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IC 443 Jellyfish Nebula

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#1 gustave

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Posted 01 February 2020 - 11:59 AM

Any info would be appreciated on your experience viewing IC 443.  I've found a absolute magnitude discrepancy between resourses.  One cites a value of 9, an another 12. I was unable to find any sketches by amateurs as to what it may appear as through a  mid range scope. I use an 11" CPC.

Thanks...


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#2 chrysalis

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Posted 01 February 2020 - 01:14 PM

I have tried repeatedly from Bortle 5 skies with and without narrow band and OIII filters (DSM, Lumicon) to no avail.

 

Data for my sky below from https://www.lightpollutionmap.info/

 

SQM 20.31 mag./arc sec2
Brightness 0.815 mcd/m2
Artif. bright. 644 μcd/m2
Ratio 3.76
Bortle class 5
Elevation 273 meters


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#3 havasman

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Posted 01 February 2020 - 02:57 PM

From the club dark site with average SQM-L @ 21.3 via 16" f4.49 Dob, largest exit pupil and O-III narrowband filter IC443 is a faint, very large nebula with a brighter region arcing across 30' or so of a field with the fainter regions extending about twice that. Individual nebular streams are seen curving away from the brighter arc, mimicing the tendrils of a jellyfish but wider. Overall, faint. Not seen at all w/o O-III.

 

Large nebulae can present the extra difficulty of missing the edge of the object in many framings and can show less apparent contrast in the small field than might be seen in a larger one at like exit pupils with the edges in view.

 

Successful observation of IC443 from a light polluted site sounds very difficult to me.


Edited by havasman, 01 February 2020 - 03:09 PM.

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#4 sgottlieb

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Posted 01 February 2020 - 10:09 PM

The sketching forum here has several examples.

 

Listed magnitudes for diffuse nebulosity are pretty useless, but it may be visible in your 11" (the smallest scope I've used is a 13") -- it really depends on the darkness of your skies.  Here are a couple of observations in my 18".

 

23 Feb 2006: easily visible at 73x and OIII filter.  The brightest portion is a 5' elongated strip that very gently curves WNW-ESE.  Faint haze extends out from this strip towards the south and west.  An extremely faint extension of the strip continues to the SE and curves towards an obtuse triangle of three stars, increasing the length of the edge of the shell to over 10'.

 

16 Jan 2002: at 64x and OIII filter, the most prominent section of this supernova remnant is a gently curving band of nebulosity oriented NW-SE, ~10'x3' with a well-defined edge along the eastern (bowed-out) boundary. A larger region of low surface brightness haze, ~20' in size, spreads out to the west of the northern end.  At the SE end, the band dims and seems to hook to the SW towards a small arrowhead of stars.


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#5 Pcbessa

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Posted 02 February 2020 - 11:46 AM

I have seen it on my 10" with an UHC filter but only from Bortle 2 and a good night. Nebula was still faint
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#6 uwe_glahn

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Posted 03 February 2020 - 04:26 PM

Unfortunately I never tried it with mid-size aperture whether its definitely worth a visit or a try.

 

Smallest aperture was 16-inch. I noted:

16", 57x-69x, [OIII], NELM 6m5+: northern main arc steadily visible, somewhat fragmented with brighter norther end (~5'), fainter opposite arc to the southwest much more difficult but also visible with averted vision as fragmented glow

 

The 27-inch showed much more detail. The main northern arc is visible over a length of around 30'. To my surprise the brighter portions shows details which remains me to much brighter detailed nebula like the Veil.

sketch: 27", 172x, [OIII], NELM 6m5+, Seeing III

IC443.jpg


Edited by uwe_glahn, 03 February 2020 - 04:35 PM.

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#7 sunnyday

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Posted 03 February 2020 - 04:31 PM

Unfortunately I never tried it with mid-size aperture whether its definitely worth a visit or a try.

