h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

My elder daughter is two and a half.

Yesterday we were in the garden & she looked up & aksed me why the sky is blue.

Now, I know about Raleigh scattering. I am aware of on axis/off axis scattering, the third power dependency upon wavelength for scattering by tiny particles, and even the possible physiological effects causing the sky to appear "blue" rather than "violet". What I am not too sure about is how I explain this to a two-year-old while making it interesting rather than making her wish she never asked.

In fact, what I did was talk about rainbows (she is aware of such things) and said that the sun gives us all colours in the rainbow but only the blue bounces out of the sky towards us.

Does anyone have any other ideas as to how I can describe this phonominen to a kiddy under three? She quite often asks the same question several times, so I may well be asked again and would like to be a little better prepared.

And yes. I was well chuffed that she asked!



Ugi

I think you did a very good job answering the question yourself, and you are correct - the sky is like a giant rainbow. We see the blue bit of it, while the red goes on to where the sun is setting to make the sunset red.

Thanks Gnomon. Like the sunset bit. Not sure that she knows that sunsets are red yet, but we'll have to see if we can see some on our upcoming holiday.

Any ideas about prisms and showing that sunlight has all colours of the rainbow? I never seen to have a triangular prism to hand! I'm sure it can be done with a glass of water, but I couldn't make it work on the spot.



Ugi

If you have an old set of prismatic binoculars that you don't want any more, you can take them apart and get wonderful prisms out of them. Prismatic binoculars are the sort where the lens you put against your eye is not lined up with the big lens at the other end.

Hummm... yes, the old heavy type - I do have some old ones of my grandfather's somewhere which are not likely to be used again. Otherwise, I'm sure it's the sort of thing a charity shop will have.

Good thought. Thanks.



Ugi