Why is the sky blue?

Question

This has always puzzled me :)

Answer 1

Blue light is scattered the most by the molecules in the atmosphere, hence that is the dominant color. The effect is called Rayleigh scattering.

More specifically, the higher frequencies of light (or light with shorter wavelengths) are more prone to scattering than light of lower frequencies (or longer wavelengths). In the span of the visible spectrum, red has the longest wavelength and violet has the shortest wavelength, with blue being just slightly longer than violet. So why isn't the sky violet then? Several reasons -- the intensity of violet light from the sun isn't as strong as blue light, violet light is more absorbed in the upper atmosphere, and our eyes are tuned in to "seeing" blue much better than seeing violet.

Answer 2

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 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.

Answer 3

The sky is blue due to an atmosphetic effect called Rayleigh scattering - certainly not because its reflecting the ocean which people sometimes say! Rayleigh scattering involves the scattering of light by molecules smaller than the wavelength of light. It has a smaller effect on colours with longer wavelengths and that is why the sky is blue - and also in fact why the sun is yellow - if you added up all the blue tint in the sky and focused it in the area of sun you would get its actual colour of bright white, which is what you’d see in space.

Physicists used to say that Rayleigh diffraction was responsible for the reddish tint in sunrise and sunset because the light had to travel through more atmosphere to reach us however this is currently disputed and there is another optical theorem at work called 'Lorenz-Mie theory'.

http://science.howstuffworks.com/question39.htm
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
http://www.exo.net/~pauld/physics/why_is_sky_blue.html

Kind regards.

Answer 4

Its been asked many times.

The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.

However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue

Answer 5

The sky appears blue because of Rayleigh scattering as others have said but red light is not scattered! The reason the sky doesn't turn (through mixtuires) is that light from the red end of the spectrum is absorbed not scattered as previously stated.

Answer 6

This must be the most often asked question, apart from the meaning of life!

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 polarised 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.

Answer 7

It's because of Raman Effect..When a beam of light traverses a dust-free, transparent sample of a chemical compound, a small fraction of the light emerges in directions other than that of the incident (incoming) beam..here light is scattered by the sea .. hence the sky is blue..

Answer 8

Rayleigh scattering. This question is asked two or three times a day, why not look back through a few similar questions to find out what Rayleigh scattering is?

Answer 9

Maybe it isn't really blue, just a little depressed from watching us make a mess of what is left of our once was wonderful world! I am amazed at the depth of blue from such places as Annapurna Sanctuary, Nepal - its blue blew me away!

Answer 10

The reason the sky is blue is because of the Ozone Layer, the sky is blue because the Ozone layer has a tint of blue.