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Thread: Can Rayleigh Scattering Explain the Sky’s Blue Colour?

  1. #1 Can Rayleigh Scattering Explain the Sky’s Blue Colour? 
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    The official explanation for the sky’s blue colour is that it is caused by the Rayleigh scattering of light off gas molecules within the Earth’s atmosphere.

    The intensity of the scattering is inversely proportional to the wavelength to the power of 4.

    The full equation is I = Io 8 πexp4 N αexp2 (1 + cosθexp2) / λexp4 Rexp2

    The equation implies that the shorter wavelengths scatter the most and this is why we see the blue colour.

    But why is the sky not violet though? Violet light has a shorter wavelength than blue and if you look at the spectrum of white light, violet is also far more extensive than blue.

    Further the (1 + cosθexp2) term in the equation would imply that the scattering at right angles is exactly half of that in a forward direction. This would tend to make the sky unevenly bright with large rings of lighter and darker areas, but this is clearly not the case.

    And finally the scattering of light should also occur along a horizontal line of sight producing a blue fog hanging on the ground. For example it has to be considered that if the Earth’s atmosphere were of an even density from top to bottom it would form a layer of around 5 miles in depth. Looking, therefore, to a point on the horizon which is 5 miles distant, you should expect to see just as much blue glow between you and the distant object as you would looking directly upwards. Indeed from some vantage points you can see as far as 30 miles or more to points on the distant horizon and in this case you would expect to see 6 times as much blue fog hanging on the ground. But you don’t.

    Can Rayleigh scattering really effectively explain the blue glow of the Earth’s atmosphere?


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    I can't give a full answer, but there are two things I can think of here.

    One, the atmosphere, besides scattering light, also absorbs light, especially the UV (and probably some violet) spectrum, so the sky turns blue instead of violet.

    Also, there is a haze associated with distance, but it's something that everyone's so used to seeing, no one but special effects people think much of. Objects in the distance do slowly turn the color of the sky.


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    Your asking the right questions.

    Violet is scattered more than blue but our eyes are more sensitive to blue so the sky looks more blue than violet. Also UV is scattered more that violet which is why you can get a sunburn while in the shade on a clear day.

    Only a small amount of light is scattered out of the line of sight, therefore looking far out on the horizon most of the spectrum makes it to your eyes. With the exception of some extreme cases like sunset or lightning seen at night from across the prairies do you see the redder colors. As far as blue up above the background is the black of space and the transverse light intensity from the sun is very bright.
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    Quote Originally Posted by MagiMaster
    I can't give a full answer, but there are two things I can think of here.

    One, the atmosphere, besides scattering light, also absorbs light, especially the UV (and probably some violet) spectrum, so the sky turns blue instead of violet.

    Also, there is a haze associated with distance, but it's something that everyone's so used to seeing, no one but special effects people think much of. Objects in the distance do slowly turn the color of the sky.
    Interesting suggestions MagiMaster.

    However one point you have not addressed is that Rayleigh Scattering does appear to be the official physical explanation as to why the sky is blue.

    The haze visible in the distance is due to water vapour and it is always white and I dispute that you have to be a "special effects expert" to see it! Where I live you can see to the horizon 9 miles away and there is no blue mist at all even through binoculars.

    You can see a blue vapour effect in the Blue Mountains of Australia (hence their name) but this is due to the eucalyptus oil in the air.
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    Quote Originally Posted by c186282
    Your asking the right questions.

    Violet is scattered more than blue but our eyes are more sensitive to blue so the sky looks more blue than violet. Also UV is scattered more that violet which is why you can get a sunburn while in the shade on a clear day.

    Only a small amount of light is scattered out of the line of sight, therefore looking far out on the horizon most of the spectrum makes it to your eyes. With the exception of some extreme cases like sunset or lightning seen at night from across the prairies do you see the redder colors. As far as blue up above the background is the black of space and the transverse light intensity from the sun is very bright.
    I dispute your point that the sky looks blue because our eyes are more sensitive to blue light.

    Firstly our eyes are most sensitive to green light and this is the colour we first see at low intensities. But in ordinary conditions green (or even blue objects) don't stand out as particularly brighter than objects of any other colour.

    Secondly if you look at the spectrum of refracted light (just hold a CD at an angle) the violet portion of the spectrum is just as visible as the blue.
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    Quote Originally Posted by galexander
    I dispute your point that the sky looks blue because our eyes are more sensitive to blue light.

    Firstly our eyes are most sensitive to green light ......
    Once again the eternal dichotomy appears. Either you are willfully ignorant, or your are thick as too short planks nailed together.

    The statement was that our eyes are more sensitive to blue light than to violet.

    Now, which of the two options presented above applies to you?
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    I dispute your point that the sky looks blue because our eyes are more sensitive to blue light.

    Firstly our eyes are most sensitive to green light ......
    Once again the eternal dichotomy appears. Either you are willfully ignorant, or your are thick as too short planks nailed together.

    The statement was that our eyes are more sensitive to blue light than to violet.

    Now, which of the two options presented above applies to you?
    From the following link:

    http://www.telescope-optics.net/eye_...l_response.htm

    I quote the following:

    Toward outer portions of foveola, and beyond, where rods become dominant, relative sensitivity increases for medium to short (green-to-violet) wavelengths, and decreases for longer (red) wavelengths, nearly vanishing for the deep red; mesopic sensitivity for this portion of the retina is approximated mainly by the left mesopic wing on the bottom right plot on FIG. 154.
    The above text would suggest that the eye is MORE sensitive to violet than to blue.

    So who is being wilfully ignorant?
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    Quote Originally Posted by galexander
    The above text would suggest that the eye is MORE sensitive to violet than to blue.

    So who is being wilfully ignorant?
    You still don't get it, do you. If the above point is accurate, which further digging on my part will reveal, then I was being ignorant, not willfully ignorant. You will find numerous occassions on this forum and others where I state that ignorance is neither unusual, nor bad. If I continued to assert that eyes were less sensitive to violet after convincing contrary evidence were presented, then I would be willfully ignorant. This will not be the case. Either your reference is inaccurate, misinterpreted, or misleading, or I am wrong. If the former I shall maintain my position, if the latter I shall change it. I am wedded to facts, not opionions, not biases, not prejudices.
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    The above text would suggest that the eye is MORE sensitive to violet than to blue.

    So who is being wilfully ignorant?
    You still don't get it, do you. If the above point is accurate, which further digging on my part will reveal, then I was being ignorant, not willfully ignorant. You will find numerous occassions on this forum and others where I state that ignorance is neither unusual, nor bad. If I continued to assert that eyes were less sensitive to violet after convincing contrary evidence were presented, then I would be willfully ignorant. This will not be the case. Either your reference is inaccurate, misinterpreted, or misleading, or I am wrong. If the former I shall maintain my position, if the latter I shall change it. I am wedded to facts, not opionions, not biases, not prejudices.
    Obviously you fancy yourself as a psychologist as well!
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  11. #10  
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    Quote Originally Posted by galexander
    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    I dispute your point that the sky looks blue because our eyes are more sensitive to blue light.

    Firstly our eyes are most sensitive to green light ......
    Once again the eternal dichotomy appears. Either you are willfully ignorant, or your are thick as too short planks nailed together.

    The statement was that our eyes are more sensitive to blue light than to violet.

    Now, which of the two options presented above applies to you?
    From the following link:

    http://www.telescope-optics.net/eye_...l_response.htm

    I quote the following:

    Toward outer portions of foveola, and beyond, where rods become dominant, relative sensitivity increases for medium to short (green-to-violet) wavelengths, and decreases for longer (red) wavelengths, nearly vanishing for the deep red; mesopic sensitivity for this portion of the retina is approximated mainly by the left mesopic wing on the bottom right plot on FIG. 154.
    The above text would suggest that the eye is MORE sensitive to violet than to blue.
    No, it doesn't. It is stating that as you move from the center of the retina(where the color sensitive cones dominate) to the out areas(where the rods dominate), the sensitivity to red decreases. But this does not lead to the conclusion that the eye is more sensitive to violet than blue.

    Each type of cone has a color range that it is sensitive to, each with a different peak frequency to which it is most sensitive. the ranges overlap. It is the combination these different cones that lead to single color sensitivity as shown here:

    http://en.wikipedia.org/wiki/File:Eyesensitivity.png

    Which shows that the human eye is more sensitive to blue than violet.

    On top of this, you must factor in that Sunlight reaching the top of the atmosphere isn't equally distributed across the spectrum either. It peaks in intensity at the green part and falls off fairly rapidly from blue to violet.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
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    Quote Originally Posted by galexander
    Quote Originally Posted by MagiMaster
    I can't give a full answer, but there are two things I can think of here.

    One, the atmosphere, besides scattering light, also absorbs light, especially the UV (and probably some violet) spectrum, so the sky turns blue instead of violet.

    Also, there is a haze associated with distance, but it's something that everyone's so used to seeing, no one but special effects people think much of. Objects in the distance do slowly turn the color of the sky.
    The haze visible in the distance is due to water vapour and it is always white and I dispute that you have to be a "special effects expert" to see it! Where I live you can see to the horizon 9 miles away and there is no blue mist at all even through binoculars.

    You can see a blue vapour effect in the Blue Mountains of Australia (hence their name) but this is due to the eucalyptus oil in the air.
    I didn't say you have to be a special effects expert to see it. I said that only special effects people think much about it.

    Also, I'm not expert. If you can find evidence that my explanation is wrong, feel free to post a link. I'm no expert and don't mind learning something new. That said, your disputing it, with no evidence given, isn't particularly convincing, or interesting.
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    Quote Originally Posted by galexander
    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    The above text would suggest that the eye is MORE sensitive to violet than to blue.