 

Smallest aperture was 16-inch. I noted:

16", 57x-69x, [OIII], NELM 6m5+: northern main arc steadily visible, somewhat fragmented with brighter norther end (~5'), fainter opposite arc to the southwest much more difficult but also visible with averted vision as fragmented glow

 

The 27-inch showed much more detail. The main northern arc is visible over a length of around 30'. To my surprise the brighter portions shows details which remains me to much brighter detailed nebula like the Veil.

sketch: 27", 172x, [OIII], NELM 6m5+, Seeing III

IC443.jpg

WOW 



#8 j.gardavsky

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Posted 03 February 2020 - 05:03 PM

Hello Uwe,

 

that's a super sketch of the shock front on the Jellyfish!

 

Through my 6", I was able just to see the extended brightening east of Eta Geminorum, the 6" aperture does not resolve any details.

 

Thank you very much for sharing the sketch,

Jiri



#9 Redbetter

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Posted 04 February 2020 - 12:05 AM

Those would be apparent rather than absolute magnitudes.  What actually matters is not the magnitude, but the surface brightness and how dark your location is.  This one is bright enough I would expect it to be visible without too much difficulty in an 11" using a large exit pupil in dark sky.  Bracken's Astrophotography Sky Atlas shows it as a bright emission nebula and my visual impression from 12/26/17 with the 20" supports that. 

 

"Bright" is a relative term though, so what is rated as bright for imaging can be faint visually.  For example Sh2-249 (IC 444) is next to it and is displayed as average surface brightness.  On the same night I saw it only as a faint smudge, but looking at my notes and Uranometria I recognize that Uranometria was likely misleading me as to what size object to look for and where Sh2-249 would be most visible.  Therefore I was using too small of an exit pupil/field to see the extent of it.

 

My description of IC 443 was "Enormous bubble/arcs of nebulosity, seen mostly as fainter southern arc trailing behind Propus and a brighter northern arc well away from the star.  Best seen with a DGM NPB in 31T5, keeping Propus out of the field."  This was at my Bortle 2/3 site with conditions tending toward Bortle 2 that night (21.6+ MPSAS.)  81x in the 20". 

 

These are two objects I should revisit.


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#10 PEterW

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Posted 05 February 2020 - 12:35 PM

Be careful with Bracken, bright in hydrogen alpha is not necessarily bright visually it doesn’t indicate how much hydrogen beta/OIII might be present. It’s more a useful resource for NV users (8” under suburban conditions shows a clear curved arc for the jellyfish). If the nearly monkeyhead is visible then the jellyfish should be possible.

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#11 Pcbessa

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Posted 05 February 2020 - 02:03 PM

The jellyfish is considerably fainter than the monkeyhead.
I would say if you see well the rosette or the flame (which become poorly visible is less ideal conditions), look out for the Horsehead and background IC nebula. If that's visible, then the jellyfish will be visible. Both are rather faint.
Another test is whether the heart and soul nebula are visible. If these somehow faint nebula are visible, then you could aim for the jellyfish (which is a bit fainter).
By the way, the nearby lower nebula is aso very faint.
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#12 j.gardavsky

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Posted 05 February 2020 - 04:00 PM

The jellyfish is considerably fainter than the monkeyhead.
I would say if you see well the rosette or the flame (which become poorly visible is less ideal conditions), look out for the Horsehead and background IC nebula. If that's visible, then the jellyfish will be visible. Both are rather faint.
Another test is whether the heart and soul nebula are visible. If these somehow faint nebula are visible, then you could aim for the jellyfish (which is a bit fainter).
By the way, the nearby lower nebula is aso very faint.

This concides pretty well with my visual experience and rating of the difficulty levels.

 

The only exception might be the Valentin's Heart and Soul nebulae.

I have seen the Valentin's Heart Nebula 95 times through the binoculars, but the Jellyfish only through my 6" F/5 refractor.

Admitted, my eyes might have been trained on the Valentin's nebulae over the years.

 

Clear skies,

JG



#13 Redbetter

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Posted 05 February 2020 - 05:11 PM

Be careful with Bracken, bright in hydrogen alpha is not necessarily bright visually it doesn’t indicate how much hydrogen beta/OIII might be present. It’s more a useful resource for NV users (8” under suburban conditions shows a clear curved arc for the jellyfish). If the nearly monkeyhead is visible then the jellyfish should be possible.
 

