# Why is the colour of sunlight yellow?

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?

• 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
• – Sklivvz 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
• 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
• 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

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.

• 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? – Schrödinger's Cat Dec 29 '12 at 18:10
• 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
• @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
• @FrankH If sunlight is yellow, why are the Lunar photographs such as taken by the Apollo astronauts and others all white? Those are colour photographs! I agree that physically, the Sun is a "yellow" star, but the blackbody spectrum looks pretty close to white to the naked eye. The Sun after filtered through the atmosphere (in particular at large zenith angles) is much yellower than the pure sunlight. For looking yellow on Earth, the dominant effect is the atmosphere, not the blackbody temperature. – gerrit Oct 20 '17 at 10:48

I think this is because of the temperature of the earth.Stars with less temperature are red in colour as visualized by us. stars with higher temp. than sun are blue. however it is actually white

• Did you mean to say, "because of the temperature of the Sun? – Solomon Slow Oct 13 '15 at 17:17

It's not. It's white.

At least, most of the time it's white. When the Sun is near the horizon, and its light is passing through ~2000km of atmosphere rather than through only ~20km, then the blueish end of the spectrum is scattered out, and the Sun looks reddish/yellow.

But when higher in the sky the Sun looks white. We just don't look at it.

Check the colour of the Moon (which is just reflecting the Sun's light) in the sky during the day or night to confirm.

Images of the Sun, whether by crayon or telescope/camera, are coloured yellow because that's what we expect to see.

(It's not pure white as in an equal intensity at every visible frequency - there's a flattish peak around green light and it tapers away quickly towards UV and much slower towards IR.)

• The sun is not white, it is yellow. It is a G class star. All G class stars are yellow. White stars are A class. – Ambrose Swasey Aug 31 '17 at 18:16
• It's basically white, alright. One cannot stretch facts. – Cosmas Zachos Aug 31 '17 at 18:57

The reason why the sun is yellow is because the color is determined by additive combination of its component spectrum.

In other words, the sun emits a range of light that we can see, from violet to red, at different intensities. To compute the net color, the color we see, you must add together the radiation. In the case of the sun, the dominant wavelengths are green-yellow-red. Those are the wavelengths with the greatest intensity and total energy. If you add green plus red, you get yellow. The sun also emits, for example, blue light, but that light is overpowered by the green and red light.

Note that this is for a human. Other creatures might see a different color. For example, cats can see farther into the red part of the spectrum than humans can. Therefore, to a cat, the sun will appear slightly more reddish orange than it appears to us.

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...

• 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.

• "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