Why is the Sky Blue?

The sky in a shade of deep blue.
The sky in a shade of deep blue.

Nature presents some mysteries on how certain things are the way they are. The color of the sky is one natural phenomenon that has attracted various opinions and mythical and scientific explanations. On clear days, the sky is blue, with the color sometimes varying more whitish, especially towards the horizon. Various scientists have developed various theories explaining the blue color. Most scientists agree that the atmosphere contributes to the color of the sky. One such myth includes the explanation that the sky is blue as light from the sun reflects the blue color from the oceans. However, that explanation is incorrect since the same phenomenon of light absorption in the atmosphere also happens in the water as the longer light waves are absorbed deeper than the short blue rays.

Scattering of Light

The most commonly accepted theory explaining the blue color of the sky is the scattering of light by the atmosphere. The atmosphere consists of gases and other particles, which collide with light particles and scatter them in different directions and intensities. Light is composed of a spectrum of seven colors of varying wavelengths. These colors include red, orange, yellow, green, blue, indigo, and violet, whose particles are scattered unevenly. Blue light travels at shorter wavelengths and is scattered more than the other colors as the sunlight passes through the air. Blue color also has a higher frequency compared to red color and scatters more. This scattering and re-scattering creates an effect where the sky appears blue. Light travels in a straight line in all directions. During these movements, it bumps with gas particles and other materials in the atmosphere, which absorb the light and radiate a similar color of light to that which was absorbed.

Tyndall and Rayleigh Theories

John Tyndall, a 19th-century scientist, was the first to develop a correct theory of the blue color of the sky. Lord Rayleigh expounded on Tyndall's theory of scattering of light by the atmosphere. Rayleigh conducted more studies on the behavior of light, finally arriving at the conclusion that blue light is scattered more than red light. He estimated that the blue light is scattered more than red color by a factor of 10. Previously, scientists believed that dust and water particles in the atmosphere contributed to absorption and scattering of light. The theories were debased, as the sky would change color with changing amounts of atmospheric dust and water.


The color of the sky has also been linked to the receptors in our eyes, which vary in their sensitivity to triggers of various color. The cones for color perceive colors of wavelengths differently. Blue receptors are known to be more sensitive than those of red and green colors, therefore, we are more likely to perceive the blue light particles that have been scattered from the sunlight.

Variations in Sky Color

Towards the horizon in the early morning or at sunset, the color of the sky appears white or red. The whitish appearance of the sky is due to more scattering of blue light by the atmospheric particles as they move through the air. The scattering disperses the blue light more making it look paler from a distance. As the sun drops lower in the sky, light passes through more air thus scattering even the longer light waves, making the red light waves more visible since blue ones are already more dispersed since they travel a longer distance before reaching the eye.


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