Why is the sky blue?

Answer 1

This question 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, 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 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 varoius contributers for correcting me on some details.

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

Answer 2

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 3

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.



The white light from the sun is a mixture of all colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

Answer 4

well its bcuz of a effect called raman effect.that means when the light passes thru the atmosphere ,the atmosphere acts like a prism & it splitz the white light & the blue colour gets refracted the most &thats why the skys blue

Answer 5

BAM!

"A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight."

Answer 6

cause as light passes through the atmosphere the uv sun rays turn the sky blue or something like that

Answer 7

because the light from the sun filters through the Earth's atmosphere and main visible light spectrum that gets through this filtration is what appears to be blue.

Answer 8

our air is full off nitrogen thus the sky is is blue , the sky on mars is reg because of carbon dioxide

Answer 9

It is an illusion. The sun reflects light from the atmosphere and bounces from the earth to everywhere and this creates the light to light up little particles that makes up atmosphere.

Answer 10

I think it's because of the light shinning through our atmosphere, without it i think our sky's would be black. I Think.