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 -- why is the sky blue?

The sky is blue due to a phenomenon called Raleigh scattering. In this phenomenon, Rayleigh scatters light from the sun into all directions. When light travels through the Earth's atmosphere, different colors scatter in different ways. If a blue sky is really pure white, then only red and green will scatter around it as it passes by. The other colors will be scattered away from the blue color because of its purity. This causes our eyes to see a bluish color that we refer to as "blue".

sky , blue, red ,color of sky

 
Within the atmosphere, the blue color is created by a layer of gas called airglow. It is best seen in the early morning and at dusk. This occurs when sulfur atoms absorb the red light from the sun, leaving behind green (which is yellow through violet) and blue light. The decreasing red light causes atoms to emit both green and blue lights that escape into space. The green light scatters off in all directions while the blue scatters downward, forming a bluish triangle of color called airglow.

 

When the sun is nearby, it gives off more visible red light because blue light is scattered away. This causes a red sunset. When the sun is further away, it gives off more blue light and less red. This causes a blue sunrise.

 

The sky can also be blue due to scattering of haze, particulates in the atmosphere or simply because the cloud droplets are larger than the wavelength of light that they scatter.

 

-- why is the sky red?

Although the sky is commonly described as being blue, it is actually red because of scattering that occurs within the atmosphere and because of light from planets and stars also scattered into space (this phenomenon is called "Rayleigh scattering" ):

"The sky looks blue to us because of an interaction with gases in the atmosphere. Those light-scattering gases are likely made up of electrons and oxygen atoms, which are relatively transparent to blue light. The red and orange, green and yellow light that we do see from the sun is being scattered away from the blue." 

The amount of scattering depends on the color of the object, wavelength and altitude. The scattering is calculated by a model called "Hanes’s Law," which assumes that all the radiation leaving a source (such as a star) can be received at only one point. 

The atmosphere also emits radiation, so visible light must pass through air molecules before it strikes our eyes. That light is called "backscattered" or "bounce" light, and the sky appears blue because it scatters around the scattering gases in the atmosphere. 

The sky looks red because of Rayleigh scattering, which describes how light scattered off particles in the atmosphere (such as dust particles) can scatter into other directions. Red shifts are more noticeable here than blue shifts because of all of the scattering that occurs in air molecules. That scattering can be seen just by looking at an airplane flying over your head, for example.

The sky is blue because of scattering by air molecules. Blue light is scattered away into all directions, while the other colors scatter away from the blue color due to the purity of the sky. This causes our eyes to see a bluish color that we refer to as "blue".

 

Within the atmosphere, the blue color is created by a layer of gas called airglow. It is best seen in the early morning and at dusk. This occurs when sulfur atoms absorb the red light from the sun, leaving behind green (which is yellow through violet) and blue light. The decreasing red light causes atoms to emit both green and blue lights that escape into space. The green light scatters off in all directions while the blue scatters downward, forming a bluish triangle of color called airglow. 

When the sun is nearby, it gives off more visible red light because blue light is scattered away. This causes a red sunset. When the sun is further away, it gives off more blue light and less red. This causes a blue sunrise.

  

The sky can also be blue due to scattering of haze, particulates in the atmosphere or simply because the cloud droplets are larger than the wavelength of light that they scatter. 

There are also several factors that can make the sky appear red, such as atmospheric optics, dust in the atmosphere and pollution.

A major cause for the red sunset is Rayleigh scattering. Because blue light is scattered away as it passes through the atmosphere, red light is visible at sunset for a long time after the sun has disappeared below the horizon.

 

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