Why is the Sky Blue?

My daughter and I were walking along a beach in Anglesey, it had been a hot and sunny day and the sun was setting, putting on a beautiful display of fiery reds and oranges as it slowly disappeared over the horizon. I was explaining to Abbey why the sun was disappearing and how the Earth was actually a giant ball which was spinning once every 24 hours when she asked me ‘why did the sky go red’.

I thought about this for a while, certain that I knew the answer and it was just a case of digging it out from one of the dusty files packed away in a long forgotten filing cabinet, deep inside my ageing mind. When suddenly I realized, I didn’t know, I didn’t have a clue, I didn’t even know why the sky was blue for that matter, or why, if the moon reflected sunlight why didn’t the moon appear yellow?

I had to admit to Abbey that I didn’t know the answer to that question and that when we got home we should endeavor to find out.

After our beach holiday we arrived home and immediately Abbey and I began our search for the answer to our question.

We looked through a number of Abbey’s science books, she was only 6 and yet had a rather substantial collection, and she has always been keen on science and had amassed quite a collection of educational books and Science toys. We eventually found our answer in a small hardback book about weather. In addition to the answer, it also suggested a science experiment you could do in your home to recreate this phenomenon.
The answer given in the book was something like this….

Why is the sky blue?
White light contains light of every color. Blue light has the smallest wavelength and therefore is reflected here, there and everywhere from dust in the atmosphere, red light is not so much. This is rather like small ripples on a pond reflecting back from the floating body of a duck, whilst larger swells do not reflect back.

So when the sunlight passes through the atmosphere, the blue light bounces about up there making the sky appear blue.

Why does the sun turn red at sunset?
When the sun is low in the sky it has a lot more atmosphere to pass through before it gets to you. The more atmosphere the white light has to pass through, the more light from the blue end of the scale is refracted away leaving only light from the red end of the spectrum.

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