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Then I saw it, now I don't

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#1 Michael Rapp

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Posted 03 November 2013 - 08:10 PM

I've only been doing double stars since late this summer, in which Southeast Texas generally has very good seeing due to the high pressure systems that park themselves over our State.

In a recent thread, I related how I had split Delta Cygni with relative ease.

Imagine my surprise when last night I tried to split Delta Cygni again -- same scope, same eyepieces -- and could not detect the companion! A cold front moved through the area two nights ago so the seeing is much, much worse.

Moreover, the star was moving around in the field of view! I'm not used to using such high magnifications, so this affect of bad seeing was fascinating to view.

While this may seem obvious to many, this past night gave me a wonderful introduction to how seeing really matters on close pairs!

#2 Asbytec

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Posted 03 November 2013 - 09:04 PM

I'd agree, Micheal. I've had difficult success on one night and a complete failure on another. The difference may well be the conditions on each night.

I have seen that rapidly jumping star image, it's pretty prevalent in modest apertures due to some larger scale atmospheric tilt component during modest seeing - rapidly changing the apparent position of the image. Otherwise, the images stays pretty much intact depending on aperture and the severity of smaller scale seeing. It just bounces around a lot. If I understand it, that's the same property that begins to make larger instruments break into a speckle pattern while smaller apertures still enjoy some semblance of better seeing.

#3 azure1961p

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Posted 03 November 2013 - 09:46 PM

Delta Cygni for me is one that sits on the fence between 6 and 4-5 Pickering. Poor or less than mediocre and its gone. Its a good thing its summer constellation or Id be totally out of luck or nearly so in January for example.

Pete

#4 Bonco

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Posted 04 November 2013 - 04:22 PM

I just posted another thread about delta then I read this one. In general the night following a cold front has great transparency but very unsteady air resulting in bad seeing. With really good seeing the secondary can be viewed with a 60mm, but its not easy. Typically my 75mm shows it just fine in mediocre steadiness. But as most probably know if its real shakey air nothing will show it. Bill

#5 azure1961p

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Posted 04 November 2013 - 08:36 PM

Hi Bill,

The one time I tried with my 70mm I didn't have a chance in spit - the seeing was 4 Pickering and it just wouldn't allow even a passing mirage to pop through. I would like to bag it with that scope though.

Pete

#6 Bonco

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Posted 05 November 2013 - 05:10 PM

Pete,
I really enjoy using minimum aperture to obtain results on double stars. Why? Because the star images are so pure and less affected by seeing conditions. Additionally small telescopes are easy to setup and takedown. I'm sure your Ranger can split Delta Cyg if conditions are right. Bill






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