Author Topic: Super Limits  (Read 450 times)

luseatcidood

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Super Limits
« on: December 27, 2017, 11:00:42 AM »
We are all familiar with our threshold limits - or most are anyway. There's a star magnitude that telescopically is as far as you can go. With skys willing, you kno if you set out to see such a faint star - with effort, you kno you can get some glimpses.

I see those kind of limits as our own common threshold. We can duplicate it elsewhere.

What about sightings that break all the rules?

The other night I glimpsed a star for a third of a second or so nearly 2 full magnitudes fainter than my common threshold. I wasn't thinking of it and really wasn't even aware it was there consciously. But it appeared - vanished and never returned again over the course of that hour. I was always observing within about 80 seconds of it - but it never reappeared and I know I saw it. It turned out to be 15.7v while the common threshold was 14.1.

Another time I was viewing an edge on galaxy with God surface brightness and nice dimensions at least on paper. At over 300x for a flash of a moment the center area squirmed a confused texture and finito. Gone. I tried that night again - what was that afterall? I was very seasoned with observing many an NGC galaxy - what was this cryptic flash of unresolved texture? I tried the next night and some nights after. Nothing. Not a quiver. It turns out this object has a very very thin delicate dustlane bisected it that's normally the reach of bigger scopes, not 8 inchers. I found this out after the fact and even knowing then what to search for it didnt reappear.

It made me wonder...

Beyond our common established threshold detections - is the eye/brain complex enough to offer very narrow and brief sightings in a realm we normally can't attain or even repeat? Our roving eyes particularly with averted vision are always sampling in active sweeps across so many retinal receptors. Shouldn't there be unrepeatable moments of ultra sensitivity by random chance?

In these cases I should mention these moments do not illuminate an entire FOV in heretofore new waus. These are instead almost tunnel vision like sensory things where nothing else but this star or feature momentarily materializes.

I mention deepsky here so far but I would have to believe photo pic observation has its super limits as well.

Any thoughts?

Pete



kocewaffre

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Re: Super Limits
« Reply #1 on: December 28, 2017, 02:04:44 AM »
I haven't encountered anything unrepeatable so far.
<p class="citation">QuoteWhat about sightings that break all the rules?
[/quote]
Do you mean seeing color in deep sky objects?

Mario Carpenter

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Re: Super Limits
« Reply #2 on: December 28, 2017, 07:59:30 PM »
I've experienced this sort of thing before, but rarely. Several of these instances occurred during extended observations of Jupiter, where for a few seconds the level of detail appeared to increase by an amount that was far more than the aperture used was capable of. Similar observations took place while viewing diffuse nebulae, where filamentary and other details were observed which should have been well beyond the reach of the instrument involved.

While seeing was excellent at the times this occurred, I seriously doubt that even a perfectly steady atmosphere could account for such views (I have experienced absolutely perfect seeing conditions a very few times, and it did not exhibit this effect); thus I attribute these experiences to my mind "filling in blanks" during a long and sometimes difficult observation, with the detail cobbled together from photographs and descriptions of the obects that my subconscious mind had picked up in the past.

Cesar Norris

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Re: Super Limits
« Reply #3 on: December 28, 2017, 09:45:56 PM »
There is a seeing characteristic called "scintillation".
Basically, the back and forth focus difference in the atmosphere briefly brings into tight focus a star fainter than you think you have seen before.
After eleven years of testing a 8" SCT and reliably hitting 15.6 at an absolute minimum, I expected my 12.5" to reach 16.6 at a maximum.
Instead, the first time I really plumbed the depths with the 12.5", I reached 17.1 and since have occasionally gone to 17.3-17.5.
How?
Smaller secondary? Higher transmission? Better MTF curve? Not sure.
And how did the 8" SCT, which barely reached 15.6 as a deepest magnitude see a planetary nebula of m.16.5?
Well, momentary superior transparency and scintillation and, perhaps, momentary dark adaptation beyond our ordinary.
Otherwise, I characterize it as going to an art gallery whose halls are filled with smoke, to occasionally find the hall free of smoke.
In those moments: magic.
Enjoy it: it's not common.

writgobetfcoo

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Re: Super Limits
« Reply #4 on: December 29, 2017, 01:26:40 AM »
+1 Amicus and Starman, very logically thought out !
One of the reasons, I love reading this site for all the input from way more experienced observers. Amicus gave a very good possible cause but I immediately thought "Well, what about a random star 2 mag's deeper that probably isn't on any chart; and even if so, the observer wouldn't 'fill it in' as it's not something he has been exposed to repeatedly?" But Starman's scintillation explanation answered that nicely!

