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.
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.
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.
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

To start of with we must understand what light is.

Light isnt just made up of 1 colour, it contains a number of different colours each of which has a different wavelength. Light is split up into the following colours with the first having the longest wavelenght and the last having the shortest.

Red
Orange
Yellow
Green
Blue
Indico
Violet

An easy way to rememeber this is ROY G BIV (my year 12 geology teacher taught me that about 8 years ago)

As light moves through the atmosphere, most of the longer wavelengths are able to 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 in the atmosphere which is mainly nitrogen (78%) and oxygen (21%). The absorbed blue light is then scattered in all different directions. Since you see the blue light from everywhere overhead, the sky looks blue.

On Earth, the sun appears yellow. If you were out in space, or on the moon, the sun would look white. In space, there is no atmosphere to scatter the sun's light. On Earth, some of the shorter wavelength light (the blues and violets) are removed from the direct rays of the sun by scattering. The remaining colors together appear yellow.

Answer 3

The sky is blue because of the phenomenom called the Tyndall effect. This is the scattering of light as it passes through particles in suspension. Due to its short wavelength, the elements in the atmosphere happen to scatter blue more than other colors.

So, when the sun is shining down on the earth, most of the other wavelengths or colors travel in a relatively straight line. The sun appears white because it contains almost all the visible colors. The rest of the sky appears blue because we are seeing the blue light that has been scattered by the atmosphere.

Sunsets and the sun during dusk appear as red and orange because there is more atmosphere for the light to travel through and more blue is deflected. Red is one of the longer wavelengths so it is scattered the least, thereby making the sun and sky appear more red.

Answer 4

I know that only certain light frequencies from the sun can get through, and their blue ones - I forget why, I think it might be to do with the ozone layer. Also why water is blue aswell (not ozone, but same thing with frequencies). Maybe its to do with the oxygen in the air as Ozones formulae is O3 (3 oxygens) and water is H2O (one oxygen) Probabyl wrong though.

Water is not blue because it reflects the sky as many wrongly believe.

Look on wikipedia, most questions on this site could be answered if peeps did a little research

Answer 5

The sky is blue because the light passes through the air. The wavelengths of the other colors of the spectrum are not absorbed as much by the atmosphere.

Answer 6

White light is made up of the rainbow colours; violet, indigo, blue, green, yellow, orange and red. The section of the spectrum with violet, indigo and blue lights have SHORTER wavelengths than the other end. This shorter wavelength enables these colours (violet, indigo and blue) to BEND MORE than the orange and reds.

When the sun's light hits our atmosphere, REFRACTION occurs, and light is bent. Having a shorter wavelength, the blue family bends more and we thus see the blue sky.

Similarly, in the mornings and evenings, the sun shines from the horizon and the orange and reds having a longer wavelength, do not bend and hence come straight to us, resulting in beautiful orange-red sun rises and sunsets.

Answer 7

Because the atmosphere allows bluish wavelengths to pass it. Others are just absorbed (energy-drained) in the atmosphere and don't reach to our eyes that strong.

Answer 8

Because of light reflecting off dust particles and such like

Answer 9

Click this link for Detail Answer..


http://www.squidoo.com/sky_blue/

Answer 10

It is refletion of a rainbow because blue is the strongest colour in the rainbow