For many a year scientists and poets alike pondered on why the sky was blue. Many thought that it was due to small droplets of water vapour in the atmosphere and indeed many still do. If the droplets of water vapour did indeed cause the blue colour we see, there would be more variation of sky colour depending on the variation of humidity, and this isn’t the case. A cloudless sky is as blue in Saudi Arabia as it is in Connemara.
So what does cause it?
We can thank County Carlow and one of its resident scientists John Tyndall for the answer to this question.
Tyndall discovered that when light passes through a clear fluid which has small particles suspended in it, the blue light scatters more strongly than red light. This can be easily shown with a tank of water and a little soap; when a beam of white light flows through the tank from one end to the other, at the sides the beam of light can be seen through a blue light while the light seen directly from the end is reddened.
The Tyndall Effect can be seen in this piece of opalescent glass where the orange light shines through while the blue light gets scattered within the glass.
So the next time you look up at the sky while the sun shines white light at the earth, its the blue light being scattered by the molecules in the sky that is giving the sky its blue colour while the red and orange colours shine through to us on the ground, giving the sun its yellow/red/orange hue.