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How do rainbows work?

There’s nothing so welcome on a hot day as summer rain. And where there’s sunshine and rain together it usually means a beautiful, clear rainbow! Why? Let’s find out by making a rainbow of our own.

Rainbow over Carnarvon Reserve in Queensland. Photo Wayne Lawler/EcoPix.
Rainbow over Carnarvon Reserve in Queensland. Photo Wayne Lawler/EcoPix.

What you’ll need:

  • A dish of water (not too deep)
  • A small mirror
  • White paper
  • A sunny day
Sun shining through a window, reflecting off a mirror in a bowl of water, to make a rainbow.

Procedure:

  1. Place the mirror in the dish of water so that the sun shines onto it
  2. Hold up your sheet of white paper facing the mirror and adjust position until a shimmering rainbow appears on it.

How it works:

When sunshine hits water drops it slows down and is bent because water is more dense than air. The water acts much like a mirror, reflecting light, but at slightly different angles, which causes light to be split and reflected back in different colours of the rainbow.

You can only see a rainbow if the sun is behind you and you’re facing the rain.