When the weather is clear, the sky looks blue. Why that color? Why not red or purple? What is the color of the end of the universe?
Quoted from the official page NASAthe blue color of the sky as seen by the human eye comes from sunlight that reaches the earth’s atmosphere and is scattered in all directions by all gases and particles in the air.
Blue light is scattered more than any other color because it propagates as shorter and smaller waves in the spectrum. Therefore, blue light becomes more visible.
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Furthermore, quoting from the UK’s BMKG website, Met Office, the blue color of the sky is associated with light. Even though it looks white, sunlight is actually made up of a spectrum of different colors, as seen in a rainbow.
Light is said to be a wave of energy, and each color has a different wavelength. Red being the color with the longest wavelength and blue and purple having a much shorter wavelength.
When sunlight reaches Earth’s atmosphere, it is scattered or bent by small molecules of gas, usually nitrogen and oxygen in the air.
Since these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength. This effect is called Rayleigh scattering after its discoverer, Lord Rayleigh.
The shorter wavelengths (purple and blue) are most strongly scattered, so more blue light is scattered into our eyes than other colors.
However, why is there no purple in the blue sky? This is because there is not much purple in the sun, and our eyes are much more sensitive to blue.
The blue light that gives color to the daytime sky is also bright enough to make all the stars we see at night disappear. This is because the light that the stars emit is much dimmer.
You may also notice that the sky tends to be clearest overhead and fade to a paler color as it reaches the horizon. This happens because the light from the horizon has had farther to travel through the air so it has scattered back.
The earth’s surface also plays a role in scattering and reflecting this light. As a result of increasing the amount of scattering, the dominance of blue light is reduced so that humans can see an increase in the amount of white light.
(ttf/lth)
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