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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
I see the gray of M43 and nearby NGC1977 as bluish-gray.
These pics tell the story as to why. M43 dominates in the HBeta emission, and NGC1977 is a reflection nebula (at least part of it is), so both are dominated by the blue.
You are right. I forgot of Hbeta. M43 would be theoretically red (strong Ha poor OIII) without Hb (of course if it is still mesopic: it is about 17 in V band). But with Hb the red blends with the blue.
You can download the three narroband pictures and play with them. You can change the lightness of them (to simulate different eye sensitivity) combine them. You get different possible aspects of the M42.
Quote:
I've always seen this as a gray, with a very pale greenish tint to it. In a 32" scope, the reds dominate for me and the greenish tints in M42 nearly disappear unless an O-III filter is used.
I suppose the exit pupil in the 32" is larger (I have a 16"). The maximum surface brightness is achieved when the exit pupil matches the eye pupil. In that case you nearly get the "nominal" brightness of the nebula. Smaller pupils produce lower brightness: For example 3.5 mm means minus 1.5 mags that translates 14 (the huygenian region) to about 16 (including losses). Now, if you look at the second paper (color appearance in mesopic conditions) it shows that the sensitivity of cones drops more rapidilly than that of the rods. The ratio L-cones to rods (which determines the redness) worsens at lower brightness (ad drops to zero below the threshold for L-cones). So, if you use a reduce e3xit pupil your rods tend to prevail and the tint moves towards green. At maximum exit pupil (I suppose in the 32") the opposit happens and the tint moves towards red.
In othe words the gray you percive depends on the brightness (or exit pupil). As the brightness approaches the limit of L-cones the tint moves towards green (or lesser red) (and fainter linghts may become reddishh... illusory reddish).
Quote:
What is interesting to me is that I have always seen one "lobe" of the nebula (one side of the central region) as somewhat "peach" colored as opposed to the "dusty rose" of the other lobe. The lobes are the section of the nebula inside the "ring" and separate from the "arches" or "wings".
Peach is a combination of yellow, red, and gray. I suspect, after all our conversation, that this may be an illusory color.
As for the HAlpha test, the weather forecast for SoCal for Thursday through Tuesday is clouds and rain. I may not get to test the filter this weekend, but we will see.
There the ratio Ha to OIII is high. So, if you can see Ha there..... there is a hope. If you do not the colour is a contrast effect.
Mybe friday will be clear here.
Edited by Mauro Da Lio (12/05/07 02:47 AM)
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6787
Loc: Beatrice, Nebraska
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Well, tonight, I ran into my friend with the extended red sensitivity. It turns out that from his old physics undergraduate lab notes, he had actually been also using a Xenon emission lamp. With the spectrometer he was doing the lab with, he had been seeing way out to the 7548 angstrom, 7642 angstrom, and 7671 angstrom lines. Needless to say, his red sensitivity is somewhat better than most (and better than mine). With his red sensitivity, I decided to sort of "blind" test him on M42 using his 8 inch f/5 Newtonian from my home location (ZLM 5.5). M42 was near the meridian, so there would be little atmospheric reddening and as much transparency as possible.
Without filters, the skyglow made it difficult to see much color other than a faint sky bluish with hints of greenish colorations in the Huygenian region. I put in the DGM Optics NPB filter and he immediately commented that he saw faint red at both 32x and 51x. The central core was somewhat bluish with maybe just a hint of green, but any green color was somewhat subdued to him. The reds he reported were somewhat farther out. I put in my OIII filter (the one *without* the red passband), and he said that he no longer saw any reds. I also tried my new Lumicon UHC (which also has no red passband) and he again reported no red. I tried my new 2" Lumicon H-Beta (which also has high transmission in the red), and he said the reds were back and a little more visible, although the nebula was somewhat smaller than with the NPB filter. We increased the power, and at or beyond 101x, he said the reds were somewhat marginal, although he still loved the almost 3D effect the NPB filter gave him. I had a look and I could also see faint reddish coloration with the NPB and H-Beta filters in M42, confined mostly to the areas a bit away from the really bright central region and at powers of less than 101x.
