"Hey Daddy, why is the sky blue?"

One of my most favourite things to do that I can't do anymore is to hold my sons hand. When he was small I would drop him off and pick him up from school. Sometimes I'd put him on the crossbar of my bicycle, other times we'd walk with his little hand in mine. I always loved that time. He was, as most kids are, intensely curious about the world, and would constantly ask me questions about the people in his life and the world around him.

Most of the time I could answer his questions fairly easily. I'm not saying that I'm super intelligent or anything, but sometimes the questions of kids are very basic. "What is that man doing?", "Why does he want to cross the road?", What would happen if a bus hit him?" "Why are bus's so big", "Can you drive a bus?", "What would happen if no-one was driving the bus?", "Yeah but what would happen if the bus was still going and no-one was driving it?".

My son was very much into the "What if" scenarios. He asked hypothetical's about everything. "What would you do if a tidal wave came down the street?", "That's not likely to happen?", "Yeah but IF it did happen, what would you do?", "I'd swim to higher ground, "Yeah but what if you couldn't swim?". "I CAN swim!", "But what if you couldn't", "I'd grab onto something that's floats", "But what if there were no floaty things?", "I'd grab a lamp post!", "Yeah but what if the water was deeper than the lamp posts?". He would always counter each answer with another question until he had reached some arbitrary junction in his head that told him that he had gotten enough of an answer. He still does it to a certain extent, even though he's now nearly 27.

The question that really stumped me when he was 5 though was, "Why is the sky blue?". It was the first time I'd ever been asked that and when I thought about it I realised I didn't have an answer. I knew there was no way he was going to accept the "It just is!" answer, and also realised that I had probably been given that answer when I was a kid as I had no information as to why the sky was blue. As I said I loved the time we spent just walking and talking and I loved the questions because I knew I was helping him figure out the world. I always wanted to be able to give him a proper answer to his questions rather than the brush off answers, "It just is" or "because God made it that way" or some other inane comment that really just proves that the person answering either doesn't know or doesn't care. When he asked me why the sky was blue and I realised I didn't know I told him that I would go and find out. And so, I did.

The answer to "why is the sky blue?" is, because of the 'Tyndall effect'. It is named after the man who discovered the effect, John Tyndall. If you want to read a short biography then look here: http://www.rigb.org/our-history/people/t/john-tyndall

The 'Tyndall effect' is the effect sunlight has when it interacts with particles in the upper athmosphere. Basically the light is scattered by the particles and broken up into the different colour wavelengths. Our eyes more readily see the shorter wavelengths and hence perceive the sky as blue.
To read a more detailed explanation of the 'Tyndall effect' try here: http://www.rigb.org/our-history/iconic-objects/iconic-objects-list/tyndall-blue-sky

My son was happy enough with the information I gave him and even remembers why the sky is blue now that he's an adult. Hopefully you also have the enquiring mind of a 5 year old and this knowledge will help satisfy your curiosity!

All images are from https://pixabay.com/

Now you can safely answer that the reason the sky is blue is mostly due to an Irishman! Not ME, John Tyndall! ;)