Rainbows appear in the sky after it has rained, when the sun shines on tiny drops of water in the sky. Rainbows form an arc (or a 'bow') of colours in the sky, with red light on the outside of the arc, and violet inside.
The order of the colours is always red, orange, yellow, green, blue, indigo (a very dark blue), and violet. This order is remembered by the mnemonic (or memory aid) Roy G. Biv or alternatively VIBGYOR. The range of colours is called the 'spectrum'.
Rainbow colours result from the splitting of the white light of the sun, or even the white light from a light bulb. This light looks white but is actually made up of a blend of all the colours of the rainbow. Each colour has a different energy - with violet having the most energy and red, the least.
If light from the sun is white, why is the sky blue? Normally the sky appears blue, because the higher energy blue part of the spectrum in the white light from the sun is scattered around more in the gases of the sky. At the horizon, less scattered light reaches your eyes, so the sky usually seems paler. Sometimes at sunset, particles of dust scatter the light differently and red/orange colours may predominate.
Natural phenomena such as rainbows have always fascinated humans. In Aboriginal culture, the Rainbow Serpent (Nagalyod) is one of the Dreamtime creators who moves around the sky. The Rainbow Serpent is seen as both a creative spirit and a natural destructive force and is always associated with creeks and billabongs. It is a source of life and protection for the land.
Coloured cellophane produces magic results since colours become muddled up when placed under it.
Colours can appear to mix up when they move past your eye quickly.
For the really adventurous, boil up a quarter of sliced red cabbage in water and leave it to cool. Pour off the purple juice. Taking small samples of juice in a spoon or glass, add a little sample of a variety of household products and watch the colour change. Try adding salt as your first test. There is no colour change. This is your scientific control.
This juice is an example of an acid/base indicator - much like the indicator you might use to check the pH (or acidity) of your swimming pool, to keep it near neutral.
You could try this experiment using juice from a can of beetroot - rather than making the cabbage indicator. Beetroot juice is already acid, so lemon juice won't make much difference to the very dark red colour. Strong bases like laundry products will change the coloured dye to purple or even blue.
Vegetable dyes have been used for centuries to colour paints and materials for coloured clothes, to decorate and brighten our human activities.
All activities are designed to be performed under the supervision of a responsible adult who is aware of any conditions which might preclude the safe participation of the child with regard to allergies to food, or other household or environmental agents.
http://www.weatherwizkids.com/rainbow2.htm (examining primary colours)
http://www.youtube.com/watch?v=6OWxI1nD8Hk (make an origami rainbow)
http://en.wikipedia.org/wiki/Rainbow (about rainbows)
Also check the websites of the Bureau of Meteorology, Museum Victoria or the Powerhouse Museum Sydney.
Article written by Kathy Andrewartha (B.App.Sci., M.Sc., B.A., Grad Dip. Info. Sci.). Kathy studied Biochemistry at Swinburne and La Trobe Universities and has worked on research topics involving both plants and animals. She enjoys teaching science at all levels. She particularly likes presenting science to young children, and is passionate about stimulating active learning and analytical thinking about scientific topics.