Why is the Sky Blue
Short Answer : As it passes through the atmosphere, the light is absorbed by the gases and particles in the air and then scattered in different directions according to the wavelength. Blue rays with the shortest wavelength are scattered over a wider area. This is why the sky looks blue.
The explanation for why the sky is blue came from the English physicist Lord Rayleigh at the end of the 19th century.
Sunlight is white but contains many different colors. As Newton discovered, white light contains all the colors of the rainbow, from the shortest wavelength blue to the longest wavelength red.
- The air is transparent like a prism and when white light is passed through a prism it scatters these colors. Like the circular waves in water, the light is a wave.
- There is 78% nitrogen and 21% oxygen in the atmosphere, and the remaining 1% contains mostly argon gas and water vapor. There are also particles such as dust, ash and pollen in the atmosphere. Oxygen/nitrogen molecules in the air are capable of scattering blue light more. So as white light passes through the air, especially blue light changes direction (scattered) and a blue background emerges.
In the upper atmosphere of the earth, the number of molecules to scatter sunlight is small. That’s why the sky is not blue, but black.
And during sunrise or sunset, when the sun is close to the horizon, the sun’s rays travel longer through the atmosphere. Therefore, blue light is scattered more than when the Sun is high. In this case, less scattered red-orange rays reach our eyes more. That’s why we see the sky in red-orange colors during sunrise and sunset.
Fun fact : The most scattered rays are the violet and blue rays with the shortest wavelengths.
If the violet and blue colors scatter together as a result, why do we see the sky as blue and not purple? The answer to this is that the rays coming from the Sun contain less violet light than blue light. Wouldn’t it be cool if the sky was purple? 🙂