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M31 Dark Lanes and Gamma Cygni Greater Metropolitan Area

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#1 Eddgie

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Posted 05 October 2018 - 04:03 PM

10/4/18.   Perdenales Falls State Park, Tx.

 

Variable clouds.

 

SQM-L readings on the west side of Milky Way were about 21, and to the east (which is toward the sky glow of Austin, SQM-L was 20.9.    Austin light dome prominent to the east, and while far less easily visible, San Antonio, about 75 miles to the south, showed low wide dome close to the horizon, but tapered much before Sagittarius.  So, all combined, a solid Borte 4.

 

Milky Way Great Rift was easily visible, but to the naked eye or binoculars, did not show a lot of structure (though in my image intensified binocular, it was pretty breathtaking. I must have spent a full 20 minutes just on MW at 1x and 3x).  MW Is my favorite DSO of all time, but most of my session was spend on the vast nebula field in Cygnus.  I did though spend some time elswhere.

 

Andromeda was well above the Austin Light Dome, being half way to zenith, but this was not the best sky to see it.   I used my Mod 3 binocular with a pair of 3x lenses.  Because I was mostly free of light pollution, I left of the IR Pass filter because while it does suppress most light pollution, it also soaks up some energy, so while it is indespensible for city use, I go nude outside of Bortle 6.

 

At 3x, Andromeda is very large.  My true field at this power is about 10 degrees, and I would say that M31 extended out to a bit less than 3 degrees. From really dark skies, I have followed it out to well over four degrees, but this is about as good as I have seen it under Borte 4 skies.

 

I was not really expecting to see any dark lanes, but I was very pleased to see that two lanes did show, though I will qualify this.   The lane closest to the core on the M110 side was faint but not difficult to see. As with pictures, the lane seemed to stretch from just to the north or the core (about 1/3rd of the length) following a shallow arc to the south west of the core.   Again, thin and very delicate but not difficult. 

 

The outer lane, once again, on the M110 side, was more "Inferred" than seen.  To see a lane properly, one would think that one needs to see both of the brighter sides, but this lane sits on the side of M31 that fades quickly once past this lane, so that what is best seen is the inside edge of this lane. Past this, and without very careful study, it looks like the edge of the galaxy, but with some work, it can be seen that the galaxy extends past this dark edge to the west.  Under very dark skies, one can see this lane actually arc all the way the north and then hook back but conditions were not good enough to see this last night.  I would say the dark edge extended out a little more to the north, but not dramatically so. 

 

The galaxy itself always seems to have a bright spray coming out from the north to me but I think this is perhaps an illusion because picture show the core centered (as gravity would suggest) but while I could not follow the lanes around to the south side, I know that they are there and my guess is that they just dim the eastern end bit so that the northern side really does appear brighter in pictures (and in in the view of my Mod 3 binocular).

 

Standard 10x40 binoculars showed mostly the core glow, but I think one needs to have pretty dark skies to get the lanes to show in a binocular.  Maybe I am wrong.   The core though is pretty prominent in binoculars under these conditions and the extension is well over 1 degree, maybe more. One really needs dark skies to get a 2.5 degree extension out of this target I think but under Bortle 2 skies with the Mod 3, it is a very big object at 3x.

 

I have seen hints of the inner lane on the M110 side from my home (red zone) sky, but this galaxy gets better and better with darker skies.  My best view has been under Bortle 2 and here the lanes will much more pronounced, but I worked with what I had. 

 

I did a lot of observing, but the other cool thing was a visit to Gamma Cygni.   As an experiment, I used a 12nm on one side of the binocular and a 5nm on the other.  The problem with 5nm is that you can't come close to fitting this giant nebular metropolis into the non-band shifted portion of the field so while it does really bring out the dimmest nebula, only the central 1/3rd of the field is in band.    I had started with a 5nm on one side and a 7nm on the other, but just out of curiosity, I decided to try the 12nm on the side that had the 5nm.  Wow!   How cool.   The 12nm as almost no band shift, so this meant that I could see a far greater amount of extension all in the field without having to sweep, but clearly the center of the field was not as bright in the dual narrow notch view.  It was though very rewarding to see the hybrid view of this really staggering area.  

(A side note.  Even without filter, the Crescent was pretty easy to see using the 6" f/2.8.  There is some pretty bright stuff there).

 

One last observation with the Mod 3 binocular.   While low in the southwest, using two 7nm's the glow of the giant ball around Zeta Oph was pretty amazing even under Bortle 4 skies.  I have seen it under 3 and 2 and while it is of course better, Bortle 4 is good enough to show it as a very large irregular puff with a bit of structure, but I found that with narrow filters, it was best to pan over it to really see it well.    I tried the 12nm on this, but for this target, I think the two narrow band filters working together really did help here.   This is not as bright as the Angel Fish, but I think larger.  If you transported it across the sky, it seems like it would be a perfect fit just inside the curve of Barnard's Loop.  Maybe it ran away and is playing hide and seek?