    So who is being wilfully ignorant?
    You still don't get it, do you. If the above point is accurate, which further digging on my part will reveal, then I was being ignorant, not willfully ignorant. You will find numerous occassions on this forum and others where I state that ignorance is neither unusual, nor bad. If I continued to assert that eyes were less sensitive to violet after convincing contrary evidence were presented, then I would be willfully ignorant. This will not be the case. Either your reference is inaccurate, misinterpreted, or misleading, or I am wrong. If the former I shall maintain my position, if the latter I shall change it. I am wedded to facts, not opionions, not biases, not prejudices.
    Obviously you fancy yourself as a psychologist as well!
    There is absolutely nothing in my objective statements that indicates any perception on my part that I am a psychologist. Janus's observations appear to devalue your claim and attribute it to misinterpretation on your part. This was my initial impression also, but I'm bending over backwards to give you the benefit of the doubt. Until and unless I have compared your document with others and found your interperation wanting, or confirmed, then I shall continue with the belief that I may be mistaken.
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    The above text would suggest that the eye is MORE sensitive to violet than to blue.

    So who is being wilfully ignorant?
    You still don't get it, do you. If the above point is accurate, which further digging on my part will reveal, then I was being ignorant, not willfully ignorant. You will find numerous occassions on this forum and others where I state that ignorance is neither unusual, nor bad. If I continued to assert that eyes were less sensitive to violet after convincing contrary evidence were presented, then I would be willfully ignorant. This will not be the case. Either your reference is inaccurate, misinterpreted, or misleading, or I am wrong. If the former I shall maintain my position, if the latter I shall change it. I am wedded to facts, not opionions, not biases, not prejudices.
    http://en.wikipedia.org/wiki/Luminosity_function

    http://eosweb.larc.nasa.gov/EDDOCS/W...or_Colors.html
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    Quote Originally Posted by DrRocket
    http://en.wikipedia.org/wiki/Luminosity_function

    http://eosweb.larc.nasa.gov/EDDOCS/W...or_Colors.html
    Dr. Rocket,
    thank you for doing my work for me.

    galexander,
    if you refer to the data in the first reference you will see that human eye sensitivity is greater towards blue, than towards violet. This is true even for low light levels, where there is a pronounced shift of the sensitivity distribution towards the violet.

    While wikipedia should only be used for general overviews and an entre to a topic, you will note that reference 2, is from the CIE (Commission Internationale de L'Eclairage) a valid primary source.

    I am no longer ignorant in this area. Will you now concede that you were mistaken, that you misinterpreted your source, or will you dig your heels in?
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by DrRocket
    http://en.wikipedia.org/wiki/Luminosity_function

    http://eosweb.larc.nasa.gov/EDDOCS/W...or_Colors.html
    Dr. Rocket,
    thank you for doing my work for me.

    galexander,
    if you refer to the data in the first reference you will see that human eye sensitivity is greater towards blue, than towards violet. This is true even for low light levels, where there is a pronounced shift of the sensitivity distribution towards the violet.

    While wikipedia should only be used for general overviews and an entre to a topic, you will note that reference 2, is from the CIE (Commission Internationale de L'Eclairage) a valid primary source.

    I am no longer ignorant in this area. Will you now concede that you were mistaken, that you misinterpreted your source, or will you dig your heels in?
    As I have already stated "sensitivity" only applies to extremely low levels of light. This is why the Orion nebula looks green through a medium sized telescope (and I have seen it myself), the eye is more sensitive to green light.

    But in every day lighting conditions green objects do not glare back at you and dazzle you when compared to blue objects. And the same applies to violet.

    If you think violet objects are dim when you look at them, well that's your choice, not mine!

    In fact Ophiolite I can even see violet in the image you use to picture yourself. The violet looks pretty bright to me! Look for yourself!
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    Quote Originally Posted by Janus
    On top of this, you must factor in that Sunlight reaching the top of the atmosphere isn't equally distributed across the spectrum either. It peaks in intensity at the green part and falls off fairly rapidly from blue to violet.
    Exactly. There is both less violet radiation to scatter than blue AND due to that fact our eyes evolved to better detect the stronger blue.
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    Quote Originally Posted by galexander
    [As I have already stated "sensitivity" only applies to extremely low levels of light. This is why the Orion nebula looks green through a medium sized telescope (and I have seen it myself), the eye is more sensitive to green light.

    But in every day lighting conditions green objects do not glare back at you and dazzle you when compared to blue objects. And the same applies to violet.

    If you think violet objects are dim when you look at them, well that's your choice, not mine!

    In fact Ophiolite I can even see violet in the image you use to picture yourself. The violet looks pretty bright to me! Look for yourself!
    Do you have any form of measuring instrument available to you? Such as a foot ruler, or the like. If so, would you report back to us as to how far up your ass your head is buried.

    I'm done with you. Feeding trolls and responding to morons is for younger, more tolerant persons than I.
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    [As I have already stated "sensitivity" only applies to extremely low levels of light. This is why the Orion nebula looks green through a medium sized telescope (and I have seen it myself), the eye is more sensitive to green light.

    But in every day lighting conditions green objects do not glare back at you and dazzle you when compared to blue objects. And the same applies to violet.

    If you think violet objects are dim when you look at them, well that's your choice, not mine!

    In fact Ophiolite I can even see violet in the image you use to picture yourself. The violet looks pretty bright to me! Look for yourself!
    Do you have any form of measuring instrument available to you? Such as a foot ruler, or the like. If so, would you report back to us as to how far up your ass your head is buried.

    I'm done with you. Feeding trolls and responding to morons is for younger, more tolerant persons than I.
    Attaboy. That's the way to sugar coat it !!!

    Do you wish for a referral to my PR team ?
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    Quote Originally Posted by Lynx_Fox
    Quote Originally Posted by Janus
    On top of this, you must factor in that Sunlight reaching the top of the atmosphere isn't equally distributed across the spectrum either. It peaks in intensity at the green part and falls off fairly rapidly from blue to violet.
    Exactly. There is both less violet radiation to scatter than blue AND due to that fact our eyes evolved to better detect the stronger blue.
    BS! :x
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    [As I have already stated "sensitivity" only applies to extremely low levels of light. This is why the Orion nebula looks green through a medium sized telescope (and I have seen it myself), the eye is more sensitive to green light.

    But in every day lighting conditions green objects do not glare back at you and dazzle you when compared to blue objects. And the same applies to violet.

    If you think violet objects are dim when you look at them, well that's your choice, not mine!

    In fact Ophiolite I can even see violet in the image you use to picture yourself. The violet looks pretty bright to me! Look for yourself!
    Do you have any form of measuring instrument available to you? Such as a foot ruler, or the like. If so, would you report back to us as to how far up your ass your head is buried.

    I'm done with you. Feeding trolls and responding to morons is for younger, more tolerant persons than I.
    And I take that as a sign of reluctant defeat! :-D
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    Quote Originally Posted by galexander
    And I take that as a sign of reluctant defeat! :-D
    I would prefer you took it as a ****ing personal insult. Fools such as yourself enrage me because you represent the very antithesis of science, yet lack the intended sincerity of a religious fanatic. It appalls me that from the weakness of your profound ignorance you choose to pontiifcate on diverse matters, always criticising the current scientific consensus when you have zero idea how that consensus was arrived at. Please go away, get an education, then return and apologise to your fellow members.
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    Looks like things have gotten out of control here so here is some math to help make everyone happy.

    I said the sky looked blue because of the eye's sensitivity, the sun's spectrum and the scattering as a function of wavelength however I have not done the math until now and I got blue.

    The eye: I have used the x,y,z functions called the color matching functions color matching functions


    Then I took what is called the D65 Illuminant which is basically the solar spectrum at ground level.


    and just the shape of the Rayleigh scattering. I do not need the full equation because the final color space is normalized anyway. I used:



    Then I put it all together using the equations from: Useful Color Equations

    which gave me blue:
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    Nice work.
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    Quote Originally Posted by Ophiolite
    Quote Originally Posted by galexander
    And I take that as a sign of reluctant defeat! :-D
    I would prefer you took it as a ****ing personal insult. Fools such as yourself enrage me because you represent the very antithesis of science, yet lack the intended sincerity of a religious fanatic. It appalls me that from the weakness of your profound ignorance you choose to pontiifcate on diverse matters, always criticising the current scientific consensus when you have zero idea how that consensus was arrived at. Please go away, get an education, then return and apologise to your fellow members.
    By the way, everything you are saying about me I could very easily have said about yourselves.

    I suggest you don't like be shown up.

    Scientists are meant to be so fantastic and they never, ever get it wrong.

    I claim that this is not necessarily so. The threads I have introduced on this forum quite satisfactory prove my way of thinking is correct, that scientist often get it wrong.

    Bad luck Ophiolite!
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    Quote Originally Posted by c186282
    Looks like things have gotten out of control here so here is some math to help make everyone happy.

    I said the sky looked blue because of the eye's sensitivity, the sun's spectrum and the scattering as a function of wavelength however I have not done the math until now and I got blue.

    The eye: I have used the x,y,z functions called the color matching functions color matching functions


    Then I took what is called the D65 Illuminant which is basically the solar spectrum at ground level.


    and just the shape of the Rayleigh scattering. I do not need the full equation because the final color space is normalized anyway. I used:



    Then I put it all together using the equations from: Useful Color Equations

    which gave me blue:
    And of course we are meant to believe you on the basis that these diagrams look so impressive!

    Nice try though!

    If you want to glimpse the real situation see the spectra of white light below and observe how much violet there is. And does the violet look dimmer than the blue to you on screen? To me it looks brighter:

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    Quote Originally Posted by Ophiolite
    Nice work.
    So you think violet is dimmer than blue?

