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View Full Version : If Brown Isn't a Color, What Color are Brown Dwarfs?



Fraser
2009-Jan-07, 01:10 AM
We've talked about brown dwarfs here on Universe Today for years and years. These are the "failed stars"; objects with too little mass to fully ignite nuclear fusion in their cores. Instead of blazing with red, yellow or the white light of our own stars, they're heated by the gravitational collapse of material. They're called [...]

More... (http://www.universetoday.com/2009/01/06/if-brown-isnt-a-color-what-color-are-brown-dwarfs/)

George
2009-Jan-07, 03:41 AM
Brown dwarfs have so many organics in their atmosphere, I would be surprised if some of them are not brown. They definetly will not be blackbody radiators, so they are not restricted to the hotter star temperatures that produce light somewhat evenly across the visible spectrum.

I recall a T-class brown dwarf that had, essentially, only red and a lesser amount of blue light. This star is likely a maroon star, not far from brown. [There is an old thread on it somewhere. It was Grant's first post, IIRC. :)]

George
2009-Jan-07, 03:43 AM
Oh, and when astronomy books favor the correct color of our own star, I will feel more confident in their assesment of others. [Not that "true" color is all that important to doing serious astronomy, in case people don't understand the colorful tone in my remarks. :)]

Jeff Root
2009-Jan-07, 06:02 AM
Okay, astronomers think that brown isn't a color, that there are no
mixtures of photons that can produce light that looks brown to our
eyes, that carbon, nitrogen, and oxygen are metals, and that the
Universe is homogeneous and isotropic.

That red-orange color sample appears to be somewhere in the range of:


800 deg C Dull cherry-red
900 deg C Cherry-red
1000 deg C Bright cherry-red
1100 deg C Orange-red
Saying that brown is a de-saturated yellow is about 1/2 right.
The term "de-saturated" means that colors other than yellow are
mixed in. On a computer monitor or TV, of course, there is no yellow
at all, only a combination of red and green. Adding some blue to
de-saturate it makes it whiter. So a de-saturated yellow would be
a yellowish-white. Brown can be reddish, orangish, yellowish, or
greenish, and I won't explicitly say where the "ish" comes from, but
I think you've seen it for yourself. De-saturate brown enough and
it becomes beige.

-- Jeff, in Minneapolis

Ronald Brak
2009-Jan-07, 06:17 AM
I assumed that it would be possible that brown dwarfs (cherry-red dwarfs?) could be banded as the one in the artists impression in the article is. Is this correct?

George
2009-Jan-07, 11:56 PM
Okay, astronomers think that brown isn't a color, that there are no
mixtures of photons that can produce light that looks brown to our
eyes, that carbon, nitrogen, and oxygen are metals, and that the
Universe is homogeneous and isotropic.
Huh? I can understand this if we are talking about near-blackbody radiators, but not sub-stellar bodies loaded with a host of organics in its photosphere. Perhaps they are rare, but, considering their number, they are bound to be out there. :)

Brown is definitely producible using red, green, and blue colors as found on our monitors. But this is obvious, so what are you saying?

grant hutchison
2009-Jan-08, 12:09 AM
I recall a T-class brown dwarf that had, essentially, only red and a lesser amount of blue light. This star is likely a maroon star, not far from brown. [There is an old thread on it somewhere. It was Grant's first post, IIRC. :)]Was indeed (http://www.bautforum.com/astronomy/19534-magenta-brown-dwarfs.html).
The sodium lines in the T-dwarf spectrum are so broad they take a chunk right out of the centre, leaving a mix of blue and red. Adam Burrows described the result as "magenta" in a paper about T dwarfs. L dwarfs turn out to be reddish, as Fraser's sample shows.

Grant Hutchison

George
2009-Jan-08, 01:20 AM
Was indeed (http://www.bautforum.com/astronomy/19534-magenta-brown-dwarfs.html). :) A memorable one for me as I did run that through the old SPACC and got somewhat favorable results, IIRC.

Perhaps we should wait a month on this topic so we can have a 4th year anniversary and pick up where we left off. ;)



The sodium lines in the T-dwarf spectrum are so broad they take a chunk right out of the centre, leaving a mix of blue and red. Adam Burrows described the result as "magenta" in a paper about T dwarfs. L dwarfs turn out to be reddish, as Fraser's sample shows.
Are Brown Dwarfs very convective (I assume so)? If not, perhaps compounds could remain in the photosphere after impacting it. I would expect there isn't that many SEDs on these little guys to indicate clearly that no brown one is likely.

timb
2009-Jan-08, 01:44 AM
Huh? I can understand this if we are talking about near-blackbody radiators, but not sub-stellar bodies loaded with a host of organics in its photosphere. Perhaps they are rare, but, considering their number, they are bound to be out there. :)

Brown is definitely producible using red, green, and blue colors as found on our monitors. But this is obvious, so what are you saying?

I think Jeff may have been employing an ancient rhetorical device known as sarcasm to express his disagreement with some of the statements in the article linked to in the OP and elsewhere in the astronomical literature.

According to wikipedia, T dwarfs are the color of magenta coal tar dye, which I have never seen. I suspect they would look fairly dull.

Jeff Root
2009-Jan-09, 02:47 PM
Okay, astronomers think that brown isn't a color, that there are no
mixtures of photons that can produce light that looks brown to our
eyes, that carbon, nitrogen, and oxygen are metals, and that the
Universe is homogeneous and isotropic.
Huh? I can understand this if we are talking about near-blackbody
radiators, but not sub-stellar bodies loaded with a host of organics
in its photosphere. Perhaps they are rare, but, considering their
number, they are bound to be out there. :)

Brown is definitely producible using red, green, and blue
colors as found on our monitors. But this is obvious, so what
are you saying?
I thought that what I was saying was obvious, too, and I am
competely at a loss as to why we don't understand each other.
You seem to be arguing something about the nature of brown
dwarfs, while I was only talking about the nature of color, vision,
and the semantics of terms used to describe them. Obviously
brown IS a color. Obviously there are MANY mixtures of
photons that can produce light that looks brown to our eyes.
So why do these people say that brown is NOT a color and
that there are no mixtures of photons that can produce light
that looks brown to our eyes? It's just goofy!

-- Jeff, in Minneapolis

George
2009-Jan-09, 03:09 PM
I thought that what I was saying was obvious, too, and I am
competely at a loss as to why we don't understand each other.
You seem to be arguing something about the nature of brown
dwarfs, while I was only talking about the nature of color, vision,
and the semantics of terms used to describe them. Obviously
brown IS a color. My thought here [for their reasoning] is that it isn't part of the spectrum, but it is certainly a color as you say, only one made-up of more than one color of the spectrum. The other thought I had was they were thinking in terms of bb radiators which eliminates green, for instance.

I assume then that you, like me, suspect some brown dwarfs might look brown?

grant hutchison
2009-Jan-09, 04:21 PM
So why do these people say that brown is NOT a color and
that there are no mixtures of photons that can produce light
that looks brown to our eyes?Because there is no mixture of photons from a single luminous source that will uniquely convey the sensation of "brown" to your eyes, any more than there is a mixture of photons from a single luminous source that will uniquely convey the sensation of "grey" to your eyes (or of "black", for that matter).
Judging "brown" and "grey" needs other cues, which are extracted from contrast effects and estimates of the ambient illumination. They're properties of illuminated surfaces, rather than luminous surfaces. You see them in an environment, rather than in isolation.

Grant Hutchison

George
2009-Jan-09, 04:40 PM
Because there is no mixture of photons from a single luminous source that will convey the sensation of "brown" to your eyes, any more than there is a mixture of photons from a single luminous source that will convey the sensation of "grey" to your eyes (or of "black", for that matter).
Judging "brown" and "grey" needs other cues, which are extracted from contrast effects and estimates of the ambient illumination. They're properties of illuminated surfaces, rather than luminous surfaces. You see them in an environment, rather than in isolation.

Grant Hutchison
That's an interesting explanation that would explain some things. However, such a claim is easy enough to test, I think...

I filled my montior screen to output "brown" and eliminated ambient lighting and surroundings so that all I could see was the center of my screen. It still looked brown, though there may have been some slight variation to it, perhaps.

