Tuesday, January 22, 2013
The question “Why is the Sky Blue?” is probably the most asked science question by kids in the world. The first steps to answering this question occurred when Sir Isaac Newton split ordinary white light down into its constituent colors ---
The final piece of the puzzle as to why the sky was blue was put in place by John Tyndall in 1859. He discovered that if you have a clear liquid and mix in some very small molecules the blue portions of the white light are scattered more than any other. You can test this at home with some water in a bottle and adding either milk or a small amount of soap. The image below replicates this experiment – there are two bottles filled with water, the one on the right has just ordinary tap water in it, the bottle on the left has tap water and a small amount of soapy water mixed in. As you can see they both have the same white beam passing through them, yet the one with the soapy molecules in it clearly has a more blue color to it. This is The Tyndall Effect in operation.
It is the Tyndall Effect that explains why the sky is blue. the Tyndall Effect can also be called Rayleigh Scattering, as it was examined more extensively by Lord Rayleigh in the years following Tyndall’s discovery.
So now that we know how molecules can change the color of light, we then need to transfer the experiment above with Earths atmosphere and why our sky is blue -
As sunlight passes through our atmosphere it interacts with the molecules of Oxygen and Nitrogen in the atmosphere. These two elements scatter the blue light in all directions in a similar way to which the light was scattered by the soapy water in the image above.
