why is the sky blue?

Answer 1

It's grey here today...

Answer 2

My standard answer to this question, using as little physics as possible:

The correct answer is that the blue light is scattered by the air molecules in the atmosphere (Rayleigh scattering, or the Tyndall effect), and that the blue light is scattered more, because the scatteing varies with the inverse of the fourth power of the incident wavelength. OK, but I've known science graduates who don't understand this.
Here's my attempt at an answer without too much physics:

I think most people know that sunlight is made up of light of several different wavelengths, and can be split up into the colours of the rainbow. Blue light has the shorter wavelength, and red the longest wavelength.

When sunlight hits the molecules in the atmosphere, the light gets bounced around by the molecules (what actually happens is that the light strikes the molecules and is absorbed, causing the molecules to vibrate and give off, or 're-emit' the lightt; but 'bounce around' is close enough).

Because the blue wavelength is shorter and more energetic, it reacts much more with the air molecules than the red and yellow wavelengths; which tend to pass straight through. Because the blue radiation is re-emitted from the air molecules in all directions ('scattered'), it seems to us looking from the ground that the blue light is coming from everywhere; hence the sky seems blue.

Near sunset, because of the low angle of the sunlight, we see more of the red and yellow wavelendth passing straight through, hence the colours of the setting sun.

BTW: The sky isn't blue because of a reflection of the sea; its the other way round, although the colour of the sea is also due to the scattering effect of the water molecules. This also gives the intense blue colour to ice, if we look down a crevasse in a glacier.

Answer 3

The sky appears blue because of the light from the sun is scattered by small particles in the atmosphere.The amount of scattering depends upon the wavelength .Accordingly the blue light which has the lowest wavelength in the solar light spectrum is scattered the most.So the sky looks blue.This also explains why the sky is red at sunset.The light has to travel through more atmosphere before it reaches us, at the time of sunset.So the blue light is completely scattered away by that time and only the red light remains.

Answer 4

It's due to the scattering of sunlight off of molecules in the atmosphere. The shorter wavelengths of light (blue) scatter more than the longer wavelelngths (like red). So the blue light bounces around in the atmosphere making a blue background while the other colors tend to come more directly to the ground.

Answer 5

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.


More.

Answer 6

When the white light from the sun passes through the Earth's atmosphere, a fraction of any given frequency is scatterd off of particles in the atmosphere. The higher the frequency of the light the more likely it is to scatter. Blue light is pretty much the highest frequency of visible light. When the sun's light has to pass through a greater portion of the atmosphere, a greater portion of the blue light is scattered and the light coming directly to your eye looks reddish, sunrise and sunset are such times.

Answer 7

red light has the shortest wavelegnths, so when the sun in up, the red light quickly scatters and the blue light is the only light that is visible. violet light is hard to see against the blue, so when the sun is setting, all the red light comes out, the blue scatters and the dust reflects the short wavelength light turning the sunset beautiful and red.

Answer 8

. It is the water that reflect to against the sky. The earth is 70% water, if the earth was 70 dry land , we probiply would have have a green or brown sky

Answer 9

refraction of light from the sun in the upper atmosphere - I forget the exact details after many years; check a high school physics text

Answer 10

Rayleigh scattering

Answer 11

Old question.

Rayleigh Scattering

http://en.wikipedia.org/wiki/Diffuse_sky_radiation