We have witnessed how the sky changes its colour in different phases of the day. The colour of the sky depends on various factors. We all know that the atmosphere is colourless but the sky sometimes appears blue. It also attains an orange colour during sunrise and sunset. What is the scientific reason behind it?
The change in colour of the sky is a physical phenomenon where the light rays scatter to form certain colours at a particular time of the day. Here is what you need to know about why the sky is blue generally, and how it forms different colours during sunsets and sunrises.
We all know that the sunlight is colourless. It contains seven different colours to form a VIBGYOR. It all happens when the white sunlight falls on the gas molecules and the suspended particles present in the atmosphere. This phenomenon is called Rayleigh’s Scattering.
We all know that white light is made of colourful rays with different wavelengths. In this phenomenon, the light rays of smaller wavelengths fall on the particles and scatter more, whereas the light rays of higher wavelengths pass through. The smaller wavelength light rays fall in the violet, indigo and blue categories resulting in the formation of blue colour of the sky during the daytime. Hence, the sky appears blue due to the scattering of the blue light more than the red light.
The same phenomenon that gives the sky its blue colour is also responsible for the formation of other colours in different phases of the daytime. The effect changes due to the position of the sun in the sky.
During sunrise and sunset, the light rays coming from the sun cross more air in the atmosphere. When the sun is closer to the horizon, the light rays in the blue wavelength range scatter more. It means that these light rays scatter away from our eyes.
The remaining light rays falling in the wavelength ranges of red, orange and yellow directly fall on our eyes. Due to the scattering of blue light away from our eyes, we can only see these colours prominently; although you will need some clouds to understand the colour of light rays falling during the sunset and sunrise.
The different combinations of red, yellow and orange light rays emitting from the sun cause the different colours of the sky. These colours of longer wavelengths become more in the sun rays resulting in colours that do not contain violet and blue colours. This is why the sunrise and sunset sky colour is different from the rest of the day.
On the other hand, when the sun rises up in the sky above the horizon, the scattering phenomenon reduces and makes the sky look blue. As the path of the light travelling through the atmosphere reduces, the sky turns out to be bluish. Hence, the same scientific explanation of Rayleigh’s Scattering is responsible for the sunset and sunrise colours. It is because of this reason the sun also appears reddish or orange in colour during the sunset and sunrise.
The Colour of the Sky Changing With the Position of the Sun
Now that you know why the sky is blue in colour, another question in your curious mind will appear. Why is the sky not violet in colour? We all know that the shortest wavelength we can see in light is violet. It is obvious that the lights with shorter wavelengths tend to get more reflected and scattered. It means that the sky should be violet not blue in colour. What is the reason behind it? Let us delve deeper into physics.
The violet rays fall in the range of 380 nanometres of wavelength. On the other hand, the wavelength of blue light is bigger. It falls within the range of 450 and 495 nanometres. Hence, the wavelength of blue is bigger than violet.
You will be surprised to know that the sky is actually violet in colour. On the other hand, the amount of blue light emitted by the sun is more than the violet. Moreover, the human eyes cannot perceive the violet colour the way it processes blue. This is the reason why the colour appears to be blue, not violet in our eyes.
The light rays coming out of the sun contain all the colours of a VIBGYOR. It means the sun will show all the colours at once. All these colours are the prime components of white light. As we have studied Newton’s Colour Wheel, the proper combination of these seven distinct colours leads to white. Hence, the sun is actually white in colour.
Considering Rayleigh’s Effect, we can clearly understand that the different colours of the sky are due to the presence of a thick atmosphere. The planets with minimum or no atmosphere will not see the sky as blue or any colour. It will appear dark. In fact, we can see stars during the daytime on the planets and moons with no atmosphere.
On the other hand, Venus has a thick atmosphere and receives nearly 1.9 times more sunlight than the Earth. This is why the sky appears orange. Mars’ atmosphere appears yellowish during the daytime as its atmosphere is less than 1% of the Earth’s atmosphere.
We now clearly understand that the diffraction of various light rays in the atmosphere actually is responsible for the changes in the colour of the sky. This is why the sunrise and sunset colours of the sun and the sky vary. We hope you enjoyed reading the blog and will now be able to tell your friends why the sky is blue in colour.