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Thread: Why is the Sky Blue?

  1. #1 Why is the Sky Blue? 
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    Hey guys, AbhiKap55 here

    So tomorrow I have to give a little presentation (under 10 minutes) about why the sky is blue. This is what I know so far, can you please correct any of this if it is wrong.

    Sunlight is actually a mixture of all the colors of the rainbow, and when they enter the atmosphere, the molecules scatter the blue more because the blue wavelength is the perfect size. Since it is scattered everywhere, it looks blue to us.

    Questions that I have:

    So why is the sky orange at dawn?

    If the blue gets scattered, where do the rest of the colors go?

    The Electromagnetic Spectrum is a range of all possible colors, correct?

    How do our eyes play a role in this?

    Thanks,
    Help is greatly appreciated


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    Because it's sad that we pump pollution into it relentlessly.


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    Quote Originally Posted by AbhiKap55 View Post
    So why is the sky orange at dawn?
    When the Sun appears low on our horizon, the atmosphere that light is moving through has greater distance and is thicker from your perspective, unlike the atmosphere at zenith from your perspective.
    The light needs to travel through more atmosphere to reach your eyes.
    The more air to travel through and the closer to the horizon, the greater the dust count in the air that light will encounter on the trip to your eyes. Dust can scatter the short blue wavelengths and as the light works through the greater distance and interference, this leaves more of the red and orange wavelengths to reach you.
    Quote Originally Posted by AbhiKap55 View Post
    If the blue gets scattered, where do the rest of the colors go?
    All the wavelengths get a certain amount of scattering- some more than others. Scattering will send the light in various directions, back to Earth, out into space (You can see the lit Earth from the Moon) pretty much all over...

    Quote Originally Posted by AbhiKap55 View Post
    The Electromagnetic Spectrum is a range of all possible colors, correct?
    It includes the spectrum far beyond what we perceive as colors.

    Quote Originally Posted by AbhiKap55 View Post
    How do our eyes play a role in this?
    For me, I do not understand this question.
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  5. #4  
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    Quote Originally Posted by AbhiKap55 View Post
    How do our eyes play a role in this?
    For me, I do not understand this question.[/QUOTE]

    What I mean is that how do our eyes affect this. For example, I heard that violet is scattere along with blue (and other colors) but we see blue more clearly or something?
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  6. #5  
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    Quote Originally Posted by AbhiKap55 View Post
    How do our eyes play a role in this?
    For me, I do not understand this question.[/QUOTE]

    What I mean is that how do our eyes affect this. For example, I heard that violet is scattere along with blue (and other colors) but we see blue more clearly or something?
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    Quote Originally Posted by AbhiKap55 View Post
    What I mean is that how do our eyes affect this. For example, I heard that violet is scattered along with blue (and other colors) but we see blue more clearly or something?
    First, let's check some references...:
    Visible spectrum - Wikipedia, the free encyclopedia

    Our eyes only perceive a small portion of the EM spectrum. I think you may be asking whether our eyes cause us to perceive the sky as blue whereas a bee's perception would have more color.
    Yes, the bee would not see a blue sky as we see it.
    But that's not really relevant to the physics, involved. We can set our perception as a control group or a relative point of view.
    It's the changes in perception that are interesting, not which perception sees what differently.
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    Yet if you cannot see the whole picture then you cannot assume the most prominent colour in the sky is blue therefore your eyes have decieved you and your observed results are invalid. Would it not be more accurate to say that the sky isnt blue its a mix of a wide spectrum of color the list the average spectrum of visible and invisible light.
    Last edited by fiveworlds; March 24th, 2013 at 07:08 PM.
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    Quote Originally Posted by fiveworlds View Post
    Yet if you cannot see the whole picture then you cannot assume the most prominent colour in the sky is blue therefore your eyes have decieved you and your observed results are invalid. Would it not be more accurate to say that the sky isnt blue its a mix of a wide spectrum of color the list the average spectrum of visible and invisible light.
    No one is assuming that the most prominent color in the sky is blue. The question asks about why we see a blue sky.
    The observations are quite valid and your entire post seems more a red herring than a contribution.
    Last edited by Neverfly; March 24th, 2013 at 07:32 PM.
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  10. #9  
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    Quote Originally Posted by Neverfly View Post
    No one is assuming that the most prominent color in the sky is blue. The question asks about why we see a blue sky.
    The observations are quite valid and your entire posts seems more a red herring than a contribution.
    Sadly, this is hardly a unique instance of his post having this problem..
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    thing is i dont see a blue sky its night. secondly not everyone sees blue the spectrum we see is eyesight dependent if you have small differences in your eyes you see differently so. biology we cant even see all the shades of blue our eyes are so unreliable i mean real blue can be artificially produced easy but most light we see is a mixture. Its like saying why is a rock grey? it doesnt have chlorophyll to absorb light spectra so how is the light absorbed?
    Last edited by fiveworlds; March 24th, 2013 at 07:34 PM.
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  12. #11  
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    afaik, our eyes perceive the rgb colors. and blue light scatters about 5x times more than red and about 2x more than green. so red can pass 5x the distance through our atmosphere than blue and 2.5x the distance of green, making blue the dominant color.
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    But that would assume that the sun emits the exact same amount of red, green and blue how do you know the light from the sun wasnt 80%red,2%blue and 28%green before entering the atmosphere? you are saying that the natural light on earth is sky blue not white
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  14. #13  
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    because in that case the sky wouldn't be blue and a prism would show different results
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    so all rgb. How does a rock appear grey? one hypothesis might say that the chemical composition of the rock alters light, another might say that certain types of light are deflected at much greater angles so only colours which make grey appear, another could say that the collision with the rock converted some of the light energy into kinetic energy resulting in a frequency change which is correct?
    Last edited by fiveworlds; March 24th, 2013 at 08:06 PM.
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  16. #15  
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    Wait, so our eyes ONLY see RGB colors?
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    yeah and not even all of them terribly unreliable. well at least thats computers for you mixtures of red green and blue can make up every colour but purple and a few other could do the same so i guess not just different light frequencies
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    Quote Originally Posted by fiveworlds View Post
    But that would assume that the sun emits the exact same amount of red, green and blue how do you know the light from the sun wasnt 80%red,2%blue and 28%green before entering the atmosphere? you are saying that the natural light on earth is sky blue not white
    It does not emit the exact same amount of each wavelength.
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    Quote Originally Posted by AbhiKap55 View Post
    Wait, so our eyes ONLY see RGB colors?
    First: Pay no attention to fiveworlds posts.