With these results, I have little doubt that the red he saw was indeed real and not just some illusion. Clear skies to you.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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sixela
Postmaster
Reged: 12/23/04
Posts: 9499
Loc: Boechout, Belgium
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Quote:
Thus: if you no longer see green because of increased magnification, you will no longer see red as compensation color.
The point is that I continue to see green but not red when I lower exit pupils. Of course, I'm perfectly aware that I see "red" mainly because it's "redder", but then you're starting to split semantics hairs, because the low red sensitivity of vision means that it's really redder than the slightly red the eye registers...if the brain is partly compensating for what the eye fails to register, are you seeing or imagining?
You're imagining things when the same mechanisms for "correcting" are fooled into revealing something that isn't there, but that's not what's happening here.
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Orion Starblast (114mm f/4 reflector, Alt/Az)
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Post deleted by Mauro Da Lio
Edited by Mauro Da Lio (12/05/07 04:42 PM)
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
Neitz, Jay & Jacobs, Gerald H. (1986). "Polymorphism of the long-wavelength cone in normal human colour vision." Nature. 323, 623-625.
As for numbers, it won't take a long search of available literature to bring up some study, but suffice it to say that there is some variation in the color sensitivity of different people. In any case, there is enough evidence to consider the reports of sightings of color in bright emission nebulae (even red) to be possible.
The paper gives strong evidence that there are variations in the L-cones of humans. More precisely it shows elements that support the thesis that there are two genetic types.
A color matching experiment was carried out in which two monochromatic sources, respectively green at 546 nm, and red at 690 nm, were to be adjustend in intensity so that their mix looked the same color of a 600 nm yellow monochromatic sources.
The amount of red and green needed to match the yellow was recorded. The distribution is bimodal. In one case the proportions of green and red were 0.47 to 0.53 and in the other mode 0.54 to 0.46 (approximately). That was considered as the evidence of two types of red cones. The researchers carefully considered other possible causes producing the same results (differences in transimissivity, photopigments etc, and experiments were set up which ruled out those possibilities).
Since the gene for the L-cones stands in the X-chromosome, an additional experiment was carried out with females who, having two X-chomosomes, may happen to have only type (a), type (b) or both. The distribution confirmed the expected occurence of a, b, and a+b.
Thus researchers concluded that there appears to be two types of L-cones. They also estimated peak sensitivity wich resulted at 556 and 559 nm respectively (3 nm apart).
Thus, the sensitivity of L-cones needed a stimulus of 0.47/0.53 = 0.89 for the first type and 1.17 for the second type to see the same yellow. The overall ratio in L-cones sensitivity is therefore 1.17/0.89=1.32 which means a mere 0.30 magnitudes.
Is that "much" "enough"? If the average threshold for color detection is between 17 and 18, can we conclude that somebody can see colors at surface brightness of 20-22 based on those findings?
Edited by Mauro Da Lio (12/06/07 05:07 PM)
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
We increased the power, and at or beyond 101x, he said the reds were somewhat marginal.
At 101x in a 200 mm diameter the surface brightness of an extended object is 2.7 - 3 magnitudes less than the original. Thus the huygenian region in the scope was shining at about 17 mpsas. The nearby region,s which starts at 17-18, were shining at 20-21 and above. You are saying that *real red* can be seen at 20 and above (depending which was the actual region).
I renew you the question: Do you think there is some limit or not? Which is, according to you, the threshold for L-cones inactivation?
