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Color in Orion

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#51 GlennLeDrew

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Posted 25 November 2012 - 04:25 PM

When different colors are present, the resulting color we see depends on the relative intensity. For any given image point, its color results from an admixture. The more dominant any particular wavelength, the more strongly the perceived color shifts to it. And so what red there is to be seen must 'fight' to get through the much more easily perceived blue-green.

Photographically, the vast majority of emission nebulae are red dominant, but visually the red contributes essentially nothing. One does not find on offer visual H-alpha filters for a good reason; in only a tiny handful of all nebulae (including planetaries, of which Campbell's Hydrogen Star is a standout example) can any red be detected, and mostly with difficulty.

The eye's poor red response, the visual dominance of other colors, the low surface brightness of most nebulae in the first place, and the light of the sky itself all conspire to make visual red detection in all but a few exceptionally bright examples impossible. Bias borne of familiarity with color images must to some extent be operating nowadays, else how to account for the lack of such reports in pre-color photography times, when even meter class and larger instruments were peered into? And knowing the numbers regarding the relative contributions of the light sources involved, and the human visual response, only reinforces this. It's so very easy to color the imagination with a combination of illusion and bias.

The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.

#52 Jon Isaacs

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Posted 25 November 2012 - 07:48 PM

The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.



A few thoughts:

- While informative, I think this thread is beyond the experience and reach a beginner. Any colors detected or perceived in nebulae are subtle at best.

- It is probably worth distinguishing between actually detecting a color and perceiving/seeing that color. The assumption here seems to be that perceiving/see red means that one was detecting a red color... I suggest that the fact that something appears red, particularly in the presence of other other colors, does not mean that it actually is red. The eye-brain is an amazing image processor but it is not fool proof.

Jon

#53 Meadeball

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Posted 25 November 2012 - 10:00 PM

Let me sum everything up to date ...

M42 is FREAKIN' GORGEOUS!!!

:refractor::rolling: :refractor::rainbow:

#54 dan_h

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Posted 25 November 2012 - 10:17 PM

When different colors are present, the resulting color we see depends on the relative intensity. For any given image point, its color results from an admixture. The more dominant any particular wavelength, the more strongly the perceived color shifts to it. And so what red there is to be seen must 'fight' to get through the much more easily perceived blue-green.

Photographically, the vast majority of emission nebulae are red dominant, but visually the red contributes essentially nothing. One does not find on offer visual H-alpha filters for a good reason; in only a tiny handful of all nebulae (including planetaries, of which Campbell's Hydrogen Star is a standout example) can any red be detected, and mostly with difficulty.

The eye's poor red response, the visual dominance of other colors, the low surface brightness of most nebulae in the first place, and the light of the sky itself all conspire to make visual red detection in all but a few exceptionally bright examples impossible. Bias borne of familiarity with color images must to some extent be operating nowadays, else how to account for the lack of such reports in pre-color photography times, when even meter class and larger instruments were peered into? And knowing the numbers regarding the relative contributions of the light sources involved, and the human visual response, only reinforces this. It's so very easy to color the imagination with a combination of illusion and bias.

The $64 question is: Can the variation in color sensitivity among individuals amount to something of an order of magnitude, or a factor of ten? Specifically, can some enjoy a tenfold increase above the norm in red sensitivity? For that's about what it would take to permit red detection at all near to that claimed.


Once about five years ago I was looking at M42 in late spring and there was very vivid pink coloring around the outer portions. And this was with my 120mm refractor. I have looked at this object many times, often in much larger scopes than mine, and I have never seen any colors other than the often stated blue/green glow in the centre. I was amazed to see the pink when I did. It was as colorful as a photograph.

I have come to believe that what I saw was an atmospheric affect of some sort and did not represent the true color of M42. I am open to other explanations. It sure was pretty and captured my imagination for a number of days.

dan

#55 Meadeball

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Posted 25 November 2012 - 10:20 PM

OMG ... it's the CHEMTRAILS!!!! :whee:

#56 Dave Mitsky

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Posted 26 November 2012 - 02:28 PM

A few thoughts:

- While informative, I think this thread is beyond the experience and reach a beginner. Any colors detected or perceived in nebulae are subtle at best.

- It is probably worth distinguishing between actually detecting a color and perceiving/seeing that color. The assumption here seems to be that perceiving/see red means that one was detecting a red color... I suggest that the fact that something appears red, particularly in the presence of other other colors, does not mean that it actually is red. The eye-brain is an amazing image processor but it is not fool proof.