Assuming color constancy or some other pyschological effect was influencing my deciesion, since I already knew it was brown before I looked, I added overlays of various colors that I then deleted leaving the original brown-colored screen. It seems to me that the brain will register brown if the right combination of r,g,b intensities are used, regardless of ambient influences.

grant hutchison
2009-Jan-09, 04:48 PM
And yet it's easy enough to convert brown to orange-yellow and back again, simply by adjusting external cues.
The two coloured spots here (http://upload.wikimedia.org/wikipedia/commons/9/9a/Optical_grey_squares_orange_brown.svg) are the same colour. And, perhaps even more surprisingly, the two grey squares on which the coloured spots lie are the same shade of grey.

Grant Hutchison

Jeff Root
2009-Jan-09, 05:26 PM
I thought that what I was saying was obvious, too, and I am
competely at a loss as to why we don't understand each other.
You seem to be arguing something about the nature of brown
dwarfs, while I was only talking about the nature of color, vision,
and the semantics of terms used to describe them. Obviously
brown IS a color.
My thought here [for their reasoning] is that it isn't part of the
spectrum, but it is certainly a color as you say, only one made-up
of more than one color of the spectrum.
So according to you, it isn't part of the spectrum, but it is parts
of the spectrum. :need a cross-eyed smiley:



The other thought I had was they were thinking in terms of bb
radiators which eliminates green, for instance.
Although the list of colors/temperatures I gave a few posts back
(from an old Starrett Tools catalog) was indeed for approximate
blackbody radiators (judging the temperature of steel by sight,
in that case), the idea that anybody would limit their definition
of "color" to that which can be emitted by a black body is just
goofy. Goofy Goofy Goofy. Maybe Donald Duck, too.



I assume then that you, like me, suspect some brown dwarfs
might look brown?
I haven't given it as much thought as you, but that seems likely.
With Jupiter and Saturn as our closest comparisons, brown dwarfs
would be very likely to look at least partly brown by reflected light.
I'd expect a fairly dim brown dwarf to look dull cherry-red by its
own emitted light, with no significant orange, yellow, green, or blue.

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-10, 05:11 AM
So why do these people say that brown is NOT a color and
that there are no mixtures of photons that can produce light
that looks brown to our eyes?
Because there is no mixture of photons from a single luminous source
that will convey the sensation of "brown" to your eyes, any more than
there is a mixture of photons from a single luminous source that will
convey the sensation of "grey" to your eyes.
Both depend on what you mean by "from a single luminous source".



Judging "brown" and "grey" needs other cues, which are extracted
from contrast effects and estimates of the ambient illumination.
They're properties of illuminated surfaces, rather than luminous
surfaces. You see them in an environment, rather than in isolation.
I don't entirely disagree with that, but...

Without external cues, you can't tell any difference between a
luminous surface and an illuminated surface. If the arrangement
of materials, geometry, colors, and lighting is right, you could not
see that a heating element glowing red is not just red paint.

As George's test and my own observations suggest, the idea that
brown can only be seen in context isn't always true. Any color's
appearance depends to a large extent on what else is going on in
the visual field. That may be more true for brown than for most
colors, but it isn't absolutely true. Brown will still look brown in a
very wide range of circumstances, and that does not depend on
whether the light is reflected, transmitted, or emitted from the
surface being viewed.

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-10, 05:48 AM
And yet it's easy enough to convert brown to orange-yellow and back
again, simply by adjusting external cues.
Well, duh! orange-yellow = brown. They are different names for
the same thing.

(I feel the need to note again at this point that "brown" covers an
extremely wide range of colors, from red-orange through yellow to
yellow-green, and from nearly black to light beige.)



The two coloured spots
here (http://upload.wikimedia.org/wikipedia/commons/9/9a/Optical_grey_squares_orange_brown.svg) are the same colour. And, perhaps even more surprisingly, the two grey squares on which the coloured spots lie are the same shade of grey.
I haven't had much success with SVG files. Is the format very new
or very old? In IrfanView 4.20, most of the top of the checkerboard
is solid almost-black (000504). Reduced-size screenshot below.

-- Jeff, in Minneapolis

tdvance
2009-Jan-10, 01:47 PM
Technically, gray and brown aren't colors, but "shades". Both depend on surrounding context--there is no such thing as brown light. Feynman's Lectures on Physics (I forgot which volume--probably the first) explains this in detail in the lecture on color vision.

grant hutchison
2009-Jan-10, 01:53 PM
As George's test and my own observations suggest, the idea that
brown can only be seen in context isn't always true. Any color's
appearance depends to a large extent on what else is going on in
the visual field. That may be more true for brown than for most
colors, but it isn't absolutely true. Brown will still look brown in a
very wide range of circumstances, and that does not depend on
whether the light is reflected, transmitted, or emitted from the
surface being viewed.Have you been working off-line on this reply for twelve hours? Your quote from me misses a clarifying edit I made quite soon after posting (the word "uniquely").
I don't contest that there are photon combinations that will elicit the sensation "brown" under some circumstances. It's just that the same combination of photons will elicit the sensation yellow (or greenish-yellow, or orange-yellow) under other circumstances. You can search as long as you look on the CIE colour triangle, and you won't find a mix of red, green and blue that you'd call brown: that requires a change in luminance as well as hue.
Brown is not a property of the power spectrum of light of alone, in exactly the same way as grey is not a property of the power spectrum of light alone.

Just saying "goofy, goofy, goofy" probably won't change that for you. :)


Well, duh! orange-yellow = brown. They are different names for
the same thing.Reclassifying brown to include its high-luminance equivalents is certainly one way to defend your point. But perhaps not a good way.

Grant Hutchison

grant hutchison
2009-Jan-10, 03:35 PM
I haven't had much success with SVG files. Is the format very new
or very old?Kind of middling. It has been around since the turn of the millennium, and is one of those web standards that Microsoft has contrived to ignore while everyone else implemented them.
I'm therefore guessing that you're running a very old browser, or a current version of Internet Explorer. :)
If you have IE, you need to download an ActiveX plug-in in order to view SVG. Adobe SVG Viewer (http://www.adobe.com/svg/viewer/install/) is one such. I just hunted down IE on my own machine and installed the plug-in, and can confirm that the image is then viewable with IE7 under Vista, although the plug-in itself is only XP-rated.

Grant Hutchison

grant hutchison
2009-Jan-10, 03:53 PM
Technically, gray and brown aren't colors, but "shades". Both depend on surrounding context--there is no such thing as brown light. Feynman's Lectures on Physics (I forgot which volume--probably the first) explains this in detail in the lecture on color vision.Yes, section 35-3 in Volume 1. To judge from the text, it looks as if Feynman did some sort of experiment during the lecture, mixing red and yellow spotlights and then increasing the level of surrounding illumination to shift the visual sensation from orange to brown.

Grant Hutchison

m1omg
2009-Jan-10, 04:36 PM
What are these brown dwarfs what are they talking about?M class brown dwarfs would have the same color and light intensity as the lowest mass M stars (lightbulb white), L class dwarfs are still hotter or around the temperature of wood or candle flame or lava and T dwarfs are around the temperature of a dimly burning fire, T8 brown dwarfs are still as hot as just visible smoldering cinders.

You shouldn't imagine brown dwarfs as "extremely dim", they are, but only relatively, compared to most other stars, in fact even these "red" dwarfs that are typically portrayed on artists impressions as "crismon red" are WHITE, and such stars as Barnard's star are about as hot as acetylene torch, most "brown" dwarfs are still hotter than ordinary fire or about the same temperature so IMHO they are NOT banded purple dim cinders, only the coolest T dwarfs are like that, most of BDs should appear as bright balls of bright orange or cherry color, they still radiate more energy than we will ever produce on Earth if we mined all the hydrogen and deuterium and tritium from all the water here and fed it to the most effective theoretical nuclear fusion plant.

It doesn't matter if the energy is from active fusion or not, temperature still makes L and M class BDs dazzlingly bright from close distances.

Practically every star close up would appear white, just differently tinted, and even L class BDs should still appear as fire orange.

