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Enke Minima on Saturn

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#51 E_Look

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Posted 22 June 2014 - 09:31 PM

Possibly; the human retina may not respond exactly like an artificial sensor, or a piece of photographic film. I have never thought about what function might better describe the photoelectric response of these.

Also, the sensor/receptor density would differ among these cases.

I wonder, are there known illusions people see that do not show up on film or sensor, or with film and not eye and sensor, etc.?

This is all very fascinating!

I believe Norme mentioned edge-spread functions vs. point-spread functions; I wonder if in a similar vein, there might not be such differences between images recorded by a photoelectronic sensor (CCD, diode array, even a photomultiplier) and that caught on film. There is bound to be a bit of granularity in the solid state devices, although I believe the photomultiplier tube can be employed in an analog fashion, whereas film is chemically continuous, assuming one does not use high grain film.


And how does the visual image differ? Can the eye see what images and photos have trouble recording?



#52 BillP

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Posted 23 June 2014 - 07:24 AM

Hi Pete, I remember soiling my undergarments one evening when I thought I observed Enke gap in a 6".


:roflmao:

#53 Asbytec

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Posted 23 June 2014 - 08:20 AM

Bill...Hehehehe :)

Ed, "I wonder, are there known illusions people see that do not show up on film or sensor, or with film and not eye and sensor, etc.?"

The mach band illusion is one that seems to apply. Basically, the border of a uniformly bright area will appear brighter along the adjoining edge with a darker area. The brighter A ring would appear bright along it's border with the dark of space. As I understand the illusion, this is because the image of the edge is placed appropriately over a cluster of photo receptors on the retina. The inner A ring would be outside that area and thus the eye would not process as much light from it (and no light from space itself.)

What's fascinating, though, is the evidence of greater transparency (optical depth) in the center of the A ring. That should make it appear darker (less reflective), too, as a very real feature of the A ring itself. Provided, of course, the contrast is high enough to afford visual perception. Apparently it is, because we do observe the minimum.

#54 BillP

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Posted 23 June 2014 - 10:30 AM

Evidently, when the rings are edge-on oriented, the brightness of the ring will seem to modulate and be brighter outside the planet and darker on portion over the orb. This is a confirmed illusion. Scroll down here to see example.

On another note, and interesting project paper here.

#55 Asbytec

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Posted 23 June 2014 - 12:14 PM

Thanks, lemme mull them over.

#56 E_Look

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Posted 23 June 2014 - 12:15 PM

Apparently, these illusions impact our observations of Saturn, and other planets!

#57 DesertRat

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Posted 23 June 2014 - 02:25 PM

The nomenclature for the A-ring 'gaps' are not the result of the finest IAU decisions. For a good background article on this see:

"Keeler's Gap in Saturn's A Ring" by Osterbrock and Cruikshank in the August 1982 Sky & Telescope.

What we refer to today as Encke's division was never seen by Encke. It was discovered by James E. Keeler in 1888. And what is now known as Keelers gap was never seen by Keeler but discovered by Voyager 2. The gap now known as the Encke division, discovered by Keeler, is only 0.05" in width.

It is possible Lassel and Dawes together observed (in 1843 using a 9" newt) what Keeler discovered. It would appear so anyway from their drawings.

Its important to keep the concept of detection, or seeing something, at least discriminated (since they are related) from the criteria of resolving or separating nearby structures of points or linear features. Cassini's division for example was discovered with a scope with lesser resolving power than what would be required to separate nearby lines of that width, which is approx 0.7". Isolated features may be seen well below the Rayleigh criterion, but not strictly resolved, as long as there is a sufficient contrast differential.

The Encke minimum, or the gradation of intensity in the 'A' ring is often sharpened by imagers to appear as a division, when in fact it is an artifact. Only a few have successfully imaged it and processed it properly. Most reports of imaging it are flawed. And even fewer have imaged any divisions in the 'C' ring. But it has been done.

