I've always wondered, why is the sky blue?

Question

I thought it was because liquid oxygen was blue, but nitrogen makes up most of the atmosphere. I know that its not because the sky is a reflection of the ocean. Please help me out here.

D

Answer 1

Because God made it that way. =D

Answer 2

the angel we view it from. the light from the sun makes a rainbow-like a crystal chandalier-but due to our angel of view and the dust and chemicals in the sky it is blue.

Answer 3

http://math.ucr.edu/home/baez/physics/Ge... simple and well illustrated

Answer 4

The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths 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. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.

Answer 5

This question has been asked over 8000 times so far.  When I was at university, it was the most frequent question asked of the physics department.

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, 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.

BTW: The sky isn't blue because of a reflection of the sea. its the other way round. As well as reflecting the blue from the sky at the surface, sea water also scatters the blue light. The blue colour of the sea is a little more complicated, because as well as the water molecules scattering the blue light, the water absorbs more of the red and yellow wavelengths, leaving the blue part of the spectrum, as well as part of the green (which is why deep water can appear bluish-green).

This scattering 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..

My thanks to various contributers for correcting me on some details.

For complete, scientific explanations, look up 'blue sky' in Wikipedia, and follow through the references.