And I think the molecules would cause some of the effects typically seen in flames, like soot, mega fire tornadoes etc., not Jupiter-like cold chemical colors.

Think of a BD as a giant ball of fire the size of two Jupiters and you'll get the idea.

There is no reason to expect temperature and intensity colours would appear anyhow different that they do in things with similiar temperature on Earth -that's why I used the fire comparision.

George
2009-Jan-10, 05:46 PM
Technically, gray and brown aren't colors, but "shades". Both depend on surrounding context--there is no such thing as brown light. Brown may not be an allowable monochromatic color, but that is not the general use of the meaning of color. I do agree that a good way to see brown is with the understanding of our use of color that includes gray or white. Nevertheless, all of these are found in my Crayola box, so they are colors. :) [Here again, science lacks an appropriate term that could be used to help eschew obfuscation. "Metamer" kind of works since it is associated with more than one "color", but something that sounds like color should be found. Colorply or colorplex or something to indicate that more than one wavelength is involved in producing the sensation. Cougar? :)] "Shade" seems a bit weak.


You can search as long as you look on the CIE colour triangle, and you won't find a mix of red, green and blue that you'd call brown: that requires a change in luminance as well as hue.
This may be part of the confussion, if my assumption of what you are saying is correct. [I assume the CIE color triangle use only even luminance values? That would explain some things.] But, of course, there is no reason a star is restricted to a flat spectral luminance. Brown dwarfs may have a vast number of different SEDs due to all the various molecular cocktails allowable in its outer atmospheres.

Using your old T-class brown dwarf SED, which has strong red and weak blue (maroon, if an object has blue at half or less of the intensity of red ), were to include green at an intensity of about 20% or so more than blue, then brown it is. If you prefer a lighter tone of brown, then add yellow in lieu of green. Brown is what we would see to be the color of the star. [Assuming it is one of the hotter ones and not 700K, for example.]

The bigger problem is whether such mid-range wavelength peaks would ever be found in their SED. Admitedly, it seems unlikely given that their magenta or maroon (depending on blue intensity) comes from the absence of the midrange colors -- apparently due to sodium and potasium absorption.


Brown is not a property of the power spectrum of light of alone, in exactly the same way as grey is not a property of the power spectrum of light alone. My spectrum can whip your spectrum. :p ;)


Just saying "goofy, goofy, goofy" probably won't change that for you. :) Well.... nevermind, I may have said too much already. ;)


Reclassifying brown to include its high-luminance equivalents is certainly one way to defend your point. But perhaps not a [I]good way. I don't understand this. Why not?

George
2009-Jan-10, 06:00 PM
You shouldn't imagine brown dwarfs as "extremely dim", they are, but only relatively, compared to most other stars, in fact even these "red" dwarfs that are typically portrayed on artists impressions as "crismon red" are WHITE,... You are right that they would be much brighter than they are portrayed, but they would only be white if their spectrum were more that of a blackbody, which is true of most of the hotter stars. Brown dwarfs are not blackbody radiators due to the host of molecular compounds in their atmospheres.

grant hutchison
2009-Jan-10, 06:21 PM
Reclassifying brown to include its high-luminance equivalents is certainly one way to defend your point. But perhaps not a good way.I don't understand this. Why not?Because I would guess your crayon collection contains both an orange-yellow and a brown crayon. And I would guess that you don't see a stripe of brown between the orange and green of a rainbow.
We have different names for things because we perceive salient differences between them.

I'm untroubled if you and Jeff want to call "brown" a colour. I was just responding to Jeff's question "So why do these people say that brown is NOT a color and that there are no mixtures of photons that can produce light that looks brown to our eyes?"
The answer is that, because astronomers deal with pure photon mixtures, they use the word "colour" to designate the combination of hue and saturation; relative luminance (the sort of effect that produces brown) is not part of their colour language. That's how life is. Poor Jill Tarter was just being reprimanded for a non-technical usage.

Grant Hutchison

m1omg
2009-Jan-10, 06:33 PM
You are right that they would be much brighter than they are portrayed, but they would only be white if their spectrum were more that of a blackbody, which is true of most of the hotter stars. Brown dwarfs are not blackbody radiators due to the host of molecular compounds in their atmospheres.

Yeah, but flames are not perfect blackbodies either, and I would guess the molecular components would create some interesting freatures but not attenuate the radiation too much, definitely not to the "crismon, blood red, or pink ball with stripes that shines like a 10 W lightbulb from China" point as on usual illustrations.

And I wrote that red dwarfs (that are much closer to perfect blackbodies) would be white when viewed from close distances, not brown dwarfs, these would be more orange to cherry color, or like smouldering embers with a more maroonish color in case of colder T dwarfs.

George
2009-Jan-10, 06:57 PM
Because I would guess your crayon collection contains both an orange-yellow and a brown crayon. Wrong, I ate the orange-yellow one long ago. [Not near the citrus flavor that I had for, admittedly.] ;)


I would guess that you don't see a stripe of brown between the orange and green of a rainbow. Quite true, but why are we chasing rainbows, not that I don't like gold? Polychromatic radiance is a given for brown dwarfs. [Perhaps, polychromatic illuminance from brown dwarfs would be more a accurate statement.]


I'm untroubled if you and Jeff want to call "brown" a colour. I was just responding to Jeff's question "So why do these people say that brown is NOT a color and that there are no mixtures of photons that can produce light that looks brown to our eyes?"
The answer is that, because astronomers deal with pure photon mixtures, they use the word "colour" to designate the combination of hue and saturation; relative luminance (the sort of effect that produces brown) is not part of their colour language. That certainly makes sense for those that study blackbody objects, but this seems much too restrictive now that much diversity is found in the SEDs of so many new objects since the days before Hubble [person and telescope]. Astronomers should be light experts more than most the other scientists, including their view of the " true spectrum" (quintessential superspectrum (http://en.wikipedia.org/wiki/List_of_Crayola_crayon_colors)), which is inclusive of metamers, shades, etcs.


That's how life is. Poor Jill Tarter was just being reprimanded for a non-technical usage. All heliochromolgists feel her pain.

grant hutchison
2009-Jan-10, 07:05 PM
Quite true, but why are we chasing rainbows, not that I don't like gold? Polychromatic radiance is a given for brown dwarfs. [Perhaps, polychromatic illuminance from brown dwarfs would be more a accurate statement.]

That certainly makes sense for those that study blackbody objects, but this seems much too restrictive now that much diversity is found in the SEDs of so many new objects since the days before Hubble. Astronomers should be light experts more than most the other scientists, including the spectrum (quintessential superspectrum (http://en.wikipedia.org/wiki/List_of_Crayola_crayon_colors)), which is inclusive of metamers, shades, etcs.This has nothing to do with black body spectra (emission nebulae have provided astronomers with a fine range of colours ever since the advent of photography). And it has nothing to do with spectral colours, or with the difference between pure colours and metamers.
The only thing of relevance here is that I cannot, even in principle, take a box of photons, analyse their spectral mix, and say unequivocally that they will appear brown to the human eye. That information just isn't present in the box. All I can do is assign them confidently to the yellow region of the hue chart, and predict that under some conditions, when their relative luminance is perceived to be low, they may induce a brown sensation.

It's because astronomers are light experts that they make this distinction, which is not intuitively obvious to the average crayon-user.

Grant Hutchison

George
2009-Jan-10, 07:26 PM
Yeah, but flames are not perfect blackbodies either, and I would guess the molecular components would create some interesting freatures but not attenuate the radiation too much, definitely not to the "crismon, blood red, or pink ball with stripes that shines like a 10 W lightbulb from China" point as on usual illustrations. Yet flames come in many colors. Incandescent lighting (tungsten) is close to behaving like a blackbody radiator, but at a temperature between 2000K to 3300K. These temperatures still produce light across the spectrum, but 2000K is weighted heavily on the red end. It will not look white if the Sun or similar more color-balanced bright light source is arround.


And I wrote that red dwarfs (that are much closer to perfect blackbodies) would be white when viewed from close distances,... Are they close to blackbody radiators? If so then they should look at least as white as a light bulb, though a hotter neighbor in the picture would yellow it.

