What Makes a Rainbow?
Raindrops are tiny prisms
A rainbow needs two things at once: sunshine and raindrops in the air. Each falling raindrop acts like a tiny glass prism.
When sunlight goes into a raindrop, it bends. Because every colour bends by a slightly different amount, the white light splits apart into all its colours.
Bouncing back to your eyes
Inside the drop the light bounces off the back like a mirror and comes back out, now spread into a fan of colours: red on the outside, violet on the inside.
Millions of raindrops doing this together make the huge curved rainbow you see in the sky.
Always behind you
To spot a rainbow, the Sun has to be behind you and the rain in front of you. That is why rainbows often appear right after a shower, when the Sun peeks back out.
💡 Did you know? A rainbow is actually a full circle! We usually only see the top arc because the ground gets in the way — but from a plane you can sometimes see the whole ring.
🧪 Try this at home: On a sunny day, stand with your back to the Sun and spray a fine mist of water from a garden hose in front of you. Tilt the spray until a little rainbow appears in the droplets.