    Take a closer look:

    VIOLET





    BLUE




    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    LOOK AGAIN MORE CLOSELY.

    LOOK AGAIN MORE CLOSELY.
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    Quote Originally Posted by galexander

    If you want to glimpse the real situation see the spectra of white light below and observe how much violet there is. And does the violet look dimmer than the blue to you on screen? To me it looks brighter:

    It only looks brighter because the way it is represented in that particular image, which is artificially generated IOW, it is only brighter becuase whoever made that image made it brighter.

    To get a better idea you must look at an image made from the actual solar spectrum:



    And here, it is easier to see that blue is brighter than violet.
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    Quote Originally Posted by galexander
    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    LOOK AGAIN MORE CLOSELY.

    LOOK AGAIN MORE CLOSELY.
    Not that it's actually a relevant test, but the blue text is considerably clearer to me than the violet.

    Quote Originally Posted by galexander
    Scientists are meant to be so fantastic and they never, ever get it wrong.

    I claim that this is not necessarily so. The threads I have introduced on this forum quite satisfactory prove my way of thinking is correct, that scientist often get it wrong.

    Bad luck Ophiolite!
    Galexander, stop acting like an idiot or I will start putting your posts in the trash where they belong. I can write it in violet if it will make it clearer to you.
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    Quote Originally Posted by TheBiologista
    Quote Originally Posted by galexander
    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    LOOK AGAIN MORE CLOSELY.

    LOOK AGAIN MORE CLOSELY.
    Not that it's actually a relevant test, but the blue text is considerably clearer to me than the violet.

    Quote Originally Posted by galexander
    Scientists are meant to be so fantastic and they never, ever get it wrong.

    I claim that this is not necessarily so. The threads I have introduced on this forum quite satisfactory prove my way of thinking is correct, that scientist often get it wrong.

    Bad luck Ophiolite!
    Galexander, stop acting like an idiot or I will start putting your posts in the trash where they belong. I can write it in violet if it will make it clearer to you.
    I claim you are biased TheBioligista.

    Consider this:

    The intensity of scattered light in inversely proportional to the wavelength top the power of 4.

    Blue light is 530nm.

    Violet light is 400nm.

    This makes the violet portion of the spectrum 3 times as bright.

    How does your graph of the sensitivity of the human eye account for this?

    Again I would suggest you look at the spectrum as produced by a CD. The violet portion of the spectrum is quite vivid.

    The sky would look violet.
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    Further if I were inclined to be particularly fussy I would point out that there is no SKY BLUE on the spectrum of white light.

    After green/blue you get electric blue and then indigo.

    There is no pale blue or sky blue to be seen.

    How do you explain this? :P
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    Quote Originally Posted by TheBiologista
    Quote Originally Posted by galexander
    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    CAN YOU SERIOUSLY TELL ME THAT YOUR EYES ARE MORE SENSITIVE TO THE BLUE THAN THE VIOLET?

    LOOK AGAIN MORE CLOSELY.

    LOOK AGAIN MORE CLOSELY.
    Not that it's actually a relevant test, but the blue text is considerably clearer to me than the violet.

    Quote Originally Posted by galexander
    Scientists are meant to be so fantastic and they never, ever get it wrong.

    I claim that this is not necessarily so. The threads I have introduced on this forum quite satisfactory prove my way of thinking is correct, that scientist often get it wrong.

    Bad luck Ophiolite!
    Galexander, stop acting like an idiot or I will start putting your posts in the trash where they belong. I can write it in violet if it will make it clearer to you.
    Just to prove you are completely biased TheBioligista you have not even taken into account the fact that the two other points I have raised against Rayleigh scattering have not sufficiently been answered by your team of professional apologists.
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    I don't care about the topic galexander.

    I care that you responded to someone pointing out a logical fallacy by making an ad hominem argument. Ophiolite suggested you were drawing a false dichotomy, and you sneered at him, suggesting he fancies himself a psychologist (though he made no psychological claims). I care that you responded to Dr Rocket and Janus pointing out that you've misinterpreted a source, by ignoring their points and instead making a tangential argument. I care that c186282 took the time to post some nice graphical sources and you sneered at that too, suggesting that he was attempting to deceive and yet not showing us any evidence of that. I care that you responded to Janus' latest point by ignoring it entirely.

    And now I care that you responded to my moderation comment by first calling me biased and then trying to draw me into an argument about the topic itself rather than the moderation of the topic.

    To be clear- I don't care why the sky is blue. I care that you're being disrespectful to people who didn't have to bother with your topic but were generous enough to contribute in good faith. Keep it up and I will see to it you have no audience for your ignorance.
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    I'm disappointed with all the nonsense in this thread.

    If this thread is to reside in the Pseudoscience bin I request that my posts be removed.
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    Quote Originally Posted by c186282
    I'm disappointed with all the nonsense in this thread.

    If this thread is to reside in the Pseudoscience bin I request that my posts be removed.
    I understand where you're coming from, but that makes things worse IMO. You ruin the flow of a thread (even those which are filled with strangeness like those where galexander posts) when you delete things after the fact in the manner you requested.

    Your responses remaining serves a very useful purpose to people who may stumble on this thread in the future. It allows them to understand a topic better, to read input from someone knowledgeable, and to grasp why folks like galexander are so wrong.

    In short, allowing your posts to remain does a great service to readers, and deleting them does those readers a disservice. Just something to consider.


    Kudos to TheBiologista for laying out the circumstances so clearly. Nice post.
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    Quote Originally Posted by inow
    Quote Originally Posted by c186282
    I'm disappointed with all the nonsense in this thread.

    If this thread is to reside in the Pseudoscience bin I request that my posts be removed.
    I understand where you're coming from, but that makes things worse IMO. You ruin the flow of a thread (even those which are filled with strangeness like those where galexander posts) when you delete things after the fact in the manner you requested.

    Your responses remaining serves a very useful purpose to people who may stumble on this thread in the future. It allows them to understand a topic better, to read input from someone knowledgeable, and to grasp why folks like galexander are so wrong.

    In short, allowing your posts to remain does a great service to readers, and deleting them does those readers a disservice. Just something to consider.


    Kudos to TheBiologista for laying out the circumstances so clearly. Nice post.
    Right.

    It is pretty much a foregone conclusion that any thread started by galexander will eventually be consigned to Pseudoscience. Any substantive post will go with it, but will still serve the worthwhile purpose of demonstrating to innocent lurkers just how crazy galexander's ideas rwally are. There is value in exposing lunies, fools and trolls, and at least triple the value in exposing a combination of all three.
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    Quote Originally Posted by TheBiologista
    Galexander, stop acting like an idiot or I will start putting your posts in the trash where they belong. I can write it in violet if it will make it clearer to you.
    This was a wonderful way to start the day for me. Thank you. :-D

    c186282,
    I just want to heartily endorse the points made by inow and Dr. Rocket. Your posts are an important part, in this thread, of showing the nonsense of galexander's position. He is a fool, but that foolishness is not immediately obvious to those inexperienced with the scientific method, or scientific knowledge. Retaining the counter arguments, regardless of where the thread lies, is an important part of science education of the general populace. True, it reaches only a tiny number of people, but every small step forward is a positive one. I hope you will reconsider your position.
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    You say that if you mix violet light with blue you will not see any violet because the blue is brighter.

    According to this logic if you mix blue light with yellow you will not see any blue because the yellow is brighter.

    But some would claim you would see green.

    I have already shown that the violet would look three times as bright as the blue based upon the intensity being inversely proportional to the wavelength to the power of 4.

    But this is assuming that there is the same amount of blue in the spectrum as violet. There is not.

    Blue is just a narrow band between green and violet, and the violet band is far more extensive.

    Take a CD, which acts like a diffraction grating, and with the Sun behind you (or at least a bright open window if it is cloudy) and adjusting the angle of the CD so that the light comes over your shopulder, you will see the violet quite clearly and how it is far more extensive than the blue.

    Still believe that Rayleigh scattering would produce a pale blue sky?
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    Galexander seems to have a knack for making people see red.
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    Quote Originally Posted by TheBiologista
    I don't care about the topic galexander.

    I care that you responded to someone pointing out a logical fallacy by making an ad hominem argument. Ophiolite suggested you were drawing a false dichotomy, and you sneered at him, suggesting he fancies himself a psychologist (though he made no psychological claims). I care that you responded to Dr Rocket and Janus pointing out that you've misinterpreted a source, by ignoring their points and instead making a tangential argument. I care that c186282 took the time to post some nice graphical sources and you sneered at that too, suggesting that he was attempting to deceive and yet not showing us any evidence of that. I care that you responded to Janus' latest point by ignoring it entirely.

    And now I care that you responded to my moderation comment by first calling me biased and then trying to draw me into an argument about the topic itself rather than the moderation of the topic.

    To be clear- I don't care why the sky is blue. I care that you're being disrespectful to people who didn't have to bother with your topic but were generous enough to contribute in good faith. Keep it up and I will see to it you have no audience for your ignorance.
    With Red at one end of the spectrum forming one prime colour, Yellow in the middle another, the third prime colour should be rightfully recognised as Violet which forms the end of the spectrum at the shorter wavelengths.

    Again with far more Violet than Blue at a ratio far exceeding 3:1, Rayleigh scattering would produce a violet sky.

    Shame this colour cannot be produced on the colour monitors we have which cannot produce the true colour of violet, only a representation of it.
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    Quote Originally Posted by jsloan
    Galexander seems to have a knack for making people see red.
    What I was hoping for jsloan was that eventually you would see violet.
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  42. #41  
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    Quote Originally Posted by galexander
    Quote Originally Posted by TheBiologista
    I don't care about the topic galexander.
    With Red at one end of the spectrum forming one prime colour, Yellow in the middle another, the third prime colour should be rightfully recognised as Violet which forms the end of the spectrum at the shorter wavelengths.

