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Mistaking M11 (the Wild Duck cluster) for a nebula

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#1 TicoWiko

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Posted 05 February 2025 - 06:13 AM

I was curious if anyone had, like me, initially had trouble finding M11 because I kept mistaking it for a nebula. I was scanning for it at around 60x using a custom pushTo modification I made to my dob (a degree circle and an inclinometer, there's a very long thread about it on CN). My pushTo had been working very well throughout the night, always landing me very close to my target, always well within my field of view when using my 20mm XWA. So when I went hunting for M11, I thought it would be easy. Open clusters are generally very easy to spot, even with heavy light pollution : it's just a dense star field after all. But when I land on where M11 is supposed to be, I see nothing of the sort. Instead, I find what looked like just an elongated smudgy star. I figured this was some nebula I could come back to later, and kept scanning around for M11, to no avail. I even gave up, before trying again the next night. Sure enough, nothing but smudgy star again. So I think to myself "okay to hell with M11, I'm gonna play around with smudgy star" and I replace my 20mm XWA with my 5mm XWA (240x magnification) to get a closer look. And then, behold, an incredibly dense starfield just fills my entire AFOV. It was really breathtaking, all the more because I wasn't expecting it in the least. I had no idea open clusters could visually behave that way. I did not expect a low power nebulosity to turn into a high power field of well resolved stars. After the fact I rationalized it by considering that M11 is a distant (so angularly small) but very dense open cluster requiring high power to resolve its tightly packed stars, but I simply didn't see it coming and I let out a definite "holy ****" when I switched to the 5mm.

 

I'm curious if I'm the only one who saw it that way or if this has happened to any of you as well, and very open to hearing about other potential objects that behave similarly. I found the shift from one sight to a profoundly different one to be quite magical. This may just be me, but a big part of the magic of visual observing for me is manually designing your optical path using eyepieces, correctors, barlows, filters etc. and tailoring it to different objects. As a result, I always make it a point to look at M11 in that order : first as nebulous, then as cluster, a little tradition in memory of my first time observing it.


Edited by TicoWiko, 05 February 2025 - 06:15 AM.

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#2 scottinash

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Posted 05 February 2025 - 06:32 AM

Well, considering that "M11" was originally discovered by Gottfried Kirch in 1681 and described as a "nebulous star similar to a comet".  in 1764, Charles Messier noted as individual stars but also "resembles a comet and mingled with faint light."  Several other early astronomers/observers called out "nebulosity".   I think William Herschel was the first to rule out nebulosity even though he noted a "glare." was present among the individual stars that made up the cluster.    

 

EDIT to add:    I failed to say previously that I enjoyed your observation noting the adventure to explore and understand!    That is where so much of the satisfaction is (my opinion)!   

 

Also, you may enjoy playing around with the following tool(s) - https://astronomy.to.../field_of_view/


Edited by scottinash, 05 February 2025 - 07:07 AM.

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#3 Astrojensen

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Posted 05 February 2025 - 06:42 AM

I am very surprised that you couldn't at least partially resolve M11 at 60x in your dobsonian (8"?), even if your observing location was heavily light polluted. 

 

 

Clear skies!

Thomas, Denmark


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#4 TicoWiko

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Posted 05 February 2025 - 07:08 AM

I am very surprised that you couldn't at least partially resolve M11 at 60x in your dobsonian (8"?), even if your observing location was heavily light polluted.


Clear skies!
Thomas, Denmark

10" dob, very heavy light pollution. I could make out what seemed to be a somewhat bright and diffuse central star, and the surroundings looked like high surface brightness nebulosity.

Edited by TicoWiko, 05 February 2025 - 07:08 AM.

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#5 Tony Flanders

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Posted 05 February 2025 - 08:39 AM

Like Astrojensen, I'm a bit surprised that you couldn't resolve M11 at 60X in a 10-inch Dob. However, your experience with M11 is if anything the norm rather than the exception for open clusters. And it's very much the norm for globulars.

 

Consider, for instance, the naked-eye view. Quite a number of open clusters are readily visible to the unaided eye under reasonably dark skies. The Double Cluster is a prime example; I can even see it from my local city park on a good night. And it looks absolutely nebulous, not a hint of resolution even under very dark skies. Likewise with M44 -- though a few people have resolved it without optical aid under superb conditions. Only a tiny fraction of the naked-eye open clusters appear as individual stars, with the Pleiades and Hyades of course leading that list.

