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brianb11213
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Reged: 02/25/09

Loc: 55.215N 6.554W
Re: Aerosol Diffusion new [Re: Asbytec]
      #6182990 - 11/08/13 01:43 PM

Quote:

The concept I am trying to get my head around is the decrease in blur visibility (falling off below the visible threshold) still affects a dimmer companion that would otherwise be visible...bright enough to peek above a dark sky background but not a background that 'appears' dark.



The way I read this:

If you have for instance a double star with 5 mags difference between primary & secondary, the contrast in the image will be the same irrespective of the brightness of the primary.

The issue with vision is that the smallest contrast that can be discerned decreases as the brightness falls towards the limit of vision (the same effect that makes low contrast planetary details harder to see when the magnification is pushed too high, even when the seeing is "perfect"), so brightening the image (without affecting anything else) should theoretically make the secondary easier to see, despite the glare.


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WRAK
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Reged: 02/18/12

Re: Aerosol Diffusion new [Re: Asbytec]
      #6183019 - 11/08/13 02:02 PM

Later in the night the clouds disappeared and I could do some observing - had to improvise a bit as it was already too late for my prepared session. Although Deneb was already rather low with about ~35 - my personal limit for reasonable double star resolving - I had also a look at Deneb.
Halo was again about ~60, may be a tad more and the +11.76mag companion was rather hard to resolve. I then had Deneb wandering out of my field of view and suddenly the companion "jumped out of the dark" - so this seemingly halo was more glare than haze. So transparency was rather good and I had a reasonable good session then in Peg. The most difficult object seemed HO480 0.9" +8.72/10.03mag - no resolution and because of the faint fuzzy impression my conclusion was that some haze even if low was enough to make the resolution impossible. My RoT showed for HO480 anyway 179mm so also here no real chance with 140mm. Later I found out that the current WDS separation is 0.3" - something must have happened here to WDS as in the version 12.05 the notes read "AB. First: 1892|225deg|0.7. Last: 2009|2deg|0.9. #Obs: 29" and in 13.08 suddenly "RA PM:17, Dec PM:-6, AB. First: 1892|225deg|0.7. Last: 1993|270deg|0.3. #Obs: 28". This would then require an aperture larger 400mm.
Thus are the adventures of the double star observer with catalogs.

Tonight I have the chance of some more haze and will try to get a better grip on the assumed relevance of the halo size for resolving doubles and also use a handicrafted half cover for the eyepiece to easier eliminate Deneb glare.
Wilfried


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Asbytec
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Reged: 08/08/07

Loc: La Union, PI
Re: Aerosol Diffusion new [Re: WRAK]
      #6183561 - 11/08/13 07:44 PM

Brian, okay if we're talking contrast similar to overly magnified planetary contrast, that makes some sense. I would imagine more sparely populated rods play a bit of a role with dimmer stars, too. Still, at some point in the magnification process of point sources, contrast improves as the extended sky object dims more rapidly until the disc behaves is magnified enough to behave in the same way. Fred often talks about dim companions near 10th magnitude, but I am not sure about the mechanics. Lemme mull it over.

Wilfred, I tried the occulting technique trying to observe the Pup as Sirius left the FOV. No luck with that, but should have paid closer attention to the extent of the halo size as the primary left the FOV. Will try that again. Gonna have clear skies tonight, if the seeing holds with a Typhoon just passing south of us.


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WRAK
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Reged: 02/18/12

Re: Aerosol Diffusion new [Re: Asbytec]
      #6184091 - 11/09/13 05:26 AM

Quote:

...The jury is still out for me as to how much light pollution reduces limiting magnitude...




Norme, I think Schaefer has done a good job here. There is even an online TML calculator on the Web (http://fisherka.csolutionshosting.net/astronote/astromath/SchaeferLMCalc.html) based on his work - the missing factor here is certainly the influence of transparency but the values for TML reduction due to light pollution and extinction seem very realistic.
Wilfried


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Aerosol Diffusion new [Re: WRAK]
      #6184227 - 11/09/13 08:51 AM

Yea, I saw that. But I'm obstructed and will loose about 10% illumination above and beyond other factors (unless he includes it in the "telescope type" variable.) Part of my problem is finding good magnitude references I can trust to evaluate field stars. Closer to 13th is about right and in accord with your 0.6 magnitude extinction.

