The atmosphere is blue by reason of the darkness above it because black and white make blue.

Leonardo had also been wrestling with the question of why the sky appears blue, and around that time he had correctly concluded that it had to do with the water vapor in the air. In the Saint Anne painting, he portrays the sky’s luminous and misty gradations of blue as no other painter had done. The recent cleaning of the painting fully reveals the magical realism, veiled in vapors, of his distant mountains and skyline.

If a little kid ever asks you just why the sky is blue, you look him or her right in the eye and say, "It's because of quantum effects involving Rayleigh scattering combined with a lack of violet photon receptors in our retinae."

We have seven colours — violet, indigo, blue, green, yellow, orange and red (Roy G. Biv). Our atmosphere has a number of particles and when light falls on them, it gets scattered. With blue colour having less wavelength and more scattering qualities, it scatters and makes the sky blue. While red colour has opposite qualities than blue so traffic lights are of this colour.

The sky was rarely more than pale blue or violet, with a profusion of mighty, weightless, ever-changing clouds towering up and sailing on it, but it has blue vigour in it, and at a short distance it painted the ranges of hills and the woods a fresh deep blue.

Experience shows us that the air must have darkness beyond it and yet it appears blue. If you produce a small quantity of smoke from dry wood and the rays of the sun fall on this smoke, and if you then place behind the smoke a piece of black velvet on which the sun does not shine, you will see that all the smoke which is between the eye and the black stuff will appear of a beautiful blue colour. And if instead of the velvet you place a white cloth smoke, that is too thick smoke, hinders, and too thin smoke does not produce, the perfection of this blue colour. Hence a moderate amount of smoke produces the finest blue.

This blue is the light that got lost. Light at the blue end of the spectrum does not travel the whole distance from the sun to us. It disperses among the molecules of the air, it scatters in water. Water is colorless, shallow water appears to be the color of whatever lies underneath it, but deep water is full of this scattered light, the purer the water the deeper the blue. The sky is blue for the same reason, but the blue at the horizon, the blue of land that seems to be dissolving into the sky, is a deeper, dreamier, melancholy blue, the blue at the farthest reaches of the places where you see for miles, the blue of distance. This light that does not touch us, does not travel the whole distance, the light that gets lost, gives us the beauty of the world, so much of which is in the color blue.

You know that in an atmosphere of uniform density the most distant things seen through it, such as the mountains, in consequence of the great quantity of atmosphere which is between your eye and them, will appear blue. Therfore you should make the building... wall which is more distant less defined and bluer. ...five times as far away make five times as blue.

The sea is blue because the sunlight is reflected back to our eyes from the water molecules or from very minute particles suspended in the sea. In the journey of the light rays downward into the water and back to our eyes, all the red rays of the spectrum and most of the yellow have been absorbed, so it is chiefly the cool, blue light that we see.

'Father, why is the sky blue?' - the child is not really interested in the sky as such; the real stake of the question is to expose father's impotence, his helplessness in the face of the hard fact, to present the whole chain of reasons leading to it. The blue of the sky thus becomes not only the father's problem, but in a way even his fault. The sky is blue, and you're just staring at it like an idiot incapable of doing anything about it!

It is sometimes said that scientists are unromantic, that their passion to figure out robs the world of beauty and mystery. But is it not stirring to understand how the world actually works — that white light is made of colors, that color is the way we perceive the wavelengths of light, that transparent air reflects light, that in so doing it discriminates among the waves, and that the sky is blue for the same reason that the sunset is red? It does no harm to the romance of the sunset to know a little bit about it.

Me: The sky is blue.
Twitter: No, it's not.
Also Twitter: Trump said the sky is blue. He's lying.
More Twitter: Sometimes the sky is red. Why do you hate red sky?
Even More Twitter: You're stupid because you think the sky is blue.
Yet More Twitter: Republicans say the sky is blue. The sky must be a different color. It doesn't matter what color. It just isn't blue.
Additional Twitter: Technically, the sky only appears blue due to the atmosphere's charged particles oscillating and scattering the sunlight passing through it. Blue is scattered more than other colors. Hence, the sky's blue hue.
Translation: You don't understand science...
...and you're stupid.
Have a great day, everyone!

The world is blue at its edges and in its depths. This blue is the light that got lost. Light at the blue end of the spectrum does not travel the whole distance from the sun to us. It disperses among the molecules of the air, it scatters in water. Water is colorless, shallow water appears to be the color of whatever lies underneath it, but deep water is full of this scattered light, the purer the water the deeper the blue. The sky is blue for the same reason, but the blue at the horizon, the blue of land that seems to be dissolving into the sky, is a deeper, dreamier, melancholy blue, the blue at the farthest reaches of the places where you see for miles, the blue of distance. This light that does not touch us, does not travel the whole distance, the light that gets lost, gives us the beauty of the world, so much of which is in the color blue.

For many years, I have been moved by the blue at the far edge of what can be seen, that color of horizons, of remote mountain ranges, of anything far away. The color of that distance is the color of an emotion, the color of solitude and of desire, the color of there seen from here, the color of where you are not. And the color of where you can never go. For the blue is not in the place those miles away at the horizon, but in the atmospheric distance between you and the mountains.

There was one of those sunsets beginning — the kind we've been having for months. Buildings and telephone poles were punched black against a watercolour sky into which fresh colour kept washing and spreading, higher and higher. We've never seen so high before; every day the colours go up and up to a hectic lilac, and from that, at last, comes the night. People carry their drinks outside not so much to look at the light, as to be in it. It's everywhere, surrounding faces and hair as it does the trees. It comes from a volcanic eruption on the other side of the world, from particles of dust that have risen to the upper atmosphere. Some people think it's from atomic tests; but it's said that, in Africa, we are safe from atomic fallout from the Northern Hemisphere because of the doldrums, an area where the elements lie becalmed and can carry no pollution.