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General Astronomy >> General Observing and Astronomy

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David Knisely
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: blb]
      #6143402 - 10/17/13 05:45 PM

Quote:

David wrote;
Quote:

...Viewing the central star in M57 depends largely on the stability of the atmosphere, so if seeing isn't rock-solid, you won't see it no matter how big the telescope is. Clear skies to you.



Does that mean that seeing any stars of 15th mag. and fainter is totaly seeing dependent even with larger telescopes. I mean, most people who have 18-inch to 24-inch telescopes have trouble seeing the central star. True?




No, the problem is that the diffraction disk of the central star is imbedded in faint nebulosity. When the seeing blurs the disk, it then blends perfectly into that faint glow and vanishes. Outside of the ring against the dark background of space, a 15th magnitude star has little to compete with, although you will be able to see slightly fainter stars when seeing is very good. When I saw the central star from my driveway in my 9.25 inch SCT, I could see a magnitude 15.3 star well ouside the ring much of the time, but only occasionally when the seeing got really really good would the central star finally pop out. Larger scopes (10 inches and larger for example) will show stars fainter than 15th magnitude seen against the dark background of space when seeing isn't necessarily rock-stable, but when it comes to the central star in the Ring, unless seeing is very very good and relatively stable, no telescope no matter how large will show that star. Clear skies to you.


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Charles Funk
member


Reged: 09/06/05

Loc: W. Tennessee
Re: M57 central star? new [Re: David Knisely]
      #6143625 - 10/17/13 07:58 PM

I have seen this winking in and out of stars in M42 on many occaisions. When you look long enough, it puts on an interesting show.

I have never tried seeing the CS in M57, but you can bet I will give it a whirl next time out. Just recently I observed M57 at around 300x on a whim and it was awesome in the 12.5 But I didn't think to look for the CS. I do like a challenge.


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Kfrank
Carpal Tunnel


Reged: 12/20/08

Loc: Northern Colorado
Re: M57 central star? new [Re: Charles Funk]
      #6145029 - 10/18/13 02:45 PM

Several people have described the central star as "fading in and out". This is due, essentially to the same visual phenomena that make 'the "Blinking Planetary" appear to blink.

Remember also that the "Ring" Nebula is not really a ring - it's roughly spherical in nature and simply appears to be a ring. We're actually looking at the center of the "ring" through the cloud of the nebula.


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David Knisely
Postmaster
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Reged: 04/19/04

Loc: southeastern Nebraska
Re: M57 central star? new [Re: Kfrank]
      #6145791 - 10/18/13 10:58 PM

Quote:

Several people have described the central star as "fading in and out". This is due, essentially to the same visual phenomena that make 'the "Blinking Planetary" appear to blink.

Remember also that the "Ring" Nebula is not really a ring - it's roughly spherical in nature and simply appears to be a ring. We're actually looking at the center of the "ring" through the cloud of the nebula.




No, the "blinking" of the Blinking planetary (NGC 6826) is due to the difference between direct and averted vision in moderate to small telescopes. Looking directly at NGC 6826 may cause it to dim or nearly vanish, while using averted vision will allow it to be seen. The variable sighting of the central star of the Ring nebula is almost entirely due to seeing variations causing the central star's diffraction disk to be blurred. When this happens, it totally blends in to the surrounding faint nebulosity, rendering it invisible unless seeing is rock-stable, no matter how big the telescope is or whether averted vision is used or not. When I saw the central star in a 20 inch Dobsonian, I was able to use direct vision on it, as it was bright enough in that scope. When the stability of the seeing became degraded, the star vanished, again, for the reason stated above. Clear skies to you.


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Starry eyes
super member


Reged: 04/30/10

Re: M57 central star? new [Re: David Knisely]
      #6146339 - 10/19/13 10:20 AM

I would say seeing is the main criteria to see the CS.
When seeing is decent I can see it in my 18" Split Ring, flickering in and out @ 320x. A smooth drive helps. In a 30" it is visible pretty much all the time with good seeing.


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Skylook123
Postmaster
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Reged: 04/30/05

Loc: Tucson, AZ
Re: M57 central star? new [Re: Starry eyes]
      #6146370 - 10/19/13 10:33 AM

Up at 7000 feet about four years ago on one night of exceptional transparency and seeing at the Grand Canyon Star Party, Mike Spooner was able to easily show the central star in one of his awesome 14" mirrors in a home made Dobsonian mounted reflector. Even visitors never having looked through a telescope before were able to see it. Quite striking.

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