Why is the sky blue?

Perhaps you often hear the question from curious children about stuff happening in the surroundings. Questions like ‘why does the sun move around the earth’ or ‘how many stars are there in the sky or ‘why does the tide come in the river’ or ‘why the sky is blue etc. This article entirely focuses on why sky is blue in color. Perhaps you have the answer when a child of 5 years asks you. But when a boy or a girl from the 10th standard asks you ‘why sky is blue color’, you need to have enough scientific knowledge to provide the answer to that teenager. So, the article continues with the answer of ‘why sky is blue in color’.

Myths about the Color of the Sky

There are several myths which are extremely popular nowadays. Students and children sometimes receive those answers, but these are incorrect. One should not manipulate the fact regarding the color of the sky. Sometimes, it can be heard that the color of the oxygen gas is blue, and there is more than 30% oxygen in the air. This is the reason for which the sky is blue. Apart from that, the reflection of the ocean makes the sky blue, or the light that comes from the sun has a blue tint. These are some of the misconceptions and fake reasons circulated as the answers to why sky is blue.

Understanding the white light

To discuss this section, first, you need to know the characteristics of light and how it works. To discuss the characters, you must know about the light of the sunlight and how it reacts to the sky visible from the earth. The sunlight has seven different colors. The sun emits white light, which has red, orange, yellow, green, blue, indigo and violet colors. The mixture of all these colors creates white light. You might know that light is nothing but a wave. Wave has its wavelength. So, it can be stated that the above mentioned seven different color lights have seven different wavelengths. The sun emits white light with a wide spectrum. The colors are from different wavelengths. Red has the highest wavelength, and violet has the lowest one.

Reasons for ‘Why the sky is blue’?

There are three real factors for which you can see the blue sky.

First reason

Firstly, the lights with various wavelengths, the earth are molecular atmosphere, and finally, the sensitivity of your vision. The highest-energy light has the shortest wavelength, and the lowest energy light has the highest wavelength. To prove this, take a prism and put it under the sun; you can see seven different colors and a formation. As you know, red light has a larger wavelength, and violet has a minimal wavelength. So, red will be on the top of the rest of the six lights, and violet will be at the bottom.

Second reason

There is another concept called scattering. The less the wavelength is, the more the light will scatter. Red has the highest wavelength. Hence the scattering capability of red is minimal. On the contrary, violet and indigo have the most scattering capability. But the amount of scattering of these two lights is extremely high, which does not allow them to form color in the environment. After these two lights, blue light has the highest scattering ability. This is because when the sunlight touches the molecules like dust and water particles, it reflects—all the seven lights scattered in different directions. When the particles are smaller, the blue light scatters the most as it has a tinier wavelength. The earth’s sky has minor microscopic air particles, which helps the blue color scatter the most. Hence we see the color of the sky as blue.

Third reason

Here comes the third and final reason mentioned before: the sensitivity of our eye vision. You might have thought, why can’t we see the violet or the indigo lights as these two scatters more than the blue color. To answer this question, you need to know about the law of Rayleigh scattering. You will be able to know that the human eyes cannot read the wavelength of violet and indigo. The theory states that ‘the violet light has the short-wavelength limit of the human eyes scatters more than nine times more frequently than the red light at the long-wavelength limit.

Why is sky orange during sunrise and sunset?

When the sun is just above the head or at least high in the sky, it is more likely that the color of the sky is blue. This is because the sun's light scatters the blue light more than any light. Hence, the color of the sky shows blue most of the day. However, the sky seems orange and red in the evening time. This occurs because of the position of the sun. The sun goes below the horizon in the evening. Hence, the light has to travel more, and the blue light scatters more which is hardly visible with your eyes. At this moment, the orange and the red light scatter less. The light scatters just once or twice before you see the light with your naked eyes. Due to this reason, you see the evening lights red or orange.

If you wonder about the color of the sky on other planets, you need to understand that the color of the sky on other planets is not always blue. From the above theories, it is clear that the color depends upon the planet's atmosphere. For example, mars have a thinner atmosphere than earth which scatters light differently. As the amount of scattering is lower, the color of the sky on mars shows reddish or orange in the daytime. Hence, it is clear that the color of the sky does not depend upon the planet, but the planet’s atmosphere is the reason which decides the color of its sky.  


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