Edited by Mauro Da Lio (12/06/07 05:09 PM)
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Starman1
Vendor - Scope City
Reged: 06/24/03
Posts: 10962
Loc: Los Angeles
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Mauro,
The variation in sensitivity of rods varies substantially more than 0.3 magnitudes. This is to be expected, since the dark adaptation process improves sensitivity by a factor of 90,000x ( I have no idea if that is an average or an extreme). I have, however, participated in many "field" experiments in which the visibility of faint stars in a field with known magnitudes varied by over a full magnitude from individual to individual. Momentary clearings could account for some of that difference, as could experience in simply focusing, but I think that degree of variation among experienced viewers is fairly common. Schaefer's work suggests that inexperienced viewers may lose a couple magnitudes and more. I have seen proof that details of magnitude 25 mpsas are visible in large scopes, despite the fact that this is literally 3 or more magnitudes fainter than the sky brightness at the same site (magnification being the reason, of course). Other people had a hard time seeing details at the magnitude 22 mpsas level on the same object
There is reason to suspect the variation in the cones at daylit levels of illumination varies less. That makes sense from the standpoint of survivability in evolutionary terms.
What isn't well known from field tests (as opposed to lab tests) is if the threshold of mesopic vision varies by a similar amount. The red-green mix study to which you refer has a flaw in that the threshold for the yellow color of matching may have a large variation (not tested), and the color sensitivity at the lowest possible limit was not tested.
Since the eye is so much more sensitive to green light than red light, it's logical to assume that red has to be a lot brighter to be visible to the cones.
How deep into the twilight do you see the color red? My own car is red, and I cannot tell it is red under a dark sky (mag.21.5mpsas), but I definitely see it as red (not gray) at a brightness of sky of mag.18mpsas. I will do a test to see at what point the red becomes indeterminate as the twilight deepens.
The point is, I expect the threshold for red is indeed brighter than mag.20mpsas. But are your calculations for the nebula correct? I've observed a lot of galaxies where the peak brightness for the galaxy (per the RC3) is magnitude 18 mpsas, and this peak brightness is a lot fainter than 90% of the Orion nebula. I suppose what would help, here, is a drawing of the nebula marked with where each color is seen. Also what would help is a map showing surface brightness at each location in the nebula.
Perhaps there is no disagreement at all, and the nebula sections where color is seen are simply above the human threshold.
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Don Pensack
12.5" Truss Dob, 5" Maksutov
Sustaining Lifetime IDA member, TeleVue junkie
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6787
Loc: Beatrice, Nebraska
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Mauro Da Lio posted:
Quote:
You mean that to see real red you need somebody who sees 7671 angstrom?
No, I *never* stated nor implied that. My friend does indeed have extended red and near-infrared sensitivity in direct vision, so it is logical to assume that if anyone could see red color (and not just some "illusion"), he could. He did when those filters passing red light were used and did not when those with only a blue or blue-green passband were used. Again, this is reasonably good evidence that what he is seeing is red light (mostly from the H-alpha emission line) and not some illusion. I saw it too, so at least from my viewpoint, red color is being seen rather than some contrast effect.
As far as "limits" are concerned, I never said that there were not any. However, what they are exactly for telescopic views of emission nebulae with the human eye (and its low-light variability) has not really been fully determined. Thus, using simple surface brightness figures to attempt to "prove" that red features are impossible to view in M42 with moderate to large apertures may not be a very realistic approach. Red colors in emission nebulae are difficult to see visually, but they are at least possible given the right conditions and equipment.
Edited by David Knisely (12/05/07 11:08 PM)
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
Mauro,
The variation in sensitivity of rods varies substantially more than 0.3 magnitudes. This is to be expected, since the dark adaptation process improves sensitivity by a factor of 90,000x ( I have no idea if that is an average or an extreme). I have, however, participated in many "field" experiments in which the visibility of faint stars in a field with known magnitudes varied by over a full magnitude from individual to individual. Momentary clearings could account for some of that difference, as could experience in simply focusing, but I think that degree of variation among experienced viewers is fairly common. Schaefer's work suggests that inexperienced viewers may lose a couple magnitudes and more. I have seen proof that details of magnitude 25 mpsas are visible in large scopes, despite the fact that this is literally 3 or more magnitudes fainter than the sky brightness at the same site (magnification being the reason, of course). Other people had a hard time seeing details at the magnitude 22 mpsas level on the same object
There is reason to suspect the variation in the cones at daylit levels of illumination varies less. That makes sense from the standpoint of survivability in evolutionary terms.