I'll have to throw out the explanation I immediately thought of.  Glitches in the Matrix.

Manuel Ghumare

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Re: Super Limits
« Reply #5 on: December 29, 2017, 05:23:54 AM »
Not common at all. I agree. I was thinking of your NGC206 sighting of its brighter stars when I was thinking the idea of it over.
Particularly with averted vision, it's always a querky method of observing in that when details emerge it's not necessarily repeatable for the same eye movements as we scan about. It comes in its own time it would seem. With the exceptional super limits perhaps one time only is all we get.

Amicus, I understand what you are saying but it's proven to happen to me when I wasn't aware of the feature or object through prior reading etc.

Chass, I am agreeing with the scintillation theory and the serendipity of our sense from time to time having these peaks of perception that randomly arise and vanish. Sure I'd bet some is imagined but then there's those examples that ring with a mysterious reality that isn't explained away so easily by imagination.

The trouble is its so exceedingly elusive.

Pete

Robert Bilbruck

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Re: Super Limits
« Reply #6 on: December 29, 2017, 05:25:54 AM »
Quote
I haven't encountered anything unrepeatable so far.

<p class="citation">QuoteWhat about sightings that break all the rules?
Do you mean seeing color in deep sky objects?

[/quote]
I wasn't referring to that but that's fair game too .
A momentary heretofore unseen sensing of a hue would seem to follow along here. It's the once in a rare blue moon experience of short duration I'm referring to however.

Pete

opalytun

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Re: Super Limits
« Reply #7 on: December 29, 2017, 02:25:10 PM »
Quote

During my extended observations, I have noticed Jupiter began to "freeze" in place and color became much more apparent. I cannot explain or describe it much better than that. It's as if the universe opened up and Jupiter simply revealed itself nicely. I cannot say whether the level of detail was or was not within the scope's capabilities. Jove just seemed 'etched', maybe that's a better term we can relate to, as opposed to it's normal cycle of sharpening during calm moments and softening during lesser seeing. When it does 'etch', the amount of detail explodes.

I am not sure I can say with any certainty that I have seen Jovian details below the scope's capabilities, mostly because I am not sure what those limits are. I have seen white ovals subtending 1" arc and less on a few occasions. That seems near the boundary of what 150mm of aperture can do it we consider (just for a second) this is near Raleigh limit of point sources. It maybe simply coincidental for lower contrast detail being observed on an extended object. I am not saying that Raleigh applies, just that it's interesting the smallest low(er) contrast detail I've seen is in that range. So, is Raleigh (even though it is defined by point sources) an approximate limit for such bright low contrast extended object detail? Is Dawes?

What is the limit in terms of both resolution and contrast, the latter being estimated at about 5% remaining after image transfer. The higher contrast "monolith" trailing oval BA a few years ago was much easier and I believe smaller than 1" arc. Sometimes it was a faint blur, sometimes it was a tiny speck. I believe those are about the smallest bright low contrast planetary detail's I have seen. For larger details, contrast (or color) is the defining factor. I am not sure where this limit lies, but probably well above what an image can capture. But how close can we get to an image?

It seems with bright higher contrast, the smaller you can observe until you reach some resolution limit (at or even below Dawes). Small lower contrast detail becomes increasingly more difficult, but it might surprise how small we can go an increasingly rare occasions as long as contrast transferred is sufficient for the eye (both acuity and image scale) to detect it. But these limits are not set in stone, surely, as conditions change all the time and observers have varying degrees of acuity. Diffraction should be the ultimate limit - the size of the spurious disc, at best. But even that changes with magnitude, seeing, acuity and whatever else. And extended objects are very complex things - again, having seen a full blown crater with a grey floor and a dimly lit rim that subtended the FWHM of a single point source. It should have been blotted out by that diffraction, but was not.