That is not my experience with Bracken.  While I am sure there are exceptions, the emission/reflection objects in Bracken are visible to the eye.  I find the relative brightness correlates reasonably well to the visual.   The nebulae shown as bright are indeed relatively bright in their emissions, but it requires dark sky and appropriate filters to really show the detail.  I can and have shown complete novice members of the public such objects.  Targets shown as moderate intensity become difficult to discern detail visually, and for ones shown as truly faint the overall level is mere detection of very general shape.  Seeing Barnard's loop stretching between the feet of Orion is an example of the very faint, while the northeast arc is of moderate intensity.

 

This is more a matter of calibrating one's eyes to what given levels mean, and learning how to do threshold detection of faint nebulosity.  To me an H-Beta filter is often more useful for this than OIII or narrowband, but most visual observers don't employ their H-Beta filters frequently enough from what I have seen. 

 

I have had the impression that many NV users never learned to recognize fainter nebulae in dark sky.   Of course that is not true of all NV users and there is crossover, but there have been frequent posts suggesting something was an NV target and not a visual target...yet I see them without NV.  I don't doubt that NV makes these easier to see (particularly not requiring dark sky) and reveals more detail, but there is more in reach of the eye than many appreciate.      


Edited by Redbetter, 05 February 2020 - 05:13 PM.


#14 Jeff Morgan

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Posted 06 February 2020 - 12:51 AM

I have had the impression that many NV users never learned to recognize fainter nebulae in dark sky.   Of course that is not true of all NV users and there is crossover, but there have been frequent posts suggesting something was an NV target and not a visual target...yet I see them without NV.  I don't doubt that NV makes these easier to see (particularly not requiring dark sky) and reveals more detail, but there is more in reach of the eye than many appreciate.      

 

I have followed Pcbessa's posts over the last year with great interest as he explores faint emission nebula by conventional means. He has racked up an impressive list of accomplishments in a very short time!

 

Indeed, being a fan of Walter Scott Houston I was also pushing the back the list of "photographic only" nebula in the 1980's as nebular filters came into widespread use.

 

Your sweeping generalizations of NV users are greatly mistaken. Like most expensive astro gear, very little of it is going into the hands of beginners. Many NV users have been on CN for a decade and more, and observing faint fuzzies long before that. Check the bios.

 

Back on topic, this is what the Jellyfish looks like to an NV user (from my observing log):

 

Mar 31, 2019, Z16, Home: bright and detailed, definitely a Top Tier nebula! It is easy to see why this is called the Jellyfish. The eastern edge is sharply defined with tendrils that bleed away west. There is a ton of filamentary detail (reminiscent of the Eastern Veil). Nebulosity (faint) extends all the way down to Eta Gem (Propus).



#15 Redbetter

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Posted 06 February 2020 - 03:27 AM

Indeed, being a fan of Walter Scott Houston I was also pushing the back the list of "photographic only" nebula in the 1980's as nebular filters came into widespread use.

 

Your sweeping generalizations of NV users are greatly mistaken. Like most expensive astro gear, very little of it is going into the hands of beginners. Many NV users have been on CN for a decade and more, and observing faint fuzzies long before that. Check the bios.

 

 

It wasn't a sweeping generalization because I acknowledged that there are a mix of NV observers and crossover.  However, what I have definitely noticed is a tendency of NV proponents to underestimate what nebulae can be observed visually.   (While you came to mind when I typed that, there have been similar examples by other NV proponents that have led me to this conclusion about underestimating the visual, so it is not all on you. ) 

 

How long someone has been observing does not really inform me about how proficient they have become in seeing faint nebulosity, or whether they are employing the proper filters or if they are observing in dark enough skies.  As an example:  From what I recall you were not finding an H-Beta filter helpful for conventional visual on H-Beta targets (e.g. the large around of nebulosity around Gamma Cygni.)  As you stated: "my overall impression was UHC was better on most of David Knisely's H-Beta list."  Giving you the benefit of a doubt then and now, it still seems likely to me that you had a rusted H-Beta that was hindering your ability to see fainter nebulosity.

 

However, there was also this comment by you in another thread:  "For the folks not using NV - they need a medium aperture telescope to have a ghost of a chance of seeing the HorseHead (and even then ... it will be a marginal sighting)." 

