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Thread: Why are pictures of the sun yellow?

  1. #1 Why are pictures of the sun yellow? 
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    As I understand it, the sun gives off all the electromagnetic spectrum, the one we are able to see being the visible light part.
    So what we 'see' is the sun giving off white light. Its obviously not yellow light (or else the light coming to the earth would be yellow), or any other colour, but white light?
    Then if the sun is giving off what light, and what we perceive is the visible spectrum, shouldn't the sun be white and not yellow?
    In all the pictures from telescopes, documentaries, the sun is always yellow...
    But if it gives off white light, shouldn't the telescopes see it as white?
    If the sun was yellow, it would mean the light coming off it would be yellow, since it is what we see...
    I'm confused, and none of my high school teachers can answer this, please help [/u]


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  3. #2  
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    http://en.wikipedia.org/wiki/Sun
    The Sun's color is white, although from the surface of the Earth it may appear yellow because of atmospheric scattering.[12]


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    That's not the answer I'm looking for, or maybe I just don't understand.
    I already googled that stuff, which is why I'm here
    Telescopes in space, largely uneffected by atmospheric distortion, see the sun as yellow? Documentaries, others, see the sun as yellow?
    Should they not see the sun as white? Yet it seems like a giant ball of fire in all the NASA videos from their spacecraft.
    And if the sun is white, as you kindly quoted from wikipedia, why are they labled as 'yellow' suns? E.g. blue sun red suns etc...
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  5. #4  
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    Most of the photos you will see of the sun, taken from space, will be in specific frequencies. In other words, seen through filters.
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  6. #5  
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    The sun is a G2V star: a yellow dwarf. It gives of more radiation in the yellow part of the spectrum than any other. It is yellow.
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  7. #6  
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    Its because of the Suns temperature:
    http://www.universetoday.com/guide-t.../yellow-stars/
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  8. #7 good question 
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    It's not easy to find a right answer. That is what makes it nature and mysterious
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  9. #8  
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    @ Ophiolite: If the sun is YELLOW, then should not the light being cast on earth be YELLOW. ?
    I compare it to a lightbulb with a yellow covering; the light being given off will be yellow.
    If the sun also gives off light, and is yellow, would not the light being cast on earth be yellow, not white?
    Yellow cannot become white, as far as I know...
    If it is yellow, our eyes see things through light, so we would indeed see the sun as yellow, but it is WHITE light that is being given off; therefore, should not the sun be white?
    I am so confused -_-
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  10. #9  
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    Let me cut through this bulldust.

    No, the sun is not yellow. Compared to some stars, it has more yellow in it than some other stars, but in absolute terms, it is not yellow.

    If you are silly enough to look directly at the sun, it is white. And in fact, its light is that combination of frequencies that we call white.

    Sometimes, however, we can perceive the sun to be yellow. In the early morning and late evening, that is due to refraction of the sun's light by the atmosphere. At other times, it is an artifact of our vision.
    http://www.astronomycafe.net/qadir/q819.html
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  11. #10  
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    THANK YOU VERY MUCH SIR!
    Jeese :P
    Now, next main question:
    Why do nasa telescopes/spacecraft in space, outside earth's atmosphere, see the sun as orange/yellow/giant fireball?
    I don't think its filters...or is it? Can anyone confirm that...
    Should not the cameras see it as white? In space?
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  12. #11  
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    Just to clarify my point. Our sun compared to other stars is often described as 'yellow'. This just means that it has a little more yellow in its spectrum than other stars. To our eyes, the direct light of the sun is white.

    There are, of course, red giant stars like Betelgeuse, and hot blue giants like Sirius. They have spectrums with more of those colours, due to different temperatures. Betelgeuse is cooler and Sirius is hotter compared to our sun.

