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Observation Gamma andromedae AB (9,6") +BC (0,16")

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#1 Konstantin 1980

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Posted 12 September 2019 - 09:29 AM

fifth day  is a very calm atmosphere. I try these days to observe all the most complex objects that are visible in the sky. I watch the gamma of Andromeda for the third day in a row, and every day I see the elongation of component B. I have repeatedly seen such close pairs, although there were not many. Every day I try to double-check this observation to avoid mistakes. But every day I see the same thing, so I can say that the winners of component C are visible with confidence. The elongation is small, but it is fixed very well in such a calm atmosphere. And is constantly visible. I made a small drawing of what I seeGAM ANDRM.png


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#2 rugby

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Posted 15 September 2019 - 08:19 PM

My hat is off to you Konstantin 1980 for this observation. Can anyone confirm the accuracy of 0.16? 



#3 fred1871

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Posted 15 September 2019 - 09:23 PM

The accuracy of 0.16" is not really in question. The orbit of Gamma And BC is well-enough known for that to be a good number. The question is how someone has the eyesight to see a disturbance in the diffraction image that translates to an elongation, when the telescope used has a Rayleigh criterion of 0.543", so that it is detection at 0.3-Rayleigh for 0.16". The usual detection limit is around 0.5-Rayleigh, with some observers using moderate to small scopes achieving 0.4-Rayleigh.

 

Christopher Taylor in his well-known discussion of limits of detected elongation in his article in Bob Argyle's book Observing and Measuring Visual Double Stars, claims 0.4-Rayleigh with a 12.5-inch Newtonian (detection at 0.175"). That was with 825x. Taylor was optimistic that somewhat better might be achieved, though without achieving it himself. His hoped-for level of detection was about 0.13", which for 12.5-inches is 0.3-Rayleigh. It isn't clear from his article what he based this on, apart, perhaps from a feeling that the closest pair he'd seen elongated was not as near the limit of perception as to suggest one couldn't go further.

 

Seeing conditions, even with near-perfect (as estimated) seeing appear to set more stringent limits with larger scopes. It's never as steady as hoped. Around 0.6-Rayleigh is usual for the big refractors (24-inch to 40-inch). Couteau got to 0.5-Rayleigh with the Nice Observatory 20-inch. Various observers have recorded 0.4-Rayleigh with smaller scopes, as per Taylor above. RTA Innes, notable for his Southern Hemisphere double star work (1890s to 1920s), found a detection limit around 0.4-Rayleigh with a 9-inch refractor.

 

So the answer for 0.3-Rayleigh detection seems most likely to be exceptional eyesight, in conditions of "as good as it gets" atmospheric steadiness. The use of binocular viewing may well help too. All the observers I'm familiar with who observed exceptionally close pairs (for the aperture) were using monocular vision.


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#4 rugby

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Posted 16 September 2019 - 10:33 PM

Given that seeing is ideal and the observer is experienced, sightings of pairs below the rayleigh limit are not rare. Like you Fred 1871 my eyesight is only average. But look again at an observation I made of Stt381 in Aquila in July this year. I suspected strongly that the diffracton disc was irregular  in the correct PA. which for an 8-inch was .6 Rayleigh. Perhaps Constantin would try his hand on this one.



#5 RadioAstronomer

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Posted 17 September 2019 - 12:17 AM

The accuracy of 0.16" is not really in question. The orbit of Gamma And BC is well-enough known for that to be a good number. The question is how someone has the eyesight to see a disturbance in the diffraction image that translates to an elongation, when the telescope used has a Rayleigh criterion of 0.543", so that it is detection at 0.3-Rayleigh for 0.16". The usual detection limit is around 0.5-Rayleigh, with some observers using moderate to small scopes achieving 0.4-Rayleigh.

 

Christopher Taylor in his well-known discussion of limits of detected elongation in his article in Bob Argyle's book Observing and Measuring Visual Double Stars, claims 0.4-Rayleigh with a 12.5-inch Newtonian (detection at 0.175"). That was with 825x. Taylor was optimistic that somewhat better might be achieved, though without achieving it himself. His hoped-for level of detection was about 0.13", which for 12.5-inches is 0.3-Rayleigh. It isn't clear from his article what he based this on, apart, perhaps from a feeling that the closest pair he'd seen elongated was not as near the limit of perception as to suggest one couldn't go further.

 

Seeing conditions, even with near-perfect (as estimated) seeing appear to set more stringent limits with larger scopes. It's never as steady as hoped. Around 0.6-Rayleigh is usual for the big refractors (24-inch to 40-inch). Couteau got to 0.5-Rayleigh with the Nice Observatory 20-inch. Various observers have recorded 0.4-Rayleigh with smaller scopes, as per Taylor above. RTA Innes, notable for his Southern Hemisphere double star work (1890s to 1920s), found a detection limit around 0.4-Rayleigh with a 9-inch refractor.

 

So the answer for 0.3-Rayleigh detection seems most likely to be exceptional eyesight, in conditions of "as good as it gets" atmospheric steadiness. The use of binocular viewing may well help too. All the observers I'm familiar with who observed exceptionally close pairs (for the aperture) were using monocular vision.

Totally agree. Let me add this chart from Couteau's book Ces astronomes fous du ciel : Ou l'histoire de l'observation des étoiles doubles with the resolving power vs inches of the instrument. He claims that Burnham has the record with the discovery of the companion of Rigel B. He also mentions that smaller apertures are more likely to deeper under the resolving power than larger apertures.

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  • Screen Shot 2019-09-16 at 7.48.39 PM.jpg

Edited by RadioAstronomer, 17 September 2019 - 12:18 AM.



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