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WRAK
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Reged: 02/18/12

Re: Aerosol Diffusion new [Re: Asbytec]
      #6184833 - 11/09/13 02:51 PM

Norme, I can offer an UCAC4 based map for NGC6811 in Cyg up to +13.5mag and I am preparing one for NGC7789 in Cas - if you are interested just give me the orientation you need.
Wilfried


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: Aerosol Diffusion new [Re: WRAK]
      #6184928 - 11/09/13 03:39 PM

Last night I got what I asked for (some haze in the air) but the results I got were mixed. The sky was clearly brighter than the night before and SQM reading was ~16.8mag meaning one mag brighter but NEML was the same with ~3.2mag - no idea how this may be to explain.
Deneb showed despite the haze a halo of similar size ~60" radius, but the companion was somewhat harder if barely to resolve. Occultation of the primary (my ideas how to do this better proved to be a desaster so it was again leaving the field of view) had this time only minor effect - the halo remained and the companion was equal hard to see as before.
Seeing was not this bad with estimated Pickering ~6 as the diffraction pattern was to my surprise rather crisp and not at all fuzzy but jumping according the Pickering scale for ~6.

Then I started my session in Peg beginning with wide and easy STF2986 31.2" +6.61/8.88mag and limit aperture was 80mm against 26mm RoT proposed - so I assumed this result was the effect of bad transparency. Only later on I found the the companion is probably much fainter.
Next came the surprise with HU987 1.1" +9.2/9.7mag and proposed aperture 145mm. I did not expect much but got already a rod with x140 and a clear split with x200 if only for repeated fractions of seconds but distinctive. With a CO of 0.15 I got a more stable split, same with x200. Same with 0.2 CO. Crisp spurious disks - no sign of fuzzy cotton balls.
Later on results were similar may be with only an exception for very faint doubles - here it was not possible to get to a reasonable high magnification without loosing resolution.

Conclusion: Naked eye haze means in the lower atmospheric layer may not be this problem for resolving doubles. The cotton ball effects must have reasons in haze in the higher atmospheric layers not to be seen with naked eye but only with scopes.
Wilfried


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Aerosol Diffusion new [Re: WRAK]
      #6185549 - 11/09/13 10:19 PM

Thanks, Wil, but I don't want to rely on asking each time. Need a good reference I can access at Wil (pun intended.) Actually, I found wikisky quite good. It gives magnitude for stars in overlaid images that can be glimpsed at the eyepeice. Haven't tried it for tight doubles, though.

http://www.wikisky.org/?object=NGC+7662&img_source=DSS2

Mulling over your next post...

Edited by Asbytec (11/09/13 10:20 PM)


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WRAK
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Reged: 02/18/12

Re: Aerosol Diffusion new [Re: Asbytec]
      #6185930 - 11/10/13 04:21 AM

Have seen that in my Deneb map I have also +13.01/13.30/13.67/13.89mag stars included. Should do it too to some degree.
According to my TML check implementation for the RoT the TML for your 155/0.31 scope with NEML ~+4.5mag should be about +13.2mag but currently I assume there is still the factor extinction to consider - so with an average extinction value of 0.3 this should give a ~+12.9mag limit relevant for resolving wide >15" doubles with a companion this faint.
Wilfried


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Asbytec
Guy in a furry hat
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Reged: 08/08/07

Loc: La Union, PI
Re: Aerosol Diffusion [Re: WRAK]
      #6185945 - 11/10/13 05:06 AM

Yes, got it (Deneb map) and will check it tonight. Weather is holding but seeing might be terrible. More later.

Edit: The dimmest star I could see was the 13.01 mag star west of Deneb. The nimbus was extensive tonight, reaching out to the 12th mag star trailing Deneb. Seeing was horrendous at 4/10 Pickering. Blew my difficult observing list out of the water. Shame for such a clear night, but apparently the typhoon is still drawing a lot of moisture and stirring upper level winds.

Edited by Asbytec (11/10/13 08:42 AM)


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