    Second: I posted you a link, earlier. Please read it...
    Here, I narrowed it down a bit...
    Visible spectrum - Wikipedia, the free encyclopedia
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  20. #19  
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    because it reflects the rgb colors equally. one is scattering of light and reflecting/absorbing is another thing.
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    sorry
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    tell me if i mix blue and green to make yellow do i see both frequencies together to make yellow or just one changed frequency or are there cases for both occurances in certain conditions? If i use a prism to separate colours does that mean its the only thing that separates colours how do you know if your prism is influencing your results? do different prisms disperse light differently?
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  23. #22  
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    Ok, look- both of you. He's trying to get accurate information for his Science Project. Do not go confusing it with confounding posts.
    Seriously.

    And AbhiKap55, do your job. Research and read the information in the links. If you do not understand something particular, feel free to ask for some tutoring.
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  25. #24  
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    Quote Originally Posted by AbhiKap55 View Post
    What I mean is that how do our eyes affect this. For example, I heard that violet is scattere along with blue (and other colors) but we see blue more clearly or something?
    Remember there is a continuous spectrum of colours, not a number of discrete colours. So there is a range of frequencies which will be scattered more than others. This corresponds to a range we perceived as blue.
    ei incumbit probatio qui dicit, non qui negat
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  26. #25  
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    Quote Originally Posted by curious mind View Post
    afaik, our eyes perceive the rgb colors.
    There is a lot of confusion on display here about how vision works. Maybe one of you should start a thread on the subject to avoid hijacking this one any more.

    Our eyes do have three sets of colour sensors but these are not red, green and blue. They are closer to yellow, green and violet. But they are also very wide and overlap quite a lot. The RGB system is an approximation that allows us to reproduce a similar gamut of colours that the eye can see.

    Quote Originally Posted by fiveworlds View Post
    tell me if i mix blue and green to make yellow do i see both frequencies together to make yellow or just one changed frequency or are there cases for both occurances in certain conditions? If i use a prism to separate colours does that mean its the only thing that separates colours how do you know if your prism is influencing your results? do different prisms disperse light differently?
    If you use a prism (or anything else) to split the different frequencies (colours) of light then each colour corresponds to a single frequency. So, for example, there is a single frequency that corresponds to a particular shade of yellow. This happens to stimulate each of the different receptors in your eye to different amounts to cause you to perceive "yellow".

    But if you mix RGB colours to generate that same shade of yellow, then you will be getting a mixture of frequencies that just happen to stimulate those sensors in a similar way and hence make your brain think it is seeing the same colour.

    (Bear in mind that almost everything you see is generated by the brain rather than in the eye.)
    Last edited by Strange; March 25th, 2013 at 04:08 AM. Reason: hadn't noticed there were two equally confused posters...
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    Quote Originally Posted by Neverfly View Post
    Ok, look- both of you. He's trying to get accurate information for his Science Project. Do not go confusing it with confounding posts.
    Seriously.

    And AbhiKap55, do your job. Research and read the information in the links. If you do not understand something particular, feel free to ask for some tutoring.
    Thanks, and yes, I shall read all the things and research
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    Quote Originally Posted by PhDemon View Post
    It is not dust or particles that scatter the light to give the blue colour, it is actually the gas molecules in the air. If it were dust or particles there would be a lot more variation in sky colour with haze and humidity than is observed.

    Blue Sky - Why is the Sky Blue?

    is a good general introduction.
    I was responding to why at dusk or dawn the sky can appear orange.
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  29. #28  
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    actually nf the sky appears orange because the volume of air(gas molecules) the light must pass through to get to the observer is increased. This therefore increases the amount of rayleigh scattering and limits the visible light to bands of longer wavelength ie orange
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