Why The Sky is Blue | C. V. Raman

(Adapted from an English lecture given by “C. V. Raman” to school children on December 22, 1968, in his 80s)

Nature – A Wonder | Why The Sky is Blue

Every element of nature is a miracle. We do not see their miraculous nature because of our intimate habits. “Flowers bloom; it rains; the wind blows; day and night alternate …” These are just some of the everyday events. Try to look at it from a slightly different perspective. Definitely “looks amazing.

The sky is blue during the day. What a wonderful sight it is to see the clear sky so unblemished blue.

VIBGYOR – We do not have to go to test roads to find the answer to this question of why the sky is blue, leaving the other river in seven colors: red, orange, yellow, green, blue, dark blue, and purple (VIBGYOR). All you have to do is look at it and think about it. Usually it is not enough just to discover the mysteries of nature. You need to think deeply about them and unravel the problems embedded in them. It is very easy to answer these superficially. If you ask a botanist “why do the leaves look green” he will answer in a single word “chlorophyll“. With such answers you can get good marks in exams but such answers are not real answers.


Now let us look at some other things related to our question. Sunlight illuminates the sky and the atmosphere. At night we can see the invisible atmosphere through sunlight. Now let’s look at another question. You would have seen the clear sky on the full moon. You also know that lunar light is only 60 reflections of sunlight. Is it not strange that the sky does not look blue when viewed in moonlight? The sky, which looks blue in sunlight, does not look like that in moonlight. The answer is that lunar light is much less than sunlight. By comparison, lunar light is about one in five millionths of sunlight. Although it is very small, the reason we see it bright at night is because our eyes see the blue color of the sky because it is too bright for humans to see the true colors of human vision when compared to low light.

Spectrum and Atmosphere

Why do we see only blue when there are so many colors in the spectrum? What happened to the other colors? This is our question. This question becomes more complicated when it is linked to the next topic. That is, blue has the lowest brightness in the spectrum of sunlight: about one-fourth (1/40) of the total brightness of blue is only about one-fourth of what we see in the sky. Other colors that are too bright disappear. The blue color obscured the other colors. This is a remarkable fact.

Occasionally there are white clouds in the sky. The sight of such white clouds floating in the sky is one of the most amazing. Thus you will have seen the sky turn blue when there are white clouds. This is because when these clouds form, they absorb dust from the atmosphere and clean it up. The view of the sky with its spectacular blue color amidst the bright white clouds is something that everyone should enjoy. Now let’s see what’s in these white clouds. Many would call this steam. This is incorrect. In fact, white clouds are made up of droplets and dust. The remarkable thing is that clouds cannot form without dust.

Thus clouds form and clean the atmosphere to some extent. In fact when we look at the blue sky we look at the atmosphere of the earth. There is light scattering. We see only blue is still the answer to our question.

The weak light shines

In fact, the sky is green, yellow, and red. They are also brighter than blue. Yet why do we only see blue when they are missing? Here the human visual system (Vision) is a factor. The blue part of the spectrum, though less bright, hides other colors under certain conditions and is only visible to our eyes. Let’s see what those “conditions” are.

The Enemy of Colors

Let us learn about the nature of colors through an experiment. Take water and put some copper sulphate in it. Mix more ammonia in it. This solution is called kupramonium. When the solution is solid it will turn dark purple and now add more and more water to the solution. Now you can see the blue color of the penetrating light. Similarly dark blue is becoming more and more light blue but in the end it is light blue. The red and green light of the light spectrum penetrate the solution. Ain yellow light does not penetrate through the solution. Although blue is a small part of the spectrum, no other color seems to come through our solution. Let the reason for this come. Observe the light coming through the solution with the help of the Spectroscope. It can be seen that the yellow color is greatly reduced due to cuprammonium and it absorbs the yellow part. We don’t need to know here how this happens. The blue color is visible to our eyes as the yellow color of the light is absorbed. If only the brightness of yellow in the spectrum is reduced and then only blue is visible to our eyes. Generally, if you want to know any color, it should not be yellow. The enemy of yellow, for example, is because the leaves are green. However, the reason for the green color of the leaves is that they absorb the yellow color of chlorophyll.

Look at the land where the paddy crop has grown with anger. Its spectrum can be seen to be similar to the spectrum of the blue sky. However, a clear difference can be seen that the blue color in the spectrum is not present because it is removed by a pigment called ‘chrotinoid‘. If you look closely, you can see that there is no yellow color. If you want to see the green color in the leaves, you should not have yellow color. Yellow always plays an important role in the spectrum. But if yellow is removed then blue plays an important role. If the yellow color is not removed, the blue color will not appear. So these two work against each other.

In fact the entire spectrum can be divided into two where blue ends – i.e. green, yellow, orange and red one part and the other the second part.


Place of separation

The other colors in the first part are yellow though. Similarly, in the second part, blue is the most important color. Blue is the most important color in the yellow area. If you take the yellow part of it, it looks blue. This is the reason why the sky looks blue. It should be noted that the yellow brightness is reduced but not completely removed. Now before us it is my. The question arises as to how it is reduced. Let us look at the second part of the explanation of our question ‘why the sky is blue.

Why The Sky is Blue | C. V. Raman
Why The Sky is Blue | C. V. Raman

Just as the single word ‘chlorophyll’ answers why the color of the leaf is green, it can be answered in a single sentence by the scattering of light by molecules in the atmosphere.

Why do the masses of the atmosphere scatter light? Now we need to know about light waves. Some colors have large waves (Longwaves) and some small waves. Red, yellow and green are the big waves. So their scattering takes place less. The scattering of the remaining colors takes place very quickly (Quite Strongly). Because of this it is not visible to our eyes. The latter looks good.
Well, why is this difference in light scattering of colors?

The masses of the atmosphere are very, very small. Light waves are very small in comparison Let’s look at the water of a lake to understand this. Waves appear when the wind blows. A small piece of wood on it

Watch it float. Can you see this piece vibrating fast? The size of the mammoth is comparable to that of a tidal wave. Now look at a boat floating on the water that does not vibrate like a log. The size of the waves and the size of the float cause its vibration to be low or high. On the same basis colors with small waves scatter more and colors with large waves scatter less.

So the reason why the sky turns blue is because of the scattering of light by the elements in the atmosphere. Since the scattering of yellow with large waves (Longwaves) is less and less dense, only the scattering of blue at high and high intensities is much better.

In short, the reasons why the sky is blue are as follows.

  • We need very bright light to see the colors is a basic aspect of our visual ability so the sky is blue only in sunlight during the day.
  • Another aspect of our visual acuity – the blue part of the spectrum, which gains prominence when the yellow color is minimal even though it is weak.

One thought on “Why The Sky is Blue | C. V. Raman

  • September 11, 2020 at 2:07 am

    Nice information all in one post


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