Also, it seems they are hot enough that their flux would exceed our photopic vision range and also force a white image, regardless of its color if seen at a lower flux. [BTW, getting closer to the disk will not make it more or less white except for this flux issue. Once you are close enough to see it as a disk, its surface brightness does not increase as you get closer.]

George
2009-Jan-10, 07:47 PM
The only thing of relevance here is that I cannot, even in principle, take a box of photons, analyse their spectral mix, and say unequivocally that they will appear brown to the human eye. That information just isn't present in the box. All I can do is assign them confidently to the yellow region of the hue chart, and predict that under some conditions, when their relative luminance is perceived to be low, they may induce a brown sensation. Odd, I can, at least in principle. Give me a box of "blue" photons that are half as many as "red" photons, then throw in about 20% more "green" ones [than blue ones] and, after appropriate shaking of course, ta dah... we will be bathed in the sensation of "brown" light. That is why my brown crayon looks brown, right?

Give me an object's SED in the visible spectrum and I will give you an accurate "color" (colorplex) of the object presented. Your Spectrum(?) software package you shared with us does the same, but it may not be super accurate. But this you know, so where did I miss the bridge?


It's because astronomers are light experts that they make this distinction, which is not intuitively obvious to the average crayon-user. Hence the problem, they should never have skipped those early coloring grades!! I hate to pick on my favorite scientists dedicated to my favorite hobby, but color is not their strong suit. This is justifiable as color alone is very limited information about an object compared to what they find in absorption and emission spectrums. So, it is unfair for anyone to be too critical of their colorful errors, but I feel obliged being that I am their friend and a volunteer heliochromologist. :)

m1omg
2009-Jan-10, 07:53 PM
Yet flames come in many colors. Incandescent lighting (tungsten) is close to behaving like a blackbody radiator, but at a temperature between 2000K to 3300K. These temperatures still produce light across the spectrum, but 2000K is weighted heavily on the red end. It will not look white if the Sun or similar more color-balanced bright light source is arround.

Are they close to blackbody radiators? If so then they should look at least as white as a light bulb, though a hotter neighbor in the picture would yellow it.

Also, it seems they are hot enough that their flux would exceed our photopic vision range and also force a white image, regardless of its color if seen at a lower flux. [BTW, getting closer to the disk will not make it more or less white except for this flux issue. Once you are close enough to see it as a disk, its surface brightness does not increase as you get closer.]

Yeah that's right.I haven't meaned perfect white for red dwarfs,more like the yellowish white you get from classic lightbulbs, and perfect white also depends on the definition, if you define Vega as being perfect white Sun will not be perfect white from space even if it is white (atmosphere scatters light so it appears yellow, Vega would probably look almost perfectly white even through an atmosphere.

And brown dwarfs are not white, but definitely not like in the artist impression pictures.

Even blue giants are not drawn right, I hate when I see a "bright blue hypergiant" depicted as a deep blue ball with darkness around it and not anything resembling a real star.
Stars would look relatively similiar to the Sun in that they will shine like hell from Earthlike insolation distances, through looking at a O or B class sun would burn your eyes out and it would appear as a point, and you would be able to look at big (apparent size on the sky) M or L class sun just like you can look at a bright incandescent lightbulb or a fire.
Of course there would be color difference, but I think the most noticeable sign would be the sky - purplish black sky on Earthlike planets illuminated by cool suns, and violet-blue skies on Earthlike planets (1 G and 1 bar) around hot stars http://www.orionsarm.com/whitepapers/sky_on_alien_worlds.html.

Buttercup
2009-Jan-10, 07:57 PM
Doesn't matter to me if they're "brown" or not (or if brown's actually a color, and autumn leaves says it is :D )...what I'd like to know is whether BD's are failed stars or grossly oversized planets. Star...planet...stanet?

m1omg
2009-Jan-10, 08:30 PM
Doesn't matter to me if they're "brown" or not (or if brown's actually a color, and autumn leaves says it is :D )...what I'd like to know is whether BD's are failed stars or grossly oversized planets. Star...planet...stanet?

Yes they are "failed stars".

The principal difference between a brown dwarf and a supergiant planet is that brown dwarfs did not form by planetary accretion process - they were born in the same collapsing gas clouds as stars and this is not just a hypothesis Orion's nebula for example is full of them...

And the difference between a rogue supergiant planet and a brown dwarf is that rogue planets were ejected from a planetary system, while the brown dwarfs formed the way ordinary stars did.

Also the >13 Jupiter mass BDs (lower mass BDs such as this http://en.wikipedia.org/wiki/Cha_110913-773444 are not BDs proper, but rather sub-brown dwarfs) can fuse deuterium and thus have a relatively steady source of energy for at least some time, and >65 Jupiter mass BDs can also fuse lithium, so at least the >13 Jupiter mass BDs are definitely divided by this from big planets, they just cannot fuse ordinary hydrogen but they have a fusion heat source in their cores at least for some time, they work just like the first expected fusion plants that will use deuterium-deuterium or deuterium-tritium fusion as these are much easier to start.

Also, I find these planet/dwarf planet, supergiant planet/brown dwarf arguments extremely silly.Those are just human words, they doesn't change the nature of an object.

George
2009-Jan-10, 08:42 PM
Yeah that's right.I haven't meaned perfect white for red dwarfs,more like the yellowish white you get from classic lightbulbs, and perfect white also depends on the definition, if you define Vega as being perfect white Sun will not be perfect white from space even if it is white (atmosphere scatters light so it appears yellow, Vega would probably look almost perfectly white even through an atmosphere. When mostly overhead, our atmosphere does not cause extinctions that is too disruptive to the true color of the object. Of course, along the horizon, which is equivalent to about 35 atmospheres, we see a reddened version -- yellow, then orange, and sometimes red for the Sun for example -- of the object.


And brown dwarfs are not white, but definitely not like in the artist impression pictures. You would have to see their spectral energy distribution (SED) or their spectral irradiance data -- I assume these are synonymous. [Is this equivalence correct?]


Even blue giants are not drawn right, I hate when I see a "bright blue hypergiant" depicted as a deep blue ball with darkness around it and not anything resembling a real star.
Pretty, ain't they. That is art making them more attractive, but you are correct, blue stars are much more blue-white stars due to the fact that they still are prodigous in the red end of the spectrum. Venus will produce only about 2x as many far blue photons than far red photons. Enough that allows for to appear to have a bluish tinge.

m1omg
2009-Jan-10, 08:50 PM
When mostly overhead, our atmosphere does not cause extinctions that is too disruptive to the true color of the object. Of course, along the horizon, which is equivalent to about 35 atmospheres, we see a reddened version -- yellow, then orange, and sometimes red for the Sun for example -- of the object.

You would have to see their spectral energy distribution (SED) or their spectral irradiance data -- I assume these are synonymous. [Is this equivalence correct?]


Pretty, ain't they. That is art making them more attractive, but you are correct, blue stars are much more blue-white stars due to the fact that they still are prodigous in the red end of the spectrum. Venus will produce only about 2x as many far blue photons than far red photons. Enough that allows for to appear to have a bluish tinge.

Well, but Sun IS yellowish when seen through our atmosphere, but white when seen from outer space.

And about the art making these stars more attractive, I don't think so.
Somehow I like bright shiny stars better than a big blue bloated balloon.

George
2009-Jan-10, 09:07 PM
Well, but Sun IS yellowish when seen through our atmosphere, but white when seen from outer space. Here is a nice color photo of the Sun's projection through the McMath-Pierce unfiltered telescope at Kitt Peak. The fact that it is not yellow in the slightest is a very powerful argument that the Sun can not and is not yellow.


And about the art making these stars more attractive, I don't think so. Somehow I like bright shiny stars better than a big blue bloated balloon. Go to SOHO's site and you will see only colorful images of the Sun, with some exception of a dull white one. These colors are quite useful as they often are assigned to certain ranges in the em spectrum.

m1omg
2009-Jan-10, 09:18 PM
Here is a nice color photo of the Sun's projection through the McMath-Pierce unfiltered telescope at Kitt Peak. The fact that it is not yellow in the slightest is a very powerful argument that the Sun can not and is not yellow.

Go to SOHO's site and you will see only colorful images of the Sun, with some exception of a dull white one. These colors are quite useful as they often are assigned to certain ranges in the em spectrum.

