The quick answer
A rainbow appears when sunlight shines into raindrops while the Sun is behind you. Each drop bends the light and splits it into its colours. Millions of drops together paint the bow in the sky.
RankiTanki, how does the sky make a rainbow? Is there someone up there with a giant box of paints?
TankiNo paint needed. Just sunshine and raindrops, in exactly the right places. Let me show you how it works.
What you need for a rainbow
A rainbow needs two things at the same time: sunlight and raindrops. That is why rainbows often appear just after a shower. The Sun comes out, but the air is still full of drops.
There is one more rule. The Sun has to be behind you, and the rain has to be in front of you. So if you want to spot a rainbow, turn your back to the Sun and look towards the rain.
- Bright sunshine, best when the Sun is low in the sky.
- Lots of raindrops in the air in front of you.
- The Sun shining from behind you.
Raindrops bend the light
Sunlight looks white. But it is really a mix of many colours travelling together. A raindrop can sort them out.
When light goes into a raindrop, it bends a little. Scientists call this bending . Then the light bounces off the back of the drop, like a ball off a wall. This bounce is called a . When the light comes out of the drop again, it bends one more time.
Each colour bends by a slightly different amount. bends the most and red bends the least. So the colours spread out like a fan, and you see them one next to the other.
RankiSo every raindrop is like a tiny colour machine?
TankiExactly. One drop sends you one colour. Millions of drops together make the whole bow.
The colours always come in the same order
Look closely at a rainbow, and the order never changes. Red is always on the outside. Violet is always on the inside. In between are orange, yellow, green, blue and , a deep blue with a hint of purple.
Long ago, the scientist Isaac Newton split sunlight with a piece of glass. He named seven colours. Really, the colours blend into each other without any lines between them.
A rainbow is really a circle
From the ground, a rainbow looks like an arch. But the ground hides the bottom part. From a plane high in the sky, people can sometimes see a whole circle of colours. The plane’s shadow sits right in the middle.
Sometimes you can see a second, paler bow above the first one. This is a . The light bounces twice inside each drop. That flips the order, so the second bow has red on the inside and violet on the outside.
Try it
Make a rainbow on paper
You need
What to do
- Fill the glass with water almost to the top.
- Stand the glass on a table in bright sunshine.
- Lay the white paper on the table next to the glass.
- Move the paper slowly around until a small rainbow appears on it.
- Count the colours you can see. Which one is at the edge?
RankiSo a rainbow is sunlight, millions of raindrops and me standing in just the right spot.
TankiThat’s it. Next time the Sun shines while it rains, turn your back to the Sun and look!
Big words
- refraction
- When light bends as it goes from air into water or glass.
- reflection
- When light bounces off something, like a ball bouncing off a wall.
- indigo
- A deep blue colour with a little bit of purple in it.
- violet
- A purple colour at the very inside edge of a rainbow.
- double rainbow
- Two rainbows at once. The outer one is paler, with its colours swapped round.
Quick quiz
1. Where must the Sun be when you look at a rainbow?
You see a rainbow when the Sun is behind you and the rain is in front of you.
2. Which colour is on the outside of a normal rainbow?
Red bends the least, so it always sits on the outside of the bow.
3. What shape is a rainbow really?
The ground hides the bottom half, but from a plane you can sometimes see the whole circle.
For parents and teachers
Rainbows bring together three ideas from physics: refraction, reflection and dispersion, the splitting of white light into colours. On a sunny day you can make rainbows together in the fine spray of a garden hose, as long as the Sun is behind you.
Pictures marked “AI generated” were made with AI tools. Ranki and Tanki are AI generated characters. Found a mistake? Write to info@pr-geo.com and we will fix it.