 

M11 is particularly prone to look nebulous because it's abnormally rich for an open cluster and is completely lacking any outstandingly bright stars. M37 is similarly rich, but it has a couple of red giants near the center that tend to stand out fairly easily. But when you're working near any telescope's limit under any sky, most of the open clusters that you can barely see appear nebulous at low power.


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#6 TicoWiko

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Posted 05 February 2025 - 09:22 AM

Like Astrojensen, I'm a bit surprised that you couldn't resolve M11 at 60X in a 10-inch Dob. However, your experience with M11 is if anything the norm rather than the exception for open clusters. And it's very much the norm for globulars.

Consider, for instance, the naked-eye view. Quite a number of open clusters are readily visible to the unaided eye under reasonably dark skies. The Double Cluster is a prime example; I can even see it from my local city park on a good night. And it looks absolutely nebulous, not a hint of resolution even under very dark skies. Likewise with M44 -- though a few people have resolved it without optical aid under superb conditions. Only a tiny fraction of the naked-eye open clusters appear as individual stars, with the Pleiades and Hyades of course leading that list.

M11 is particularly prone to look nebulous because it's abnormally rich for an open cluster and is completely lacking any outstandingly bright stars. M37 is similarly rich, but it has a couple of red giants near the center that tend to stand out fairly easily. But when you're working near any telescope's limit under any sky, most of the open clusters that you can barely see appear nebulous at low power.

While that's been my experience with some globulars (though the stars on the outer edge tend to betray their true nature), I founs all open clusters, at least the ones I've looked at, to be readily resolved even at low power. Not naked eye as you say, except the Pleiades, but at 60x everything else was clearly stars. Perhaps a relevant factor here is that M11 is fairly low for me, 35 degrees at best, and I usually won't catch it exactly at its peak.

Clear skies

Edited by TicoWiko, 05 February 2025 - 09:58 AM.

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#7 TicoWiko

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Posted 05 February 2025 - 09:38 AM

Well, considering that "M11" was originally discovered by Gottfried Kirch in 1681 and described as a "nebulous star similar to a comet". in 1764, Charles Messier noted as individual stars but also "resembles a comet and mingled with faint light." Several other early astronomers/observers called out "nebulosity". I think William Herschel was the first to rule out nebulosity even though he noted a "glare." was present among the individual stars that made up the cluster.

EDIT to add: I failed to say previously that I enjoyed your observation noting the adventure to explore and understand! That is where so much of the satisfaction is (my opinion)!

Also, you may enjoy playing around with the following tool(s) - https://astronomy.to.../field_of_view/


Thank you for the kind words :)

That's a handy tool indeed, but I find the same functionality in Stellarium, and it lets me pan the sky with my different EPs and even sensors to see what they frame. Very useful for star hopping as well : "2 more FOVs to the right and I'm there" is the kind of thing I do often when my ground isn't flat enough for my degree circle to be reliable.

Clear skies
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#8 JoeFaz

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Posted 05 February 2025 - 09:55 AM

While that's been my experience with some globular (though the stars on the outer edge tend to betray their true nature), I founs all open clusters, at least the ones I've looked at, to be readily resolved even at low power. Not naked eye as you say, except the Pleiades, but at 60x everything else was clearly stars. Perhaps a relevant factor here is that M11 is fairly low for me, 35 degrees at best, and I usually won't catch it exactly at its peak.

Clear skies

If you're currently mostly working through Messier objects, that might be why Tony's comments seem a little odd to you. The Messier OCs are, in my opinion at least, not really representative of most of the observable OCs out there (in the sense that they are much more "impressive"). Most are much smaller, fainter, and require more magnification to resolve many, or even any, member stars. Even some of the brighter NGCs don't resolve very well at low power, let alone the smaller and fainter ones. "What does the 'average' OC look like in a telescope?" will probably get pretty different answers depending on the experience of the observer asked, whereas anyone that's seen any elliptical galaxy in any instrument will probably give the same basic answer for the "average" one, if that all makes sense.


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#9 TicoWiko

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Posted 05 February 2025 - 10:04 AM

If you're currently mostly working through Messier objects, that might be why Tony's comments seem a little odd to you. The Messier OCs are, in my opinion at least, not really representative of most of the observable OCs out there (in the sense that they are much more "impressive"). Most are much smaller, fainter, and require more magnification to resolve many, or even any, member stars. Even some of the brighter NGCs don't resolve very well at low power, let alone the smaller and fainter ones. "What does the 'average' OC look like in a telescope?" will probably get pretty different answers depending on the experience of the observer asked, whereas anyone that's seen any elliptical galaxy in any instrument will probably give the same basic answer for the "average" one, if that all makes sense.

