Why do we see rainbows?

The rain stops, the sun peeks out, and suddenly a huge arc of colours stretches across the sky. A rainbow! It looks like magic. So how does the sky paint one?

Sunlight is secretly all the colours

Sunlight looks plain and white, but that is a clever disguise. Hidden inside white light are all the colours mixed together — red, orange, yellow, green, blue and purple, all blended into one.

You usually cannot see them separately. You need something to pull them apart.

Raindrops bend the light

That something is a raindrop! When sunlight shines into a tiny round drop of rain, the light slows down and bends, just a little. Each colour bends by a slightly different amount, so they spread out and split into a band — like a fan of colours.

Millions of raindrops each do this, and together they make the big arc you see in the sky.

You need sun AND rain

This is why you only spot a rainbow when there is sun and rain at the same time. The sun has to be behind you, shining onto the raindrops in front of you. No rain, no rainbow. No sun, no rainbow. You need both!

Wonder fact: A rainbow is not really a thing in the sky — it is light made just for you. Your friend standing nearby sees their very own rainbow!