I have seen double stars a few ticks below Dawes. Apparently this is not so uncommon as I might have guessed. But, what's interesting is I have also noted high contrast lunar detail in full crater form below Dawes, too, say down toward 0.70" arc which is near lambda/D or Dawes with obstructed diffraction. Both my tightest doubles actually split (as reported) and the crater resolved (as calculated using the small angle formula) were very near the same angular diameter at 0.70" arc, give or take a few hundredths. I am not sure how common that is given that it took an exceptionally good moment or two even in excellent tropical seeing generally. But, it shows it can be done.

I was observing a Messier (can't remember which one) galaxy and noted what looked to be a fleeting, thin dark wisp that might have been a dust lane. It was fleeting and never repeated. The interesting thing is, there is a dust lane there. I doubt I could have seen it, though. But, the observation was striking. Memorable (well, maybe not that memorable since I cannot remember which galaxy I was viewing...LOL...but I remember the event and wrote it off as spurious.)

Another one is G and H trap. I observe the trap often enough because it's beautiful. E and F are often seen, sometimes as bright pin points on exceptionally clear nights rather than dim points fading in and out. Always enjoy that. But, the kicker is, there have been a few times I swore I saw G and H fading in and out. They are a magnitude or two below the theoretical threshold for a 6" scope. I often wondered if it was possible to actually observe them given the magnitude of the feat with such faint stars embedded in a nebula. To this day, I am unsure but open to the possibility and keeping it in the back of my mind. I never told anyone outside a few close observing buddies, cuz you'd get laughed off of CN as a quack. I need what little cred I might have to discuss other, more concrete observations.

I guess if we want to know if something is possible, like a very faint and fleeting star siting, we have to know what the limit actually is and what theory applies. And what the statistical likelihood of theory might imply. Does the limiting magnitude imply 100% (in a given set of conditions) while stars dimmer than that might be seen 1% of the time in a different set of conditions? One might imagine such things are possible if you're there during that 1% of the time.

Oh, and surface albedo on Ganymede in an aperture where Ganymede is roughly the same diameter as the Airy disc. Absolutely. I find brighter albedo features, such as Osiris, are easier (not easy, just easier) than the darker lower contrast features. This is not resolution, I guess, in the strictest sense of the word as resolution is defined by the Airy disc (or spurious disc) and we're seeing features within that angular area...which is amazing in and of itself. But, it would be almost like the Airy sized disc of Ganymede is not uniform in brightness as a star's image would be. It has peaks and valleys strewn across it. But at such small angular diameter, the contrast has to be pretty high, IME. Not 100%, but high enough to survive contrast loss during the image formation by the aperture. Ganymede fits that bill. And, it requires diffraction limited conditions.

So, yea, there is lots to see out there and I doubt there are any firm limits...just approximations. Maybe we can see a much dimmer star from time to time.

Gregory Station

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Re: Super Limits
« Reply #8 on: December 31, 2017, 01:56:47 AM »
I have detections like this fairly frequently but have come to regard them as mostly spurious because they're often far too obvious. That's not to say that some of them weren't real, but when I've been able to see the actual object three times or more within five minutes it's always been much fainter than the original and much brighter flash. It seems more likely, at least in my case, that something went haywire with my vision rather than it getting a sudden turbocharge. Also, sometimes I can see the same effect when I intentionally try to see something where I know there's nothing. When I start to see things that aren't really there it's time to move on to much brighter objects!

cicacating

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Re: Super Limits
« Reply #9 on: January 02, 2018, 12:19:31 AM »
A good example of the scintillation I mentioned earlier is the center star in M57.
In my 12.5", it's never been visible 100% of the time--it always is intermittently visible.
But one night it will be visible 5% of the time and another night 50% of the time,
yet seeing appears about the same.
One night has more scintillation in seeing that another.
If intensity of focus can change the visibility of a star, it can obviously work both ways, too.