 

(There is something funny too.  I go to dark skies more with NV than I used to before NV.  Before, I always thought I needed to bring a big telescope so organizing the outing seems to be far more daunting.  With NV, it seems almost effortless to take a small scope and some hand hold lenses to have a really fun session. Don't let NV lull you into not going out to darker skies.  Everything is better when the sky is darker.)


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#2 GeezerGazer

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Posted 05 October 2018 - 06:02 PM

Great observing report Ed!  I certainly agree that NV visual observing is convenient... and there is SO much to see.  It's hard to believe the extent of H-a nebulosity in the MW.  Sept. 7th, I took a 20 degree image within Cygnus with a 2" 7nm filter in front of a Nikon 50mm f:1.4 lens which shows just a small part of what you have described.  But it fairly represents the extent of nebulosity that glass eyepieces will never see.  I hope you don't mind, but this seems like the right place to put this photo. It does show how much H-a is up there!  The edge is a little dark, probably from band shift.  The main thing is that we commonly look at the Veil, Gamma Cygni complex or the North American/Pelican, or we slide down to the Crescent or the Tulip... but the reality is that the MW offers an incredible variety and amount of nebulosity.  ISO 80, 1/2s for 8s, unprocessed.

 

IMG_2365 2.jpg


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#3 Eddgie

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Posted 05 October 2018 - 06:30 PM

Yeah, that is a good shot.   This area is so incredibly complex.  I come back to it over and over and over, and it looks so different with different focal length SLR lenses and small scopes, and even in the 12" at f/4.9, I always feel like I see some new detail.   Not that it is an inexhaustible area, but it just boggles my mind that it can have such incredible variety in the structure.

 

Your picture captures the range of it pretty well. Everything from a giant continent, to a great valley, and down to tiny islands in the sea of stars.      

 

I wish I could be there every time someone uses NV to see this area for the first time. Frankly, it makes M31 look kind of boring. 



#4 Jeff Morgan

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Posted 05 October 2018 - 09:36 PM

I did a lot of observing, but the other cool thing was a visit to Gamma Cygni.   As an experiment, I used a 12nm on one side of the binocular and a 5nm on the other.  The problem with 5nm is that you can't come close to fitting this giant nebular metropolis into the non-band shifted portion of the field so while it does really bring out the dimmest nebula, only the central 1/3rd of the field is in band.    I had started with a 5nm on one side and a 7nm on the other, but just out of curiosity, I decided to try the 12nm on the side that had the 5nm.  Wow!   How cool.   The 12nm as almost no band shift, so this meant that I could see a far greater amount of extension all in the field without having to sweep, but clearly the center of the field was not as bright in the dual narrow notch view.  It was though very rewarding to see the hybrid view of this really staggering area.  

(A side note.  Even without filter, the Crescent was pretty easy to see using the 6" f/2.8.  There is some pretty bright stuff there).

 

What a cool idea! I wonder if the brain would be able to merge the images if you used h-alpha on one side and long-pass on the other?



#5 GeezerGazer

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Posted 05 October 2018 - 11:08 PM

What a cool idea! I wonder if the brain would be able to merge the images if you used h-alpha on one side and long-pass on the other?

Another good reason why Ed is the NV evangelist.  His passion and curiosity have yielded a phenomenal wealth of knowledge that he willingly shares here.  Using different filters in his NV binocular is but one example.  Thanks Ed for all you do for this community.  

 

Jeff, that sounds like an experiment that needs to happen!  I would love to hear the results.  



#6 Eddgie

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Posted 06 October 2018 - 01:31 PM

What a cool idea! I wonder if the brain would be able to merge the images if you used h-alpha on one side and long-pass on the other?

I have actually tried this in the past. but I had limited success with it.

 

The issue I believe is that the view is very dark in the H-a filtered side, but much brighter in the long pass side, so the side with the far brighter image dominates the view even if it was on the non-dominant eye.   This can be compensated for to some degree by turning down the gain on the long pass side, but by the time you get the brightness equalized, you loose some of the stars.  

 

It worked better with 12nm than with 7nm.   

 

It is though hard to merge the really bright view with the dark view so the long pass side has to be throttled.

 

I do a lot of low power observing with the binocular though.  In fact, I am in the market for a new Mod 3, but I may go with and Harris F9815 M24H thin film P43 tube.  I think I have come to prefer the P43.    I observe so much with the binocular that I dislike having to take a module off to use in the telescope.


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#7 Eddgie

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Posted 06 October 2018 - 01:33 PM

And speaking of merging. as an experiment I tried holding a P45 Mod 3 up to one eye and a P43 Micro to the other eye just to see what would happen.  As it turns out, it was dead easy to merge the two colors.   The eye simply seemed to blend them together.  So, it was easier to merge these two colors than it was to merge long pass and H-a unless the long pass side was dialed down quite a bit. 




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