Sunday, February 05, 2012

Why Is The Sky Blue?

While browsing through the bookstore, as I am wont to do, I happened upon a really interesting book.
It’s called
Why Does A Ball Bounce? 101 Questions You Never Thought of Asking.
It’s written by Adam Hart-Davis and published by Firefly Books (2005).
So I bought it.
It's filled with really neat one page explanations of stuff.
My favorite page, thus far, is this one entitled Why is the sky blue?
It's a question I have wondered for a long time. The following is not my paraphrase [can I go to jail for doing this? Because seriously, jail does not appeal to me one bit] but in fact, it is the actual verbatim words:

This question was first answered by John Tyndall (1820-93), who in 1867 took over the running of London’s Royal Institution from Michael Faraday (1791-1867). A keen mountaineer, Tyndall was one of the first people to climb the Matterhorn. Before he attempted this, he calculated that the energy needed for the climb would be exactly the same as he would get by eating a ham sandwich; so that was all the food he took.
Back at the Royal Institution, he filled a glass tank with filtered, dust-free air, and noticed that he could not see a beam of light passing through it. He could see a beam of sunlight slanting across the room, and he realized it was visible only because the light was scattered by dust particles in the air. In his filtered air there was no dust to scatter the light.
He experimented by filling another tank with water and adding a teaspoonful of small particles (milk powder works well). A beam of light shone through it appeared bluish – the small particles scatter blue light. With a leap of imagination he realized that the sky is blue because small particles in the atmosphere – actually molecules of air – scatter blue light from the sun.
The sun lights up the whole of the sky during the day, and because air molecules scatter blue light in all directions, the whole sky looks blue. The light from the sun looks yellowish because although it is really white, some of the blue has been scattered away, and white minus blue makes yellow.
At sunrise, as in this photograph, [NOTE: the image I have attached above is not the same as that in the book, but it is similar] the sunlight arrives at a low angle and has to travel through much more atmosphere than later in the day. As a result more blue light is scattered, the sky looks deeper blue, and the sun looks yellow, orange or even red. At the same time it lights the clouds pink or orange.

It’s an interesting book.
Go buy it.
You will learn tons of interesting things, like (for instance), did you know that a million sugar cubes, piled vertically, would be 10 kilometres high? Yep, higher than Mount Everest. [No doubt, I’ve probably plopped a few kilometres worth into my coffees, over the years!]
If I were to ask the 102nd question though, it would not have to do with sugar cubes.
My question would be addressed to Mr. Tyndall, and it would be.... “Tell me John, was that ham sandwich enough?”

Note: For a more poetic and Biblically-inspired version of why the sky is blue, written at a time when I was more... Biblically-inspired, click -->


Alyce said...

That is exactly what I wanted to know (about the sandwich)! I can't imagine it was. This book looks like it would cover some of the same info that I've been reading in Bill Bryson's A Short History of Nearly Everything. It is such an enlightening read.

Cipriano said...

I've read that Bryson book and found it incredibly astute and entrancing.
As for the sandwich?
I would have needed a sandwich and a satchel filled with burgers!