Why is the sky blue?

Answer 1

The sky is blue partly because air scatters short-wavelength light in preference to longer wavelengths. Where the sunlight is nearly tangent to the Earth's surface, the light's path through the atmosphere is so long that much of the blue and even yellow light is scattered out, leaving the sun rays and the clouds it illuminates red, at sunrise and sunset.

Scattering and absorption are major causes of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described, for spherical particles, by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.

Individual gas molecules are too small to scatter light effectively. However, in a gas, the molecules move more or less independently of each-other, unlike in liquids and solids where the density is determined the molecule's sizes. So the densities of gases, such as pure air, are subject to statistical fluctuations. Significant fluctuations are much more common on a small scale. It is mainly these density fluctuations on a small (tens of nanometers) scale that cause the sky to be blue.

Answer 2

Here goes !
Forget about the atmosphere as a whole and instead imagine a single electron and a red photon (which has not much energy) and a blue photon (which has a lot of energy).
A blue photon has nearly enough energy to lift the electron to a higher energy state. It doesn't have quite enough so it borrows the extra energy from nothing at all (really energy is borrowed from nothing !!!). Mother natures rule for borrowing energy is "the more you borrow the sooner you have to give it back". So now we have an electron in a high energy state held there by the energy from the blue photon and the borrowed energy. Because only a little bit of energy was borrowed (remember the rule) it can stay in this state for quite a long time before mother nature asks for her energy back. When that happens the blue photon is kicked back out of the electron. The key point is that the electron is part of an atom (say an oxygen atom in the atmosphere) and that atom is spinning so it can turn quite a long way in the time between when the blue photon was absorbed and emitted. The practical upshot of which is that the blue photon comes in (to the atom) from one direction and departs in a very different direction or is "scattered". So all blue light is scattered from all atoms in the atmosphere all around so the sky appears blue. Voila !

A red photon has much less energy so for it to boost an electron to a higher level it has to borrow a lot of energy so it has to pay it back sooner. That means the atom won't have turned very far before the red photon is fired out again. So its fired out in pretty much the same direction as it arrived.
That why the setting sun appears red.
Phew, clear as mud right ?

Answer 3

When you look up at the sun, the sky directly "underneath" the sun does not look blue. It looks roughly white.

However, the rest of the sky looks blue. This is because the blue light from the sun gets "scattered" by the rest of the sky. Instead of coming straight down, like the rest of the white light, it gets spread across the sky. Thus, the blue that you see in the rest of the sky is blue light that has been bent away from the direct path that the rest of the light took.

It just happens that the atmosphere scatters blue light better than it scatters white light. That's why blue light gets bent away from the direct path more than the other colors of light.

Actually, our sky is VIOLET, not blue. However, your eye is better at seeing blue rather than violet, so the violet that you see in the sky looks blue.

Answer 4

Rayleigh Scattering

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html

Answer 5

Blue you say?
In my world the sky is pink.

Answer 6

because blue is the only color water vapor and ice reflects

Answer 7

Like I tell my kids when I don't know or don't feel like explaining-cuz God wants it to be!

Answer 8

because God made it that way.

Answer 9

it's not.... like life it is a illusion.

Answer 10

gasses!