Why is the sky blue? Seriously!!?

Question

My grandaughter is 5 and asking alot of questions!!

Answer 1

pigments

Answer 2

Because light from the sun is scattering by atoms and molecules in the atmosphere.

Light scattering by particles depends on the relative "sizes" of the photons and the particles.

In the case of visible light, molecules are much smaller than the wavelength of light, so blue light gets scattered much more than red light.

So as light from the sun enters the atmosphere, more blue photons get reflected (not absorbed) by molecules than red photons - but then the blue photons get reflected again and again until they reach us. So the blue light comes from all over, the red light comes almost straight from the sun.

This is also why the sun looks redder at sunrise and sunset - the light's path through the atmosphere is longer when the sun is on the horizon than when it is high in the sky.

Interaction of light with the atmosphere does all sorts of weird and wonderful things that physics can explain:

http://hyperphysics.phy-astr.gsu.edu/Hba...



Or look at the many times this question has been asked before by searching for your question – I think it has been asked over 8000 times

Answer 3

Because all the other colors are absorbed by the air, and blue is left, or rejected, by the sky. In truth, the sky is all colors BUT blue!

Answer 4

This is one of the most popular questions on Yahoo, and has been asked over 8000 times.

The technically correct answer is that the blue light is scattered by the air molecules in the atmosphere (referred to as Rayleigh scattering).  The blue wavelength is scattered more, because the scatteing effect increases with the inverse of the fourth power of the incident wavelength.

OK, but I've known science graduates who don't understand what this means.

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 is absorbed; causing the molecules vibrate and and give off, or 're-emit' the light. Because the molecules vibrate in all directions, the light is emitted in all directions (called 'scattering'). 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, or get absorbed by the atmosphere (which warms the air and gives rise to the world's climate).

Because the blue radiation is re-emitted from the air molecules in all directions, and it also gets 'bounced around' from molecule to molecules in this way before it reaches us, it seems to us looking from the ground that the blue light is coming from everywhere; hence the sky seems blue. And of course; we are looking upwards through several kilometres of air; so there are plenty of molecules to scatter the blue light.

Near sunset, because of the low angle of the sunlight, the blue light has already brrn scattered away, and we see more of the red and yellow wavelendth, hence the colours of the setting sun.

Answer 5

Raleigh scattering.  Air molecules scatter sunlight's blue wavelengths more.  See http://www.sciencemadesimple.com/sky_blu... or http://math.ucr.edu/home/baez/physics/Ge...

I don't know how much of it you want to explain.

Answer 6

the sky isn't actually blue it is purple but since we see in a specific way we see blue. But it would be purple if there was no sunlight.

Answer 7

its not..Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.the shorter the wave the more powerful the colour realy. theres short strong waves then theres long lazy waves. youl notice this when u look up at the stars at night the skys still there u just cant see it. during the day when u do see the sky the stars are still there but u just cant see them because the sun is out its reflecting the light therefore giving us a blue sky effect you will also notice if u look out to the horizon the sky seems pale and almost white and not actualy blue. this is because its further from sight and we are not being blinded by the sun that is reflecting or shinning on colours that are directly around us.and id like to add that the sky isint purple lol some say its white some say tan but realy the sky is made up of nothing but gasses and molucules so it really has no colour at all if it wasnt for the sun reflecting light we probly would have never known of such sky

Answer 8

The reason for the blue color is a bit complicated, but I'll try to keep things simple.

The answer for your grandaughter:

The air consists of tiny invisible bits called molecules. Light bounces between these molecules many times, like billiard balls. The bounces of the red light don't chage it's direction of  very much, like a very heavy stone that doesn't bounce. But the bounces of the blue light change it's direction very strongly, like a bouncing ping-pong ball. These bounces are called scattering. If you look into the sky then you see all the blue light that bounces in your direction. You don't see the sky red because the red light from the sun does not bounce as much and does not reach you as easily as the blue light.

Then you can explain the red sky at sunset, if she asks why the sky at dawn/sunset is red and not blue. See below.

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And the "scientific" explanation (not completely correct, but therefore easy enough to understand, I hope):

The light coming from the sun is scattered through the atmosphere by air molecules. That's the so-called Rayleigh scattering. The formula uses the wavelength of light in the denominator, but as wavelength^4.

We can see wavelengths from about 360 nm (blue) to 830 nm (red).

If you rise both red and blue wavelenghts to the power of 4 you get the numbers:

blue: 360^4 = 1,679,616,000

red: 830^4= 474,583,210,000

The inverses (indicate the strength of scattering) are:

blue: 0.0000000000595

red: 0.000000000002107

You see that red is scattered  about 30 times weaker than blue. This makes the sky look blue. It's almost unimportant in what direction you look, there's always blue light scattered to you - if you take a closer look then you can see that the sky isn't uniformly colored, but the principle applies nevertheless.

Red light passes the atmosphere at daytime (sun high in the sky) almost on a straight line because the light travels a too short distance through the air to be influenced strongly enough.

At sunset/dawn the sun is at a very low angle and travels a much longer way through the atmosphere. On the way through the air the blue light is scattered away from the viewing direction and the red light is left (more accurately: long wavelenghts are left, short ones are scattered away form the observer).