Why is the sky blue?

Classical Mechanics Level 1

The color of ozone in the stratosphere is blue. Blue is faster than other colors, and thus our eyes receive more blue photons. Blue has a shorter wavelength than other colors, and thus scatters here and there. The red color of the sun makes us perceive the sky as blue as a relative effect.

6 solutions

Ishan Mishra
Jul 13, 2015

Sunlight is essentially white light, composed of all the different colours (including the visible spectrum VIBGYOR).

When this sunlight passes through the Earth's atmosphere, the air & gas molecules in the air cause light to scatter. The colour blue is scattered more than other colours because it travels as shorter, smaller waves, and thus the sky is blue during most of daytime.

That is a partially true answer and it is the one you find all over the web. The true reason that blue is the predominant color above us is that Oxygen (the major component of the air we breath) does not absorb blue light. You can say it is because blue light has a shorter wavelength but that does not explain why it scatters. There many are other elements and/or compounds that do absorb blue light that do not appear in our upper atmosphere, but if they did our sky would most assuredly would not be blue. Everything you look at is not actually a color but the reflection of a color because that item does not absorb that particular wavelength of light.

Robert Shaw - 5 years, 10 months ago

Oxygen IS NOT the major compound of the air we breath. Nitrogen (78% of the air) is the major compound.

Sebastian Bernal Gallo - 5 years, 10 months ago

wavelength is REALLY STRONGLY relevant to scattering as the scattering chance depends upon wavelength to the FOURTH power. That's why there's such a strong distinction between blue and red given that the spectrum places them really close together.

adam keller - 5 years, 10 months ago

Wavelength of the color violet is shortest, but we can not see the sky as violet . Why?

Mahmudun Nabi - 5 years, 10 months ago

"If shorter wavelengths are scattered most strongly, then there is a puzzle as to why the sky does not appear violet, the color with the shortest visible wavelength. The spectrum of light emission from the sun is not constant at all wavelengths, and additionally is absorbed by the high atmosphere, so there is less violet in the light. Our eyes are also less sensitive to violet. That's part of the answer; yet a rainbow shows that there remains a significant amount of visible light colored indigo and violet beyond the blue. The rest of the answer to this puzzle lies in the way our vision works. We have three types of color receptors, or cones, in our retina. They are called red, blue and green because they respond most strongly to light at those wavelengths. As they are stimulated in different proportions, our visual system constructs the colors we see."

{Obtained from the website: http://www.math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html.}

Lu Chee Ket - 5 years, 8 months ago

I'm guessing every science class I ever had was wrong, I've always learned the sky was blue because:

Water droplets in the air, water is blue, light also defracts, or refracts, when going through a medium. So, the blue light put off by the water droplets, spreads across the sky, but I guess that's incorrect?

After further research, I either explained it more in depth, or the rest of you commonly accept something I'm missing, the reason it picks up blue light specifically, is because of water in the air, which is why it is the color blue, if it were leaves in the air, it would be green.

So, either way, the answer is not complete.

Specifically blue, because: Water molecules in the air.

Michael Crane - 5 years, 9 months ago

"A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colors because the blue light has been scattered out and away from the line of sight."

{Obtained from the website: http://www.math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html}

Lu Chee Ket - 5 years, 8 months ago

Response to Lu Chee Kat:

But like I said, it's specifically because of the water molecules in the air, the question is "Why is the sky blue?" And the answer mentions nothing about the water molecules in the air, I mean, it's not just because light because scatters, the question is WHY BLUE? Because of WATER?

Michael Crane - 5 years, 8 months ago

@Michael Crane – The cartoon at http://www.math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html shows how we see a far sky near the "sight border" of sky and sea level. Thickness of water probably droplets as you meant should be more significant, yet we see pale blue, yellow or even red according to position of the sun. This suggests for how the light is scattered or directed rather than a layer of color filter inserted before our sight.

Lu Chee Ket - 5 years, 8 months ago

The scattering answer is not scientific. It is more reasonable to say we are seeing blue reflected off particles. in the atmosphere. It makes the answers misleading. This would be more in harmony with spectronomy. which is the study of light reflected from various gasses. or distant galaxies. Surely redshift galaxies are not red because it is the longest wavelengths. that is scattered here and there. That would be nonsense.

Gray Matter - 5 years, 10 months ago

The sky is generally not absorbing any light but scattering it. Blue scatters at greater possibility due to the shorter wavelength of blue vs red. the scattering chance goes roughly 1/λ^4 so the small change in wavelength in the visible spectrum causes a huge change in what scatters. This also explains why sunrise and sunset is red. you are viewing all the photons that managed to not scatter much which is the white light of the sun minus the blue end.

adam keller - 5 years, 10 months ago

Response to Gray Matter also: No, I'm the the band wagon of scatter being about as scientific as it gets, I'll try to paint a better picture, think about when light goes through a prism, water molecules in the air, to a degree, are the exact same concept, sunlight is coming across the sky, and it's scattering through water droplets. Butt they could really make the solution to this a lot better, the wording is just horrendous.

Michael Crane - 5 years, 8 months ago

Michael Mendrin
Jul 13, 2015

Either it's because of Rayleigh Scattering or the sky is just having a bad day.

Blue days/All of them gone/Nothing but blue skies/From now on ....

Brian Charlesworth - 5 years, 10 months ago

now that's a real answer! Upvote Infinity!

Lukas Loskot - 5 years, 10 months ago

Jerby Cristo
Jul 16, 2015

Nitrogen and oxygen are most abundant in the earth's atmosphere and they scatter most of the colors with very high frequency such as violet and blue. But our eyes are not sensitive with violet so our retina receives much of frequency of light equivalent to blue color that's why the sky appears to be blue in our sight.

Are you meaning that our eyes can not see violet?

Sazzad Hossain Khan - 5 years, 10 months ago

Ribhav Johar
Nov 6, 2015

We see sky as blue because blue colour has shooter wave length and one of the main reason that we see colour all around us is because all the other colour are absorbed and the colour which we see is colour reflected

Mahesh R J
Aug 1, 2015

Exactly blue colour has shorter wave length and in atmosphere o2 wont absorb the blue colour

Hadia Qadir
Jul 21, 2015

because blue has shortest wavelength than other colors that's why scatters here and there . we see sky in blue color

Violet and Indigo has shorter wavelengths, isn't it?

Sazzad Hossain Khan - 5 years, 10 months ago

thank you for pointing out my mistake I just wrote down very quickly . I've explained below as you can see . Best Regards . Hadia

Hadia Qadir - 5 years, 10 months ago

Write a comment or ask a question...it is the reflection of the sea

Arvind Manwati - 5 years, 10 months ago

Why is the sky blue?

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