Why does the sky change colors?

I have learned that the sky is blue because it is reflected in the surface of the ocean. But why does it turn red at sunset?

I have learned that the sky is blue because it is reflected in the surface of the sea. But why does it turn red at sunset?

The clouds reflect the colors of the light and the effect is greatly amplified when the sun is low in the sky.


When people see the sky as blue, it is not the color of the sky that we see, but one color in the light of the sun that is spread out by molecules in the atmosphere.


The light of the sun contains all colors and therefore appears white.


But when the light passes through the Earth’s atmosphere, it hits fire and carbon molecules that split the light.


Molecules scatter blue light in the sky

Blue is one of the colors with the shortest wavelength in the spectrum that the human eye can detect.


Fire and carbon molecules are abundant in the Earth’s atmosphere, and their size is such that the molecules scatter light with short wavelengths the most.


Therefore, the blue light of the sun splits to the greatest extent and becomes the dominant color in the sky.


Yellow and red become visible at sunset

Green light passes almost undisturbed through the atmosphere, while yellow and red light are on long waves and do not scatter much.


When the sun is setting, the light has to pass through much more of the atmosphere than when the sun is at its highest point in the sky.


This means that even more short-wavelength blue light is scattered.


What remains is a red-yellow and yellow light that can be seen at sunset.


At night, there is no sunlight that the molecules of the atmosphere can scatter, so the sky is black.


The scattering of sunlight in the atmosphere is called Rayleigh scattering after the British physicist Lord Rayleigh who explained the blue color of the sky in 1871.


Particles in the atmosphere split the light

When sunlight hits the Earth’s atmosphere, the light is split by molecules in the atmosphere.


Blue light has short wavelengths and scatters more efficiently than red.


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Before sunlight reaches the atmosphere, it travels undisturbed in parallel lines through space. The light contains different wavelengths, which together form white light.


Since the blue wavelengths are shorter than the redder ones, they collide more with small molecules in the atmosphere and scatter in all directions.


Long-wavelength light, such as red and yellow, travels almost undisturbed through the atmosphere.


When the sun is low in the sky, the light passes through more molecules. Therefore, the blue light diffuses until it is no longer visible, while the red-yellow and red light become more prominent.

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