Where do rainbows come from?

What is a rainbow?

A rainbow is something we can see, most often when there is a mix of sun and rain showers. But how do rainbows form?

In this article you can learn:

This resource is suitable for weather topics for primary school learners.

Watch this video to discover more about rainbows, their shape and colours.

This video can not be played

For rainbows to form, we need two things - sunlight and rain.

Sunlight looks like white light but white light is actually made up of a spectrum of different colours mixed together.
Rainbows appear when white light is spread out into all these different colours. This is called .

When sunlight enters a raindrop, the different colours are bent at different angles. We call this .
The different colours reflect off the inside of the back of the raindrop.
When the sun is behind you and the rain is in front of you, a rainbow of colours is reflected back from the inside all the raindrops.
The seven main colours we see are red, orange, yellow, green, blue, indigo and violet.

We can separate the colours in white light easily by using a triangular glass prism.

Rainbows are curved because we see light reflected at different angles from raindrops all around the direction you are looking in.
We usually see rainbows as arches. That is because the land gets in the way.
If you're up in an airplane or at the top of a mountain, you might see a rainbow as a whole circle.

This slideshow shows some of the rainbows you might see after a rainy day.

Image caption,
When there's sunshine and rain together, you might see a rainbow. The rainbow has an arch shape because the ground stops us seeing any more of its full curve.
Image caption,
If you're lucky enough to see a rainbow from a plane or the top of a mountain it appears as a circle because there is nothing in the way to stop you seeing light reflected from all around.
Image caption,
When light reflects twice of the inside of the back of a raindrop you will see a double rainbow. In the second rainbow the colours are much fainter and the opposite way round, with red at the bottom and violet at the top.

rainbow - an arch of different colours that happens when sunlight shines through rain.
prism - a 3D object that is the same size and shape all the way through. A triangular glass prism can separate white light into different colours.
refraction - the change of speed of light that can cause different colours to bend at different angles when it passes from air into glass or another material.
dispersion - the separating of white light into a spectrum of different colours.
spectrum - the range of colours that white light can be separated into.