What isn't well known from field tests (as opposed to lab tests) is if the threshold of mesopic vision varies by a similar amount. The red-green mix study to which you refer has a flaw in that the threshold for the yellow color of matching may have a large variation (not tested), and the color sensitivity at the lowest possible limit was not tested.
Since the eye is so much more sensitive to green light than red light, it's logical to assume that red has to be a lot brighter to be visible to the cones.
How deep into the twilight do you see the color red? My own car is red, and I cannot tell it is red under a dark sky (mag.21.5mpsas), but I definitely see it as red (not gray) at a brightness of sky of mag.18mpsas. I will do a test to see at what point the red becomes indeterminate as the twilight deepens.
The point is, I expect the threshold for red is indeed brighter than mag.20mpsas. But are your calculations for the nebula correct? I've observed a lot of galaxies where the peak brightness for the galaxy (per the RC3) is magnitude 18 mpsas, and this peak brightness is a lot fainter than 90% of the Orion nebula. I suppose what would help, here, is a drawing of the nebula marked with where each color is seen. Also what would help is a map showing surface brightness at each location in the nebula.
Perhaps there is no disagreement at all, and the nebula sections where color is seen are simply above the human threshold.
Don, maybe we agree more than it appears. The 0.3 mags is the result of the paper pointed out by DaveK in order to justify color vision. I read it and found that the genetic difference accounts for only 0.3 mags, at 1000 trolands retinal illuminatin (full photopic). What the paper measures is the difference of the response curves of two types L-cones at photopic level at 690 nm. Spectral relative sensitivity has nothing to do with mesopic threshold (this is another big mistake when infrared sensitivity -should it be proved- is invoked to demonstrate real red perceptions at faint levels). But since that paper was pointed out to provide a justification I thought it was worth to disclose what actually that paper says.
I too think that mesopic thresholds varies approximately 1 magnitude (somewhat less). In Fact I often write 17-18. That is also hinted by the data in the first two papers. Curiously the mesopic limit matches the full moon illumination. I think this is not casual.
The viewing of details at mpsas 25 is another matter. Even in a 22 mpsas sky background vieweing the details is more a matter of contrast detection that actual sensitivity. I understand that you own a SQM. Try in a closed room. I found I am able to see shadows cast by a small led onto the wall at surface brightness of 24+. I have not found exactly the thresholds of rods, but in a very dark room, the SQM read below the lower limit (once) and about 27 (If I recall correctly, another time) and that was absolutely dark. I think we can sense light at about 25 with the rods.
I read somewhere that the difference between rods and cones mostly lies in the fact that many rods are "binned" together and provides a cumulative stimulus to ganglion cells (thus they give low spatial resolution but high sensitivity). On the countrary cones are connect one to one (approximately I think) so that the maximum spatial resolution is achieved but at the expense of sensitivity. L-cones, being the most numerous, perhaps have some kind of "binning" and they are probaly the most sensitive.
The 90000 adaptation to light is achieved by regeneration of rhodospin. Again it has little to share with the maximum sensitivity (nobody has a 9.000.000 times range).
I have made tests with a pure monochromatic red light (633 nm) and with broadband red samples. I am not sure I can take the SQM readings as correct (SQM has a different color sensitivity than the conventional photopic curve, which in turn is different than that of L-cones). Thus I cannot say exactly what is the limit of my L-cones but two things are clear: monochromatic light provides a lesser coupling L-cones to M-cones and makes red visible to lower levels than the broadband red cards. A faint "red" say at 19 looks as brigh as a fain "blue" at 22 (quotions means the source color). If I mix a faint red 3 mags brighter that the blue I get an undoubtely gray. For example a monochromatic red at 18 appears colored. A blue at 21 appears "grue". When they are superimpose they no longer appear colored. Thus I suspect that even the faintest OIII can cancel real red percetion. If we see Ha somewhere with Ha filter, there is still the possibility that without filter some fainter green and blue (Hb and OIII) can cancel the red perception: more precisely: L-cones see red, rods see fainter grue but produce a stronger stimulus and the region is not recognized as red a low level sensorial fusion (but maybe then later it is assumed red because it is a mediul light).
