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Sunday, 16 July 2017

Why the color of sky is blue?


When we see the blue colour of the sky, then a question comes to our mind that why the colour of the sky is blue instead of green, red or yellow. In order to understand the phenomenon behind the blue colour of the sky, we should keep in mind the following things.

SUNLIGHT


Sunlight is actually a white light. It consists of seven colours and the wavelength of each colour is different. Seven colours of white light (sunlight) along with their wavelengths are given below;


blue sky
why the colour of the sky is blue
                


                                       1)      Violet 380 - 450 nm

                                       2)      Blue 450 - 490 nm


             
                          3)      Cyan 490 - 520 nm

                                       4)      Green 520 - 560 nm

                                       5)      Yellow 560 - 590 nm


                                       6)      Orange 590 - 635 nm


                                       7)      Red 635 - 700 nm

               

What is the wavelength of visible light?

The wavelength of visible light is in between 400 - 700 nm. The human eye can see only the lights which have wavelengths 400 – 700 nm. The lights which have wavelengths less than 400 nm and greater than 700 nm are invisible to the human eye.

Scattering phenomenon of lights


Different lights have different wavelengths. Some lights have narrow wavelengths and some lights have wider wavelengths. Lights with narrow wavelengths scatter more than lights with wider wavelength.

WHY THE COLOUR OF SKY IS BLUE?


After understanding these things, we will be better able to understand the phenomenon behind the blue colour of the sky. Let’s try to know the cause of this interesting phenomenon.
As we know that sunlight is actually a white light. This white light consists of seven colours and the wavelength of each colour is different. This white light enters the earth’s atmosphere. In earth’s atmosphere, there are particles of air. When white light strikes with these particles than the scattering of light take place. As we know that the light with narrow wavelength scatters more than the light with wider wavelength. In these seven colours of white light, the violet light has the narrow wavelength. It means that the violet light scatters more than the other lights. The wavelength of scattering violet light is less than 400 nm. As we know that the wavelength of visible light is 400-700 nm. In this way, the violet light is invisible to the human eye. After the violet light, there comes the blue light with narrow wavelength. The wavelength of blue colour is 450-490 nm. It means that the blue light scatters in the visible region. After blue light cyan, green, yellow, orange and red lights also scatter. These lights have wider wavelengths. As we know that the light with wider wavelength scatters less than the light with narrow wavelength. That’s why the colour of the sky is blue rather than green, red or yellow.







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