 

Contrasting this is that as a complete novice I didn't find the HH all that challenging with an 8" SCT and H-Beta at what was roughly a Bortle 4 site at the time.  More recently I detected/observed it with a 127mm Mak with a marginal exit pupil in not particularly good Bortle 3 conditions.  I have seen the notch with smaller aperture, others have seen the HH with ~3 and 4" scopes. 



#16 PEterW

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Posted 06 February 2020 - 07:15 AM

It’s very interesting to hear how many of these nebulae are there for the taking, but I guess people go looking for stuff they believe is visible. Many people focus on aperture, when exit pupil might be more important. It would be good to know what combination of exit pupil, optics, filter type etc people have found to be best.
Not sure how widespread filter use is with binoculars as they don’t come with filter threads, also many don’t use hydrogen beta filters as they are normally dismissed as Horsehead only filters for big apertures only. I have UHC as it still blocks light pollution, but gives me OIII AND H-beta, which I though better value, of course if hydrogen nebulae are the goal then the OIII reduces the blocking.

Although most NV users are seasoned observers, many get into it as they live in cities and so may have less dark sky/faint observing experience than others may have. We use it see more from the crappy skies where we live.
I use sweeping and averted vision as normal observers do to help detect subtle changes. NV is at affected by optical speed, filter bandwidth and transparency, darker skies still improve things).

Peter
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#17 Pcbessa

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Posted 06 February 2020 - 03:39 PM

I have no NV but I do not doubt how astonishing emission nebula look with it, as compared with visual observation. If they weren't so expensive, I would certainly go for them.

At the same time there is a certain magic doing eye visual only under dark skies.
Most nebula are very faint observed visually as compared to NV.

Under dark skies with a medium aperture (10") and a filter, there are about 30 large emission nebula (not counting planetary nebula) that will look nice, with many dozen others being visible but very faint.

A non complete list, from brightest to faintest, would be: Orion, lagoon, M17, M16, M78, Veil, north America, monkeyhead, running man, pacman, crescent, Rosette, Flame, pelican, skull, northern lagoon, Sadr complex, Thor's helmet, Helix, Ic410, coccoon, iris, bubble, footprint, Medusa, ngc1980, ngc2170, California, wizard, Heart, Soul, Seagull, Fox fur, cosmic bat, Merope and maia, Elephant trunk, gamma Cass, lion mace, Dryer complex, Horse head and Ic434, lobster claw, propeller, lambda orion, jelly fish, barnards loop, flaming star, cave, tulip, flying bat, witch head and lower nebula.

The nebula listed after the Elephant Trunk are quite faint and the ones listed after the propeller are very faint.

I omitted many small bright nebula and some very faint unnamed sharpness nebula.
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#18 Jeff Morgan

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Posted 06 February 2020 - 09:58 PM

From what I recall you were not finding an H-Beta filter helpful for conventional visual on H-Beta targets (e.g. the large around of nebulosity around Gamma Cygni.)  As you stated: "my overall impression was UHC was better on most of David Knisely's H-Beta list."  Giving you the benefit of a doubt then and now, it still seems likely to me that you had a rusted H-Beta that was hindering your ability to see fainter nebulosity.

 

I did see something about the oxidized filter concern on the forums some months ago. Assuming that controversy is true I could have been vulnerable as I buy many items on the used market, including filters. Plausible, but nebulous (so to speak).

 

Or, it could be a product of Expectations. Expecting to see significant improvement and seeing very little improvement vs. UHC, I stuck with UHC (which included the h-beta line anyway).

 

The third possibility is that h-Beta offers no significant gains with IC 1318.

 

To check the last possibility I did a search on IC 1318 hoping to turn up research papers that would show the spectrum. Most of the emission nebula spectra I have seen are dominated by h-alpha. O-III output is usually around half of that, and h-beta a distant third. But all nebula are not identical, neither are their ionizing stars.

 

But no immediate hits to nail it down. It then occurred to me that imagers would know what is effective on IC 1318. They are driven and competitive. And they spend lots of money, so a $200 line filter would certainly be used where effective.

 

Going to astrobin.com and doing a search on IC 1318 turned up 3000+ images. Scanning the first two pages (114 color images), guess how many listed h-Beta subs in their images?

