Why is the sky blue?

Question

I hheard some mumbo jumbo that its an optical illusion bt i want 2 hear opinions.

Answer 1

It's due to a phenomenon called Rayleigh scattering. When light encounters particles much smaller than the wavelength of light, the light scatters. Atmospheric gas is an enormous resevoir of such particles. Short wavelengths scatter the most effectively, and blue has a short wavelength, so the blue light scatters and appears to fill the sky. Note that violet has a shorter wavelength than blue, but the human eye is not very good at seeing violet, so blue appears to dominate instead.

Answer 2

The real answer is Raman Scattering. The sky is blue due to Raman Scattering from the Oxygen molecules. This is a Quantum Mechanical Effect due to the energy with which electrons are bound in the Oxygen molecule and the specific vibrational states that are available to them. There happens to be a resonance between the frequency of the blue light and the blue light is scattered much more easily than the other "frequencies" of the spectrum.

Basically the electrons are free to vibrate at the frequency of the blue light, so the blue light is was scatters.

There are several other effects that do cause color effects, which are not responsible for the blue sky. Diffraction is responsible for the red and orange color of the sunset, and the shift in color but is not responsible for the blue sky. Paints and dyes work by absorbtion, but that is not what causes the blue sky.

The Suggestion that Rayleigh Scattering is responsible for the blue sky seems to be pervasive on the web, including the hyperphysics site and a NASA atmospheric sciences site. Rayleigh scattering does apply to colloids, suspensions of particals which are very large compared to molecular dimensions, but still microsopic.

This is where we get to roll up our sleves and learn how the think like a physicist. If we look a the equation for Rayleigh Scattering on Wikipedia, It calls for an n or index of the scattering partical. for Air n is essentially 1 and that n^2 -1 will be very close to zero. Also the equation calles for a diameter of the scattering partical which is the partical was the oxygen atom you would have an value of 10^(-10) to the 6th power or 10^(-60) now, that gets divided by the wavelength to the forth power which for visible light is on the order of (10 ^ -7) and to the fourth power gives (10 ^-28) the ratio of d^6 / lambda ^4 gives (10 ^-32) which is a very small number, Even though sunlight is quite bright, the intensity of sunlight times the factor to ( 10^ -32) would be total darkness. If Rayleigh scattering were responsible for the blue sky, the sky would be black. A key point to take home here is that Rayleigh scattering requires a scattering object on the order of the size of the wavelenght of light being scattered. Michael Faraday made some coloidal suspensions of gold and by very carefully getting the same size particles in each different suspension produced an array of very bright colors.

The Hyperphysics site also incorrectly attributes the blue sky to Rayleigh Scattering. (Shame on you Hyperphysics) and their equation refers to a a polarizability for the particle which is doing the scattering.

One way to understand Raman Scattering is to say that the polarizability is a strong function of the wavelength, and for a particular very narrow range of wavelength the polarizability of the Oxygen Molecule is 10,000 times higher than at other wavelengths, so that particular color of light is strongly scattered by the atmosphere.

Another way to see that the sky is blue due to a Quatum Mechanical Raman Scattering Effect and not a classical Rayleigh Scatteriing is to realize that the blue of the sky is very nearly monochromatic. Its essentually one pure color, not a range of colors.

Answer 3

It is not an optical illusion. Visible light is made up of different wavelengths. Each wavelength has its own colors. The same colors are the rainbow. A rainbow comes from the wavelengths of light being split up (like a prism) by the droplets of water molecules. Blue is the shortest wavelength of light and is scattered by the particles in the atmosphere, therefore the sky is blue. The sunset is red because the sun is setting and light has much more atmosphere to travel thourgh (because of the angle), the blue wavelengths are scattered before they reach us. We see red because red is the longest wavelength of light.

Answer 4

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. The white light from the sun is a mixture of all colors of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colors and so form a spectrum. The colors of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of color receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our color vision

Answer 5

Not again!
Sorry but I have answered this about 10 times already.
Brief summary, light is scattered by the air and shorter wavelengths (bluer) light is scattered more so when you look across a beam (I.E. up) that is what you see. If you look along the beam (into the sun) you see reddish light because some of the blue is missing.

Answer 6

At noon, directly over head the sun would effect the darkest blue because the ring of earth's atmospheric vapor at that angle is at it's thinnest and most transparent and ..."It's darkest next to the light and lightest next to the dark."

The dark sky color is Ultramarine Blue, an equal mix of Cyan and Magenta pigments.

The average color of the sky is the mix of Ultramarine Blue and Cyan (Thalo Blue) pigments. This color mix is equal to the pigment Cobalt Blue with all it's tints.

Pure Cyan "Phthalocyanine" Blue tints appear in the lower third of the sky. Magenta and yellow are diminished by atmosphere.

The color of water is physically present in the atmosphere, we are looking through small water molecules that are dispersed by gasses in air. This blue transmitted light filters out the opposite color yellow light so we see a blue sky as opposed to a black one. This light blue color of water molecules in the air will filter out all other colors given enough distance. From space the atmosphere looks like a blue ring around the earth, mountains in the far distance are filtered through air and appear blue.

Clear water given enough depth will appear blue, clear glass given enough depth will appear blue green.
Clear air given enough depth will appear blue as sunlight passes through water molecules.

Seeing more atmosphere toward the horizon line will remove more Magenta from the Ultramarine blue and lighten the sky to Cyan.

We can see the effect of the atmospheres color and filter properties in any distant mountain. The light blue translucent vale of atmosphere absorbs color, turning shadow colors tints of blue and light colors higher tints with blue added.

The shadow color on the closer mountain becomes blue first than the whole mountain if it's far enough away.

This effect starts 10 yards away from you. The artist can see the color shift in that distance and will categorize two to five different concentric plains or rings in each picture. The colors values in each group are not interchangeable.

Answer 7

It is caused by the diffusion of sunlight which is caused by the atmospheres tendency to split the light into its component colours. Our particular mix of gases causes an overall effect of blue different gas mixtures would result in different shades or colours

Answer 8

Well the ozone layer diffracts any solar radiation and because of this, it only reflects blue light. This is cause by the heat radiation of the ultra-violet light from the sun.

Answer 9

The atmosphere around our glob makes the sky seem blue.
I have no more time to explain it.

Answer 10

It's the Ozone layer, which is blue, that gives the 'sky' its colour.