I mean colors naturally viewed with my human eyes.
Because I SEE the Sun as yellowish through my naked eyes is a proof that for naked human eyes Sun viewed through the atmosphere IS yellowish.
Color is not an objective property, but our perception of a physical property that is NOT objective, it depends on the atmospheric and light conditions etc...

Of course I know that when viewed from space it IS white, the yellowishness seen from our planet is caused by the atmosphere, but this still doesn't change the fact that from Earth, viewed by naked human eyes, Sun IS yellowish.

And I have nothing against good art pictures or real images captured in certain light bands or filtered, but pictures like this; http://www.space.com/php/multimedia/imagedisplay/img_display.php?pic=060130_dwarf_planet_02.jpg&cap=Artist+impression+of+the+view+from+the+surface +of+a+rocky+planet+in+orbit+around+a+red+dwarf.+cr edit%3A+David+A.+Aguilar%2C+CfA

http://www.daviddarling.info/images/red_dwarf_art.jpg

http://en.wikipedia.org/wiki/File:Sol_Cha-110913-773444_Jupiter.jpg

http://en.wikipedia.org/wiki/File:L-dwarf-nasa-hurt.png

http://commons.wikimedia.org/wiki/File:T-dwarf-nasa-hurt.png

http://commons.wikimedia.org/wiki/File:Late-M-dwarf-nasa-hurt.png

http://astro.nuigalway.ie/research/super-aurorae.jpg

http://members.wri.com/jeffb/vistapro/rising_redgiant.jpg

http://members.wri.com/jeffb/vistapro/browndwarf.jpg

http://members.wri.com/jeffb/vistapro/rising_yellowgiant.jpg

http://members.wri.com/jeffb/vistapro/redgiant.jpg

http://www.boulder.swri.edu/~terrell/redgnt.jpg

http://www.space-art.co.uk/images/artwork/diagrams/Stars-Compared.jpg

In all of these images, the star doesn't look like it is even a shining body, just a painted Christmass ball...it looks...lifeless...like a body that only reflects some dim light and not as a luminous object.

grant hutchison
2009-Jan-10, 09:45 PM
Odd, I can, at least in principle. Give me a box of "blue" photons that are half as many as "red" photons, then throw in about 20% more "green" ones [than blue ones] and, after appropriate shaking of course, ta dah... we will be bathed in the sensation of "brown" light. That is why my brown crayon looks brown, right?Wrong. It looks brown because it reflects an appropriate mix of photons, at low luminance. The same mix of photons at high luminance will appear somewhere in the vicinity of yellow.


Give me an object's SED in the visible spectrum and I will give you an accurate "color" (colorplex) of the object presented. Your Spectrum(?) software package you shared with us does the same, but it may not be super accurate. But this you know, so where did I miss the bridge?You missed the effect of luminance. The software gives us hue and saturation, but not luminance. This isn't often a problem, because dark green is still green and dark purple is still purple, but it turns out that "dark white" is grey and "dark yellow" is brown.

Grant Hutchison

George
2009-Jan-10, 09:55 PM
I mean colors naturally viewed with my human eyes.
Because I SEE the Sun as yellowish through my naked eyes is a proof that for naked human eyes Sun viewed through the atmosphere IS yellowish. If the Sun is directly overhead, you might first notice how bright it is. It is thousands of times brighter than the upper threshold limit for your color cones. You might see still see it as yellow, but that may be an after effect or some other reason. The trick is to reduce the Sun's intensity to a level conducive to your vision. This happens often as the Sun sinks over the horizon due to the additional 35x or so atmospheric scattering.


Of course I know that when viewed from space it IS white, the yellowishness seen from our planet is caused by the atmosphere, but this still doesn't change the fact that from Earth, viewed by naked human eyes, Sun IS yellowish.
You might enjoy this trilogy on the Sun's color.
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/blog/the_color_of_the_sun
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_part_ii
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_revelation


In all of these images, the star doesn't look like it is even a shining body, just a painted Christmass ball...it looks...lifeless...like a body that only reflects some dim light and not as a luminous object. Merry Christmas! Not many Christmas tree decorators like white ones, btw.

I don't mind the color, but I it would be nice to see white shown as its natural condition once in a while.

m1omg
2009-Jan-10, 10:07 PM
If the Sun is directly overhead, you might first notice how bright it is. It is thousands of times brighter than the upper threshold limit for your color cones. You might see still see it as yellow, but that may be an after effect or some other reason. The trick is to reduce the Sun's intensity to a level conducive to your vision. This happens often as the Sun sinks over the horizon due to the additional 35x or so atmospheric scattering.


You might enjoy this trilogy on the Sun's color.
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/blog/the_color_of_the_sun
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_part_ii
http://www.scientificblogging.com/solar_fun_of_the_heliochromologist/the_color_of_the_sun_revelation

Merry Christmas! Not many Christmas tree decorators like white ones, btw.

I don't mind the color, but I it would be nice to see white shown as its natural condition once in a while.

You have misunderstood me, I like colorful pictures of stars, they are very colorful in telescope photographs even in reality.
I like colorful AND bright, what I hate are these painted ball looking stars that have extremely strong colors but dim and don't even shine, do you understand me?

George
2009-Jan-10, 10:12 PM
Wrong. It looks brown because it reflects an appropriate mix of photons, at low luminance. The same mix of photons at high luminance will appear somewhere in the vicinity of yellow.How high are you going? I adjusted the ratio we are using in my graphics program and maxed the red value, then adjusted the other two proportionately. The brown became brighter and appeared more of a tan color, but it was still more brownish than yellowish.

Are you saying that if we did have a photon mix that matches our "brown" mix, that a brown dwarf star's intensity would still be so great that we would have to call it yellowish more than brownish? That would explain a number of posts, I think.


You missed the effect of luminance. The software gives us hue and saturation, but not luminance. I didn't know that. Isn't the monitor's flux increased (luminance) with the higher settings, or is it adding a whiteness by bumping the all three settings, too.

George
2009-Jan-10, 10:14 PM
You have misunderstood me, I like colorful pictures of stars, they are very colorful in telescope photographs even in reality.
I like colorful AND bright, what I hate are these painted ball looking stars that have extremely strong colors but dim and don't even shine, do you understand me?
Now I do. Giving them anything close to the intensity that they really are, however, would whitewash the entire image. You seem to be hoping for something inbetween.

grant hutchison
2009-Jan-10, 10:51 PM
Are you saying that if we did have a photon mix that matches our "brown" mix, that a brown dwarf star's intensity would still be so great that we would have to call it yellowish more than brownish?No. I'm saying that the difference between brown and yellow doesn't come from the relative mix of photons: it comes from the luminance when compared to the illuminants, to other source of colour, and to neuropsychology. Didn't the picture (http://upload.wikimedia.org/wikipedia/commons/9/9a/Optical_grey_squares_orange_brown.svg) I linked to a while back demonstrate how very different the same colour can appear, displayed on the same monitor, under the same viewing conditions, with the only difference being luminance hints in a flat picture?


I didn't know that. Isn't the monitor's flux increased (luminance) with the higher settings, or is it adding a whiteness by bumping the all three settings, too.The software doesn't give us luminance because no luminance data are input: it reports colour according to the relative intensity at different wavelengths. I'd guess it just maxes the dominant component of the RGB. Adding white would be completely wrong, because it would change the saturation.
And there's no point in attempting to adjust the colour according to luminance, because it's impossible to predict the viewing circumstances, either of the original colour source or of the colour displayed by the software.

Grant Hutchison

m1omg
2009-Jan-10, 11:23 PM
Now I do. Giving them anything close to the intensity that they really are, however, would whitewash the entire image. You seem to be hoping for something inbetween.

Yeah, that's exactly what I want.

Bright enough to appear live and real + nice color, but not so bright that it would whitewash the image.

timb
2009-Jan-11, 12:07 AM
Yes they are "failed stars".

The principal difference between a brown dwarf and a supergiant planet is that brown dwarfs did not form by planetary accretion process - they were born in the same collapsing gas clouds as stars and this is not just a hypothesis Orion's nebula for example is full of them...