Glenn

#58 idp

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Posted 23 June 2014 - 02:57 PM

The Encke minimum, or the gradation of intensity in the 'A' ring is often sharpened by imagers to appear as a division, when in fact it is an artifact. Only a few have successfully imaged it and processed it properly. Most reports of imaging it are flawed. And even fewer have imaged any divisions in the 'C' ring. But it has been done.

Glenn


I would concur with this. I think that's what the example I posted above shows. No hint of a gap can be detected in the original image, but processing has created one there (and elsewhere).

#59 Asbytec

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Posted 23 June 2014 - 06:52 PM

Apparently, these illusions impact our observations of Saturn, and other planets!


No doubt. But if a feature can be shown to exist (optical depth), how is that an illusion? It's hard to separate illusion from reality, we have to be aware of them. I observe the Enke minimum every time I look at Saturn. It could be an illusion. However, if the central A ring is more transparent and provides enough contrast it very well could be an actual feature of the A ring. Since some anomaly (optical depth) can be show to exist, there should be no reason why we could not (and very often do) observe it.

Its important to keep the concept of detection, or seeing something, at least discriminated (since they are related) from the criteria of resolving or separating nearby structures of points or linear features. Cassini's division for example was discovered with a scope with lesser resolving power than what would be required to separate nearby lines of that width, which is approx 0.7". Isolated features may be seen well below the Rayleigh criterion, but not strictly resolved, as long as there is a sufficient contrast differential.


Glenn, yea, that's a great point to keep straight. I actually confuse them all the time, that being observed is being resolved. Not in terms of Raleigh, of course, but in differentiating one point from another in terms of contrast, as you say. Ganymede, and extended object, is a perfect example. It has essentially the diameter of a 150mm Airy disc, yet it is not a single Airy disc (as evidenced by it's washed out diffraction ring structure.) Yet, you can see brighter points on it's disc.

Another stunning example was a small craterlet 'g' on Plato's floor subtending just 0.7" arc (well below Dawes and the Airy disc diameter closer to lambda/D). During one night on several occasions in the most excellent seeing moments, there it was plain as day in full crater form. Was it resolved? Is Lambda/D closer to the real limit of resolution? One image of Plato also showed small craters in crater form (bright limb and dark floor) very near Lambda/D (for that aperture.)

If the Enke minimum reflects less light, it's conceivable it will not be as bright as the less transparent parts of the A ring and provide some level of contrast to the observer. In this case, it can be (and is often) seen as a separate feature, because it is a feature of the A ring. The dimming of the inner B ring might be similar in this respect, which we observe often enough, as well. No Mach band there, but there should be if the illusion is at work.

#60 BillP

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Posted 24 June 2014 - 08:42 AM

But if a feature can be shown to exist (optical depth), how is that an illusion? It's hard to separate illusion from reality, we have to be aware of them. I observe the Enke minimum every time I look at Saturn.


HST and Cassini data all show a minimum in the central portion of the A-Ring compared to it's outer most edges. No illusion.

#61 Asbytec

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Posted 24 June 2014 - 08:47 AM

HST and Cassini data all show a minimum in the central portion of the A-Ring compared to it's outer most edges. No illusion.


That's cool. Thanks. I never gave it much thought until you're report. There have been hints of it being an illusion, or possibly one, but it's just there when seeing permits. And seeing almost always permits during our tropical dry season. Knowing (or believing) it's an actual feature just gives more depth to observing Saturn. I could stare at it's rings for hours...and have. :)

#62 BillP

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Posted 24 June 2014 - 11:36 AM

FWIW, here's a full res raw image from Cassini of the A-Ring. Fairly easy to see visually that the portion to the outside and just inside Enke is lighter and brighter than the center. Same also holds true for region of A-ring just outside the Cassini. So the ring's center is bounded by brighter edges. I do think that the human perception system naturally accentuates this, resulting in the minimum in the center appearing darker than it actually is, but our perception system does this for everything we observe!

I usually don't get that wrapped up in legalism and what is or is not or partially or in whole an illusion. If I was doing scientific research on the target, then it would be important. But since I am not, it is not important and what becomes important is *observational* features and the act of observing. As you said, easy to stare at Saturn and the rings all night...me too! It is a beautiful target and rewarding to observe various features, whether 100% real or even less so.

