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Rainbow FAQ

Make a Rainbow - More Questions?

1. Where does the colour in rainbows actually come from?

Simple answer

The colour was actually in the sunlight all along – it’s just that normally all the colours of light are mixed together. Your eyes see a mixture of different colours of light as white. Rainbows are what happens when those colours split up and then your eyes can tell the colours apart! 

Complicated answer

Light is made up of waves and each wave has a wavelength – your eyes will see different wavelengths as different colours! Longer wavelengths of visible light are more red and shorter wavelengths of visible light are more blue. The light from the sun is a mix of different wavelengths so your eyes see this mixture as white. When a rainbow forms the different wavelengths are split up so your eyes can tell the colours apart. 

2. Why do rainbows only come out after rain? 

Simple answer

Rainbows are formed by light bouncing around inside droplets of water but the different colours of light bounce about in the droplets differently so by the time the light leaves the droplets the colours have split up! After a rain shower when the clouds clear and the sun shines again there are still droplets of water in the sky and they cause the rainbow! 

Complicated answer

The rainbow is formed by light refracting inside droplets of water. Light travels slower in water than in air and as the light enters the droplet the wave gets bent slightly because it has to slow down. Different wavelengths of light (colours) get bent to different angles so they split up. 

3. Why is red always on top? 

An animated graphic showing red light bending more than green or purple, leading to a rainbow
Why is red on top of a rainbow?

Simple answer

Pretend you had a tiny mirror and you wanted to see your own eye in it. You would have to hold it at a certain angle! Then to see your nose you'd have to hold it at a different angle. For your knees, another angle. And so on. The rain drops that form the rainbow do the same - the ones high in the sky bounce the red light to you with the ones lower down in the sky bouncing blue light towards you.

Complicated answer

The wavelengths of light at the red end of the spectrum get bent less than the wavelengths of light at the blue end so droplets higher up in the sky bounce red light towards your eye. Droplets lower down in the sky bounce green light towards your eye and even lower still droplets bounce purple light towards your eye. You can’t see light that is bounced away from your eyes so you see red high up, then through the colours down to purple. 

4. Is this why the sky is blue?

A diagram showing white light from the sun splitting as it hits the atmosphere and only blue light spreads out to reach us at the surface, making a blue sky.

Why is the sky blue?

Simple answer

Yes. All the different colours of light are mixed together in sunlight but they get split up as the light travels through the air to get to you! It just so happens that the colour that reaches us is blue!

Complicated answer

Yes – when light from the sun hits the earth’s atmosphere it all gets bent a little bit. Red light isn’t bent much at all so it misses the surface of the earth but blue light is bent more so it can be bent down from its original path to crash into the earth!