As an aside, though there is obviously light loss through a coma corrector, it wasn't too long after
I got a coma corrector that I started noticing that I was seeing really faint stars over more of the field
than I had before adding it. I think that really faint stars were being stretched into invisibility by coma
prior to the corrector that were now in tight focus.

My comments here point out that taking the time to get the best possible focus is essential to see
faint stars AND faint DSOs. You want the maximum intensity of light possible.

ecidjapa

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Re: Super Limits
« Reply #10 on: January 03, 2018, 08:29:25 PM »
There is no questions that rare moments of extremely steady seeing in an ultra-clear sky do occur and when they do amazing detail can be rendered visible in a telescope that otherwise would never be expected to reveal it.

However, gliimpsing or believing you are glimpsing a stellar or an extended object like a galaxy or comet some two magnitudes beyond what you have ever detected before with your scope, eyepiece and skies, is likely to be just some sort of a mistake. This is especially true when one thinks that they are glimpsing some very faint star for just an instant, or perhaps even 5% of the time, yet find it totally undetectable otherwise. Astute long time observers soon learn that the eyes can play tricks and most of these folks will not accept the sighting of an object as real unless it is repeatedly and frequently glimpsed (say 30-50% of the time) over the course of the observing session and always in exactly at the same spot.

I think it was Starman1 who somewhere above mentions seeing a planetary nebula whose cataloged magnitude should have placed it a full magnitude beyond the reach of his instrument. Such sighting often DO prove real simply because the integrated magnitudes of many such objects are far off from the truth. A nonstellar object, even one of very small angular diameter, is always much more difficult to detect than a star of the very same magnitude. So, if you are not seeing stars at least a half magnitude fainter than the nonstellar object in question, then it is very unlikely to really be there unless there is a mistake in its listed magnitude.

Don't overlook being unconciously biased by either your observing buddy telling you that he's seeing something actually too faint to be real, or after having read such a claim on CN. I've seen some amazing examples of unconcious influence in the course of my years of writing for S&amp;T. One instance that I vividly recall involved a young Western European comet observer who claimed spotting a particular returning period comet. He reported it as 13th magnitude with an small obvious diffuse coma using his 8 or 10-inch scope, even though the comet had been anticipated to be no brighter than 18th or 19th magnitude at the time. Within a day or two another of his countrymen had reported having made a definite confirmatory observation. By week's end a further three observers from the same general region had joined in and were reporting multiple positive observations. In the meantime several of us here in the States looking in very good skies with scopes of 16-inches aperture could detect nothing at the comet's expected location!

A request was made by us through contacts at JPL to arrange for one of the big West Coast Schmidts to image the object to see just what was happening. The results came back that the comet appeared as a nearly stellar object of 18th-19th magnitude on a rather lengthy exposure, just as had been expected. When the Europeans were advised of our results from the imaging one by one they withdrew their sightings. Only the fellow reporting the initial observation held fast, but he did not report any further sightings of that comet. I can relate many such stories, including mistakes made by members of the AAVSO who are well known for their accuracy.

Believe me, if you think that you are glimpsing something that should be far beyond what you instrument is capable of and only catching sight of it for an instant every few minutes...it aint likely to really be there! The mind has a powerful influence over what you think you are seeing and the eyes themselves can create momentary point source flashes. So always try to be highly objective when observing and be critical of marginal sightings of things that should be well beyond your telescope's range.

BrooksObs

Lesego Dowdy

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Re: Super Limits
« Reply #11 on: January 04, 2018, 03:58:39 PM »
I may be dating myself BrooksObs, but was that Comet Halley you are referring to? Wasn't it a S&amp;T contributor known for extremely gifted sight and observational skill(Steven J. O'Meara?) that was the first to see it return in 86 from an extremely tall mountain top (Hawaii?) while breathing from an oxygen tank? Wasn't that supposed to be an 'impossible' super-sighting that proved true when his nightly drawn trajectory matched up and ws confirmed with professional observatory photographs?
Or have I messed up the timeflow with my T.A.R.D.I.S again like when Nixon landed the new shuttle Columbia on the moon to celebrate his fourth presidential victory in 1980?

