Why is the sky blue in the day and black in the night? asks Lamar (12)

Lamar – a brilliant question. I will ask my friends to think about it.

blue-sky

Lamar. I hope that you have had the opportunity of passing ‘white light’ through a prism and see the fantastic ‘spectrum’ of coloured light that results. If not then try ‘creating’ white light by using torches and ¬†coloured cellophane (blue, red, green) on each torch and shining them at a white piece of cardboard. Let me know what happens.

Things then get a little difficult. You have to think of the Sun’s white light reaching the atmosphere of the Earth. The two major components of the atmosphere¬†are nitrogen and oxygen. The structure of the molecules of these two components makes them very receptive to the blue part of the white light from the Sun. The air molecules absorb this blue part and then re-emit it in all directions. This is a process called ‘scattering’. Thus the blue sky. The rest of the (white minus some blue) sunlight passes onwards.

At night the Sun is shining on another part of the Earth, so no white light is falling on your part of the Earth. No light ….blackness.

Lamar . An interesting question, a complex answer. Feel free to ask another question.

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