    When scientists photograph the sun directly from satellites, they can make it any damn colour they like, depending on both spectral and digital filters. Also on which wavelength it is photographed in.
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  13. #12  
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    There is nothing like absolute white. You will see many different spectra as white, color perception is adaptive.
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  14. #13  
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    Alright, thanks a lot guys
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  15. #14  
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    Quote Originally Posted by skeptic
    Let me cut through this bulldust.

    No, the sun is not yellow. Compared to some stars, it has more yellow in it than some other stars, but in absolute terms, it is not yellow.l
    Crap. Yellow (with a trace of green) dominates the wavelengths in the visible spectrum. It is yellow. A yellow car is also reflecting light that is green and blue and red, just not that much of it.

    The sun has a B-V index of 0.656. If you are going to talk colour when you talk of stars then that makes it yellow.
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  16. #15  
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    Ophiolite

    If you let direct sunlight land on anything that reflects all wavelengths diffusely, we will see that object as white. eg. a sheet of white paper.

    Now I agree with you that in scientific terms it is proper to describe the sun as yellow. In terms of what our eyes see, though, it is white. I believe the OP was talking about human perception - not about astronomical classifications.
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    Yep, was talking about human perception, and I figured that space cameras would generally take pictures the same way cameras down here do
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  18. #17  
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    Quote Originally Posted by skeptic
    Now I agree with you that in scientific terms it is proper to describe the sun as yellow. In terms of what our eyes see, though, it is white. I believe the OP was talking about human perception - not about astronomical classifications.
    Then I apologise, for I have still not been clear.

    1. In the past astronomers would refer to the sun as a yellow dwarf.
    2. I did an extensive search of recent peer reviewed literature on the sun and could find almost no instances where it is now described as yellow. For astronomers of today yellow is inappropriate to describe a colour that is not monochromatic. Today astronomers prefer the use of the colour index, where the colour is expressed as the difference between the intensity of light detected using two of three filters, either U (for ultraviolet), B (for blue light) and V (for greenish/yellow light). This places the definition of colour on an objective, readily measurable scale.
    3. The sun looks yellow to me. (Fortunately as I am currently in Houston rather than Scotland I can actually see the ruddy thing. [In describing it as ruddy I am not implying that it looks red, except at sunset.])
    4. It appears that the sun looks yellow to TPhaoimnaes, since he says "...shouldn't the sun be white, not yellow?".
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  19. #18  
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    We see the sun through an eye, which doesn't let through nor translates to the brain non visible light and the light they feel just as skin in the way skin does.
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    http://www.nasa.gov/worldbook/star_worldbook.html
    If you look carefully at the stars, even without binoculars or a telescope, you will see a range of color from reddish to yellowish to bluish. For example, Betelgeuse looks reddish, Pollux -- like the sun -- is yellowish, and Rigel looks bluish.
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    You're overlooking the obvious!

    Almost no astronomical photos are taken using visible lights spectrum, they use Infrared, or ultraviolet, not visible light.
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  22. #21  
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    Quote Originally Posted by zazzerak
    You're overlooking the obvious!

    Almost no astronomical photos are taken using visible lights spectrum, they use Infrared, or ultraviolet, not visible light.
    Err, no. In particular the HST operates mostly in the visual light spectrum, with some extension into the near infrared.
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    Don't shoot me down here, I'm just expressing some puzzlement over various observations and things that I have read over the years.

    1) When you project the Sun's image through a telescope on to a piece of card or paper, does the image appear completely white or can any yellow be detected at all?


    2) I once read, can't recall where though, that a great deal of the Sun's apparent yellowness is an illusion brought about by the way that the eye perceives a very bright white light source against the backdrop of the sky. The article I read even suggested that we were pre-conditioned from early childhood to perceive the Sun as yellow, which reinforces the illusion. I've no idea if this was a psuedo-science article or flat out nonsense - it was maybe a decade ago that I read this.
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  24. #23  
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    Zwirko:

    2)Our eyes automatically accomodate to perceive daylight as white. Daylight consists of sun and diffuse light from atmospheric scattering. The diffuse light is blue and complementary to blue is yellow. So no, it is not pre conditioned, the sun indeed looks yellow.
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  25. #24  
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    Isn't that what I was saying? The Sun is white, but it looks yellow due to the way our eyes and brain work? Perhaps my use of the word "illusion" was a mistake.

