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

Answer 2

The molecules which make up 99% of the earth's atmosphere do not absorb any wavelengths of visible light. Molecules in the air are not like indigo molecules which absorb red light and give blue cloth its color. Molecules in the air are not pigments. However, molecules in the air do scatter blue light more strongly than red light. This means that white sunlight has its blue components scattered to the side while its red components keep traveling straight. White sunlight bathes the atmosphere of the earth. The sky is blue because molecules in the air scatter blue to your eyes more than they scatter red.
But why do molecules in the atmosphere scatter blue light more than red? The oxygen, nitrogen, and water molecules plus the argon atoms that make up most of the air do absorb ultraviolet light, in the region of the spectrum known as UV-C. (It is a good thing they do too, these dangerous germicidal UV wavelengths from the sun are stopped by the atmosphere before they can damage you and become homicidal.) The molecules in the air absorb the ultraviolet because their electron clouds have a resonance frequency in the ultraviolet. This means that if you hit the electron clouds, for example by colliding one atom into a molecule, the electron cloud in the molecule will shake back and forth about the nuclei at a resonant frequency in the ultraviolet.

Answer 3

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 4

This question gets asked several times a day. When will Yahoo Answers get a subroutine that refers repeated questions to a previously answered section? Meanwhile, I continue to rate them as bad questions.

Answer 5

Well, I saw this cartoon.

Jesus is walking hand in hand with God.

Jesus asks, "Dad, why is the sky blue?"

God says, "Cause, I said so." (lol)

Answer 6

because the water is blue, it reflects off and makes it blue, i think

Answer 7

defraction of light through the chemicals that make up the air

Answer 8

The Ozone layer does that!

Answer 9

In London it's gray.

Answer 10

this question has been asked for many times