I think we have the narrowband color photographs. Let us see where we see Ha.
About the computation of apparent brightness I will better explain in another reply.
PS in addition the V brightness of an object tells little of its Ha brightness. To evaluate red visibility we need to know brightness in the "red" and L-cones threshold. Noting the regions seen in Ha tells where L-cones are really stimuylated (which does not automatically mean that the region is red, beause the other colors are also to be accounted).
Edited by Mauro Da Lio (12/06/07 05:39 PM)
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BillFerris
Carpal Tunnel
Reged: 07/17/04
Posts: 2582
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Quote:
You mean that to see real red you need somebody who sees 7671 angstrom?
This raises a point that's been largely ignored in this thread: where does the reality of color lie? I would argue that color perception is largely subjective and, as a result, it doesn't make much sense to argue that the red one person sees is less "real" than the red another person sees. When someone says, "There goes a red balloon," they're saying the balloon looks red to them. That's a subjective judgment and it's very different from saying, "There goes a balloon that is brightest at 650 nanometers."
In truth, color is not synonymous with wavelength and wavelength is not synonymous with color. While it is true that, under "normal daylight conditions," humans tend to see an object that does a really good job of reflecting 650 nm wavelength radiation as red, it is also true that not everybody will see red when looking at that object. And under different conditions, many humans would see that same object as a different color. One could even imagine a different life form that would perceive that same 650 nm radiation as a smell, a taste, a sound or as having some other sensory quality that we humans can't even begin to imagine.
The question of how an object interacts with electromagnetic radiation is very different from the question of how a human being will perceive that object. The spectral profile of a balloon can be objectively measured. It's equally possible to measure the spectral sensitivity of an individual person or a group of persons. The science of visual perception allows us to make reasonable predictions about what most people will see under specific circumstances. But real world experience also teaches that no two people are exactly alike. If you measure the spectral sensitivity of a group of people under various lighting conditions, no two will exactly match. In fact, as you increase the test population, you increase the number of people who will have significantly different spectral sensitivity profiles than the majority of subjects.
How do you characterize the results of that test? If 20 people look at a balloon and say, "That balloon's red," but two test subjects look at the same balloon under the same conditions and say, "That balloon's purple," do you conclude that the purple people are wrong...or lying...or seeing something that's less real? I would argue, no. The perception of purple is just as real as the perception of red. And with further testing, you may be unveil a physical explanation for why the minority saw a different color than the majority. That said, the minority's experience is no less real. Nor is it wrong. It's just different.
The recent trend of this thread has been something of an apples and oranges debate. On one hand, there's the debate about human visual performance as objectively tested under various lighting conditions. Scientific research in this area informs our understanding of color perception but it does not tell the whole story. On another hand, there are countless reliable reports by observers who have seen a broad range of colors when looking at celestial objects. These subjective reports also inform our understanding of color perception while also not telling the whole story.
To answer the question, "Is is possible to see nebulae with color?" all you have to do is ask an observer if he's ever seen color when looking at nebulae. Google "colorful nebulae" and in a fraction of a second you'll get about 220,000 responses in the affirmative. The fact is, observers see color in nebulae. Accepting this fact does not, however, tell us how or why people see color in nebulae. That's a different question; it's the question that's been at the focus of most of the recent discussion in this thread. Unfortunately, that very interesting discussion is being muddied to some extent by the debate about whether some observed colors are more or less "real" than others. That's a debate that never gets resolved in online forums. Google "green stars" if you want to get a sense of the vast bandwidths and rivers of time that have been expended in the effort to count the angels on the head of that pin.
Bill in Flag
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Mr. Bill
Carpal Tunnel
Reged: 02/09/05
Posts: 2761
Loc: Just passing through.....
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What Bill F. just said.....
As I said many posts ago in this thread....
"Mauro
Your explanations are impressive....I guess the word "see" in the title is the issue.
Maybe we need an epistemological discussion here."
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
This raises a point that's been largely ignored in this thread: where does the reality of color lie?
