Why is the sky blue during the day and red at sunset?

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In order to understand why the sky is blue during the day, and appears red at sunset, one must first realize that the sun emits all wavelengths of the visible spectrum. The reason the sky appears blue was discovered by John Tyndall in 1859. He realized that shorter wavelengths of...

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In order to understand why the sky is blue during the day, and appears red at sunset, one must first realize that the sun emits all wavelengths of the visible spectrum. The reason the sky appears blue was discovered by John Tyndall in 1859. He realized that shorter wavelengths of light, such as blue, are scattered much more than longer red wavelengths by particles in the atmosphere. This occurs when the sun is at a more extreme angle relative to the observer. An example of this is when the sun is directly overhead at mid-day. This scattering of blue wavelengths makes the sky appear blue to the human eye, while all other wavelengths pass through the atmosphere more directly and are not visualized.

The difference in color at sunset is due to the change in the observers angle of view of the sun. As the sunsets, it moves further away from the observer, leading to an even greater scattering of both blue light and red light due to a longer distance and shorter angle of observation as seen in the figure. This greater scattering of light, due to a smaller angle between the sun and the observer, allows a greater scattering of red wavelengths creating the red sky that is seen at sunset. This effect can be amplified by water or other particles in the atmosphere making some sunsets appear more or less red than others. Hope this helps!!!  

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