 

https://tinyurl.com/t4gpbur

 

h-alpha, O-III, and S-II are the runaway winners in that sample. And probably in the next 2900 too.

 

Somewhere in those 3,000+ images someone has undoubtedly tried h-Beta on IC1318. But not finding it in the first 114 images is a rather poor sampling rate. It would seem imagers as a group know something which confirms my 2011 observations of UHC vs. H-beta.

 

I'm glad it is working for you however. 


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#19 Redbetter

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Posted 07 February 2020 - 12:27 AM

Apples-to-oranges comparison for visual.  Why would imagers do H-Beta when they can do H-alpha which will be much stronger where the H-Beta is present?  They have the OIII for the regions that have enough oxygen.  Yes, OIII tends to be brighter where it is present.  If our eyes could see H-alpha well at night, then we would use it rather than H-Beta, but out scotopic vision doesn't pick up the H-alpha wavelength well.

 

The problem with hydrogen rich clouds is that the OIII components tend to be weaker or spotty.  The OIII regions tend to have stronger emissions, but are typically not as extended.  So while local contrast is often enhanced with OIII alone where it overlaps, extent is often lost where oxygen is missing. 

 

UHC/NPB filters typically have over twice the band pass of an H-beta, and that poses a significant contrast problem when the OIII emissions are weak or non-existent, but H-Beta is present.  (This is akin to using UHC/NPB rather than an OIII filter for an OIII region.)  Why cut your contrast in half or worse if you don't have to?  When I expect/suspect a region will be strong in hydrogen and weak in oxygen I tend to use the H-beta.  The narrower bandwidth also helps to considerably dim the stars (especially in a cluster or star could where these nebulae often reside.)  Not that UHC/NPB style filters aren't useful or preferable for many things.

 

This gets back to the difference between looking for the brighter regions, vs. detecting fainter nebulosity and its extent.  With wider filters one might indeed see brighter portions better, or be happier with the presence of more/somewhat brighter stars.  But that is not where the limit of the fainter nebulosity resides from what I have seen.  For fainter Sharpless nebulae the H-Beta filter is one of the more useful tools I have.


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#20 j.gardavsky

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Posted 07 February 2020 - 12:00 PM

Nearly all DWB nebulae in the Cygnus X-1 region are HII objects, and so are practically all Lynd's nebulae, which are not listed in NGC/IC or in Sharpless (Sh2-) catalogues. Moreover, most of the planetary nebulae not listed in the NGC/IC are dominated by HII.

 

So, there are some 1,300 nebulae, visually for the H-Beta filters, and in fact most of these faint fuzzies require more aperture, less magnification, and narrower H-Beta filters to dim the sky background and the interfering stars.

 

When hunting these galactic nebulae, I mount on the filter wheel two H-Beta filters with different passbands, and for the other galactic nebulae two OIII filters and again with different passbands.

 

Even if I have a bunch of the UHC filters, they don't find frequent use.

 

Best,

JG


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#21 Jeff Morgan

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Posted 07 February 2020 - 03:03 PM

Why would imagers do H-Beta when they can do H-alpha which will be much stronger where the H-Beta is present? 

 

I'm not am imager (yet), but I'll take a cut at this: Could it be to make color images?

 

Specific nebular lines can be combined into a color image. A little digging show the overwhelmingly popular lines for IC 1318 are H-alpha, S-II, and O-III like these images:

 

http://cs.astronomy....lae/491310.aspx

https://astro.nights...318_Newton.html

http://www.qdigital-...utterfly-nebula

 

And so forth and so on. In the interest of fairness, images of this target using H-Beta do appear from time-to-time:

 

https://www.astrobin...?page=2&nc=user

 

Imagers seem to consider H-Beta as a very minor player on IC 1318. Visually, I found the same thing.

 

I'm not sure what agenda you have introducing something I said in another thread regarding a 2011 observation of a totally different object into this one. Maybe I should not believe my Lying Eyes?

 

Maybe we should just go back on the topic of IC 443.



#22 Jeff Morgan

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Posted 07 February 2020 - 03:04 PM

Nearly all DWB nebulae in the Cygnus X-1 region are HII objects, and so are practically all Lynd's nebulae, which are not listed in NGC/IC or in Sharpless (Sh2-) catalogues. Moreover, most of the planetary nebulae not listed in the NGC/IC are dominated by HII.