    Again with far more Violet than Blue at a ratio far exceeding 3:1, Rayleigh scattering would produce a violet sky.

    Shame this colour cannot be produced on the colour monitors we have which cannot produce the true colour of violet, only a representation of it.
    I don't care about the topic galexander. It means I don't care about the topic.
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    Quote Originally Posted by TheBiologista
    Quote Originally Posted by galexander
    Quote Originally Posted by TheBiologista
    I don't care about the topic galexander.
    With Red at one end of the spectrum forming one prime colour, Yellow in the middle another, the third prime colour should be rightfully recognised as Violet which forms the end of the spectrum at the shorter wavelengths.

    Again with far more Violet than Blue at a ratio far exceeding 3:1, Rayleigh scattering would produce a violet sky.

    Shame this colour cannot be produced on the colour monitors we have which cannot produce the true colour of violet, only a representation of it.
    I don't care about the topic galexander. It means I don't care about the topic.
    It's one thing TheBiologista lecturing me on how I happened to address other participants on this thread but please take into account the manner in which they have repeatedly addressed myself.

    For example didn't you yourself earlier on call me an idiot?
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  44. #43  
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    If the shoe fits...
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    All, thank your for the support. I'm still disappointed that this thread has been moved into the Pseudoscience bin but so be it.

    I would like to say that galexander points out a good question about the color of the sky. And I must say myself that I have always taken Rayleigh Scattering as a clean explanation that the sky is blue without having done the calculation. But now I have done the calculation and I now I have proof that Rayleigh Scattering is a sufficient explanation for a blue sky. There can still be other mechanisms that contribute to the sky color. For example clouds are white because of Mie scattering and I expect that the normal lighter blue sky than what I have shown earlier is due in part to Mie scattering. The only thing that remains is convincing a skeptical audience of the validity of the calculation.

    galexander, I will not call you names and I will respect your questions. (I also request that others do this.) Are you interested in working through the details of this question? If so I suggest we start with addressing how it is possible to measure the eye's response to color and do calculations predicting the color of a given spectra.
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  46. #45  
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    Quote Originally Posted by galexander
    It's one thing TheBiologista lecturing me on how I happened to address other participants on this thread but please take into account the manner in which they have repeatedly addressed myself.

    For example didn't you yourself earlier on call me an idiot?
    No. I said you were behaving like an idiot.

    I can only comment on your behavior on these forums. A handful of pieces of text written by you don't give me near enough evidence to call you an idiot. But many of those pieces of text have been idiotic. Whether they reflect the totality of your personality or intellect is very difficult to know.

    The others, Dr Rocket and Ophiolite in particular, make a habit of making such judgments. I don't agree with that practice, and I have challenged both of them on it before, though not in this thread. What they also do, however, is make insightful and productive contributions to most of the threads they post in. When you start doing that, you'll see a lot less commentary from me.

    Now, if you have any further comments regarding my moderating, please direct them to me by PM, or send a PM to one of the admins or start a thread in the feedback forum. I will not be discussing this further here.
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    Quote Originally Posted by TheBiologista
    No. I said you were behaving like an idiot.

    I can only comment on your behavior on these forums. A handful of pieces of text written by you don't give me near enough evidence to call you an idiot. But many of those pieces of text have been idiotic.
    Stupid is as stupid does -- Forrest Gump
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    Quote Originally Posted by c186282
    All, thank your for the support. I'm still disappointed that this thread has been moved into the Pseudoscience bin but so be it.

    I would like to say that galexander points out a good question about the color of the sky. And I must say myself that I have always taken Rayleigh Scattering as a clean explanation that the sky is blue without having done the calculation. But now I have done the calculation and I now I have proof that Rayleigh Scattering is a sufficient explanation for a blue sky. There can still be other mechanisms that contribute to the sky color. For example clouds are white because of Mie scattering and I expect that the normal lighter blue sky than what I have shown earlier is due in part to Mie scattering. The only thing that remains is convincing a skeptical audience of the validity of the calculation.

    galexander, I will not call you names and I will respect your questions. (I also request that others do this.) Are you interested in working through the details of this question? If so I suggest we start with addressing how it is possible to measure the eye's response to color and do calculations predicting the color of a given spectra.
    I have read your above comments c186282 but perhaps you would like to consider the following:

    I mentioned that the colour ‘Sky Blue’ is not found on the spectrum. There is a good reason for this.

    As any artist will tell you, there is only one way to mix a colour to represent the sky: Lots and lots of white paint and just the smallest spot of prime blue.

    The sky’s colour therefore is not predominantly blue but white.

    Further the sky is exceptionally bright as any photographer will tell you and what is causing the brightness is the white light. If you look at a tree with a blue sky behind it, the sky is far brighter than the foreground object.

    Rayleigh scattering cannot account for this white light as it assumes a bias towards the violet end of the spectrum.

    So what does cause the pale blue colour of the sky?

    I suggest some form of scattering associated with altitude is possibly causing the white light. Perhaps light at all frequencies is being scattered by the Earth’s ionosphere, the lowest and densest layer of which only exists during the day. Also the Earth’s atmosphere is made up of 1% Argon which can fluoresce an electric blue colour in UV light. If you mix white with electric blue then you would probably end up with Sky Blue.
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by TheBiologista
    No. I said you were behaving like an idiot.

    I can only comment on your behavior on these forums. A handful of pieces of text written by you don't give me near enough evidence to call you an idiot. But many of those pieces of text have been idiotic.
    Stupid is as stupid does -- Forrest Gump
    And I thought we were here to discuss the science.

    You've reduced yourself to name calling.
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    Another objection that can be raised against Rayleigh scattering is that immediately after sunset you would see the Earth’s shadow rising on the opposite side of the sky.

    (Refraction of the Sun's light through the atmosphere would not explain the absence of this shadow as such refraction would cause you to see the image of the Sun providing the light!)

    But this does not happen. Instead the sky’s glow gradually fades in a uniform manner after sunset.

    This would suggest that the sky’s glow is stored like a battery which rapidly drains after sunset.

    The lowest and densest layer of the Earth’s ionosphere, the D region, quickly disappears after dark. This is because the density of this layer, below 100 km, is enough to encourage rapid recombination of electrons with their ionized parent atoms and molecules. Of course when such recombinations occur light is given off.
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  51. #50  
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    Quote Originally Posted by galexander
    And I thought...
    There is no evidence to support that assertion.

    Lacking any cogent thought and in the demonstrated absense of both willingness to engage in and ability to understand rational scientific explanations, discussion is futile. But the debunking of fools, trolls, idiots and combinations of same continues unabated.
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by galexander
    And I thought...
    There is no evidence to support that assertion.

    Lacking any cogent thought and in the demonstrated absense of both willingness to engage in and ability to understand rational scientific explanations, discussion is futile. But the debunking of fools, trolls, idiots and combinations of same continues unabated.
    But DrRocket you have not answered any of the scientific arguments I have raised in the two above posts.

    Have you finally admitted defeat I wonder.................?

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    Quote Originally Posted by galexander
    I have read your above comments c186282 but perhaps you would like to consider the following:
    Thank you
    Quote Originally Posted by galexander
    I mentioned that the color ‘Sky Blue’ is not found on the spectrum. There is a good reason for this.
    I'm not sure I understand this statement. When I use the word "spectrum" when discussing the perception of color, I mean the wavelength distribution of the electromagnetic radiation that is entering the eye. This "spectrum" contains the full information of the color to be seen.

    Quote Originally Posted by galexander
    As any artist will tell you, there is only one way to mix a color to represent the sky: Lots and lots of white paint and just the smallest spot of prime blue.
    This may very well be true. But an artist will also tell you that the primary colors are cyan, magenta and yellow. Colors of paint are call subtractive colors. If you mix them together the resulting color gets darker. With light the primary colors are red, green and blue. For proof of this I suggest you flick a drop of water on your monitor such that the water droplet will magnify the pixels. You will see red, green and blue. Therefore what an artist tells us will not help use understand the blue of the sky.

    Quote Originally Posted by galexander
    The sky’s colour therefore is not predominantly blue but white.
    This my very well be true is some cases. I live in upstate New York and you may be near York both of which have a lot of gray skies so there must be more to the story, than just Rayleigh scattering.

    Quote Originally Posted by galexander
    Further the sky is exceptionally bright as any photographer will tell you and what is causing the brightness is the white light. If you look at a tree with a blue sky behind it, the sky is far brighter than the foreground object.
    The concept of brightness is the integral over the times the . Where is the "green" color matching function. Therefore just saying that the sky is bright tells me very little about the wavelength intensity distribution.

    Quote Originally Posted by galexander
    Rayleigh scattering cannot account for this white light as it assumes a bias towards the violet end of the spectrum.
    Your are absolutely right on this. The white contribution some from wavelength independent scattering called Mie scattering. (Actually Mie's original work includes Rayleigh scattering but common usage of words "Mie scattering" implies outside the domain of Rayleigh scattering.)

    Quote Originally Posted by galexander
    So what does cause the pale blue color of the sky?
    A mixture of Rayleigh scattering and "Mie scattering". The blue I have shown above is just the Rayleigh scattering component. That is enough to address the original question on why the sky is not purple.

