why is the sky blue ?

Answer 1

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 colours 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 colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours 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 colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

Tyndall Effect
The first steps towards correctly explaining the colour of the sky were taken by John Tyndall in 1859. He discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. This can be demonstrated by shining a beam of white light through a tank of water with a little milk or soap mixed in. From the side, the beam can be seen by the blue light it scatters; but the light seen directly from the end is reddened after it has passed through the tank. The scattered light can also be shown to be polarised using a filter of polarised light, just as the sky appears a deeper blue through polaroid sun glasses.

This is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering--after Lord Rayleigh, who studied it in more detail a few years later. He showed that the amount of light scattered is inversely proportional to the fourth power of wavelength for sufficiently small particles. It follows that blue light is scattered more than red light by a factor of (700/400)4 ~= 10.

Dust or Molecules?
Tyndall and Rayleigh thought that the blue colour of the sky must be due to small particles of dust and droplets of water vapour in the atmosphere. Even today, people sometimes incorrectly say that this is the case. Later scientists realised that if this were true, there would be more variation of sky colour with humidity or haze conditions than was actually observed, so they supposed correctly that the molecules of oxygen and nitrogen in the air are sufficient to account for the scattering. The case was finally settled by Einstein in 1911, who calculated the detailed formula for the scattering of light from molecules; and this was found to be in agreement with experiment. He was even able to use the calculation as a further verification of Avogadro's number when compared with observation. The molecules are able to scatter light because the electromagnetic field of the light waves induces electric dipole moments in the molecules.

Why not violet?
If shorter wavelengths are scattered most strongly, then there is a puzzle as to why the sky does not appear violet, the colour 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 coloured 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 colour 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 colours we see.

When we look up at the sky, the red cones respond to the small amount of scattered red light, but also less strongly to orange and yellow wavelengths. The green cones respond to yellow and the more strongly-scattered green and green-blue wavelengths. The blue cones are stimulated by colours near blue wavelengths which are very strongly scattered. If there were no indigo and violet in the spectrum, the sky would appear blue with a slight green tinge. However, the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge. The net effect is that the red and green cones are stimulated about equally by the light from the sky, while the blue is stimulated more strongly. This combination accounts for the pale sky blue colour. It may not be a coincidence that our vision is adjusted to see the sky as a pure hue. We have evolved to fit in with our environment; and the ability to separate natural colours most clearly is probably a survival advantage.

Answer 2

We have all wondered, at some point, why the sky is blue. Now is the time to find out - after all, someday your kids will probably ask YOU why the sky is blue! Ready?

The light that comes from the Sun is white. That white light is actually a mixture of all colors, but because they are mixed up we don't see the separate colors just the white sunlight.

As the sun's light passes through our atmosphere, the light becomes scattered by all the air and particles such smog and dust. The part of the sunlight that gets scattered the most is the blue part. That means that the blue gets separated from the other colors and we get a blue sky!

At sunset or sunrise, the sun is at a very low angle, so the rays pass through even more molecules and particles. This scatters the light even more, separating red, orange and yellow from the white light. The more particles, the more scattering.

I hope this helps. :)

Answer 3

Ordinary light is made up of seven colors. We see each of these colors only if they are reflected by something or split off in some other way. For example, leaves reflects green light and absorbs all other colors. Black absorbs all the the colors. White reflects all of them. When sunlight hits earth atmosphere, blue light is scattered by the air and it appears that the sky is blue.

Answer 4

It's is due to an effect called Rayleigh Scattering.

"It occurs when light travels in transparent solids and liquids, but is most prominently seen in gases. Rayleigh scattering of sunlight in clear atmosphere is the main reason why the sky is blue."

Answer 5

there are tiny particles of matter in the atmosphere, as loght from the sun bounces off of them light is refracted. the particles absorb some colors and not blue. this leaves the light that we see from them blue
god had nothing to do with it

Answer 6

The atmosphere is about 20% oxygen, 80% nitrogen. Nitrogen does not absorb visable light; oxygen does and this give it the blue color.

Answer 7

Why is the sky blue?
Why is water red?
Why did Judas rat the Romans while Jesus slept?

-GZA

Answer 8

as light filters down through the different layers of the atmosphere that's the color we see.

Answer 9

Because the all knowing and warmly loving god has provided us a comforting and relaxing backdrop for our lives.

Answer 10

thats the color chosen by God