    I think the preconditioned part in the article I was reading was referring to the way that young children always draw the sun as a big yellow blob - even though I doubt any of us have actually seen the Sun look that way. This, it was suggested, reinforces the perception of yellow in later life. In effect, making the Sun more yellow than it should be. As I said, though, that article could've been pure nonsense.

    If you look at the Sun at noon, to my eyes (which may be faulty), it definitely looks white. It becomes more yellow the more you look though.
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  26. #25  
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    If you look at the sun at noon, I trust you take precautions! It can blind you.

    A good method is to poke a very tiny hole in a sheet of tin foil, and use that as a pinhole camera to project the sun's image onto a sheet of clear white paper. Do not look directly at the sun.
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  27. #26  
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    Quote Originally Posted by Zwirko
    Isn't that what I was saying? The Sun is white, but it looks yellow .
    No. It's yellow. Yellow. Y E L L O W.
    You could, if you prefer, say it is yellowish, but it is not white.

    It's yellow.


    Did I mention it's yellow?
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  28. #27  
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    Did I mention that it's white?

    Why, if it's so clearly yellow, does it appear white when its image is projected on to a piece of card through a telescope? Why does it appear white when you actually take the time to look at it when it's directly overhead? Why does it become yellow the more you look at it?





    The Sun's intrinsic colour IS white. It appears yellow due to atmospheric effects and the because of the way the human visual system works. The Sun isn't classed as a G2V yellow star because it is a nice yellow colour. If you wanted to split hairs then you could describe the Sun as green, since it emits more green light than it does yellow light.



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  29. #28  
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    Quote Originally Posted by Zwirko
    Doesn't this chart imply that it is predominantly yellow? Yellow light is light with a wavelength of 570580 nm, and that looks to be the place where the curve reaches its highest point.

    http://en.wikipedia.org/wiki/Yellow
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  30. #29  
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    To me, it looks like the peak is in the green at around 500 nm. It's probably closer to blue, so call it greeny-blue or something. A bad graph I confess, I was being lazy and grabbed one of the first I saw.

    But the point is, is that the emission is fairly broad over the entire visible spectrum - this is the reason the sun is white.
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  31. #30  
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    I don't have a final answer myself, but I could add a few facts that should be considered in the discussion. The surface (effective) temperature of the sun is around 5780 K (5778 K is the most often quoted value). If you apply Wien's displacement law, this corresponds to a black body radiation continuum spectrum with its maximum being at 502 nm. What colour this corresponds to is not a physical question, but rather a physiological one. If the scattering effect at the terrestrial atmosphere is neglected (it is most efficient for the blue part of the spectrum, i.e. this section is removed before the light reaches the eye) the spectral response of the eye is as follows:



    As you can see, 500 nm is roughly in the area that the eye interprets as green. The red and blue sensitivity is fairly the same for the human eye in that range. Now, the solar spectrum is not monochromatic, neither is the spectral response of the eye. The graphs demonstrates that even photons of the blue spectrum can produce a red signal. In addition, the solar spectrum is not a pure black body spectrum, but contains lots of spectral lines that arise from the solar atmosphere producing the peak left of the black body peak (blue).



    Furthermore, the true solar spectrum also has a deficiency in the far blue range when compared to the black body spectrum, which also changes the total reception of the colour of the sun slightly by shifting it effectively to the red side.

    The initial question is often condensed to "Why are there are no green stars?" The answer to this is that the eye mixes all spectral signals to something that is at least close to white. If you look very closely to the spectral response graph of the human eye, you see that its sensitivity for blue contributions sharply ends in the 500 nm range, while the green and red response extends far into the "red" part of the spectrum. Maybe this is a reason, why the sun can appear as yellowish.
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