double Star Atlas visible from my latitude, over 2100 in all, and there are several dozen pairs i couldn't resolve.

i plan to report those in a separate topic. meantime, i found on reexamination that many pairs i couldn't resolve a year ago i can resolve now, in some cases easily. certainly that's in part due to a year's worth of observing experience, but perhaps also to variations in seeing, atmospheric dispersion, eyepieces, etc. across observing nights.

if your own observing can't predict your own observing, what point is there in the prediction?


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fred1871
scholastic sledgehammer


Reged: 03/22/09

Loc: Australia
Re: Research project - Limit for uneven Double Stars new [Re: Fuzzyguy]
      #5344542 - 07/31/12 01:00 AM

Yes, you're quite correct about changes in central obstruction ratio.
My suggestion about stopping down telescopes would require those using reflectors to indicate the relative size of the secondary obstruction - with an SCT, a central obstruction that starts off large (35%) will be a monster by the time of half-apertture (70%) - very unsuitable for uneven doubles.

Bigger SCTs can use off-axis masks - perhaps a 12cm mask for a C14 or similar.

Netwonians can do better but the relative size of the CO still needs to be noted - so a scope with a 20% obstruction at full aperture will still be manageable, though less effective for its aperture, at 75% aperture where the CO becomes about 27%.

Refractors do best on this - no CO, so you're simply extending the f-ratio. Of course, that will lead to speculation about longer f-ratios being more effective than short (haven't we heard some comments about that before? ).

The project itself is a can'o'worms, as Bruce has now remarked, though he used other words. Even so, I think something interesting might come of it, even if only to suggest that Chris Lord's multi-factored approach represents a fair approximation to what we can predict - and that in terms of a "best-case".

I think we're all familiar with the experience of seeing/not seeing particular pairs at different times.


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