Why do rainbows appear after rain?
The short answer first, then the real reason — and a version for younger kids. Guess before you scroll to make it stick.
✅ Sunlight bends and bounces inside raindrops, splitting into colors
But why?
Every rainbow is a collaboration between sunlight and a wall of raindrops, each drop performing the same three-step trick: sunlight bends as it enters the drop, bounces off the drop’s back wall, and bends again on the way out. Water bends different wavelengths by different amounts — violet the most, red the least — so white light fans apart into a spectrum. Millions of drops, each fanning light the same way, paint the whole arc at once. Why an arc? A drop can only bounce that light to your eye when it sits at about 42° from the point directly opposite the sun. All the world’s drops at that angle form a circle around the shadow of your head — and the ground cuts the circle off. From a plane, you can sometimes see the full circle. Two lovely consequences: nobody can ever reach a rainbow’s end (it moves with you — it’s built from your line of sight), and every observer sees their own private rainbow made of different drops. Sometimes a second, fainter bow appears above — light that bounced twice inside each drop, with the colors reversed — and the sky between the two bows is slightly darker, because drops there send their light somewhere else. Moonbows exist too: raindrops plus bright moonlight, so dim they often look white to our night eyes.
🧒 For younger kids: Sunlight goes into a raindrop, bounces inside, and comes out split into colors — a water prism!
🤯 Wow fact: Nobody can reach the end of a rainbow — it moves as you move, because it exists only in your line of sight.
Good guesses kids make
“Paint mixes in the clouds” — Clouds carry plain water — no paint factories up there.
“The sky reflects flowers below” — Sweet, but the colors come from sunlight itself, not the ground.
“Rain washes the sky’s colors out” — Rain doesn’t rinse color from anywhere — it makes sunlight’s hidden colors visible.
📚 Sources
More science at home why questions
- Why is glass see-through?
- Why do black clothes get hotter in the sun?
- Why do echoes happen?
- Why do bananas turn brown?
- Why does water boil?