And the difference between a rogue supergiant planet and a brown dwarf is that rogue planets were ejected from a planetary system, while the brown dwarfs formed the way ordinary stars did.

Also the >13 Jupiter mass BDs (lower mass BDs such as this http://en.wikipedia.org/wiki/Cha_110913-773444 are not BDs proper, but rather sub-brown dwarfs) can fuse deuterium and thus have a relatively steady source of energy for at least some time, and >65 Jupiter mass BDs can also fuse lithium, so at least the >13 Jupiter mass BDs are definitely divided by this from big planets, they just cannot fuse ordinary hydrogen but they have a fusion heat source in their cores at least for some time, they work just like the first expected fusion plants that will use deuterium-deuterium or deuterium-tritium fusion as these are much easier to start.

Also, I find these planet/dwarf planet, supergiant planet/brown dwarf arguments extremely silly.Those are just human words, they doesn't change the nature of an object.

True, but you write as though they did. It would be amazing if every body that forms by accretion is less than 13 MJ and every body that forms by disk fragmentation (the favored hypothesis for BD formation, not exactly the same as the way most stars form) is greater than 13 MJ, but that is what your first and third paragraphs imply. And why can't brown dwarfs that form in a stellar system be ejected?

George
2009-Jan-11, 06:30 AM
No. I'm saying that the difference between brown and yellow doesn't come from the relative mix of photons: it comes from the luminance when compared to the illuminants, to other source of colour, and to neuropsychology. Didn't the picture (http://upload.wikimedia.org/wikipedia/commons/9/9a/Optical_grey_squares_orange_brown.svg) I linked to a while back demonstrate how very different the same colour can appear, displayed on the same monitor, under the same viewing conditions, with the only difference being luminance hints in a flat picture?Sorry, I could not load that vector graphic format. I assumed it would be like the color cubes I've seen that demonstrates how the mind can make brown from gray, IIRC, but now I see you are demonstrating luminance effects.


The software doesn't give us luminance because no luminance data are input: it reports colour according to the relative intensity at different wavelengths. I'd guess it just maxes the dominant component of the RGB. Yes, and that is what I tried. I found a brown I liked and then maxed the red (dominant) value but mainted the ratio with the green and blue values. It did make the brown a lighter tone (desaturated), but this was just a whitening effect as you stated. Going the other direction for the component values (maintaining the ratios) produces a dark brown result.

The Hue-Saturation-Luminance illustrations make sense ( here (http://en.wikipedia.org/wiki/HSL_color_space) ), but these all seem representable on a monitor even for brown. Getting darker or lighter does not seem to force brown to act dissimilar than the true hues.


And there's no point in attempting to adjust the colour according to luminance, because it's impossible to predict the viewing circumstances, either of the original colour source or of the colour displayed by the software. Are you saying this an environmental quirk for color "shades" such as brown, where illumination can play tricks?

m1omg
2009-Jan-11, 12:00 PM
True, but you write as though they did. It would be amazing if every body that forms by accretion is less than 13 MJ and every body that forms by disk fragmentation (the favored hypothesis for BD formation, not exactly the same as the way most stars form) is greater than 13 MJ, but that is what your first and third paragraphs imply. And why can't brown dwarfs that form in a stellar system be ejected?

Well, sorry, I meant that as theoretical definition.

But I think you can divide them based on velocity and direction to where they are moving, if it is moving from a direction of another star and it is moving fast it is likely that the object was ejected.

If the object moves similiar to other stars in the area, it probably formed normally.

grant hutchison
2009-Jan-11, 01:54 PM
Yes, and that is what I tried. I found a brown I liked and then maxed the red (dominant) value but mainted the ratio with the green and blue values. It did make the brown a lighter tone (desaturated), but this was just a whitening effect as you stated. Going the other direction for the component values (maintaining the ratios) produces a dark brown result.So if you could increase the luminance of your monitor you could continue the process towards yellow. Or you might be able to pull visual tricks with your surroundings, as Feynman apparently did in his lecture, or embed the "brown" mix in a picture with enough appropriate luminance cues to change the sensation to yellow.
If you can't see the SVG image, you might try downloading the free plug-in I recommended to Jeff. The image is of a chequerboard with two coloured discs placed on the squares, one on a dark square, one on a light. A shadow falls across the light square and its surrounding squares. The visual cues boost the apparent luminance of the shadowed disc, so that it appears orange-yellow, while the unshadowed disc appears brown. But on testing they both have the same RGB values.


Are you saying this an environmental quirk for color "shades" such as brown, where illumination can play tricks?No, I'm saying that the photon mix for brown and yellow is exactly the same. Brown is dark yellow. We judge dark and light from other cues, and so it's possible to make the shift from brown to yellow purely by manipulating those cues.

Grant Hutchison

Jeff Root
2009-Jan-11, 06:28 PM
Have you been working off-line on this reply for twelve hours?
Sort of. I started to reply but couldn't finish at that time so I
saved what I had and finished it much later. Same thing happened
with this post.



Your quote from me misses a clarifying edit I made quite soon
after posting (the word "uniquely").
I'll re-reply, then.



So why do these people say that brown is NOT a color and
that there are no mixtures of photons that can produce light
that looks brown to our eyes?
Because there is no mixture of photons from a single luminous
source that will uniquely convey the sensation of "brown" to your
eyes, any more than there is a mixture of photons from a single
luminous source that will uniquely convey the sensation of "grey"
to your eyes (or of "black", for that matter).
Which is a non sequitur. The fact that there is no mixture of
photons (from a single source or multiple sources of any kind)
that will uniquely convey the sensation of "brown" to my eyes
in no way implies that brown is not a color, or that there are
no mixtures of photons that can produce light that looks brown
to our eyes.

It is also true there is no mixture of photons that will uniquely
convey the sensation of "blue" to my eyes. There is no mixture
of photons that will uniquely convey the sensation of "yellow" to
my eyes. And so on.

Brown is a color. Grey is a color. Black is a color.

Different mixtures of photons will produce different browns,
different greys, different blues, and different yellows. No
photons are required for the color black, of course, but there
still are many different mixtures of photons that will produce
different blacks.



I don't contest that there are photon combinations that will elicit
the sensation "brown" under some circumstances.
I'd say that there are MANY photon combinations that will elicit
the sensation "brown" under A WIDE RANGE of circumstances.



It's just that the same combination of photons will elicit the
sensation yellow (or greenish-yellow, or orange-yellow) under
other circumstances.
I'd say that SOME combinations of photons that will elicit the
sensation "brown" in SOME circumstances will elicit the sensation
"yellow" (or "greenish-yellow", or "orange-yellow", or "orange",
or "red-orange", or "beige", or "tan", or "umber", or "sienna",
or "tangerine", or "copper", or whatever) under certain other
circumstances.

So what? Brown is still a color, and various different mixtures
of photons produce light that looks brown to our eyes.



You can search as long as you like on the CIE colour triangle,
and you won't find a mix of red, green and blue that you'd call
brown: that requires a change in luminance as well as hue.
Obviously. So?

The CIE color triangle isn't capable of mapping all colors.
it falls particularly short in mapping browns and pastels.
So what? It wasn't intended for that purpose. Other color
systems are more useful for that.



Brown is not a property of the power spectrum of light of alone,
in exactly the same way as grey is not a property of the power
spectrum of light alone.
Nobody here ever suggested that it is. Every color is the product
of both the power spectrum of the light and eye/brain mechanisms
which react to that light.



Just saying "goofy, goofy, goofy" probably won't change that
for you. :)
Of course. That isn't what I expected it to change.




Well, duh! orange-yellow = brown. They are different names for
the same thing.
Reclassifying brown to include its high-luminance equivalents is
certainly one way to defend your point. But perhaps not a good way.
I didn't reclassify anything. You did. You reclassified brown
as "not a color". Which is goofy.

You pointed out that the same spot of color can look either
orange-yellow or brown, depending on the environment. That is
because that orange-yellow and that brown are the same thing.
Or in other symbols, orange-yellow = brown. Which is pretty
much what you just said in your most recent post, today.

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-11, 06:38 PM
Technically, gray and brown aren't colors, but "shades".
A shade is a color that has black in it.
A tint is a color that has white in it.

