Rainbow of colours with red, green and blue clearly visible. Photo from iStockphoto.com/Stephan Hoerold.

White light is made up of various colors.

Splitting light

Discover how to split white light into a rainbow of colours, just as Sir Isaac Newton did hundreds of years ago.

  • 18 September 2006 | Updated 14 October 2011

Astronomers are able to determine the composition of the the Sun by studying its light, with a technique known as spectroscopy. This technique can also be used to determine the chemicals elements present in a star or planet's atmosphere.

What you need

To do this activity you will need:

  • sunlight
  • a piece of card with a one millimetre wide slit cut into the middle
  • a straight-sided glass filled with water
  • a sheet of white A4 paper.

What to do

  1. Fill a straight-sided glass with water and tape the card onto the side of the glass.
  2. Place the white sheet of paper close to a window where sunlight is entering.
  3. Stand the glass on the paper with the slit facing towards the Sun.
  4. The sunlight should pass through the slit and split into its colour components as it enters the glass. The colours should appear on the paper.

What's happening?

White light is a mixture of many different colours. Sir Isaac Newton proved this more than 300 years ago when he directed a beam of sunlight through a slit and prism in a darkened room in 1666.

The prism bent, or refracted, the white light so that it fanned out into a rainbow (spectrum) of colours.

Splitting light using prisms is known as spectroscopy. Each chemical element has a unique signature when its light is split up.

Astronomers use spectroscopy to determine what planets and stars are made of by examining their light.

See other activities from Physics activities.