When its day time and no clouds, you will see a blue sky and a yellow sun, right? Now that to me is very beautiful. Ever wondered why the sky color is not any other but blue, well as you read through you will understand this is. Rayleigh scattering is attributed to this phenomenon. What on earth is this? Rayleigh may be the vocabulary new to you but it’s nothing other than the name of the scientist who discovered the scattering of light from the sun in the atmosphere.
Rayleigh scattering is spreading out of light by particles without change of wavelength. Sun rays travel from the sun to the earth at a very high speed. Sunlight is white is color for it’s a combination of the three primary colors namely red, green and blue. When white light hits atmospheric particles, it’s radiated back with its frequency, wavelength, and energy altered or constant.
How it works
Light travels as a wave from the sun to the earth. The white light is a combination of red, green and blue light and these components have different wavelengths. The Red has the largest wavelength, blue the least, and green in between. The general size of air particles whose majority component is nitrogen oxide gas has a small diameter than the light wavelength. This is a very important aspect because when the light wave hits the particle it’s scattered or broadcasted without change of its wavelength. Another equally important phenomenon is that the smaller the wavelength in relation to the air particle the more the scattering (at the same wavelength). Remember we said blue light has the smallest wavelength, therefore its scatters more, followed by green and the least one is red.
How is the sky blue?
Flow with me, we know the atmosphere surrounding earth has a thickness of about 480km. The atmosphere has air particles while outside it is a vacuum, this is critical to objects traveling in space. Like any other object, light waves travel in a straight path without interference whatsoever until they enter the atmosphere. On reaching, the light collides with air particles and scattering occurs, this results in multiple light rays with the same wavelength. Since the Blue component is scattered the most, its color will be dominant. Rayleigh was able to establish the mathematical relationship of scattering. The intensity is inversely proportional to the wavelength to the power of four.
I = 1/λ4
Given that the wavelength of blue light is about 400 nanometer and that of red is 700 nanometers, it follows that blue light is scattered 9.38 times more than red. This explains why the sky appears blue.
The explanation is not just a nice physics story to tell neither was Rayleigh wanted to come up with a factual one for the sake of it. Colour is fascinating to man, adding beauty and unbelievably making heart happy. The flowers, the dress code, the buildings, the household items, the cars and almost everything is identified by the color. This is all because of light, and since the invention of light-emitting diodes, the color spectrum of bulbs is rich. Some applications of this principle include;
- Design and construction of color filters
- The building of light-emitting diodes
- Construction of diffusers for white light in bulbs – mostly found in entertainment joints.
The earth is rich in wonderful things, the vast sky blue being one. What are the myths and stories you heard of why the sky is blue? I advise you to visit a physics lab and do the practice of radiation of light to appreciate this principle farther. One more phenomenon to research is what causes the rainbow.