Adding a sizeable amount of black but little or no white tends
to produce earth tones, while adding a sizeable amount of white
but little or no black tends to produce pastels.



Both depend on surrounding context--there is no such thing as
brown light.
Also, there is no such thing as yellow light; there is no such
thing as orange light, there is no such thing as blue light...
or any other color.

-- Jeff, in Minneapolis

tdvance
2009-Jan-11, 06:56 PM
Also, there is no such thing as yellow light; there is no such
thing as orange light, there is no such thing as blue light...
or any other color.

-- Jeff, in Minneapolis

Now that's not true--

yellow light is about 580nm, orange light about 600nm, and blue light about 470nm. Yellow can be simulated with red and green since the cones will respond the same way in either case, and similarly with other color combinations.

There is no frequency for "gray light"--it is a superposition of all frequencies, i.e. white, seen in a context that it is dimmer than the brightest areas, brighter than the dimmest. "Brown light", against nothing but black, looks yellow or orange.

Here's one to make you think--the albedo of the moon is roughly the same as that of asphalt. So, why does the moon appear bright, silvery or yellowish? Mainly, there's a lot of it to reflect a lot of photons back--so the "dark gray" asphalt is nearly white in this context.

Also--are there no gray stars to the naked eye? No--they appear "dim white". You'd need a different context to see them as gray.

And as for silver--is there "silver light"? no--silver, or a mirror, is specular reflection, or nearly specular reflection--its the pattern of brightness that makes it look silver, not any hue.

grant hutchison
2009-Jan-11, 07:03 PM
I didn't reclassify anything. You did. You reclassified brown
as "not a color".Not me. You as asked why "these people" say brown is not a colour. I provided an explanation. There's a reason why astronomers use the terms the way they do, and it's just as good a reason as why doctors use "allergy" in a more strict sense than most folk do.
Fortunately I have no emotional investment in whether you appreciate my explanation or not. :)


You pointed out that the same spot of color can look either
orange-yellow or brown, depending on the environment. That is
because that orange-yellow and that brown are the same thing.
Or in other symbols, orange-yellow = brown. Which is pretty
much what you just said in your most recent post, today.No, I said these different sensations, which we designate with different names, are produced by the same mix of photons. Which makes them the same hue with different luminances. Or different shades of the same colour.
You get to call them different colours if you like, because that's common enough parlance.

But there is no logical argument you can construct which makes you right and others wrong. Why don't you just relax into the "common usage" justification, and allow astronomers to get on with using "colour" as a technical term?

Grant Hutchison

Jeff Root
2009-Jan-11, 09:05 PM
Both depend on surrounding context--there is no such thing as
brown light.
Also, there is no such thing as yellow light; there is no such
thing as orange light, there is no such thing as blue light...
or any other color.
Now that's not true--
If there is no such thing as brown light, which you clamed, then
there is no such thing as yellow light, no such thing as orange
light, no such thing as blue light, or any other color. I'm just
requiring you to be consistent.



yellow light is about 580nm,
Yes, of course. Brown light is, too.



orange light about 600nm,
Yes, of course. Brown light is, too.



and blue light about 470nm. Yellow can be simulated with red and
green since the cones will respond the same way in either case,
and similarly with other color combinations.
Yes, of course. Brown, too, can be produced with red and green
since the cones will respond the same way in either case.



There is no frequency for "gray light"--it is a superposition of all
frequencies, i.e. white, seen in a context that it is dimmer than
the brightest areas, brighter than the dimmest. "Brown light",
against nothing but black, looks yellow or orange.
Yes, of course. What does any of that have to do with the fact
that brown is a color, elicited in human eyes by certain mixtures
of photons?

-- Jeff, in Minneapolis

Jeff Root
2009-Jan-11, 09:41 PM
I didn't reclassify anything. You did. You reclassified brown
as "not a color".
Not me. You as asked why "these people" say brown is not a colour.
I provided an explanation.
Ooops. Sorry. Between the time I read something and the time I
reply to it I conflate seemingly-equivalent statements which are not
really equivalent. HEY! Isn't that basically what I'm complaining that
the astronomers are doing? :doh:

Maybe more of a reply later, after I've had time to confuse myself.

Oh, maybe I've had enough time. I'll just say that color /= hue,
and see what comes of it.

-- Jeff, in Minneapolis

grant hutchison
2009-Jan-11, 11:13 PM
I'll just say that color /= hue,
and see what comes of it.If you confine your definition of "colour" to the spectral colours, then "colour" would be equivalent to hue, although you wouldn't include all hues. I doubt if many people would be comfortable with so restrictive a definition.
The astronomers who told Jill Tarter that brown isn't a colour are restricting "colour" to hue+saturation: all that can be unequivocally defined from their stock-in-trade, a box of photons. I don't find this a particular offence to reason, I must confess.
Beyond that, the colloquial use of "colour" is pretty messy, and not really fit for scientific purpose. Take Berlin & Kay's "fundamental" eleven colour terms: black, white, red, green, yellow, blue, brown, purple, pink, orange and grey. Common enough in many languages so as to allow statistical analysis of trends and exceptions. We have five spectral hues, excluding violet; we have a sixth hue on the line between red and blue (purple); we have the absence of light (black); a uniform mixture (white); two low-luminance variants (grey and brown); and a desaturation (pink). But these chop up the colour solid in a way that the speakers of many different languages seem to find particularly salient.

(I'll spare you my speculative dissertation on why so many languages have a word for low-luminance yellow, but far fewer have a separate word for low-luminance blue [Russian does]; and why many languages are interested enough in desaturated red to give it its own word, but few are bothered about desaturated green.)

Is "olive" a colour? Is "olive drab" a colour? Is "medium olive drab" a colour?
How many colours are represented by the grouping "crimson", "carmine" and "scarlet"?
The colloquial use of "colour" just isn't a scientific endeavour.

Grant Hutchison

George
2009-Jan-12, 12:19 AM
...two low-luminance variants (grey and brown); and a desaturation (pink). The comparison of grey to brown seems to be the best analogy I see we have to work with at this point. If I understand you, not that I do yet, you seem to be saying that we won't see brown radiating from a box or from a planet because, like grey, we will see it differently because of luminance. If we were to have two white objects glowing in a black-walled room, for instance, then continually dimmed one, it would eventually appear as grey, if its photon flux was essentially flat (assuming this flatness is a fair white std.). If we were to remove the white light source and have only the remaing grey light showing, then the grey light would appear white to us. [I think this is a color constancy effect.]

If we now switch these lights to yellow, and conduct the same experiment, then the dimmer light will have a brownish appearance more than a yellow appearance. If we now remove the yellow, brighter light, then would the brownish light become a dull yellowish (more so than brownish) light source?

Am I close?

[BTW, the Adobe upload for reading scv files failed for me. That's fairly par for the course with me, not that I ever play par. :)]

grant hutchison
2009-Jan-12, 01:10 AM
Yep. That's what I've been saying.
There are neuropsych influences as well. For instance, I suspect your brain is pretty well trained to the luminance range of your monitor by now, so it has something of an internal reference running when it looks at colours generated by that source.

Grant Hutchison

grant hutchison
2009-Jan-12, 01:46 AM
Just to get on my soapbox again for a minute:
Isn't it interesting how we seem to imbue the "warm" end of the spectrum with so much more colour detail than the "cool" end?
Around red and green we manage to cram in orange and yellow and pink and brown; whereas the border between green and blue is notoriously vague, and poor old violet often gets mixed in with the non-spectral purples.

Grant Hutchison

Jeff Root
2009-Jan-12, 02:43 AM
I knew that I have several drawings of color wheels on the other computer
sitting on this desk, and I've been intending to plug the monitor into it and
grab them so I could show them to you. But then I had this nagging memory
of uploading some of them to my website. I looked in my "miscellaneous"
folders there with no luck. Just now I was about to try again, when it
occurred to me that I might have put them in their own folder. Ah-Ha!!!
I'd put them in a folder named "colors" and wrapped them in a web page!!!

http://www.freemars.org/jeff/colors/

For what it's worth.