#63 Asbytec

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Posted 24 June 2014 - 08:12 PM

Yea, no doubt human perception does funny things, like making the first ring of a bright star look as bright as the Airy disc, and they play tricks on us. The accentuated brightness of the A ring's edges might be some of that trickery. But it's trickery on what looks like an actual observable feature and not purely an illusion - which is what I find fascinating.

Maybe everything we observe either is part illusion and part logarithmic trickery, but we do see things in many ways as they are. Or we at least know the feature is present. Well, except at times when lunar craters look like domes. It would seem odd to attribute everything we observe to illusion, to some contrived image formed in our brain, as it would strike at the core of our ability to interpret the world around us.

Yea, the beauty of the heavens is remarkable. More folks should be aware of the magical universe circling overhead beyond the everyday grind of busy streets and televised news.

#64 BillP

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Posted 25 June 2014 - 11:02 AM

Maybe everything we observe either is part illusion and part logarithmic trickery, but we do see things in many ways as they are. Or we at least know the feature is present. Well, except at times when lunar craters look like domes. It would seem odd to attribute everything we observe to illusion, to some contrived image formed in our brain, as it would strike at the core of our ability to interpret the world around us.


Certainly would be odd...but indeed it may be true. Certainly challenges many things to ponder that it may be that way. One could easily argue that we see nothing like it is simply because we cannot see so much of the spectrum. So right off the bat the limited range of the human-visual spectrum makes us see things not as they are. And when you add the fact that our eyes have only 3 color receptors whereas other animals have 12 receptors (Mantis Shrimp) so by their standard we are color blind! :lol:

Bottom line is, IMO, that we are only seeing a partial reality. We can't see all the spectrum from an object, nor all the colors, shapes/tones/hues are all altered to some degree by our perception, and our attention and/or focus even eliminates some objects from the view. I think that in the end, reality is beyond our ability to see, and can only at best be imperfectly imagined.

#65 Asbytec

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Posted 25 June 2014 - 05:52 PM

Well, I imperfectly imagined seeing Enke minimum. So did you, apparently, and you got me all excited about it. We saw it probably because it's there even if we don't observe xray spectrum or have shrimp eyes. Ya? :)

Besides, if one could observe the underlying reality, imagine how difficult it would be to convince others. :lol:

#66 azure1961p

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Posted 25 June 2014 - 08:59 PM

The last time Out I was getting flickers of it in 7-8 seeing. The A ring almost takes on a texture then the seeing fails and it smooths out again!

Einstein was particularly taken with the understanding that we never see anything as it really is.

Pete

#67 Asbytec

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Posted 26 June 2014 - 05:25 AM

Einstein was particularly taken with the understanding that we never see anything as it really is.

Pete


By referring to Einstein, are you implying, by appealing to his credibility, that Saturn "really" doesn't have rings? That Cassini division does not exist? Or that the Enke minimum is not "really" there? :)

"I think, therefore I am." Or maybe not, because we have no right to interpret what we see, think, or feel because it's all a construct of the mind and not at all real?

Yea, Enke minimum might not really appear as it really is, but it's there and we can observe it to be something. Otherwise why do we observe at all if we cannot trust what we observe, illusions included.

Sure, illusions are at play. But, not everything is an illusion nor should be written off as one. Especially when an actual anomaly, detected by high tech space toys, shows it to exist and we see it.

I believe Einstein was referring to the quantum if he made a statement like that.

#68 BillP

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Posted 26 June 2014 - 01:17 PM

By referring to Einstein, are you implying, by appealing to his credibility, that Saturn "really" doesn't have rings? That Cassini division does not exist? Or that the Enke minimum is not "really" there? :)


Interesting question. Is something a ring if it is not continguos? I mena let's be real (pardon the pun), the rings are just a bunch of individual things all orbiting the planet. They only look like a ring because we are too far away to see the spaces between the individual components. So we are assigning it an attribute of being a ring based on that illusion. Look at it this way, would you ever call rain falling from the sky a three dimentional space of water? But it's the same concept since it is just a collection of small individual items moving in unison.

