I know that this is stupid but its just fun to ask. Is the sky really blue or is it clear?

Question

I think the sky is clear but im not quite sure if its blue. Because without water vapor reflection in the sky then the sky would be clear.

Answer 1

The question "why is the sky blue?" has been asked over 5000 times, and I've prepared a simple answer, without too much science:

The 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 strikes the molecules and is absorbed. 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'). The molecules in the air are much smaller than the wavelength of visible light, but 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, 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 blue colour of the sea is mostly caused by the water molecules scattering the blue light, in a similar way. This effect is even stronger with ice; which results in the intense blue colour we see if we look down a crevasse in a glacier, or down a hole in the snow made by a ski stock..

For a complete, scientific explqanation, look up 'blue sky' in Wikipedia.

Edit:
Of course, the sky is itself quite clear, as we know when looking at scenery. The blue colour appears because we are looking up through several miles of atmosphere. Similarly, if we see a long way horizontally, the distant scenery looks blueish.

Answer 2

The sky isn't "clear" exactly. It looks blue during the daytime because of the atmosphere, which is a cocktail of gases that surrounds our planet. The atmosphere scatters the sunlight, which comes in bands of color, like a rainbow. When the bands of color come altogether, what we see is white light. When the bands are scattered, we'll see different colors. If the sun shines through rain, the water breaks the white light up into bands and we see all of them: a rainbow.

Unlike a rainbow, the atmosphere lets some colors go directly through, absorbs other colors, and scatters the blue light all around. The blue light is REALLY there, though. And we see what's really there. But all we can see is the blue light bouncing all around. We can't see through the blue light to the stars behind it.

When the sun isn't shining directly on the atmosphere, at night, then we can see through it better to the space and stars above. But even at night, the atmosphere does block some of our view by scattering light that comes in from outer space.

Also, the pollution in the atmosphere is actually part of the atmosphere, too--it's gases we've added to the cocktail. So that keeps the sky from being clear.

We've also added light pollution to the mix. That means that we shine too much light upward from the Earth and the light reflects off the atmosphere and obscures our view. So that, too, keeps the sky from being clear.

I think what you're asking is: if we removed all these other things, would the sky be clear? If there were no human pollution, there would still be an atmosphere, which means that we still couldn't see through the atmosphere during the day, and still couldn't see entirely through the atmosphere at night.

Add to this the consideration: what do you mean when you say "sky"? I mean, really think about it. Do you just mean whatever's up? If you got into a space ship and traveled directly up, when would the sky stop ... or when would you reach the sky?

Or, another consideration: what do you mean when you ask "is something really ______?" What does "really" mean, in this case? What is real? We all see the blue in the sky. That makes it real. But we also know that when we're flying around in the blue, we can't hold anything blue in our hands. We don't turn blue when we're in the sky. So is it really blue? WHAT is blue, and the blue is WHAT?

So my answer is this: OUR sky is what we see when we look up. What we see up there is REALLY blue, or really black or really some other color, depending on the weather and the time of day. What CAUSES the sky to be those colors at different times is a different matter, but it doesn't affect the reality of the color.

Answer 3

I'm afraid not. Its blue all right.

The sky is blue due to an atmospheric 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 the sun you would get its actual colour of bright white, which is what you’d see out 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://en.wikipedia.org/wiki/Diffuse_sky_radiation
http://science.howstuffworks.com/question39.htm
http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html
http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html
http://www.exo.net/~pauld/physics/why_is_sky_blue.html
http://www.sciencemadesimple.com/sky_blue.html

Kind regards

Answer 4

i like a clean night sky beacuse i'm able to confirm the celebrities, and that i like a deep blue sky dotted with enormous puffy cumulous clouds. i like the night sky a splash greater suited than the sunlight hours cloud sky. Ooooooo! and that i like the sundown.

Answer 5

the sky i think is clear but it looks blue because of the ocean is blue and it reflects

Answer 6

Looks like this question has been answered already.

Answer 7

http://science.howstuffworks.com/question39.htm
I used to know, but here.