    Quote Originally Posted by galexander
    I suggest some form of scattering associated with altitude is possibly causing the white light.
    It is certainly true that partial size and therefore scattering varies with height.
    Quote Originally Posted by galexander
    Perhaps light at all frequencies is being scattered by the Earth’s ionosphere, the lowest and densest layer of which only exists during the day. Also the Earth’s atmosphere is made up of 1% Argon which can fluoresce an electric blue colour in UV light. If you mix white with electric blue then you would probably end up with Sky Blue.
    There is a lot of complex dynamics going on in the sky but we do not need to invoke these dynamics to understand why the sky is blue or realize that Rayleigh scattering on its own will produce the color perception of blue and not purple.
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    Quote Originally Posted by galexander
    Another objection that can be raised against Rayleigh scattering is that immediately after sunset you would see the Earth’s shadow rising on the opposite side of the sky.
    You do it is called the Belt of Venus

    The the existence or non-existence of this shadow dose not effect the scattering properties of the atmosphere.
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    This is an excellent web site, has aways been of of my favorites and it is out of the UK.

    Atmospheric Optics
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    Quote Originally Posted by galexander
    But DrRocket you have not answered any of the scientific arguments I have raised in the two above posts.

    Have you finally admitted defeat I wonder.................?

    Debating galexander on the topic of science is rather like trying to play chess with a pigeon -- it knocks the pieces over, craps on the board, and flies back to its flock to claim victory." - paraphrase of statement by Scott D. Weitzenhoffer
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by galexander
    But DrRocket you have not answered any of the scientific arguments I have raised in the two above posts.

    Have you finally admitted defeat I wonder.................?

    Debating galexander on the topic of science is rather like trying to play chess with a pigeon -- it knocks the pieces over, craps on the board, and flies back to its flock to claim victory." - paraphrase of statement by Scott D. Weitzenhoffer
    You gave me such an easy reply to that DrRocket.

    Trying to debate science with DrRocket is like trying to hold a debate with an angry bear!
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    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    I have read your above comments c186282 but perhaps you would like to consider the following:
    Thank you
    Quote Originally Posted by galexander
    I mentioned that the color ‘Sky Blue’ is not found on the spectrum. There is a good reason for this.
    I'm not sure I understand this statement. When I use the word "spectrum" when discussing the perception of color, I mean the wavelength distribution of the electromagnetic radiation that is entering the eye. This "spectrum" contains the full information of the color to be seen.

    Quote Originally Posted by galexander
    As any artist will tell you, there is only one way to mix a color to represent the sky: Lots and lots of white paint and just the smallest spot of prime blue.
    This may very well be true. But an artist will also tell you that the primary colors are cyan, magenta and yellow. Colors of paint are call subtractive colors. If you mix them together the resulting color gets darker. With light the primary colors are red, green and blue. For proof of this I suggest you flick a drop of water on your monitor such that the water droplet will magnify the pixels. You will see red, green and blue. Therefore what an artist tells us will not help use understand the blue of the sky.

    Quote Originally Posted by galexander
    The sky’s colour therefore is not predominantly blue but white.
    This my very well be true is some cases. I live in upstate New York and you may be near York both of which have a lot of gray skies so there must be more to the story, than just Rayleigh scattering.

    Quote Originally Posted by galexander
    Further the sky is exceptionally bright as any photographer will tell you and what is causing the brightness is the white light. If you look at a tree with a blue sky behind it, the sky is far brighter than the foreground object.
    The concept of brightness is the integral over the times the . Where is the "green" color matching function. Therefore just saying that the sky is bright tells me very little about the wavelength intensity distribution.

    Quote Originally Posted by galexander
    Rayleigh scattering cannot account for this white light as it assumes a bias towards the violet end of the spectrum.
    Your are absolutely right on this. The white contribution some from wavelength independent scattering called Mie scattering. (Actually Mie's original work includes Rayleigh scattering but common usage of words "Mie scattering" implies outside the domain of Rayleigh scattering.)

    Quote Originally Posted by galexander
    So what does cause the pale blue color of the sky?
    A mixture of Rayleigh scattering and "Mie scattering". The blue I have shown above is just the Rayleigh scattering component. That is enough to address the original question on why the sky is not purple.

    Quote Originally Posted by galexander
    I suggest some form of scattering associated with altitude is possibly causing the white light.
    It is certainly true that partial size and therefore scattering varies with height.
    Quote Originally Posted by galexander
    Perhaps light at all frequencies is being scattered by the Earth’s ionosphere, the lowest and densest layer of which only exists during the day. Also the Earth’s atmosphere is made up of 1% Argon which can fluoresce an electric blue colour in UV light. If you mix white with electric blue then you would probably end up with Sky Blue.
    There is a lot of complex dynamics going on in the sky but we do not need to invoke these dynamics to understand why the sky is blue or realize that Rayleigh scattering on its own will produce the color perception of blue and not purple.
    So you are saying the sky's white colour (besides the blue) is due to water vapour?

    But that would cause the sky's colour to change dramatically according to atmospheric humidity.

    When it is very humid the sky will be bright and pale and when the humidity levels are low the sky will be dark and bluer.

    This doesn't happen. I have never seen the sky change colour significantly at all and atmospheric humidity levels can vary greatly.
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    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    Another objection that can be raised against Rayleigh scattering is that immediately after sunset you would see the Earth’s shadow rising on the opposite side of the sky.
    You do it is called the Belt of Venus

    The the existence or non-existence of this shadow dose not effect the scattering properties of the atmosphere.
    Well I am a keen astronomer, have seen many interesting atmospheric phenomena but have never once observed the "Belt of Venus".
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  60. #59  
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    Quote Originally Posted by galexander
    This doesn't happen. I have never seen the sky change colour significantly at all and atmospheric humidity levels can vary greatly.
    Perhaps you should get out more.

    But seriously, this is a thoughtless comment. Perceptions of colour have a huge subjective and situational component within them. The chess board illusion is an illustration of this.

    To say you haven't noticed a change in sky colour is therefore a meaningless datum.
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    Quote Originally Posted by galexander
    So you are saying the sky's white color (besides the blue) is due to water vapor?
    The primary driver is particle size. Often water droplets are the primary driver for Mie scattering. Extreme examples are clouds and fog but a humid hazy day also results in a gray sky.

    Quote Originally Posted by galexander
    But that would cause the sky's color to change dramatically according to atmospheric humidity.

    When it is very humid the sky will be bright and pale and when the humidity levels are low the sky will be dark and bluer.

    This doesn't happen. I have never seen the sky change color significantly at all and atmospheric humidity levels can vary greatly.
    Yes. the humidity is correlated with the blueness of the sky. My examples are from the North American continent. In March in the high arctic when it is too cold to have much humidity the sky is a deep blue at sea level. (Provided that there is not much wind that has blown ice and snow into the sky at which point one is surrounded in white.) In the desert of the south west like in Death Valley which is 282ft below sea level the sky is a deep blue. On the top of the Rocky Mountains the sky is a deep blue. All of these examples are low humidity.

    In Myrtle Beach in South Carolina the sky is almost aways a pail blue-white and it is always very humid. The skies of northern Ohio and Michigan in the summer are often a pail blue-white and it is humid.
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    Quote Originally Posted by galexander
    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    Another objection that can be raised against Rayleigh scattering is that immediately after sunset you would see the Earth’s shadow rising on the opposite side of the sky.
    You do it is called the Belt of Venus

    The the existence or non-existence of this shadow dose not effect the scattering properties of the atmosphere.
    Well I am a keen astronomer, have seen many interesting atmospheric phenomena but have never once observed the "Belt of Venus".
    I'm please to be the one to have had the opportunity to point this out to you. I also did not realize what I was seeing until it was pointed out to me. Enjoy!
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    That's only true if your pail is painted blue. If you have a magenta pail, then the sky would appear magenta in it.
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  64. #63  
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    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    Another objection that can be raised against Rayleigh scattering is that immediately after sunset you would see the Earth’s shadow rising on the opposite side of the sky.
    You do it is called the Belt of Venus

    The the existence or non-existence of this shadow dose not effect the scattering properties of the atmosphere.
    Well I am a keen astronomer, have seen many interesting atmospheric phenomena but have never once observed the "Belt of Venus".
    I'm please to be the one to have had the opportunity to point this out to you. I also did not realize what I was seeing until it was pointed out to me. Enjoy!
    You may have cast some doubts on the observation that the sky should be violet according to Rayleigh scattering but why do you not see blue fog on the ground because of it?

    And why not the rings of light and dark areas around the Sun again resulting from Rayleigh scattering?

    I suggest you have shied away from these points because it is easier to cast doubt upon the sky's colour.

    So come on you folks, take it away...........!
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    Quote Originally Posted by MeteorWayne
    That's only true if your pail is painted blue. If you have a magenta pail, then the sky would appear magenta in it.
    If it wasn't for a spell checker my posts would look like a random sequence of letters.
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    Look at this view from the top of Everest .
    See how dark the blue sky can get.
    http://apod.nasa.gov/apod/ap110417.html
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    Quote Originally Posted by c186282
    Look at this view from the top of Everest .
    See how dark the blue sky can get.
    http://apod.nasa.gov/apod/ap110417.html
    Interesting, but I think it might be something to do with the photograph more than anything else.

    The sky doesn't look that dark looking out of an airliner window at 40,000 feet. No where near it. In fact at that altitude the darkening, if any, is marginal.

    But what about the two other objections I raised to Rayleigh scattering in my original post? Thought of anything yet?
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    Quote Originally Posted by galexander
    You may have cast some doubts on the observation that the sky should be violet according to Rayleigh scattering
    I have shown that viewing a Rayleigh scattering medium that is illuminated from the side will be seen as blue.

    Quote Originally Posted by galexander
    but why do you not see blue fog on the ground because of it?
    For a verity of reasons.:
    Path length is usually shorter when viewing parallel to the ground
    The angular distribution of Rayleigh scattering and Mie scattering is different. Mie scattering which is wavelength intendant has a large foreword component.
    Large component of light that has not taken part in scattering is coming from the objects in the scene.

    However you do see the other end of Rayleigh scattering, the fact that much of the short wavelength light has been scatter out of the viewing path. This is why the sun set is red and far a way lightning is orange-ish.

