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I was going through the preliminary papers of other schools and found a question that I did not know. It was "Why sunlight appears yellow?". Can anyone answer it?

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Well Hi Pranit. Your personal info could be added to your about me section of your profile. Atleast try not to add them to your posts. And, one more thing - Questions like these could be easily googled :-) –  Waffle's Crazy Peanut Dec 27 '12 at 10:02
    
related: physics.stackexchange.com/q/17/66 –  Ebenezer Sklivvze Dec 27 '12 at 10:55
    
@CrazyBuddy I tried googling but did not find any satisfactory results ..... because I could not understand the bombastic words used .... I want the answer in simple words ... And that is the reason I mentioned my age. –  Pranit Bauva Dec 27 '12 at 16:56
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The key word is indeed "appears" because "color" means one thing to astronomers and another thing to physiologists. They are often used interchangeably but this leads to many misconceptions. Of the answers given below, Sachin is the most correct. –  user11266 Dec 27 '12 at 21:55
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Take a piece of white notebook paper outside during daylight. It looks white because it recombines the sunlight that comes through our atmosphere with the scattered blue from that sunlight. If Sun were yellow, then white paper would look yellow not white. –  user11266 Dec 29 '12 at 3:52

3 Answers 3

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Color of Sunlight as seen on Earth's surface during day is yellow due to Rayleigh Scattering.

Our Sun is actually white (mixture of all wavelengths of visible spectrum) if we see it from outer space or high-altitude airplanes. Our atmosphere scatters shorter to bigger wavelengths color from sunlight when the white light travels through it. During day, it scatters violet and blue colors leaving yellowish sunlight (the reason why sky is blue and sunlight is yellow). During morning and evening, the sun appears reddish because light rays needs to travel longer distance in atmosphere which causes scattering of yellow light too.

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It is not scattering. The solar spectrum is close to a black body spectrum at a temperature of 5000 degrees which happens to have a peak near the yellow to orange part of the visible light spectrum. Sun light is not white - it is not a uniform equal intensity at all visible wavelengths. Scattering may push the yellow-orange closer to yellow by the time we observe it on the earths surface. You are right about the blue sky and redder Sun at sunrise and sunset. –  FrankH Dec 29 '12 at 17:54
    
@FrankH It doesn't matter having a peak near the yellow to orange part of the visible light spectrum, the sunlight is white. Do you have citations claiming sunlight is yellow without scattering? –  Sachin Shekhar Dec 29 '12 at 18:10
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Seriously? Everyone know white light has uniform intensity across the spectrum, colored light has a peak at a particular frequency. Black body radiation has a peak. What else do you need to know? –  FrankH Dec 29 '12 at 18:43
    
This is the perfect answer which I think correct .... and this is in our syllabus also! –  Pranit Bauva Dec 30 '12 at 8:39
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@FrankH There is no "THE peak" because where "THE peak" lies depends on how the spectrum was dispersed. See my comment below. The peak at 550 nm (or somewhere thereabouts) doesn't exist if you disperse the SAME spectrum with a prism. In the visible spectrum, the eye physiologically "squishes" the various colors together and Sun looks white. –  user11266 Dec 31 '12 at 1:10

The reason, for which the color of sunlight is yellow, is scattering. We know that sun is perfect black body and emite radiations of all wavelengths ( Visible spectrum [VIBGYOR] and invisible spectrum [Infrared etc.]).

The frequency of blue color is high while the wavelength is short. This results in scattering of blue(including The whole VIB spectrum) color, as the atmosphere contains heavy dust particles having greater diameter then wavelength of blue color(VIB spectrum), thus resulting in yellowish sunlight. This is also the reason for why sky is blue...

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Black body spectrums do not emit equal radiation at all wavelengths. The solar spectrum is close to a black body spectrum at a temperature of 5000 degrees which happens to have a peak near the yellow to orange part of the visible light spectrum. Scattering may push the yellow-orange closer to yellow by the time we observe it on the earths surface. You are right about the blue sky. –  FrankH Dec 29 '12 at 17:56

Our sun's surface temperature is about 5000K, which corresponds to a peak in the spectrum in the wavelength of yellow visible light.

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"Color" as used by astronomers is not the same as "color" perceived physiologically. The "peak" has absolutely no unique physical significance. It position in the spectrum depends on how the spectrum is dispersed. If dispersed with a grating, it lies at about $550\;\mathrm{nm}$. If dispersed with a prism, it's out in the infrared at about $810\;\mathrm{nm}$. Much has been written in the literature about this problem, but see the recent paper by Marr and Wilkin in AmJPhys 80 (5), p. 399. See also paper by Heald in AmJPhys 71 (12), p. 1322. –  user11266 Dec 27 '12 at 21:53
    
How is that of any relevance? –  WIMP Apr 6 '13 at 11:07

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