How do rainbows form, and can you walk on one?

How it works

Sunlight looks white, but it is a mix of colours: red, orange, yellow, green, blue, indigo and violet. When light enters a round raindrop it bends, which scientists call refraction, then reflects off the back of the drop and bends again on the way out. Each colour bends by a slightly different amount, so the colours spread apart.

To see a rainbow, the Sun must be behind you and raindrops in front of you. Each drop sends just one colour towards your eyes, and millions of drops together build the coloured arc. That means two people standing apart are actually seeing slightly different rainbows.

A rainbow is really a full circle, but the ground hides the bottom half; from an aeroplane you can sometimes see the whole ring. Walk towards it and it moves away, so you can never reach the end. Sometimes a fainter second rainbow appears, with its colours in reverse order.

Where to see it in New Zealand

New Zealand's changeable weather, with sunshine and showers on the same day, makes rainbows a common sight. Near Kerikeri in Northland, Rainbow Falls has the Māori name Waianiwaniwa, meaning 'rainbow waters'. On a sunny day, the spray from a waterfall can show a small rainbow when the Sun is behind you.

Try it together

On a sunny morning or late afternoon, stand with your back to the Sun and spray a fine mist from a hose or spray bottle. Look for a rainbow in the mist. You can also put a glass of water on a sunny windowsill and look for colours on white paper. Never look straight at the Sun.