Professor Kettlewick
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Try this with a grown-up

A sunset in a glass

Make the sky and a sunset in a glass of water, the way Professor Kettlewick does in Colours of the Sky.

A torch shining through a glass of milky water on the workbench

You will need

  • A tall, clear glass
  • Water
  • A little milk
  • A torch
  • A dark room

What to do

  1. Fill the glass with water.
  2. Stir in a drop or two of milk. The water should look only a little cloudy.
  3. Turn the lights off and shine the torch at one side of the glass.
  4. Look at the glass from the side. The milky water glows a little blue, like the sky.
  5. Now look through the glass towards the torch, from the other end. The light glows orange, like a sunset!

Why does it work?

The tiny bits of milk bounce blue light off to the sides, just as the air does with sunlight, so the side of the glass looks blue. The light that comes straight through has lost some of its blue, so it looks orange. At sunset, sunlight travels through lots more air to reach you, so it glows orange too.

It’s in Episode 1, Colours of the Sky.

Watch the episode