Sky why is it blue

The green cones respond to yellow and the more strongly scattered green and green-blue wavelengths. The blue cones are stimulated by colours near blue wavelengths, which are very strongly scattered. If there were no indigo and violet in the spectrum, the sky would appear blue with a slight green tinge. But the most strongly scattered indigo and violet wavelengths stimulate the red cones slightly as well as the blue, which is why these colours appear blue with an added red tinge.

The net effect is that the red and green cones are stimulated about equally by the light from the sky, while the blue is stimulated more strongly. This combination accounts for the pale sky blue colour.

It may not be a coincidence that our vision is adjusted to see the sky as a pure hue. We have evolved to fit in with our environment; and the ability to separate natural colours most clearly is probably a survival advantage.

A multicoloured sunset over the Firth of Forth in Scotland. When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun.

This is because all light is scattered relatively well through small angles—but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

A blue haze over the mountains of Les Vosges in France. Clouds and dust haze appear white because they consist of particles larger than the wavelengths of light, which scatter all wavelengths equally Mie scattering.

But sometimes there might be other particles in the air that are much smaller. Some mountainous regions are famous for their blue haze. Aerosols of terpenes from the vegetation react with ozone in the atmosphere to form small particles about nm across, and these particles scatter the blue light. A forest fire or volcanic eruption may occasionally fill the atmosphere with fine particles of — nm across, being the right size to scatter red light. This gives the opposite to the usual Tyndall effect, and may cause the moon to have a blue tinge since the red light has been scattered out.

The scattered violet and blue light dominates the sky, making it appear blue. What happens to the violet? Some of the violet light is absorbed by the upper atmosphere. Also, our eyes are not as sensitive to violet as they are to blue. Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from the horizon has passed through even more air than the sunlight reaching us from overhead.

The molecules of gas have rescattered the blue light in so many directions so many times that less blue light reaches us. As the Sun gets lower in the sky, its light passes through more of the atmosphere to reach you.

Even more of the blue and violet light is scattered, allowing the reds and yellows to pass straight through to your eyes without all that competition from the blues. Also, larger particles of dust, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows, sometimes making the whole western sky glow red.

The Short Answer:. Gases and particles in Earth's atmosphere scatter sunlight in all directions. Indeed, there actually is a greater amount of violet light coming from the atmosphere than blue light, but there's also a mix of the other colors as well. Because your eyes have three types of cones for detecting color in them, along with the monochromatic rods, it's the signals from all four that need to get interpreted by your brain when it comes to assigning a color.

The light response of the human eye, normalized, in terms of the three types of cones and dashed Each type of cone, plus the rods, are sensitive to light of different wavelengths, but all of them get stimulated to some degree by the sky. Our eyes respond more strongly to blue, cyan, and green wavelengths of light than they do to violet.

Even though there's more violet light, it isn't enough to overcome the strong blue signal our brains deliver. The gravitational pull on the gases in our atmosphere cause a substantial surface pressure, giving Image credit:.

If we could see into the ultraviolet very efficiently, the sky would likely appear more violet and ultraviolet; if we only had two types of cones like dogs , we could see the blue sky during the day, but not the reds, oranges, and yellows of sunset.

But don't be fooled: when you look at the Earth from space, it's blue, too, but the atmosphere has nothing to do with it! This is a BETA experience.

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