What's happening?

Sunlight is a mixture of all the colours of the rainbow that we see together as white light (plus lots of light energy that we can't see).

The molecules of air in our atmosphere are just the right size to scatter the blue part of sunlight. The scattered blue light spreads all over the sky. That's why sunlight looks white just where the sun is, but blue everywhere else.

The milk in the glass scatters the light from the flashlight in a similar way.

This is called Rayleigh scattering. It's also exactly what makes some people's eyes blue. Molecules in the front of the iris scatter blue light. You can think of people with blue eyes having little skies in their eyes.

The added milk in the water made the light from the flashlight look a bit orange, because the extra amount now scatters red light. This is what happens at sunset; the sun at the horizon shines through a thicker layer of the atmosphere, and the red and orange light is scattered.

• Return to the experiment.
  

Excerpt from The Jumbo Book of Science by the Ontario Science Centre, used by permission of Kids Can Press Ltd., Toronto.