Jon


While I agree in principle with the above, it should be stated that seeing colors, ranging from blue to green, in some of the brighter planetary nebulae such as NGC 3242, NGC 6543, NGC 6572, and NGC 7662 is not at all difficult, particularly through larger apertures. In fact, the nicknames of some of them are indicative of that fact, e.g., the Emerald Nebula and the Blue Snowball. No acquired observing skills are required.

Seeing color in M42 can be a bit harder. It's even more difficult for emission nebulae like M8 but on a couple of occasions I've detected a pale pink hue through 30" plus scopes. I've also seen color in Campbell's Hydrogen Star, IC 418 (the Raspberry Nebula), and Eta Carinae's Homunculus Nebula.

I'm fully aware of the argument about the ability to perceive ruddy hues in M42 as being due to visual contrast effects. What I don't understand, if that's the case, is why the only times that I have been able to do so have been when large apertures were employed at very dark sites under exceptionally good conditions. I typically don't see any color at all in M42 from light-polluted locales, even when using a dome-enclosed 17" telescope.

Dave Mitsky

#57 Jon Isaacs

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Posted 26 November 2012 - 02:49 PM

I'm fully aware of the argument about the ability to perceive reddish hues in M42 as being due to visual contrast effects. What I don't understand is why the only times that I have been able to do so have been when large apertures were employed at very dark sites under exceptionally good conditions. I typically don't see any color at all in M42 from light-polluted locales, even when using a dome-enclosed 17" telescope.

Dave Mitsky



Dave:

Seeing color in bright planetary's is relatively straightforward. One of my favorites is the NGC 6572, the Blue Racketball which looks green to me. I suspect that a bit of light pollution actually helps seeing color, the greenest I have seen it was from a typically dark site but with at least the first quarter moon.

The red I see in M42 does take dark skies and a reasonable sized telescope... But I suspect that I am not actually detecting red photons but rather some complimentary eye/brain effect.

Jon

#58 Dave Mitsky

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Posted 26 November 2012 - 03:42 PM

Jon,

A careful reading of my first paragraph reveals that I said the same thing. It's important for beginners to know that some deep-sky objects do indeed exhibit color. As far as NGC 6572 is concerned, I prefer the nickname the Emerald Nebula.

Can anyone explain then why this eye/brain effect only seems to happen under certain conditions?

Dave Mitsky

#59 cadfour

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Posted 26 November 2012 - 05:18 PM

I observed M42 (Orion Nebula) on Saturday. I saw blue..with a hint of green....am I the crazy one?

#60 Starman1

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Posted 28 November 2012 - 03:20 PM

There are two issues at play, with M42:
1) lab studies show that when 2 gray squares, illuminated to *barely* the limit of scotopic vision, but one a tiny bit brighter than the other, are presented to the observer, we all see the fainter one as "reddish" or "pinkish" and the brighter one as "greenish". This alone says we should trust our eyes very little when used at or near the limits of vision, if color is seen.
That we all see it is NOT a sign the color is there, merely that all of us have eyes that work the same way.

2) when observing M42 (and heaven knows I've looked at this nebula with 2" to 60" aperture at least a thousand times over the years), sometimes more colors than simply greenish-gray or pinkish-gray present themselves.
It seems that, on those nights, the nebula is SO bright in the telescope that a quick glance away from the scope shows that night vision has been damaged.
And the range of colors seen extends to yellowish-beige, bluish, pinkish, purplish, reddish, mauves, and simple grays, and nearby NGC1977 appears quite blue. One such night, I drew a simple map of the nebula, indicating where I saw each color, and compared it to a color photograph of the nebula, and found I had correctly indicated where each shade was found. So I am certain that, under the right conditions, colors can be seen in the Orion nebula. My vision at the time was probably mesopic, and not purely scotopic.

3) But these colors are not ALWAYS visible. As an experiment, I tried viewing the nebula through an H-alpha filter. Only the brighter sections could be seen, and the brightest part, even in H-a, was the central region.
When using a filter that transmits H-b and O-III, the entire nebula can be seen. That's not surprising since every nebula that emits H-a also emits H-b at a lower level, and because our peak sensitivity at night hovers around 500nm (near the H-b wavelength).

4) Recently, I've had a chance to compare narrowband filters that have substantial transmission at H-alpha with those that have zero transmission shorter than 700nm.
It may very well be that the restriction of bandwidth creates a greater ability to see the reddish colors than a non-filtered view, because the non-filtered view didn't present them as strongly. Or that the diminishment in brightness of the entire field resulted in that red/green illusion at the limit. How to tell?
It appears the reds I am used to seeing must be real, because they are visible in the filters WITH H-a transmission, but disappear with the filters that do not have H-a transmission.

