Look at the light beam from the end of the container and then from the middle. A card placed in front of the light at the end of the tank may help students see the colour. The room should be darkened. Light is a wave and each of these colours has a different frequency and therefore a different wavelength of light. When light collides with gases in the earth's atmosphere the light is scattered.
Blue light has a short wavelength and scatters more than red light.
The light reaching our eyes from the sky is blue. At sunrise and sunset, sunlight passes through far more air before reaching us. Extension Activities Move your eyes along the container. Try the activity using a piece of cardboard with a hole punched in it to produce a sharper light beam. Investigate the effect of placing a polarising film in the light path.