 

So, there are some 1,300 nebulae, visually for the H-Beta filters, and in fact most of these faint fuzzies require more aperture, less magnification, and narrower H-Beta filters to dim the sky background and the interfering stars.

 

When hunting these galactic nebulae, I mount on the filter wheel two H-Beta filters with different passbands, and for the other galactic nebulae two OIII filters and again with different passbands.

 

Even if I have a bunch of the UHC filters, they don't find frequent use.

 

Best,

JG

 

It was a pleasant surprise to find that planetary nebula respond very well to h-alpha. Of the 60 I have tried that filter with, only one (IC 4663) did not seem to respond to it.

 

Back on H-Beta, Checking my observing log the scopes used where a 120mm refractor and 12.5" Newtonian. Observing sites were 20.5 and 20.9 (estimated as I did not own a SQM in 2011).

 

At this point, going further on H-Beta seems off-topic, so I will start a new thread. Maybe something positive comes from this H-Beta tempest.


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#23 PEterW

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Posted 07 February 2020 - 03:09 PM

Mounting two filters... are you stacking filters to hugely improve the blocking of non-hbeta signal? (Or putti NV different pass bands into each eye?

Peter

#24 Redbetter

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Posted 07 February 2020 - 05:12 PM

I'm not am imager (yet), but I'll take a cut at this: Could it be to make color images?

 

Specific nebular lines can be combined into a color image. A little digging show the overwhelmingly popular lines for IC 1318 are H-alpha, S-II, and O-III like these images:

 

http://cs.astronomy....lae/491310.aspx

https://astro.nights...318_Newton.html

http://www.qdigital-...utterfly-nebula

 

And so forth and so on. In the interest of fairness, images of this target using H-Beta do appear from time-to-time:

 

https://www.astrobin...?page=2&nc=user

 

Imagers seem to consider H-Beta as a very minor player on IC 1318. Visually, I found the same thing.

 

I'm not sure what agenda you have introducing something I said in another thread regarding a 2011 observation of a totally different object into this one. Maybe I should not believe my Lying Eyes?

I am not an imager but HOS/SHO (H alpha, OIII, SII) or variants are the standard nebula imaging filter system from what I understand.  Since H-Beta gives much of the same information as H alpha, but is a weaker signal, why would they choose it?  Yes it is a different color, but they are already imparting somewhat a false color palette (e.g. the SII). 

 

Again, we are talking visual targets and what the eye is sensitive to versus an imaging device/NV.  For imaging/NV H-alpha is more convenient because the nebulae are brighter in H-alpha.  That isn't what the eye sees.  However, both the NV device and eye benefit from contrast enhancement of the hydrogen emissions:  H-alpha filter for NV, H-Beta for the eye.  Double the width of the band pass for either and the result won't be as good.

 

No, H-Beta is not a "very minor player" for IC 1318 for the visual.  That you would say that demonstrates a lack of familiarity/proficiency with detecting fainter nebulosity visually.  And for the visual, contrast matters, which the H-Beta is often better for in these HII regions.  I have wandered around that vast area in Cygnus a few times and there is a lot of very faint H-Beta nebulosity there, making it very tough to navigate.  I have never tried to systematically log it all--partly because I didn't have a guide that went deep enough for ID (Bracken only shows some of the brightest in that region, Uranometria has more but still not enough.)   Trying to sort where one segment begins and ends is a challenge the fainter one goes because there are often fainter extensions at the visual contrast limit for conditions.    

 

The DWB study has HII (alpha) surface brightness estimates for a large expanse of the Cygnus region, something like 193 objects, at least 40 of which appear to match brightnesses of things I have already ID'ed there, and perhaps another 60 which are within the detection threshold of some that I suspected without knowing they were real.  I recently came across the DWB study after viewing the 3 blades of the propeller in H-Beta.  The propellers are seen visually as brighter portions of the nebulosity that they lie upon--additional nebulosity detected visually with an H-Beta filter. 