If there is a *causal* effect between the spectrum of the light and the perceived color that is real.
If one "reliable" observer sees the same spectrum once as green and another as red. That is a perception (or mistakes/illusions). Not real. Those people who see the ballon purple will always say purple in response to that spectrum. That means "correct recognition" (no matter what is the internal representation: a "smell", a "taste", a "purple" object or whatsoever).
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BEHAVIORAL AND BRAIN SCIENCES(2003) 26,3–64
Printed in the United States of America
Color realism and color science
Alex Byrne Department of Linguistics and Philosophy, Massachusetts Institute of Technology
David R. Hilbert Department of Philosophy and Laboratory of Integrative Neuroscience, University of Illinois at Chicago
Abstract: The target article is an attempt to make some progress on the problem of color realism. Are objects colored? And what is the nature of the color properties? We defend the view that physical objects (for instance, tomatoes, radishes, and rubies) are colored, and that colors are physical properties, specifically, types of reflectance. This is probably a minority opinion, at least among color scientists.
Textbooks frequently claim that physical objects are not colored, and that the colors are “subjective” or “in the mind.” The article has two other purposes: First, to introduce an interdisciplinary audience to some distinctively philosophical tools that are useful in tackling the problem of color realism and, second, to clarify the various positions and central arguments in the debate.
The first part explains the problem of color realism and makes some useful distinctions. These distinctions are then used to expose various confusions that often prevent people from seeing that the issues are genuine and difficult, and that the problem of color realism ought to be of interest to anyone working in the field of color science. The second part explains the various leading answers to the problem of color realism, and (briefly) argues that all views other than our own have serious difficulties or are unmotivated. The third part explains and motivates our own view, that colors are types of reflectances and defends it against objections made in the recent literature that are often taken as fatal.
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Experiments show that starting at mesopic level there are hue and saturation shifts, errors sometimes, but the different wavelenghts are *recognized*. A color is identifyed more or less accurately depending on the illumination level (the amount of errors in hue and saturation are measured).
Starting at scotopic level there is no causal effect linking wavelenght to color. However there is a causal effect linking lightness and perceived color. We shifts gradually from the percetion of millions of colors with small errors in hue and saturation to few colors in the green-red scale, to green-red related to lightness. This progression and continuity is not casual: often (because of the purkjnie effect) the long wavelenghs are perceived as darker than the short wavelegths. Thus our cognitive system, which try to get the most probable color from *any* little bit of information, estimates *red* the dark patches and *green* the lightest.
This guess is often correct for many reflecting surfaces. It is not the same for surfaces emitting lights. In fact The medium lights in M42 are redder that the high lights and in this case the gues is (casually) correct. But the medium lights in M27 are green and the guess (they are seen reddish) is wrong.
If you see *red* the OIII M27 and *red* the ha in M42 you are not seeing the real color but the real lightness as a color.
Try this simple experiment: geta OIII filter (without the red leakage), Look throgh the filter keeping it close to youre eye so that all your field of view ic covered. You will probaly see a monochromatic scene like this:
http://bp3.blogger.com/_rzxz_YRzFn8/RyTnkZqofuI/AAAAAAAAAEU/qp7XzXy7nyo/s1600-h/IMG_5182.jpg
Note that momentarily you may have the impression that the different levels of lightness are colored. But this is intermittent.
Now move the filter away so that It intercepts only a part of the scene like here:
http://bp1.blogger.com/_rzxz_YRzFn8/RyTne5qoftI/AAAAAAAAAEM/4n4RWcv608Y/s1600-h/IMG_5186.jpg
You will probabl be able to see colors thrugh the OIII narrowband filter. Surprisingly, in an object is partly in the filter view and partly out, you also will see the correct color. But there is no doubt that your receptors are not providing a useful signal... but your cognitive system works around and in this case it arrives at a good guess.
The colors are not real, but correct. IN M27 the colors are not real and wrong. IN M42 they are probaly not real but correct.
The only way to know if real red is seen in M42 is to look at where ha in seen. If a region that looks red is not visible in Ha then that red is a brain artifact.
