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Cosmic Challenge: IC 5146 and B168

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#1 PhilH

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Posted 29 October 2016 - 08:35 AM

As a group, emission nebulae, or Hydrogen-II regions, are the most difficult deep-sky objects to see visually. The problem is that they radiate light in very narrow segments of the visible spectrum, with their brightest emissions in the red wavelengths. As luck would have it, the human eye is all but color blind to red light under dim light conditions.Arguably, the only objects more difficult to spot than emission nebulae are the opaque profiles of dark nebulae. These cosmic dust clouds are themselves invisible; we only see their silhouettes against the starry backdrop. No starry backdrop, no dark nebula; it's that simple. And that brings us to this month's double challenge in Cygnus. IC 5146, known to many by its nickname, the Cocoon Nebula, is a taxing patch of glowing gas, while Barnard 168 is a thin, sinuous lane of darkness that seems to start at the nebula and extend far to its northwest.

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#2 John O'Hara

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Posted 30 October 2016 - 04:02 PM

Phil, 

 

With the dark moon period upon us, so is the lake effect engine here in NW Pennsylvania.  I'd love to go after this object with my new 100 mm Pro ED.  I once tried the Cocoon many years ago with my old 6" f/8 AP, but I think the only filter I had in those days was the OIII and I did not succeed.  As popular as this object is, I've not revisited it despite the fact that I have better eyepieces and a better filter assortment and more experience.  Hopefully I'll get a chance before Cygnus recedes low into the northwest sky. 

 

BTW, are you still offering certificates for Star Watch?  My wife completed all of the objects and our attempts to e-mail you through your web site have all bounced.

 

Clear skies!

John O'Hara


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#3 Sasa

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Posted 02 November 2016 - 08:03 AM

Dark nebula B168 is one of the best I know for small telescopes. I have observed it several times from small 10x35 bino, and from 63mm up to 120mm refractors. Under dark sky, it is striking object, one of my favorite. Not so much under the light polluted sky from my backyard.

 

I have been trying to spot IC5146 numerous times during last couple of years, mostly using 63mm and 80mm refractors. Even under dark side I was not able to convince myself that I saw the nebulosity and not just atmospheric halos around the two stars.

 

Finally, this year late summer I got the first positive observation. It came from 150mm Cassegrain at 42x. Without filter there were two rounded halos around the two stars. With Hbeta filter, I noticed some irregularities, namely V shaped brighter line with vertex on the south star and the V was opened towards the north star. When I looked later at images, it looked like I have registered the southern edge of the nebula superimposed with the atmospheric halos. Definitely a challenging target.


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#4 Sasa

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Posted 04 November 2016 - 04:01 AM

Here is a very rough sketch from my logbook showing this V-shape line:

 

ic5146_20160908.jpg


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#5 PhilH

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Posted 06 November 2016 - 06:09 AM

Nice job all around!

 

And John, I haven't in years, but sure.  She needs to submit through my Star Watch web site.



#6 John O'Hara

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Posted 12 November 2016 - 06:13 PM

Thanks, Phil.  She'll give it another try.

 

John



#7 John O'Hara

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Posted 19 November 2016 - 08:26 AM

Phil,

 

I decided to try for this object pair with my 100 SW Ed (my first try with this scope) from my local dark sky site (about Bortle 4).  Unfortunately, the skies had high haze which hampered the observation.  At 22x with my trusty 40 Pentax XL, I could easily see B-168 and traced it to the position of the nebula.  However, with my Orion Ultrablock filter I only suspected the nebula.  I hope to try on a better night.  I later noted in that you used 46x with your 4" scope, but I'm not sure it would have made the difference with the hazy skies.  Actually, I was surprised at how well I could see B-168 in the haze. 

I've had this 4" refractor for a few months now, and wish I'd obtained such a convenient scope years ago!  I've been missing a lot of astronomy not having a good grab and go.

 

John


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