Ah yes actually, that does make sense. I don't necessarily only observe Messier objects, but I observe open clusters mostly from my highly light polluted backyard, because they tend to suffer much less than other DSOs do from light pollution, and as a result I do stick to the brighter ones, most of which indeed have a Messier designation. On the few nights I travel out to darker skies I focus on the more diffuse faint fuzzies, but maybe next time I'll try some of the fainter open clusters, or perhaps even try that from home for the faint but not too faint ones. If they do indeed shift from nebulous to resolved then I'll greatly enjoy them.

I even made my own tool that should actually help me find the fainter open clusters that are up tonight :

https://conspicuous-...lendar/nightly/

It's been neat using it in the field. Other apps certainly have their uses but it's a particular kind of pleasure when using your own app that you've tailored to improve your own experience (and hopefully other's) 😄

Clear skies

Edited by TicoWiko, 05 February 2025 - 10:05 AM.

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#10 Astro-Master

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Posted 05 February 2025 - 11:38 AM

I was curious if anyone had, like me, initially had trouble finding M11 because I kept mistaking it for a nebula. I was scanning for it at around 60x using a custom pushTo modification I made to my dob (a degree circle and an inclinometer, there's a very long thread about it on CN). My pushTo had been working very well throughout the night, always landing me very close to my target, always well within my field of view when using my 20mm XWA. So when I went hunting for M11, I thought it would be easy. Open clusters are generally very easy to spot, even with heavy light pollution : it's just a dense star field after all. But when I land on where M11 is supposed to be, I see nothing of the sort. Instead, I find what looked like just an elongated smudgy star. I figured this was some nebula I could come back to later, and kept scanning around for M11, to no avail. I even gave up, before trying again the next night. Sure enough, nothing but smudgy star again. So I think to myself "okay to hell with M11, I'm gonna play around with smudgy star" and I replace my 20mm XWA with my 5mm XWA (240x magnification) to get a closer look. And then, behold, an incredibly dense starfield just fills my entire AFOV. It was really breathtaking, all the more because I wasn't expecting it in the least. I had no idea open clusters could visually behave that way. I did not expect a low power nebulosity to turn into a high power field of well resolved stars. After the fact I rationalized it by considering that M11 is a distant (so angularly small) but very dense open cluster requiring high power to resolve its tightly packed stars, but I simply didn't see it coming and I let out a definite "holy ****" when I switched to the 5mm.

 

I'm curious if I'm the only one who saw it that way or if this has happened to any of you as well, and very open to hearing about other potential objects that behave similarly. I found the shift from one sight to a profoundly different one to be quite magical. This may just be me, but a big part of the magic of visual observing for me is manually designing your optical path using eyepieces, correctors, barlows, filters etc. and tailoring it to different objects. As a result, I always make it a point to look at M11 in that order : first as nebulous, then as cluster, a little tradition in memory of my first time obs

Another cluster that looks like a faint nebulous cloud is NGC 2158 in Gemini.  At low power it will look nebulous in your 10" Dob, but at 240x it will look like a faint globular cluster if the seeing is good enough.

 

The cluster has a magnitude of 8.6 and a size of 5' x 5' and is located about 1/2 of a degree southwest from the center of M35.  If NGC 2158 was the same distance as M35 it would the best open cluster in the sky with about 1,000 stars. 

 

This is one of my favorite clusters in my 18" Dob and truly looks like a globular cluster at 300x or more on a night with good seeing.


Edited by Astro-Master, 05 February 2025 - 11:40 AM.

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#11 TicoWiko

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Posted 05 February 2025 - 01:43 PM

Another cluster that looks like a faint nebulous cloud is NGC 2158 in Gemini. At low power it will look nebulous in your 10" Dob, but at 240x it will look like a faint globular cluster if the seeing is good enough.

The cluster has a magnitude of 8.6 and a size of 5' x 5' and is located about 1/2 of a degree southwest from the center of M35. If NGC 2158 was the same distance as M35 it would the best open cluster in the sky with about 1,000 stars.

This is one of my favorite clusters in my 18" Dob and truly looks like a globular cluster at 300x or more on a night with good seeing.


Oh **** you're right it's next to it. You can easily fit both in your FOV then zoom more into NGC 2158 to resolve it. I'm definitely trying that as soon as the skies clear. Great tip, thanks !

#12 scottinash

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Posted 05 February 2025 - 02:21 PM

A target that I have enjoyed is OC Melotte 15/IC1805/Collinder 26 in Cassiopeia, which actually resides within The Heart Nebula.  


