Why do we have sunsets?

Today in theme we were investigating why the sun makes the colours it does when it goes up and down. We did an experiment to investigate this.

Aim: To find out why the Sun makes different colours when going up and down (sunset and sunrise)

Equipment: A glass, a torch or overhead projector, a spoon, water, milk a sheet of white paper.

Method:

1. Fill the glass with water and stand it in front of the white paper.
2. Shine the torch through the side of the water-filled glass in the direction of the paper.
3. Observe what light strikes the paper. What colour is the light?
4. Add a few drops of milk to the glass and stir through ( Don't add too much milk - just enough to make the water slightly cloudy)
5. Shine the torch through the side of the glass like in step 2.
6. Observe what light strikes the paper, what colour is it now?
7. What does this mean for us on Earth?

What happened?
The water with no milk in it reflected clear onto the screen. The milky water reflected orange onto the screen.

What this means for us on Earth?
White light is a mixture of all of the colours in the spectrum. when you sine white light through a jar of milky water. The tiny milk particles scatter the blue light in all directions, and so not much of this blue light ends up striking the paper. This effect is called Rayleigh Scattering. Red light is not effected in this way. Instead it passes through the milk and can be seen as a bright orange tint on the paper behind the glass.

Rayleigh Scattering also causes Sunsets. During a sunset only the red and orange light rays get through the atmosphere directly. All blue colours are scattering by tiny particles of dust in the atmosphere. The Sun and sky therefore appear reddish orange and they light up the clouds in the same colour.