Since ancient times, many have questioned why the sky appears blue, rather than any other colour, especially since the sun gives off light in all the different ranges of visible light. It was initially thought that the sky appears blue because of water vapour droplets in the air, or because of the sea. However, these myths have now been busted by scientists, and a better understanding of the phenomenon has been achieved.

As light from the sun enters earth’s atmosphere, scattering occurs from the particles inside the atmosphere itself. It so happens that blue light, the more energetic type of visible light, is the most easily scattered in the atmosphere. As it is scattered so effectively, the blue light can be seen spread out across the entire sky as opposed to the other less energetic green, yellow, orange and red wavelengths of light. This results in our perception of the sun as a more yellow source of light as well, since the blue portion of the white light that the sun emits is scattered by the atmosphere before reaching our eyes here on the surface. Any astronaut who has been to space would tell you that the sun from above earth’s atmosphere appears white.

An interesting case is the colour of sunsets. Sunsets appear yellow, orange or even red, as does the sky closer to the horizon. The reason for this observation is the increased amount of atmosphere that the light from the sun has to pass through as it gets lower in the sky.

Light now has to travel through a longer column of air, and therefore blue light is more effectively scattered, so much so that very little blue light manages to pass through to the ground where we can see it. The redder, less energetic wavelengths of light also start getting scattered effectively, but in this case red light still makes its way to the ground where we can perceive it with our eyes.

This makes the sky appear redder closer to the horizon during a sunset, and the higher the number of dust particles present in the atmosphere, the redder it will appear.

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