Why the Sky is Blue?

National Science Day is celebrated in India on 28th February each year to mark the discovery of the Raman Effect by Sir C.V. Raman in 1928.

Sir Chandrashekhara Venkat Raman (7 November 1888 – 21st Nov 1970), an Indian physicist who carried out groundbreaking work in the field of light scattering, which earned him the 1930 Nobel Prize for physics and was the first person in Asia to obtain this award for achievements in science.

He discovered that when light traverses a transparent material, some of the deflected light changes wavelength and amplitude. This phenomenon is known as Raman scattering and results from the Raman Effect. In 1954, the Indian government honoured him with India’s highest civilian award, the Bharat Ratna.

We have been inspired by Professor CV Raman’s lecture “Why the Sky is Blue? delivered on 22nd December, 1968 at the foundation stone laying ceremony of the Community Science Centre, Ahmedabad. It serves as a sort of manifesto for us, for what we are aiming at – to involve the young people in observing and exploring the environment, trying to solve real-world problems with various projects involving Science Technology Engineering Arts and Maths (STEAM), inter and multidisciplinary approach, conducting heritage trails in sciences and art museums and workshops in the city which includes the tangible, the intangible culture and traditions of the community and the natural heritage, which lie all around us.

Excerpts from the Lecture “Why the Sky is Blue” that follow illustrate the “Spirit of Science” and Prof. Raman’s comments on how presently science is taught and suggestions how the spirit of science can be cultivated by everyone.

..As I look up and see, the sky is blue; not everywhere as there are many clouds. I choose this subject for the simple reason that this is an example of something you do not have to go to the laboratory to see. Just look up, look at the sky and I think it also is an example of the spirit of science. You learn science by keeping your eyes and ears open and looking around at this world. The real inspiration of science, at least to me, has essentially been the love of nature. Really, in this world, wherever we see, we see all kinds of miracles happening in nature. To me, everything I see is something incredible, something absolutely incredible. We take it all for granted. But I think, the essence of the scientific spirit is to look behind and beyond and to see the wonderful world it is that we live in. And everything that we see, presents to us not a subject for curiosity, but a challenge, a challenge to the spirit of man to try to understand something of this vast mystery that surrounds us.

Science continually attempts to meet this challenge to the spirit of man.


“Why the sky is blue?”
I raise this question because it is an easy subject. I only have to look up and see that the sky is blue. But why is it blue?
The interesting point is that it is easy to answer this question in a casual way. If you ask a Botanist a question, why are leaves green, he murmurs, “Chlorophyll”. Finished. You see, all scientific questions can be disposed off in that summary fashion, in one or two words. You can surely pass your examinations with that kind of answer, but that is not the real answer.. The scientific challenge of nature is to think, not only to discover but to think, to think continually, and try to penetrate this mystery; “Why is it blue?”.
Now suppose we put this problem before the young people. Don’t read any book about it, don’t ask your teacher. Let us sit down and try to think out this problem: why is the sky blue. Look at it as it is a completely new scientific problem about which nobody has troubled himself before. You sit down and think it out and you will find it the most exciting thing to ask yourself that question and see if you can discover the answer for yourself. Now I will put it to you in this way. The best way to answer a question is to ask another question…

“Why is the sky blue?” Oh, I could have started with … the scattering of light by the molecules of the atmosphere. I could have dismissed the whole lecture in one sentence. I could have said just as the botanist says “Why is it green?” “Just chlorophyll.” One sentence “Then Sir”, you would ask me, “why all this lecture?” Because, my young friends, I want you to realise that the spirit of science is not finding short and quick answers. The spirit of science is to delve deeper – and that is what I want to bring home to my audience – and deeper. Don’t be satisfied with the short and ready quick answers. You must never be content with that. You must look around and think and ask all sorts of questions; look around the problem and search, and go on searching. In the course of time, you will find some of the truth, but you never reach the end.

I think that dreams are the best part of life. It is not the realisation but the anticipation; I am going to make a discovery tomorrow, that makes a man of science work hard, whether he makes the discovery or not and this is what I want to emphasize once again. Science is essentially and entirely a matter of the human spirit. What does a poet do? What does a painter do? What a great sculptor does? He takes a block of marble, chips, goes on chipping and chipping. At the end of it, he produces the dream in the marble. We admire it. But, my young friends, please remember what a tremendous amount of concentrated effort has gone into producing that marble piece. It is the hope of realising something, which will last for every which we will admire forever that made him undertake all that work. Essentially, I do not think there is the least difference whatever between the urge that drives the man of science to devote his life to science, to search for knowledge and the urge that makes workers in other fields devote their lives to achieving something. The greatest thing in life is not the achievement, it is the desire to achieve. It is the effort that we put in that ultimately is the greatest satisfaction. Effort to achieve something, in the hope of getting something; let it come or not come, but it is the effort that makes life worth living and if you don’t feel the urge towards the search for knowledge, you can never hope to be the man of science. …The real business of a scientific man is to try to find something real and to look forward to the acquirement of knowledge.

The subject of my lecture is not the blue of the sky but, as you must have all understood by this time, it is the spirit of science. What is science? And how can we in this country hope to advance science…it is only the peg to hang the subject upon. Well, the story begins there. The question is how does light interact with molecules? And what happens with molecules and what are molecules and so on. Science never stops. It is going on. The more you find, the more that you have to find. That is the attraction of science..the real point is that it is an endless quest and every new discovery opens new paths for discovery. New questions arise requiring new answers.

The quest, you see, is more the deeper you go…my idea, as I told you is just to give you a simple glimpse into how a familiar phenomenon is linked up with deeper problems of physics and chemistry. That is the lesson we learn today from the familiar fact, it is not necessary to hunt round the textbooks to find the problems of science. You keep your eyes open and you see that all around you, the whole world bristles with problems to solve; but you must have the wit to solve it. And you must have the strength of mind to keep going at it until you get at something; this is the lesson I want to bring home to the younger generation in front of me.


What is the use of all this? Ultimately, the aim of scientific knowledge is to benefit human life and that comes automatically because the problems with which we are concerned in science are always those that lie nearest to hand. They are concerned with things about us. So long as we deal with the problems which arise out of our environment, you never can say that any particular piece of work can be useless. The most important, the most fundamental investigations, though at first might seem an abstraction of nature, are precisely those, which in due course affect human life and human activities most profoundly. This is a very heartening thing because one should not think that scientific work in order to be valuable, should be useful. Scientific work is valuable because it will ultimately prove its value for the whole of human life and human activity. That is the history of modern science. Science has altered the perception of things around us. And precisely those scientists who have laboured not with the aim of producing this or that, but who have worked with the sole desire to advance knowledge, ultimately prove to be the greatest benefactors of humanity.

From Professor C.V. Raman’s lecture, “Why the Sky is Blue”
Published as a booklet by Vigyan Prasar.

Illustration by Sanjukta Das


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