    Quote Originally Posted by galexander
    And why not the rings of light and dark areas around the Sun again resulting from Rayleigh scattering?
    One dose see this however the main player here is the fact that angular distribution of Rayleigh scattering and Mie scattering is different. The sky looks whiter the closer you view to the sun.

    One other observable that we have not talked about is the angular polarization dependence that Rayleigh scattering predicts and can be observed outside with a polarizer.
    See the end of: http://farside.ph.utexas.edu/teachin...es/node97.html
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    Quote Originally Posted by c186282
    Look at this view from the top of Everest .
    See how dark the blue sky can get.
    http://apod.nasa.gov/apod/ap110417.html
    Quote Originally Posted by galexander
    The sky doesn't look that dark looking out of an airliner window at 40,000 feet. No where near it. In fact at that altitude the darkening, if any, is marginal.
    I fly regularly and always get a window seat so I can see all the neat stuff out the window. I suggest you look more closely the next time you fly. Or do a Google image search for images outside an airplane window.
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  70. #69  
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    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    You may have cast some doubts on the observation that the sky should be violet according to Rayleigh scattering
    I have shown that viewing a Rayleigh scattering medium that is illuminated from the side will be seen as blue.

    Quote Originally Posted by galexander
    but why do you not see blue fog on the ground because of it?
    For a verity of reasons.:
    Path length is usually shorter when viewing parallel to the ground
    The angular distribution of Rayleigh scattering and Mie scattering is different. Mie scattering which is wavelength intendant has a large foreword component.
    Large component of light that has not taken part in scattering is coming from the objects in the scene.

    However you do see the other end of Rayleigh scattering, the fact that much of the short wavelength light has been scatter out of the viewing path. This is why the sun set is red and far a way lightning is orange-ish.

    Quote Originally Posted by galexander
    And why not the rings of light and dark areas around the Sun again resulting from Rayleigh scattering?
    One dose see this however the main player here is the fact that angular distribution of Rayleigh scattering and Mie scattering is different. The sky looks whiter the closer you view to the sun.

    One other observable that we have not talked about is the angular polarization dependence that Rayleigh scattering predicts and can be observed outside with a polarizer.
    See the end of: http://farside.ph.utexas.edu/teachin...es/node97.html
    And what difference does "path length" make as far as Rayleigh scattering is concerned and scatterers close to the ground?

    Mie scattering may cause a white colour around the Sun but the blue colour of the sky should vary up to and beyond 90 degrees from the Sun.
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  71. #70  
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    Quote Originally Posted by c186282
    Quote Originally Posted by c186282
    Look at this view from the top of Everest .
    See how dark the blue sky can get.
    http://apod.nasa.gov/apod/ap110417.html
    Quote Originally Posted by galexander
    The sky doesn't look that dark looking out of an airliner window at 40,000 feet. No where near it. In fact at that altitude the darkening, if any, is marginal.
    I fly regularly and always get a window seat so I can see all the neat stuff out the window. I suggest you look more closely the next time you fly. Or do a Google image search for images outside an airplane window.
    On the contrary last time I was flying I did take a close look at the colour of the sky and I repeat my initial observations.

    With all due respect I suggest you take a closer look yourself next time you are flying.
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  72. #71  
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    I'm done, I can't argue observation.
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    Quote Originally Posted by c186282
    I'm done, I can't argue observation.
    Just a minute.

    Didn't you say that the sky looks like the following image from out of a window on a passenger jet liner?



    Well it doesn't and you were wrong. it's not that dark.

    Don't try and make it sound as if it was me who was the one who made a fool of himself. It was you.

    Just be honest and own up to your mistake.
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  74. #73  
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    @ c186282, sorry you got roped in by the disingenuous troll, galexander.
    I hope you wont give up on the rest of us.

    @ galexander, Piss Off you Damned Troll!
    I was some of the mud that got to sit up and look around.
    Lucky me. Lucky mud.
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    Respect to you c186282 and a few others for showing amazing patience and a desire to edify. I have at least learned a few interesting things in this thread; a good reason to keep posts like yours in threads that have been moved to Pseudoscience.



    I was already seriously pissed off at galexander's nonsense after the first few posts. What an exasperating contrarian this guy is. :x
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
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  76. #75  
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    Quote Originally Posted by KALSTER
    Respect to you c186282 and a few others for showing amazing patience and a desire to edify. I have at least learned a few interesting things in this thread; a good reason to keep posts like yours in threads that have been moved to Pseudoscience.



    I was already seriously pissed off at galexander's nonsense after the first few posts. What an exasperating contrarian this guy is. :x
    For your information you have still not proved to me that the sky WOULD NOT look violet. Despite your arguments that yellow is the brightest of the colours.

    And you have still not properly answered the other two objection I raised against Rayleigh scattering.

    Believe me I am the one who is being exceptionally patient.
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  77. #76  
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    No, you are being intentionally ignorant in the fashion of a troll.
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    On the subject of would the sky look violet or not, the more I think of it the more silly the argument sounds that because blue light is brighter you would not see the violet.

    Red light at the other end of the spectrum is just as ‘dark’ as the violet is and yet you can still see red. If you mix red with the brighter orange the red does not disappear, instead you get a redder colour of orange. If you mix a lot of red with orange you end up with red with some orange in it.

    I can’t believe you lot can’t see this and still insist that the violet would disappear in the blue.

    The violet would appear three times brighter than the blue because of 1/λexp4 and the violet band is significantly wider than the blue. So there would be more violet in the sky than blue.

    In other words it would look violet.

    The science is simply surely? Yet you appear to have succeeded in clouding the whole issue with junk science, creating confusion in the process.
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  79. #78  
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    Quote Originally Posted by MeteorWayne
    No, you are being intentionally ignorant in the fashion of a troll.
    I can't believe you lot are real!

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  80. #79  
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    Dear moderator,
    now would be a good time to:
    a) Lock this thread.
    b) Issue a warning to galexander.
    c) Confer with other moderators and agree that in future there will be some backbone displayed in relation to obvious trolls and infants posting in the forum.

    Yours in expectation of, at best, 1/3 success,

    Ophiolite
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    Seems to me that galexander is so obsessed about Rayleigh scattering being incorrect (which it isn't as shown by many users here) that he/she is trying to convince themselves that the sky is violet.

    You were the one who stated that green is the most sensitive colour to the human eye, and so looking at the visible spectrum ROYGBIV- blue is right next to green on the spectrum, whereas violet is right at the end, and so it would only be logical that the eye is more sensitive to blue than violet!

    Either that, or you are colour blind...
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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  82. #81  
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    Quote Originally Posted by x(x-y)
    Seems to me that galexander is so obsessed about Rayleigh scattering being incorrect (which it isn't as shown by many users here) that he/she is trying to convince themselves that the sky is violet.

    You were the one who stated that green is the most sensitive colour to the human eye, and so looking at the visible spectrum ROYGBIV- blue is right next to green on the spectrum, whereas violet is right at the end, and so it would only be logical that the eye is more sensitive to blue than violet!

    Either that, or you are colour blind...
    The sensitivity of the eye to the various parts of the spectrum is included in the definition of the international lumen, so has received considerable study. The sensitivity function was discussed earlier in the thread, and, as is typical ignored by galexander.

    galexander has a history in the forum of challenging valid established science simply to create a stir, all the while feigning innocent ignorance. While he may very well be ignorant, and probably quite stupid as well, he is most certainly a troll.
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  83. #82  
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    Quote Originally Posted by x(x-y)
    Seems to me that galexander is so obsessed about Rayleigh scattering being incorrect (which it isn't as shown by many users here) that he/she is trying to convince themselves that the sky is violet.

    You were the one who stated that green is the most sensitive colour to the human eye, and so looking at the visible spectrum ROYGBIV- blue is right next to green on the spectrum, whereas violet is right at the end, and so it would only be logical that the eye is more sensitive to blue than violet!

    Either that, or you are colour blind...
    Now this is an example of wilful ignorance as I have already clearly explained this point.

    How many times do I have to answer this question?

    It makes no difference if the eye is more sensitive to blue than violet, that is not the point.

    The eye is more sensitive to yellow than red but you can still see the red when you mix lots of it with yellow.

    I think 'x(x-y)' it's not colour blindness you are suffering from.........it's something else.

    Read through my last few posts again
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  84. #83  
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    Quote Originally Posted by DrRocket
    Quote Originally Posted by x(x-y)
    Seems to me that galexander is so obsessed about Rayleigh scattering being incorrect (which it isn't as shown by many users here) that he/she is trying to convince themselves that the sky is violet.

    You were the one who stated that green is the most sensitive colour to the human eye, and so looking at the visible spectrum ROYGBIV- blue is right next to green on the spectrum, whereas violet is right at the end, and so it would only be logical that the eye is more sensitive to blue than violet!

    Either that, or you are colour blind...
    The sensitivity of the eye to the various parts of the spectrum is included in the definition of the international lumen, so has received considerable study. The sensitivity function was discussed earlier in the thread, and, as is typical ignored by galexander.

    galexander has a history in the forum of challenging valid established science simply to create a stir, all the while feigning innocent ignorance. While he may very well be ignorant, and probably quite stupid as well, he is most certainly a troll.
    For all you wilful ignoramuses, here is my full post again which answers your silly and childish argument that yellow is the brightest colour. Every five year old child knows this but the point is this doesn't really mean a thing when it comes the sky's actual, observable colour:

    On the subject of would the sky look violet or not, the more I think of it the more silly the argument sounds that because blue light is brighter you would not see the violet.

    Red light at the other end of the spectrum is just as ‘dark’ as the violet is and yet you can still see red. If you mix red with the brighter orange the red does not disappear, instead you get a redder colour of orange. If you mix a lot of red with orange you end up with red with some orange in it.