Edited by scottinash, 05 February 2025 - 02:48 PM.

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#13 zizzapnia

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Posted 05 February 2025 - 03:01 PM

When I travel to darker skies, I make it a point not only to observe the faint ones that I can't see from home, but to revisit the brightest ones, such as M11, because while from home they may be insipid and nebulous, from a darker sky they become majestic. Dark skies improve pretty much everything except the Moon and brighter planets and doubles.


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#14 TicoWiko

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Posted 05 February 2025 - 03:18 PM

When I travel to darker skies, I make it a point not only to observe the faint ones that I can't see from home, but to revisit the brightest ones, such as M11, because while from home they may be insipid and nebulous, from a darker sky they become majestic. Dark skies improve pretty much everything except the Moon and brighter planets and doubles.


That's a good point. I think to do that on some of the classics, but tend to leave out open cluster. The only exception there is the Pleaides nebulosity which is surprisingly easy to see in darker skies.

#15 Starman1

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Posted 05 February 2025 - 04:01 PM

I was curious if anyone had, like me, initially had trouble finding M11 because I kept mistaking it for a nebula. I was scanning for it at around 60x using a custom pushTo modification I made to my dob (a degree circle and an inclinometer, there's a very long thread about it on CN). My pushTo had been working very well throughout the night, always landing me very close to my target, always well within my field of view when using my 20mm XWA. So when I went hunting for M11, I thought it would be easy. Open clusters are generally very easy to spot, even with heavy light pollution : it's just a dense star field after all. But when I land on where M11 is supposed to be, I see nothing of the sort. Instead, I find what looked like just an elongated smudgy star. I figured this was some nebula I could come back to later, and kept scanning around for M11, to no avail. I even gave up, before trying again the next night. Sure enough, nothing but smudgy star again. So I think to myself "okay to hell with M11, I'm gonna play around with smudgy star" and I replace my 20mm XWA with my 5mm XWA (240x magnification) to get a closer look. And then, behold, an incredibly dense starfield just fills my entire AFOV. It was really breathtaking, all the more because I wasn't expecting it in the least. I had no idea open clusters could visually behave that way. I did not expect a low power nebulosity to turn into a high power field of well resolved stars. After the fact I rationalized it by considering that M11 is a distant (so angularly small) but very dense open cluster requiring high power to resolve its tightly packed stars, but I simply didn't see it coming and I let out a definite "holy ****" when I switched to the 5mm.

 

I'm curious if I'm the only one who saw it that way or if this has happened to any of you as well, and very open to hearing about other potential objects that behave similarly. I found the shift from one sight to a profoundly different one to be quite magical. This may just be me, but a big part of the magic of visual observing for me is manually designing your optical path using eyepieces, correctors, barlows, filters etc. and tailoring it to different objects. As a result, I always make it a point to look at M11 in that order : first as nebulous, then as cluster, a little tradition in memory of my first time observing it.

I live in LA, so increasing magnification is essential to darken the background in the eyepiece and reveal more stars due to the increased contrast.

M11:

At 30x in a 4"--one star visible and a small patch of what looks like nebula.

At 60x--a few stars but still mostly nebulous

At 90x--Looks like it might be a star cluster with most memebers below the limit, so some stars sprinkled on nebula.

At 120x--beginning to look like a nice star cluster, with a bit of nebulosity in the background.

At 150x--nebulosity gone and a very rich star cluster appears.

At 180x--many many faint stars appear and the cluster is magnificent.

 

This process occurs with globular clusters, too.  M13 at 180x is great in the 4".

By the way, I tried 24x in the 4", and the sky in the eyepiece is almost daylight-bright.

Almost nothing is visible.

Bortle Class here is unknown because it's worse than Class 9.  Many nights Jupiter is dim until it's 30° up and Venus fades out before it reaches the horizon.

The Moon rises a deep orange and doesn't turn white until it's 20-30° up.  Polaris is often an averted vision object only.

And that's on clear nights. If there is a tiny bit of haze, 1st magnitude stars are faint.

This is why I travel to observe.  The SQM reads 16.8-17.5 90% of the time and has only reached 18 a few times in the last few years.

 

P.S. NGC2158 is magnificent.  I prefer it to M35.  I use 200-260x to view it.


Edited by Starman1, 05 February 2025 - 04:05 PM.

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#16 dave253

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Posted 05 February 2025 - 07:06 PM

Yep I suspect the low elevation is the problem. M44 always appears as a nebulous patch to me, luckily M11 passes nearly overhead so I can resolve it easily in small optics.


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