5) Different observers have different sensitivities to colors, but it seems that on the nights where I see many colors, or very strong colors, so does everyone else in the observing site, and with a wide variety of apertures. I did not record particulars about the observations, but a memory search recalls that these were nights of exceptional transparency (very low extinction) and darkness.

So what can you say about the visibility of colors in M42/M43/NGC1977?
--it varies from person to person
--it varies from night to night
--it varies according to the filter used
--it varies by aperture (the reds were stronger in larger aperture)
--if "at the limit", the colors may not be real.

But if you have a night where you can see ANY tint to the fainter interior of the nebula, looks at those sections on either side of the central region and see if one side appears yellower than the other. If you see that, I believe you are seeing REAL colors in the nebula. Just don't expect to see them all the time.

#61 magic612

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Posted 28 November 2012 - 03:36 PM

I see a wide range of colors in M42, and it follows what Don concluded above: It varies. For me, and on the best of nights, I see the following in these scope sizes:

70mm refractor: Hints of blue, mostly gray
90mm refractor: A bit more blue, mostly gray
114mm reflector: Quite a bit of blue, the rest gray
130mm reflector: A lot of blue, some green, the rest gray
150mm reflector: Lots of blue, lots of green, some gray
250mm reflector: Blue, green, some orange, and a hint of dusty rose, the remainder gray

Those are on the best nights, and my eyes only. My kids see more color than me in smaller scopes; my wife sees less. I have asked other people to detail what they see, and it varies by person, quite widely.

#62 nirvanix

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Posted 30 November 2012 - 06:28 PM

On a night of excellent transparency after observing for several hours I could see hints of dusty pink in M42...and lots of green of course. So yes, I think you saw what you saw and good for you!

#63 Atl

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Posted 30 November 2012 - 10:03 PM

There are two issues at play, with M42:
1) lab studies show that when 2 gray squares, illuminated to *barely* the limit of scotopic vision, but one a tiny bit brighter than the other, are presented to the observer, we all see the fainter one as "reddish" or "pinkish" and the brighter one as "greenish". This alone says we should trust our eyes very little when used at or near the limits of vision, if color is seen.
That we all see it is NOT a sign the color is there, merely that all of us have eyes that work the same way.

2) when observing M42 (and heaven knows I've looked at this nebula with 2" to 60" aperture at least a thousand times over the years), sometimes more colors than simply greenish-gray or pinkish-gray present themselves.
It seems that, on those nights, the nebula is SO bright in the telescope that a quick glance away from the scope shows that night vision has been damaged.
And the range of colors seen extends to yellowish-beige, bluish, pinkish, purplish, reddish, mauves, and simple grays, and nearby NGC1977 appears quite blue. One such night, I drew a simple map of the nebula, indicating where I saw each color, and compared it to a color photograph of the nebula, and found I had correctly indicated where each shade was found. So I am certain that, under the right conditions, colors can be seen in the Orion nebula. My vision at the time was probably mesopic, and not purely scotopic.

3) But these colors are not ALWAYS visible. As an experiment, I tried viewing the nebula through an H-alpha filter. Only the brighter sections could be seen, and the brightest part, even in H-a, was the central region.
When using a filter that transmits H-b and O-III, the entire nebula can be seen. That's not surprising since every nebula that emits H-a also emits H-b at a lower level, and because our peak sensitivity at night hovers around 500nm (near the H-b wavelength).

4) Recently, I've had a chance to compare narrowband filters that have substantial transmission at H-alpha with those that have zero transmission shorter than 700nm.
It may very well be that the restriction of bandwidth creates a greater ability to see the reddish colors than a non-filtered view, because the non-filtered view didn't present them as strongly. Or that the diminishment in brightness of the entire field resulted in that red/green illusion at the limit. How to tell?
It appears the reds I am used to seeing must be real, because they are visible in the filters WITH H-a transmission, but disappear with the filters that do not have H-a transmission.

5) Different observers have different sensitivities to colors, but it seems that on the nights where I see many colors, or very strong colors, so does everyone else in the observing site, and with a wide variety of apertures. I did not record particulars about the observations, but a memory search recalls that these were nights of exceptional transparency (very low extinction) and darkness.

So what can you say about the visibility of colors in M42/M43/NGC1977?
--it varies from person to person
--it varies from night to night
--it varies according to the filter used
--it varies by aperture (the reds were stronger in larger aperture)
--if "at the limit", the colors may not be real.

But if you have a night where you can see ANY tint to the fainter interior of the nebula, looks at those sections on either side of the central region and see if one side appears yellower than the other. If you see that, I believe you are seeing REAL colors in the nebula. Just don't expect to see them all the time.


Awesome...well informed and written post.






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