Scott Rogers

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Re: Super Limits
« Reply #12 on: January 08, 2018, 03:56:18 AM »
Quote
I may be dating myself BrooksObs, but was that Comet Halley you are referring to? Wasn't it a S&amp;T contributor known for extremely gifted sight and observational skill(Steven J. O'Meara?) that was the first to see it return in 86 from an extremely tall mountain top (Hawaii?) while breathing from an oxygen tank? Wasn't that supposed to be an 'impossible' super-sighting that proved true when his nightly drawn trajectory matched up and ws confirmed with professional observatory photographs?
Or have I messed up the timeflow with my T.A.R.D.I.S again like when Nixon landed the new shuttle Columbia on the moon to celebrate his fourth presidential victory in 1980?


No, the instance I was referring to in my earlier post dealt with a different comet, although P/Halley's return did generate a number of reported spurious early sighting claims by amateurs using almost laughably modest apertures.

Steve's sighting of P/Halley was quite legit and not really all that exceptional relative to what might be anticipated from any other truly experienced visual observer under the same extreme circumstances. It's worth noting that Steve, Barbara Wilson and I went head-to-head at TSP one night some years later seeing just how faint we three could go using a very accurate sequence (at an elevation ~50 degrees) using Barbara's 20-inch Dob at moderately high magnification. Each of us in turn hit a wall with definite sightings at 18.6 , not bad for being at a much lower elevation than Steve had when atop Mauna Kea; for not using any oxygen; nor employing a very high quality 24-inch professional telescope at very high power. All in all, our results from TSP were reasonably in line with Steve's P/Halley sighting had we the additional advantages he had at the time.

BrooksObs

Mark Patterson

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Re: Super Limits
« Reply #13 on: January 10, 2018, 10:52:05 AM »
Quote
There is no questions that rare moments of extremely steady seeing in an ultra-clear sky do occur and when they do amazing detail can be rendered visible in a telescope that otherwise would never be expected to reveal it.

However, gliimpsing or believing you are glimpsing a stellar or an extended object like a galaxy or comet some two magnitudes beyond what you have ever detected before with your scope, eyepiece and skies, is likely to be just some sort of a mistake. This is especially true when one thinks that they are glimpsing some very faint star for just an instant, or perhaps even 5% of the time, yet find it totally undetectable otherwise. Astute long time observers soon learn that the eyes can play tricks and most of these folks will not accept the sighting of an object as real unless it is repeatedly and frequently glimpsed (say 30-50% of the time) over the course of the observing session and always in exactly at the same spot.

I think it was Starman1 who somewhere above mentions seeing a planetary nebula whose cataloged magnitude should have placed it a full magnitude beyond the reach of his instrument. Such sighting often DO prove real simply because the integrated magnitudes of many such objects are far off from the truth. A nonstellar object, even one of very small angular diameter, is always much more difficult to detect than a star of the very same magnitude. So, if you are not seeing stars at least a half magnitude brighter that the nonstellar object in question, than it is very unlikely to really be there unless there is a mistake in its listed magnitude.

Don't overlook being unconciously biased by either your observing buddy telling you that he's seeing something actually too faint to be real, or after having read such a claim on CN. I've seen some amazing examples of unconcious influence in the course of my years of writing for S&amp;T. One instance that I vividly recall involved a young Western European comet observer who claimed spotting a particular returning period comet. He reported it as 13th magnitude with an small obvious diffuse coma using his 8 or 10-inch scope, even though the comet had been anticipated to be no brighter than 18th or 19th magnitude at the time. Within a day or two another of his countrymen had reported having made a definite confirmatory observation. By week's end a further three observers from the same general region had joined in and were reporting multiple positive observations. In the meantime several of us here in the States looking in very good skies with scopes of 16-inches aperture could detect nothing at the comet's expected location!

A request was made by us through contacts at JPL to arrange for one of the big West Coast Schmidts to image the object to see just what was happening. The results came back that the comet appeared as a nearly stellar object of 18th-19th magnitude on a rather lengthy exposure, just as had been expected. When the Europeans were advised of our results from the imaging one by one they withdrew their sightings. Only the fellow reporting the initial observation held fast, but he did not report any further sightings of that comet. I can relate many such stories, including mistakes made by members of the AAVSO who are well known for their accuracy.