Edited by Mauro Da Lio (12/06/07 05:00 PM)
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jhors
Riddle me this
Reged: 07/16/07
Posts: 737
Loc: Tempe, AZ
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At the risk of dropping this conversation several dozen IQ points, I can't resist modifying the old riddle:
If molecular hydrogen is excited in a planetary nebula and no one is around to see it, is it still red?
Judging from this discussion, I guess it is, but you'd be wrong if you say you perceived it 
Anyway, back to your regularly scheduled debate...and please, pardon the interruption.
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-Josh
Florence Junction:
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10" Dob
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I believe a leaf of grass is no less than the journey-work of the stars -Walt Whitman
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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There is an interesting witness on this month's "whats up" (Eridanus) http://www.cloudynights.com/item.php?item_id=1734 .
The author, who did not participate to this thread, reports seeing NGC1535 with a green centre and a pink fringe. The pink is reported on a 36" scope.
"Using the 36" f/5 Yard Scope and a 12mm eyepiece (360X) shows a bulls-eye of nebulosity, with the inner ring as light green and a light pink outer fringe. "
I have found the following picture of NGC1535 (yes, it resembles the Eskimo nebula). I have also made some search and it seems that the nebula is an OIII object. The outer ring should really be green like in the picture.
Thus this is another case (besides the "ears" of M27) where reddish is reported in place of OIII.
In fact the theory that "every time an expert observer sees a color, it has to be real" is contraddicted once again.
On the countrary, as the studies I pointed tell, the theory that "medium lights are contextually perceived as red" is reinforced by this observation.
Note that M27 and NG1535 are relatively bright nebuale. I do not exactly know how bright are the ears of M27 or the external shell of NGC1535, but it is clear that at that level (relatively bright) red is no longer correctly identifyed.
I believe that the alternative theory that "we shift from real colors to colors mapped onto brightness levels" is strong (not all people map different levels of light in false colors: as the studies show, some simply map them in gray levels).
Edited by Mauro Da Lio (12/08/07 01:31 PM)
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6787
Loc: Beatrice, Nebraska
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Mauro Da Lio wrote:
Quote:
"Using the 36" f/5 Yard Scope and a 12mm eyepiece (360X) shows a bulls-eye of nebulosity, with the inner ring as light green and a light pink outer fringe. "
I have found the following picture of NGC1535 (yes, it resembles the Eskimo nebula). I have also made some search and it seems that the nebula is an OIII object. The outer ring should really be green like in the picture.
Thus this is another case (besides the "ears" of M27) where reddish is reported in place of OIII.
In fact the theory that "every time an expert observer sees a color, it has to be real" is contraddicted once again.
No, it is not necessarily contradicted. Images of planetary nebulae can be processed in ways which do not present the same level or shade of color detail which the eye sees. You might want to check out the following narrow-band images of NGC 1535, as the H-alpha one shows that there is definite H-alpha emission:
http://astro.uni-tuebingen.de/cgi-bin/uncgi/pn?file=n1535&name=NGC+1535
--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
No, it is not necessarily contradicted. Images of planetary nebulae can be processed in ways which do not present the same level or shade of color detail which the eye sees. You might want to check out the following narrow-band images of NGC 1535, as the H-alpha one shows that there is definite H-alpha emission:
http://astro.uni-tuebingen.de/cgi-bin/uncgi/pn?file=n1535&name=NGC+1535
Everything might be... However how *strong* is that H-alpha emission? Could one see anything there with a H-alpha filter?
Whichever Nebula will have "some" amount of H-alpha emission (including the ears of M27), the point is how faint? is that enough?.
The fact is that 1353 is (as far as I know) by large dominated by OIII; add that the eye is 10 times more sensitive to OIII than H-alpha....
In my opinion you are trying to keep alive a dead theory. Anyway we will see if your hope survives the H-alpha filter. BTW no clear weather this week end. Hope for next.