And nope...the Cassini Division is not a gap at all. Look at this closeup of Cassini (from Cassini spacecraft). So all those darker rings between the bright A and B rings shows ARE the Cassini Division. So lots of junk in there ringing around :lol:

#69 Asbytec

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Posted 26 June 2014 - 07:20 PM

Okay, you win. The gap in my argument appears very real. You can't argue with an illusionist, apparently. :lol:

In jest, of course...great topic, nice conversation. One I looked forward to each time logging on.

Cheers, Bill...until we cross paths again. Especially down here in the observing section where the rubber meets the road and some observations are simply amazing, real or imagined. :)

#70 azure1961p

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Posted 27 June 2014 - 08:33 PM

Wow actually I wasn't implying Einstein had anything to do with the A phenomenon!!!! I've been meaning to make a concerted effort on the A ring - Ive been so busy though - and the weather so choppy - and now I'm finally going on vacation - without the scope.

One good thing is my last pencil drawing if Saturn has been officially turned into a digital rendering now in color. I think once and for all I'm done with graphite - I know my paper (copier paper) makes it impossible to get a fine blend, but I've become more proficient with a touchscreen stylus and associated apps/programs that Im really sold on it for the purposes of astronomy. Not art-art but telescopic observation rendering - absolutely!

Anyway for now Im feeling the Enckes Minima has a foot in reality AND illusion.

Pete

#71 Schaden

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Posted 29 June 2014 - 12:31 AM

The rings, though, just wow...striking. Especially the Crepe ring. Well, and the various tones of the A and B ring, too...and Cassini and Enke gap. It's all good. :)


I've only seen Encke's Gap once, during an opposition at 360x.

Did you see it the night of that drawing ? Just checking because I don't see it. The gap I saw was as black as Cassini's but much thinner. And it was out on the very edge of the A Ring.

The night I saw Encke's Gap was also the night I got a good view of the minima. It was like the A Ring was split into two tones. Fatter around the ansae. The edge of the rings and planet were razor sharp, but the minima almost looked like someone painted it on with a brush. The B Ring was also split into two tones. Before this night, I had only noticed differences in tone between the A and B, a rather dramatic one, but I had never seen a separation of tones with the same ring. I observed for a few hours and it was observable the whole time. Once in a while, the only turbulence looked like a messed up vertical hold on a CRT TV, crawling very slowly across the image. The Encke Gap would momentarily blur like Cassini can wiggle on a below average night.

The next night, it was not as good. No Encke's at all. But I saw flashes of the Minima, but not unmistakable like before. Almost like I already knew exactly how it looked, and that allowed me to see it again for split seconds, when the atmosphere cooperated.

Haven't had a night like that on Saturn since.

#72 E_Look

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Posted 29 June 2014 - 01:18 AM

You've reminded me of a night I had, just like that with Saturn too, back four years ago. Nights before and nights after, the seeing was unsteady, but THAT night, it was incredibly still, which permitted me to blow Saturn up to, really, 575x. That night I got to see Enceladus for the first time, and persistently so, even though at all powers it had to be by averted vision.

Now, in fact, I got to only glimpse Enceladus last night, despite nonideal transparency, much less than perfect seeing, again by averted vision, but ONLY at a high magnification, 460x. Of course, at this power, Saturn was soft and mushy, hard to focus, but I think given the bad observational conditions last night, it was the only way I could have seen it, even if only a few times for about a second each time. The transparency got progressively worse as the night wore on. In fact, it was due to increasing thickening of the haze, let alone the sheet of cloud that washed over the skies.

The tilt of the rings this season is great for seeing the Cassini division, but the Encke gap, Encke minima, there was no way given the viewing conditions.

#73 Asbytec

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Posted 29 June 2014 - 07:00 AM

First, congratulations on sighting Enke. That's no easy feat, but it sounds like you had a great night. Sorry to hear not since has seeing been that good.

As for me, no. I have not yet seen Enke gap. (Thought I did once, still have my soiled shorts to prove it.) I've only observed the minimum, regularly in good tropical seeing.






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