    I can’t believe you lot can’t see this and still insist that the violet would disappear in the blue.

    The violet would appear three times brighter than the blue because of 1/λexp4 and the violet band is significantly wider than the blue. So there would be more violet in the sky than blue.

    In other words it would look violet.

    The science is simply surely? Yet you appear to have succeeded in clouding the whole issue with junk science, creating confusion in the process.
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    Quote Originally Posted by Ophiolite
    Dear moderator,
    now would be a good time to:
    a) Lock this thread.
    b) Issue a warning to galexander.
    c) Confer with other moderators and agree that in future there will be some backbone displayed in relation to obvious trolls and infants posting in the forum.

    Yours in expectation of, at best, 1/3 success,

    Ophiolite
    You, Ophiolite, should be issued a warning for wilful ignorance!

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    What are you on about that "it doesn't matter which colour is more sensitive to our eyes"? Of course it does, otherwise the sky would be multicoloured! There is still violet light 'in' the sky, but we can't see it as well as the blue light, and those are the facts of the matter.
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    Quote Originally Posted by x(x-y)
    What are you on about that "it doesn't matter which colour is more sensitive to our eyes"? Of course it does, otherwise the sky would be multicoloured! There is still violet light 'in' the sky, but we can't see it as well as the blue light, and those are the facts of the matter.
    I have already explained you fool!

    If you add red to the colour yellow you will get orange, you will clearly see the effects of the colour red. The yellow will in NO WAY mask the red.

    This is just so embarrassing!

    And I have already told you and everyone else time and time again, there is MORE VIOLET THAN BLUE!

    I just can't understand what you have a problem with.
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    And DrRocket, Ophiolite, Janus and C[insert number here] have explained to you time and time again that you're wrong- go back and actually understand their posts, especially the graphical one and Janus' explanation.
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    Quote Originally Posted by x(x-y)
    And DrRocket, Ophiolite, Janus and C[insert number here] have explained to you time and time again that you're wrong- go back and actually understand their posts, especially the graphical one and Janus' explanation.
    I've seen the graphics and you lot are just trying to blind (colour blind) everyone with science.

    Here are some graphics just to prove that I can make a big impression too!



    See that the red is just as dark as the violet?

    See how there is little blue compared to the violet?

    Still think the sky would be blue with Rayleigh scattering?
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    I'm going to try one last time.

    There are three main ideas that we need to include to understand what color the sky will be seen by non-color blind humans.
    1) How the human eye sees color
    2) What wavelength distribution of light in the sky is available for scattering
    3) The wavelength dependence of the scattering.

    How the human eye sees color

    The eye: I have used the x,y,z functions called the color matching functions color matching functions

    These functions are not really the eye's response to light like one might measure the response of a CCD detector. There is some freedom in their definition. To see this look at the following three integrals:



    The key requirement is that for all possible source functions there is a unique mapping into the space. This uniqueness can be preserved for any non-degenerate linear combination of the of the color matching functions. This property was used to adjust the original color matching functions into the ones we use today. The original experiment resulted in the "red" color matching function having negative values. Now all the color matching functions are positive and the "green" color matching function when multiplied and integrated gives a number that is proportional to human visual brightness.

    Where is the illuminate.

    What wavelength distribution of light in the sky is available for scattering
    The light available is simply the light from our favorite star which is almost a blackbody radiator. But what I have used is the measured solar spectra. In color science this is often called the
    D65 Illuminate

    I have updated this plot to show the colors associated with the wavelengths.

    The wavelength dependence of the scattering
    I will scale for intensities at the end, so now I just need the wavelength dependence of
    Rayleigh scattering.
    I have used: to scale the minimum wavelength to one.


    Putting it all together
    Then I put it all together using the equations from: Useful Color Equations

    First I calculate the color space values:




    The following is a plot of the integrand of preceding integrals. Notice that the "blue" color function will produce the largest value but there is still a contribution to the "red" and "green" color functions that ultimately produce the prescription of blue.


    I get the following values:



    The last step is transforming the color space values in to an RGB monitor color space. This is just a matrix transformation and should be done differently for all of our different uncalibrated monitors but I just picked a stranded off of the website linked to above.

    The matrix I use is:

    I have made the blue color strip below that shows the range of blue one can get with just Rayleigh scattering at different brightness levels. Notice there is no purple.



    Any reasonable rebuttal to this work needs to contain more than just weak words and silly colorful pictures. To show that Rayleigh scattering is not responsible for the blue we see in the sky I expect some math and references (via links). And if you can't do the math come back when you can.

    P.S. The screen name of c186282 is a little "c" for the speed of light and the 186282 is the speed of light in the crappy units we use on this side of the ocean, miles per hour.

    P.S.S Hey! I got math and silly pictures!
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    Quote Originally Posted by Ophiolite
    Dear moderator,
    now would be a good time to:
    a) Lock this thread.
    Considering it, but so long as there are more posts like c186282's than there are meta discussions and/or insults, I see no need to. Except perhaps to annoy galexander, which I admit is tempting.

    Quote Originally Posted by Ophiolite
    b) Issue a warning to galexander.
    I can't issue warnings for foolish behavior, inability to comprehend logical arguments, contranianism or blind ignorance. If there's some specific part of our posting guidelines that he's violating then I'll certainly act on that.

    Quote Originally Posted by Ophiolite
    c) Confer with other moderators and agree that in future there will be some backbone displayed in relation to obvious trolls and infants posting in the forum.
    Like, say, transparently banishing their threads to subforums which make clear our shared skepticism of the contents? We won't entertain this nonsense on the main forums. I think that's sufficient.

    My apologies for the tardy response, by the way. I was without internet access for several days whilst moving homes.
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    Quote Originally Posted by galexander
    I have already explained you fool!
    Don't do this galexander. My patience with you is already stretched. I think you like having this soapbox. Carry on like this and I'll kick it out from under you.
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    Quote Originally Posted by c186282
    I'm going to try one last time.

    There are three main ideas that we need to include to understand what color the sky will be seen by non-color blind humans.
    1) How the human eye sees color
    2) What wavelength distribution of light in the sky is available for scattering
    3) The wavelength dependence of the scattering.

    How the human eye sees color

    The eye: I have used the x,y,z functions called the color matching functions color matching functions

    These functions are not really the eye's response to light like one might measure the response of a CCD detector. There is some freedom in their definition. To see this look at the following three integrals:



    The key requirement is that for all possible source functions there is a unique mapping into the space. This uniqueness can be preserved for any non-degenerate linear combination of the of the color matching functions. This property was used to adjust the original color matching functions into the ones we use today. The original experiment resulted in the "red" color matching function having negative values. Now all the color matching functions are positive and the "green" color matching function when multiplied and integrated gives a number that is proportional to human visual brightness.

    Where is the illuminate.

    What wavelength distribution of light in the sky is available for scattering
    The light available is simply the light from our favorite star which is almost a blackbody radiator. But what I have used is the measured solar spectra. In color science this is often called the
    D65 Illuminate

    I have updated this plot to show the colors associated with the wavelengths.

    The wavelength dependence of the scattering
    I will scale for intensities at the end, so now I just need the wavelength dependence of
    Rayleigh scattering.
    I have used: to scale the minimum wavelength to one.


    Putting it all together
    Then I put it all together using the equations from: Useful Color Equations

    First I calculate the color space values:




    The last step is transforming the color space values in to an RGB monitor color space. This is just a matrix transformation and should be done differently for all of our different uncalibrated monitors but I just picked a stranded off of the website linked to above.

    I have made the blue color strip below that shows the range of blue one can get with just Rayleigh scattering at different brightness levels. Notice there is no purple.



    Any reasonable rebuttal to this work needs to contain more than just weak words and silly colorful pictures. To show that Rayleigh scattering is not responsible for the blue we see in the sky I expect some math and references (via links). And if you can't do the math come back when you can.

    P.S. The screen name of c186282 is a little "c" for the speed of light and the 186282 is the speed of light in the crappy units we use on this side of the ocean, miles per hour.

    P.S.S Hey! I got math and silly pictures!
    This is a really good post.

    It is incomplete though.

    But although the Sun gives off most of its energy in the yellow-green frequencies, the light emitted is effectively white.

    Read more: http://wiki.answers.com/Q/What_is_th...#ixzz1KIz773p6

    The energy levels of the sun are more energetic in the yellow-green range. That would account for our cone differentials in our eyes to make it appear white since the rods are energy level measuring devices. But, even that is not simple. The blue cones are more sensitive for some reason so less of them are needed to make the white color of the sun we see even though energy wise, it is not white.

    http://hyperphysics.phy-astr.gsu.edu...n/rodcone.html

    But, what is important about the sun energetic color is the color of plants.

    They are unable to process this amount of energy for photosynthesis. So, they have to reflect it and appear green to us.

    That can be seen in this graph.


    Note the low rate of absorbtion at the sun's most energetic levels.

    Now, the early objective of hydrocarbon construction is the disconnection hydrogen and oxygen using electricity with the photoelectric effect as electrolysis to later reasemble these components into a hydrocarbon.