PS I see here that the distributions of H-alpha and OIII have very similar patterns. Thus the ration Ha to OIII is *the same* all over the nebula and it *must* have the same color either green, if OIII wins, gray if OIII and Ha balance, red if Ha wins (in fact it is green). There are no regions where Ha is strong and OIII weak.
http://astro.uni-tuebingen.de/cgi-bin/uncgi/pn?file=n1535&name=NGC+1535
Here is Ha:
Here is OIII;
and here is the difference Ha-OIII (fringes are *not* dominated by Ha).
Edited by Mauro Da Lio (12/08/07 04:50 PM)
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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BTW You might want to check out the narrow-band images of IC 418, the red planetary: H-alpha here is a *lot* stronger than OIII.
http://astro.uni-tuebingen.de/cgi-bin/uncgi/pn?file=i0418&name=IC+418
No, I think that the argument that "NGC1353 might really be red" is defintely wrong.
PS And here is the difference Ha minus OIII for IC418 (it is a lot richer in Ha):
Edited by Mauro Da Lio (12/08/07 05:17 PM)
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David Knisely
Postmaster
Reged: 04/19/04
Posts: 6787
Loc: Beatrice, Nebraska
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Mauro Da Lio wrote:
Quote:
Everything might be... However how *strong* is that H-alpha emission? Could one see anything there with a H-alpha filter?
Maybe, if the observer's eye was sensitive enough (otherwise, probably not). I have only seen the typical bluish-green color in my 10 inch (but 36 inches is a lot of aperture).
Quote:
Whichever Nebula will have "some" amount of H-alpha emission (including the ears of M27), the point is how faint? is that enough?.
The fact is that 1353 is (as far as I know) by large dominated by OIII; add that the eye is 10 times more sensitive to OIII than H-alpha....
Check out the following:
http://www.williams.edu/Astronomy/research/PN/nebulae/spectra.php?neb=NGC%201535
The dominant lines in NGC 1535 are the OIII lines and H-alpha line. The H-alpha line is significantly weaker than the 5007 angstrom OIII line (the very strongest line in the planetary's spectrum) but is about the same strength as the 4959 angstrom OIII line and over twice as strong as the H-Beta line.
Quote:
In my opinion you are trying to keep alive a dead theory.
What "dead theory" are you talking about? All I have maintained here is that reddish hues are visible in certain bright emission nebulae (and even in a few planetary nebulae) under the right conditions. You seem to want to deny that reddish hues in nebulae can ever be seen at all, which is an unrealistic viewpoint. This is an argument for the sake of an argument, and is thus a waste of time.
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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info
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Mauro Da Lio
sage
Reged: 09/12/04
Posts: 223
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Quote:
Maybe, if the observer's eye was sensitive enough (otherwise, probably not). I have only seen the typical bluish-green color in my 10 inch (but 36 inches is a lot of aperture).
The maps of OIII and Ha emissions shows that the ratio Ha/OIII is greater at the centre than in the outer shell. The fringe is greener than the centre. So: if one sees geen the centre it must cannot see the fringe reddish regardless how much sensitive he is to red (the first red he should see should be at the centre).
The theory that observed colors are necessarily real is dead. This, besides the ears of M27, is a proof of false color percetion at a relatively high brightness. What hiopes remain? IC418 is much redder, so if real red is see that should happen there. Let us see if it is visible in Halpha. As for M42, the brightness levels where red is seen are similar to those of rthe above false colors. Unfortunately those regions are red so we cannot discriminate between false color perception and real perception based on the perceived color. But we only have to wait the ha test.
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semiosteve
super member
Reged: 07/03/04
Posts: 143
Loc: NEOhio
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You guys have to get a Mallincam...I see serious color (like hubble color) on a lot of objects in near real time even with my AP 180mm.
Visually I see color with my 20 inch Obsession on the Orion nebula and the Dumbell and a few other larger objects. ...Not neon, but not usually just one color either... There are numerous small blue or green planetaries especially in the summer.
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Steve Verba
7in. Astro-Physics StarFire
20in. Obsession
15 x 15 Rolloff (Backyard Observatories)
Mallincam Hyper Color video camera
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