Does anyone have a good answer as to why the sky is blue?

Question

thhe only good one ive ever heard is that the sky reflects the ocean.. but i think there could be a better one.. its been driving me crazy since i was like two.

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

The sky itself is actually black, or so I was taught many years ago in high school. The blue coloring is a refledtion of the sun into the atmosphere that gives the sky the blue color.

Answer 3

Good answer as in quick, or good answer as in thorough?
Above this response, you've got a bit of both. I'll go into a little bit of further detail because I'm avoiding homework AND studying.
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Short answer: Rayleigh scattering; light is made of of wavelengths; the short wavelengths scatters off the particles that make up the atmosphere. Scattered light reaches your eye. Depending on what has been scattered determines the colour you see.


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Long answer:
As you probably know from school, light that is transmitted from the sun is made up of a spectrum (commonly and not entirely accurately referred to as ROYGBIV: red, orange, yellow, green, blue, indigo, violet). The spectrum of light transmitted includes the range of wavelengths that our eyes can see.
As you should also know from school (U.S. 6th grade and revisited in high school physics and chemistry), visible light is made up of wavelengths. The longer wavelengths of visible light are on the Red end, and the shorter wavelengths are on the Blue/Indigo/Violet end.
Our eyes aren't especially good at seeing the full spectrum of 'visible' light always, due to the fact that it's a physical component of our eyes to percieve light and colour (number and health of rods and cones in our eyes determine this. For the same reason, certain colourblind people can say "Well... it's either blue or green. But since there are more blues in the world, I'll guess blue." ...this is more true because many shades of Blue, Indigo, and early shades of Violet tend to be picked up by our eyes as roughly the same colour.)

Sunlight traveling through the Earth's atmosphere is absorbed by and collides with the nitrogen and oxygen (etc) particles and scatters (radiates after absorbing) the light in what is called Rayleigh scattering. The colours with the shorter wavelength are scattered the most, whereas the longer wavelength colours pass straight through, and appear to us as "white light."
Blue, Indigo, and Violet are the shortest wavelengths, so ..the sky appears as shades of such. But, due to the makeup of our eyes ..and the apparent ubiquitous nature of the colour blue, we see it primarily as shades of blue and indigo.
For the most part, whatever direction you look, some of the scattered light reaches your eyes. And since the light is, roughly speaking, coming at you from everywhere overhead, the entire sky seems that colour. Look further down toward the horizon, it gets much more pale in colour. ..That's ..my guess.. because by the time it's at the horizon level, there's a lot more of the atmosphere in the way, and the number of collisions and re-radiations, etc has greatly increased, ..and the scattered blue light has been scattered further, and goes in directions that are not as apparent to your eye.



Similarly, when on earth, the Sun seems very yellow.. whereas, from outside the Earth's atmo, it's much, much more white-seeming. ..The microvaccuum of space has fewer particles through which the light must pass before it reaches your eye. The light isn't nearly as scattered. A flashlight or a light bulb may give off a decidedly yellow light, or the bulb may look yellow, but the tungsten or whatever filament ..seems to burn near-white. That goes into light intensity, I assume, more than refraction, though.

Similar to our sky, ..when you're in space, everything is mostly black... with patches of coloured gases and such. This is because there isn't much of an atmosphere in open space, except near planets and nebulae and such...whereupon you can again distinguish colours. Things look dark when they are not radiating light back toward your eyes. Things are especially good at this when they are nothing. =p


Meanwhile ..when watching a sunset, the sky is red. ..The sun is literally sinking closer to the horizon, based on where we are. (ie, if you're 30,000ft up, in a plane, you'll see a red sunset at the same time as the person 30,000ft directly below you ..still has an hour or two before sunset) ...the angle of the sun with respect to the earth (with a few mathematical assumptions as to how you're defining that..) lowers, and the light has to travel further through the atmosphere before it reaches your eyes. This is why you can look directly at the sun much more easily than you can at, say, noon. ...From this angle and distance, the green, blue, indigo, and violet are scattered even more than before. Whereas, the longer wavelengths like Red and Orange are passing through at a near direct path to your eyes.

At night, light isn't passing through the atmosphere nearly as much (it's being blocked by the other side of the planet) ...that little light means even less in the way of collisions ..which means it'll have roughly the same effect as viewing the black of space.
Light + Collision with atmo particles = Coloured sky
Take away either the amount of light, or the number of collisions, and you won't get the coloured sky.



=p So ..now you know why the sky is blueish during the day, reddish at sunset, and black at night.
I'm so gonna have that question nailed if I ever have a kid.

-maido ari~bang

Answer 4

It's actually because of how the light strikes the air molecules, so that our eyes perceive it as being blue. http://www.why-is-the-sky-blue.tv/why-is-the-sky-blue.htm

Additional fun sites (some more complicated):
http://www.sciencemadesimple.com/sky_blue.html
http://world.std.com/~mmcirvin/bluesky.html
http://spaceplace.nasa.gov/en/kids/misrsky/misr_sky.shtml

Answer 5

It has something to do with rarefaction, light bending and the atmosphere. Certain colours bend away when they hit earths atmosphere and others penetrate more easily. I

Answer 6

the sky & everything is not the color u perceive . the color u see is what is reflected from the object thus not the color of the object. no wonder ure crazy....chirp!

Answer 7

becuz light reflects off it that way

Answer 8

i thought it was because of all the "black matter" which makes space appear black so nothing reflects of tht and it was basically the sun hitting the sea and reflecting it back in the atmosphere... but i really dunno!

Answer 9

It has to do with the sun and the color spectrum

Answer 10

i say its becuz the sky reflects the ocean its wut i've been taught at school, but u never know, y is grass green, just becuz it can be