 

As for "agenda", you have once again helped illustrate my point that NV proponents have a tendency to underestimate or discount what can be seen visually without NV.  I only brought up your problematic observations about H-Beta because you pressed me on this.  I still suspect you might have had a bad H-beta filter which has colored your perception of it.  Having had my 1995 purchased new 1.25" Lumicon H-Beta go from good to bad, I can see how one could reach the wrong conclusion.

 

Again, relative scales come into play:  your faint/barely seen nebulosity seems to correlate more with what I see as moderate in intensity.  Those tracking down and sketching integrated flux nebulae might have the same relative impression of what I consider faint/barely detected, regarding what I see as moderate instead. 


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#25 j.gardavsky

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Posted 07 February 2020 - 05:45 PM

I am not an imager but HOS/SHO (H alpha, OIII, SII) or variants are the standard nebula imaging filter system from what I understand.  Since H-Beta gives much of the same information as H alpha, but is a weaker signal, why would they choose it?  Yes it is a different color, but they are already imparting somewhat a false color palette (e.g. the SII). 

 

Again, we are talking visual targets and what the eye is sensitive to versus an imaging device/NV.  For imaging/NV H-alpha is more convenient because the nebulae are brighter in H-alpha.  That isn't what the eye sees.  However, both the NV device and eye benefit from contrast enhancement of the hydrogen emissions:  H-alpha filter for NV, H-Beta for the eye.  Double the width of the band pass for either and the result won't be as good.

 

No, H-Beta is not a "very minor player" for IC 1318 for the visual.  That you would say that demonstrates a lack of familiarity/proficiency with detecting fainter nebulosity visually.  And for the visual, contrast matters, which the H-Beta is often better for in these HII regions.  I have wandered around that vast area in Cygnus a few times and there is a lot of very faint H-Beta nebulosity there, making it very tough to navigate.  I have never tried to systematically log it all--partly because I didn't have a guide that went deep enough for ID (Bracken only shows some of the brightest in that region, Uranometria has more but still not enough.)   Trying to sort where one segment begins and ends is a challenge the fainter one goes because there are often fainter extensions at the visual contrast limit for conditions.    

 

The DWB study has HII (alpha) surface brightness estimates for a large expanse of the Cygnus region, something like 193 objects, at least 40 of which appear to match brightnesses of things I have already ID'ed there, and perhaps another 60 which are within the detection threshold of some that I suspected without knowing they were real.  I recently came across the DWB study after viewing the 3 blades of the propeller in H-Beta.  The propellers are seen visually as brighter portions of the nebulosity that they lie upon--additional nebulosity detected visually with an H-Beta filter. 

 

As for "agenda", you have once again helped illustrate my point that NV proponents have a tendency to underestimate or discount what can be seen visually without NV.  I only brought up your problematic observations about H-Beta because you pressed me on this.  I still suspect you might have had a bad H-beta filter which has colored your perception of it.  Having had my 1995 purchased new 1.25" Lumicon H-Beta go from good to bad, I can see how one could reach the wrong conclusion.

 

Again, relative scales come into play:  your faint/barely seen nebulosity seems to correlate more with what I see as moderate in intensity.  Those tracking down and sketching integrated flux nebulae might have the same relative impression of what I consider faint/barely detected, regarding what I see as moderate instead. 

Redbetter,

 

I agree 100%  with you.

 

IDSA breaks the IC 1318 around Sadr into the individual DWB nebular patches, and I have been lucky to nail down most of them.

But there are some more nebulae in Cygnus not included in IDSA, even if visible through the big binoculars.

 

A very good reference for the HII galactic nebulae are the annotated astrophotos by Jim T. Hommes

http://www.jthommes.com/Astro/

and again with quite a bit of luck, I was able to break down the SNR G082.2+5.3 in Cygnus into at least the most prominent DWB filaments, http://www.jthommes....rp_anotated.jpg

 

Peter,

 

I am using a pair of the Astronomik medium passband (12nm) H-Beta filters, and another pair of the Baader narrow passband (8.5nm) H-Beta filters. The pairs are used on the big binoculars, the individual filters are mounted on the filter wheel of my telescope.

On the telescope, I eventually mount a stack of the Astronomik filters into the EP nose, leaving the filter wheel empty. It sometimes works better than a single Baader, other times is the single Baader better.

 

Best,

JG


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