-- Jeff, in Minneapolis

GeorgeLeRoyTirebiter
2009-Jan-12, 06:48 AM
Just to get on my soapbox again for a minute:
Isn't it interesting how we seem to imbue the "warm" end of the spectrum with so much more colour detail than the "cool" end?
Around red and green we manage to cram in orange and yellow and pink and brown; whereas the border between green and blue is notoriously vague, and poor old violet often gets mixed in with the non-spectral purples.

It's especially interesting considering that in the "warm" end of the spectrum our color vision is essentially dichromatic. The short wavelength cones are insensitive to wavelengths longer than greenish yellow (the maximum possible signal drops below the detection threshold), while all three types of cones contribute for wavelengths from violet through green. This means that we're perceiving a greater number of unique colors when our brains are actually receiving less information.

grant hutchison
2009-Jan-12, 12:32 PM
It's especially interesting considering that in the "warm" end of the spectrum our color vision is essentially dichromatic. The short wavelength cones are insensitive to wavelengths longer than greenish yellow (the maximum possible signal drops below the detection threshold), while all three types of cones contribute for wavelengths from violet through green. This means that we're perceiving a greater number of unique colors when our brains are actually receiving less information.The primates seem to have evolved trichromacy from dichromat mammalian ancestors, by splitting a single cone variety into our current L and M ("red" and "green"). So we've had this little creative burst as a late evolutionary addition.

Grant Hutchison

George
2009-Jan-12, 02:16 PM
Yep. That's what I've been saying. Ok, that helps.


There are neuropsych influences as well. For instance, I suspect your brain is pretty well trained to the luminance range of your monitor by now, so it has something of an internal reference running when it looks at colours generated by that source.
Your suspision seems warranted; repetitive experience should count for something.

There does not seem to be any way we could produce a single grey light source. Regardless of its intensity it would always look white even if it were dim, assuming black surroundings. Changing luminance, in this case, will not alter the white perception.

This can be verified by repeating my earlier wimpy experiment. If I make my monitor screen all grey and make the room dark, when I place my eyes up to the screen and ask myself if it is grey or white and ignoring what I already know -- the neuropsych influence you suggest is quite real -- then I will admit that it is white, even though it is contrary to what I know.

The counter to this might be the claim that Apollo astronauts saw the Moon as grey and not white. My guess is that they had some other object in their view or recently in their mind that was the superior white reference. They had a number of white objects that would have served as a white reference: Sun, spacesuits, spacecraft, paper, flag, etc...

But is this the case for brown? Repeating the wimpy experiment does not change my assesment that the light source is brown, though it becomes more of a tan at full monitor luminance (holding the mix ratios).

Assuming my experiment were validated, the problem with this "brown light" view is that it may only work at very low luminance values. For a brown dwarf to have such a low total flux may be extremely unlikely.

Of course, as someone mentioned earlier, if our brown dwarf were to have a bright white neighbor, then the illumination of its organic atmospheric soup might make it appear brown.

grant hutchison
2009-Jan-12, 02:38 PM
Of course, as someone mentioned earlier, if our brown dwarf were to have a bright white neighbor, then the illumination of its organic atmospheric soup might make it appear brown.There's a difference between reflectance and luminance, of course. Adam Burrows somewhere suggests that brown dwarfs would be blue by reflected light.

Grant Hutchison

George
2009-Jan-12, 07:19 PM
There's a difference between reflectance and luminance, of course. Yes, but illuminance is worth mentioning if these are not too uncommon as binary partners.


Adam Burrows somewhere suggests that brown dwarfs would be blue by reflected light. :wall:

He does have a nice site (http://www.astro.princeton.edu/~burrows/) that involves these matters, though I haven't time to read his works at this time.

I am curious why he has an orange star that has a planet in retrograde orbit? Has he found one of those?

George
2009-Jan-15, 10:55 PM
Just for grins, I set my screen to a brown color and placed it in the bathtub at 3 am this morning. It was pitch black in there when I placed it and then I walked away then returned to see the same brown (non-yellow) "color". Thus, there does seem to be a much greater difference in psycological effects in the comparision of brown and gray.

There is no such thing as a monochromatic brown color, but this fact should have little bearing as to whether objects in space might, under unusuall circumstances as might be found in a low temperature atmosphere of a brown dwarf, to make it appear brown.

Of course, I'm open to correction, but I'd bet a Sundae I'm right about the idea that there are metamers of brown that are essentially unaltered as stand-alone brown-looking objects in space, assuming they have the appropriate and peculiar SED.

I won't bet my reputation as a heliochromologist, at least not until I have one. :)

George
2009-Jan-17, 10:11 PM
One other minor point -- brown can be found by desaturating orange, not yellow. Desaturating yellow produces a darkening olive green color.

grant hutchison
2009-Jan-17, 10:25 PM
One other minor point -- brown can be found by desaturating orange, not yellow. Desaturating yellow produces a darkening olive green color.Well ...
Desaturating yellow produces pale yellow. Reducing the luminance of yellow produces olive-brown.
Reducing the luminance of orange or yellow-orange produces brown. Reducing the luminance of yellow-green produces olive. Or so it seems to my eye.

Grant Hutchison

Jeff Root
2009-Jan-17, 11:52 PM
Desaturating yellow produces pale yellow.
That's what I said in post #4 of this thread! :p

-- Jeff, in Minneapolis

grant hutchison
2009-Jan-18, 12:10 AM
That's what I said in post #4 of this thread! I know. Perhaps George missed it.

Grant Hutchison

George
2009-Jan-18, 06:13 AM
Well ...
Desaturating yellow produces pale yellow. Reducing the luminance of yellow produces olive-brown.
Shucks, I should have seen that. This topic intrigues me so I went to the physics forum in search of more. I read that "desaturated yellow" produces an olive color, so I tried it in my color graphics software. I cut intensities and got the olive color and assumed I was destaurating. Ug.

Then I searched for "olive" in this thread but didn't find it. Ug. So I missed Jeff's post.


Reducing the luminance of orange or yellow-orange produces brown. Reducing the luminance of yellow-green produces olive. Or so it seems to my eye.
Yep.

If I am getting close to the color methodology... desaturating can be done by adding black (shading?), white (toning?), gray, or its color complement, I think.

Jeff Root
2009-Jan-18, 08:19 AM
George,

Did you see my color wheels, which I linked in post #59? They don't
directly address any questions here, but they might possibly help...
and if there is anyone here who I wanted to see them, it's you!

http://www.freemars.org/jeff/colors/

The text under the next-to-last wheel tells how to adjust your
monitor so that it matches as nearly as possible the conditions that
the wheels were designed for.

-- Jeff, in Minneapolis

George
2009-Jan-18, 10:09 PM
Yes, I saw them. They are nicely done, too. Additive and subractive colors make sense, though I suspect I would enjoy a numerical mapping of some sort the matched the spectral sensitivity of our cones more interesting, if not more effective. If we know the spectral response for each cone and we know the spectral photon flux of the object, then I would bet we could derive a specific value for each cone. The three ratios would produce a specific response associated with a specific color (hue, saturation, brightness).

Further, since the cones are somewhat Gaussian, then a host of metamers could be created, which is what we find. Photons of different wavelength can register the same response for a given cone, but there must be one or more other offsetting flux from other photons of another wavelength or two in order to produce a matching ratio mix necessary to create a metamer.

Of course, ambient ligthing complicates the picture as the psychological factors will throw-off our color determination. For instance, a gray object will appear blue if we use yellow lighting, or it will appear yellow with blue illumination. [Dr. Lamb (Polaroid founder) seems to be somewhat famous for illumination effects on our color determination.]

Regardless, color is fun even without knowing all the rules. :) This brings us back to the original question of whether or not a brown light source might be possible in space on its own.

Since we (I assume others can) can set a monitor screen to brown and it will still appear brown without any other lighting around, will cameras, which model our eye's vision, be able to do the same. My Canon 30D is probably above average in its ability to assign color. This morning in total darkness I took pictures (below). The brown is slightly off but it is still brown.

It supports the claim favoring "brown" light, but I don't know that this addition helps all that much. A contrary result would have been more interesting, perhaps. [The most conclusive finding is that I obviously need to clean my camera lens. :) ]