    Chlorophyll is used by all photosynthetic organisms as the link between excitation energy transfer and electron transfer. Of particular note is the rate with which these transfer reactions need to occur. As the lifetime of the excited state is only several nanoseconds (1 nanosecond (ns) is 10-9 s), after absorption of a quantum, energy transfer and charge separation in the reaction center must have occurred within this time period. Energy transfer rates between pigments are very rapid, and charge separation in reaction centers occurs in 3-30 picoseconds (1 picosecond (ps) is 10-12 s). Subsequent electron transfer steps are significantly slower (200 ps - 20 ms) but, nonetheless, the electron transport chain is sufficiently fast that at least a significant part of the absorbed sunlight can be used for photosynthesis. However, in the presence of excess light, damage may occur, which may originate from the formation of chlorophyll in "triplet state". In a triplet state two electrons in the outer shell have identical rather than opposite spin orientation. This triplet chlorophyll readily reacts with oxygen, leading to the very reactive singlet oxygen, which can damage proteins. To counter this damaging reaction, carotenoids are usually present in close vicinity to chlorophylls. Many carotenoids efficiently "quench" triplet states of chlorophyll, thus avoiding formation of singlet oxygen. Chlorophyll in its free form is very toxic in the light in the presence of oxygen, because a close interaction with carotenoids is not always available under such circumstances. Therefore, all chlorophyll in a cell in aerobic organisms is bound to proteins, generally with carotenoids bound to the same protein.

    http://photoscience.la.asu.edu/photo...hotointro.html

    Now, I want to alert everyone on the pico second operationally ability of plants even 4 billion years ago. If they failed to operate in that pico second range, then the plant would fail to seperate hydrogen and oxygen from the water and hence proteins could never have been formed.

    We did not enter the technological pico second range until the last 12 years.

    That is just the beginning of protein construction by plants.

    Hopefully, all can see, we are missing something.
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  94. #93  
    Administrator KALSTER's Avatar
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    Hopefully, all can see, we are missing something.
    What's that?
    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
    "All people know the same truth. Our lives consist of how we chose to distort it." - Harry Block
    "It is the mark of an educated mind to be able to entertain a thought without accepting it." - Aristotle
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  95. #94  
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    Quote Originally Posted by KALSTER
    Hopefully, all can see, we are missing something.
    What's that?
    I don't know, but I would really enjoy the opportunity to miss chinglu.
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    Quote Originally Posted by c186282
    I'm going to try one last time.

    There are three main ideas that we need to include to understand what color the sky will be seen by non-color blind humans.
    1) How the human eye sees color
    2) What wavelength distribution of light in the sky is available for scattering
    3) The wavelength dependence of the scattering.

    How the human eye sees color

    The eye: I have used the x,y,z functions called the color matching functions color matching functions

    These functions are not really the eye's response to light like one might measure the response of a CCD detector. There is some freedom in their definition. To see this look at the following three integrals:



    The key requirement is that for all possible source functions there is a unique mapping into the space. This uniqueness can be preserved for any non-degenerate linear combination of the of the color matching functions. This property was used to adjust the original color matching functions into the ones we use today. The original experiment resulted in the "red" color matching function having negative values. Now all the color matching functions are positive and the "green" color matching function when multiplied and integrated gives a number that is proportional to human visual brightness.

    Where is the illuminate.

    What wavelength distribution of light in the sky is available for scattering
    The light available is simply the light from our favorite star which is almost a blackbody radiator. But what I have used is the measured solar spectra. In color science this is often called the
    D65 Illuminate

    I have updated this plot to show the colors associated with the wavelengths.

    The wavelength dependence of the scattering
    I will scale for intensities at the end, so now I just need the wavelength dependence of
    Rayleigh scattering.
    I have used: to scale the minimum wavelength to one.


    Putting it all together
    Then I put it all together using the equations from: Useful Color Equations

    First I calculate the color space values:




    The last step is transforming the color space values in to an RGB monitor color space. This is just a matrix transformation and should be done differently for all of our different uncalibrated monitors but I just picked a stranded off of the website linked to above.

    I have made the blue color strip below that shows the range of blue one can get with just Rayleigh scattering at different brightness levels. Notice there is no purple.



    Any reasonable rebuttal to this work needs to contain more than just weak words and silly colorful pictures. To show that Rayleigh scattering is not responsible for the blue we see in the sky I expect some math and references (via links). And if you can't do the math come back when you can.

    P.S. The screen name of c186282 is a little "c" for the speed of light and the 186282 is the speed of light in the crappy units we use on this side of the ocean, miles per hour.

    P.S.S Hey! I got math and silly pictures!
    Would you mind explaining how the first graph you quote works?

    Are you now suggesting that the human eye is more sensitive to blue light? Previously we were being told it was yellow.

    Also in the first graph it is not clear where the violet is. I detect some violet alongside the blue and if that it the case, then as already pointed out, the eye isn't really that much less sensitive to violet than blue.

    But I don't really like that first graph. It's completely different from the previous graph we were shown on eye sensitivity to colour.

    The third graph you show clearly suggests that violet is in the lead against blue and when that is added to the observation that the human eye is only slightly less sensitive to violet than blue, the conclusion would have to be the final colour strip would have to be violet.

    I would also dispute what the colour of your final colour strip actually was. It appears to show a range of colours from a lighter blue through to a dark blue that is virtually 'black'. For the blue to be this dark it would most certainly have to be proceeded by violet.

    And just to underline what I have already said, I don't know how true the colours are that are shown in your artwork really are. And if the colours aren't true then where does that leave us?
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    Another possible objection to your above calculations is that the eye is slightly more sensitive to blue than violet anyway when you see it reproduced on the screen.

    To mathematically increase the amount of blue because it is slightly brighter than violet may be entirely unnecessary therefore if if looks brighter on the screen anyway.

    It's like mixing equal amounts of yellow and red to produce orange and then saying because yellow is 3 or 4 times brighter than red you really should be adding 3 or 4 times as much yellow to make it look more realistic............... But this isn't really necessary. The yellow looks brighter anyway.

    Do you see where I am coming from?
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    Quote Originally Posted by galexander
    Would you mind explaining how the first graph you quote works?

    Are you now suggesting that the human eye is more sensitive to blue light? Previously we were being told it was yellow.

    Also in the first graph it is not clear where the violet is. I detect some violet alongside the blue and if that it the case, then as already pointed out, the eye isn't really that much less sensitive to violet than blue.

    But I don't really like that first graph. It's completely different from the previous graph we were shown on eye sensitivity to colour.
    The first graph is made from the same dataset that I have used in my first post. It is the CIE 1931 xyz color matching functions. Now I have added some flare to the plot by filling to the axis with colors that line up with the frequency, but this just adds entertainment.

    Quote Originally Posted by galexander
    The third graph you show clearly suggests that violet is in the lead against blue and when that is added to the observation that the human eye is only slightly less sensitive to violet than blue, the conclusion would have to be the final colour strip would have to be violet.
    Yes but that is only part of the story! One has to multiply the three plots together then integrate. Actually I was going to show that plot. So once I'm done here I'm going to go back and add that plot to my early post.

    Quote Originally Posted by galexander
    I would also dispute what the colour of your final colour strip actually was. It appears to show a range of colours from a lighter blue through to a dark blue that is virtually 'black'. For the blue to be this dark it would most certainly have to be proceeded by violet.
    Any color will transition to black as the brightness is turned down to zero. And none of them will pass through violet (except for violet)

    Quote Originally Posted by galexander
    And just to underline what I have already said, I don't know how true the colours are that are shown in your artwork really are. And if the colours aren't true then where does that leave us?
    Artwork!? I never really thought of myself as an artiest. But beauty does come from doing one's math correct.

    Now the very last step where I transform to the RGB space for display on a monitor is were the greatest about of color error comes in because I do no know the gambit and calibration parameters for your monitor. But the is small compared to the between blue and violet.

    I really suggest that you forget about Rayleigh scattering for a bit and just learn about human color perception. It is great fun! and the math is very simple as you have seen above.
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    Quote Originally Posted by galexander
    Another possible objection to your above calculations is that the eye is slightly more sensitive to blue than violet anyway when you see it reproduced on the screen.

    To mathematically increase the amount of blue because it is slightly brighter than violet may be entirely unnecessary therefore if if looks brighter on the screen anyway.

    It's like mixing equal amounts of yellow and red to produce orange and then saying because yellow is 3 or 4 times brighter than red you really should be adding 3 or 4 times as much yellow to make it look more realistic............... But this isn't really necessary. The yellow looks brighter anyway.

    Do you see where I am coming from?
    Quit talking and do the math!
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  100. #99  
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    Quote Originally Posted by c186282
    Quote Originally Posted by galexander
    Another possible objection to your above calculations is that the eye is slightly more sensitive to blue than violet anyway when you see it reproduced on the screen.

    To mathematically increase the amount of blue because it is slightly brighter than violet may be entirely unnecessary therefore if if looks brighter on the screen anyway.

    It's like mixing equal amounts of yellow and red to produce orange and then saying because yellow is 3 or 4 times brighter than red you really should be adding 3 or 4 times as much yellow to make it look more realistic............... But this isn't really necessary. The yellow looks brighter anyway.

    Do you see where I am coming from?
    Quit talking and do the math!
    You have completely ignored this point for your own convenience!

    I suspect you don't have a good answer for what is a profoundly obvious point.

    Is c186282 the only one here to have made this simple mistake in logic?

    You cannot, simply cannot increase the amount of blue just because it happens to be brighter. It is brighter anyway. If there is more violet than blue then you have to accept this simple fact.

    However c186282 appears to suggest that you wouldn't even get any violet in his final colour strip as he says the following!

    Any color will transition to black as the brightness is turned down to zero. And none of them will pass through violet (except for violet)
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    Quote Originally Posted by galexander


    However c186282 appears to suggest that you wouldn't even get any violet in his final colour strip as he says the following!

    Quote Originally Posted by c186282
    Any color will transition to black as the brightness is turned down to zero. And none of them will pass through violet (except for violet)
    Thats because c186282 understands that color is not affected in this way, the darker you make any color the closer it will be to being black, the lighter the color the closer it will be to white, neither of which are colors in and of themselves and thus are not found in the spectrum.

    To move a color from being blue to being violet you have the change the wavelength of the light towards the ultraviolet end of the spectrum, not make the color darker.
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