Believe me, if you think that you are glimpsing something that should be far beyond what you instrument is capable of and only catching sight of it for an instant every few minutes...it aint likely to really be there! The mind has a powerful influence over what you think you are seeing and the eyes themselves can create momentary point source flashes. So always try to be highly objective when observing and be critical of marginal sightings of things that should be well beyond your telescope's range.

BrooksObs

John,

Your post is very apropos to observing at the limit.

I should have mentioned the fact that a glimpse of something impossible is likely to be due to an incorrect magnitude in various listings.
As I started getting down to magnitude 14.5-15 galaxies, I was a little disturbed by the fact that some were easy and others simply invisible. Many of the galaxies in that magnitude range are small, too, so the surface magnitudes are usually not so far away from the total integrated magnitudes that it would explain the reason.

Of course, as you point out, there are a lot of mistakes in magnitudes, and the problem gets worse the fainter you go.

One of the main reasons, of course, is that professionals don't pay a lot of attention to magnitude in their studies of extended objects unless the magnitudes are so faint as to cause problems with instrumentation. So there isn't a lot of pressure from the professional community to more accurately assess magnitudes. And that is the reason I never take it for granted that an object cannot be seen until I can't see it.

I have reliably seen that changes in transparency can make differences of up to 0.5 magnitude in the visibility of extended objects (in dark skies), [edit: which may be due to differences in dust, smog, and water vapor and the effects on faint extended objects, not stars] while, surprisingly, that same 0.5 magnitude change in the darkness of the sky doesn't make as much difference. It seems that once a certain level of darkness is seen, the big changes in visibility come from transparency and seeing and not a minor change in the darkness of the sky.

As far as scintillation changing the visibility of something at the limit, I have not done an analysis, but I would doubt much more than 0.1-0.2 magnitudes at best, and that is not really significant. Spending more time to achieve superb focus might make just as much difference. Others report larger differences, but until I see that, I am doubtful.

As for seeing things at the limit that may or may not be there, I have some experience in that: I view a lot of Abell Galaxy clusters, and I'm always suspicious of the "objects" that wink in and out and which don't seem to be there. Obviously, not every faint object will be visible 100% of the time--even with averted vision. So where do you draw the line? 10% of the time visible? 20% visible? 30% visible?
I've taken to sketching an area and drawing in the objects I think I saw and then comparing the sketch later with a computer atlas that has objects much fainter than I can see.
And, sometimes, comparing the sketch with the DSS to see if something shows up not plotted on my computer atlas.

Somewhat embarrassingly, about 50% of the "limit" objects aren't real and are probably due to flashes in the retina or simply my eyes straining at the limit. But, about 50% of the objects caught this way are real. I would view such an observation as working at my absolute limit for the instrument, site, and physical state. And, in line with other people's estimates, the deep sky objects seen this way (and most are small (&lt;1') and have low surface brightnesses) are around 1 to 1.5 magnitudes brighter than my limit for stars. So you are quite right to note that someone is not going to suddenly see objects significantly fainter than the normal limits of a particular scope and site.

You know the old expression: "Trust, but verify."

tenewbandhams

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Re: Super Limits
« Reply #14 on: January 10, 2018, 11:16:27 AM »
Heh, as i was reading this I realized I have a totally different perspective on this stuff.

Seeing here is almost always garbage, and transparency is often both poor and changing (and even a little bit of haze really shows with all the LP I have). To top it off, my focuser isn't very good and I'm pretty lazy about collimation!

So I never have the illusion that I am seeing at the absolute best of my telescope (which I believe is around mag 13.0, from a stretch of unusually clear nights 2 years ago). Even on a fairly decent night, I will have a hard time seeing below mag 11.0. So it doesn't surprise me at all that I will get a freak glimpse of some magnitude 12.x star and then it will disappear and I won't see it again for months.

That is not really what you guys are talking about.