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Why is the sky blue?

Team StoryWeavers|August 10, 2022, 17:47 IST|

Hello young learners,

Welcome to another episode of Kiki’s Knowledge Corner. It’s a beautiful day at Electropolis. When Jax and Jane came to visit, we had fun in the garden, admiring the clear blue sky and enjoying the pleasant weather.

That’s when Jane asked me: Why is the sky blue? The science behind the colour of the sky is quite interesting, and I thought that you all young learners would be curious to know as well.

The sun connection

The colour of the sky depends on the light from the sun. Are you confused? Here is the connection: 

The light from the sun, called white light, reaches the atmosphere of the earth. This atmosphere is a layer of gas that surrounds the earth along with some solid and liquid particles. These particles in the sky split the white light from the sun and make it appear in different coloured lights.

This process is called the scattering of light into seven different colours – violet, indigo, blue, green, yellow, orange and red (VIBGYOR to remember easily). In other words, the sun’s light is made up of the colours of the rainbow. And when these particles in the atmosphere scatter the white light from the sun, it so happens that the ‘blue’ light has the perfect wavelength to get scattered. (Light travels in the form of waves and the length of each wave decides whether they are visible to the human eye)

Image courtesy: NASA

Science says that the colours with shorter wavelengths, such as violet and blue, get scattered before those that have longer wavelengths, such as orange, yellow and red. The wavelength of blue light is appropriately short and choppy. It gets scattered just enough so that the sky seems blue to us.

Why is the sky orange sometimes?

Even though the sky is blue for the most part of the day, you may have noticed that a part of the sky is orange during sunrise and sunset. It is because the rays of the sun at those times of the day are long and have to travel longer distances. The blue light waves are too short to be visible to the human eye. However, during sunrise and sunset, the orange light gets scattered just enough that orange and red colours are visible to the naked eye!

Another factor that affects the colour of the sky is – air pollution. Having more pollutants, smoke, and different gases causes the blue light to scatter away and make orange and red more visible to the human eye. 

Orange sky during sunset Courtesy: creative commons

In fact, did you know that the sky was not blue but orange about 2.5 billion years ago? That’s because the air was more toxic and made by a fog of vicious vapours: carbon monoxide, carbon dioxide, nitrogen, cyanide, and methane. This gave the sky an orange tint and the land a strange glow.

Later, photosynthesis caused by the aquatic plants pumped more and more oxygen into the atmosphere, making it less toxic and filling the sky with more oxygen. And the sky became blue!

What is the actual colour of the sky?

You may have noticed that the sky is blue in the morning, a shade of grey in the evening and black at night. That would have made you wonder, what is the actual colour of the sky? 

In simple words, the sky is a transparent layer of air. Imagine the sky as a space where different colours can play. And when coloured waves of light bump into the air, it gets the colours. 

Now that you know why the sky takes different colours, can you tell us why the seawater is blue in the comments?

About the Author

Aparna is a mom, singer and dreamer. At BYJU'S, she writes stories about learning for children. She believes in the power of music, especially ghazal, the magic of the universe and happy learners. When not writing or singing, you will find her intensely engaged in conversations about life and the power of words.

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