A rainbow is one of the most beautiful things in nature that you can actually understand. It looks like magic, jumps up out of nowhere after a shower, hangs there for a few minutes, and disappears again — without pretending to be anything other than a stripe of colours. And yet it hides on top of something completely ordinary: light that took a wrong turn on the way through. The day a child understands exactly what is happening up there, the sky is never quite the same again.
What is a rainbow?
A rainbow appears when sunlight hits raindrops that are still hanging in the air after a shower. To see one, you must always have the sun behind you and the rain in front of you. This is not a coincidence — it is a rule of physics itself.
Every raindrop is like a tiny round lens. When a sun ray strikes the drop, it bends a little on the way in — this is called refraction. The ray hits the back wall of the drop and is partly reflected back. On its way out, it bends a second time. And it is during this journey that the beautiful thing happens: white sunlight is not really white. It is a whole package of colours blended so finely that we think it is one colour. Inside the drop, each colour gets bent by a slightly different amount. Red bends the least, violet the most. As the rays exit, they fan out into a tiny rainbow.
Here is the small astonishment: one drop does not make a rainbow. It only makes one coloured flicker. It is because millions of drops hang in the air at the same time, each with its own angle, that we get a whole arc. What you see as the rainbow is really a collection of flickers from millions of drops, sorted neatly by angle — as if nature has picked light parcels from each one and laid them out on an invisible shelf.
Want to know where all that rain water came from in the first place? It is part of the water cycle, and that is just as marvellous in its own way. STEAM learning for kids always starts with questions that have surprising answers.
Why is this worth a child knowing?
The rainbow is one of the first big physics stories children can truly understand. The Norwegian LK20 curriculum asks pupils in Years 2–4 to "explore and describe phenomena related to light and sight," and in middle school to "explain how light can be refracted and split into colours." The rainbow is where both of these goals meet in the sky — always, and for free.
But the most important thing is not about curriculum. It is that a child who has understood the rainbow has understood one of the most important ideas in all of science: what we see is not always the whole truth. White light looks white, but it is actually six colours sneaking in together. That opens a door in the mind. Suddenly it becomes reasonable to ask: what else do I think I see, that is really something quite different underneath the surface?
Try it at home: make your own rainbow in the kitchen
Fill a glass nearly to the brim with water. Place a small flat mirror leaning at an angle inside the glass, so the top half of the mirror is above the water and the bottom half is under. Position the glass so a bright sun beam (through a window) or a torch hits the part of the mirror that sits under the water. Hold a white sheet of paper just above, in front of, or behind the glass and move it around slowly. When a rainbow appears on the paper, stop. Write down which colour is on top and which is on the bottom. Now tilt the mirror a little more. What happens to the colours — do they shift? Do they get clearer? Try coloured water with food dye. Try oil instead of water. The smell of rain after a shower, by the way, comes not from the water but from waiting bacteria — you can read about that in why rain smells so good.
Questions to wonder about
- Where does a rainbow begin and where does it end, and why can no one walk to either side?
- If a rainbow is made of light, what would happen if someone stood inside one?
- Could there be rainbows on other planets? And if so, would they have the same colours as ours?
A rainbow is a small miracle that needs not a single spark of magic. It is just light, water, and a quiet agreement between the sun and a raindrop about exactly how hard to bend. When children understand that, they have been given a gift they can never lose: a reason to lift their eyes every single time it rains while the sun is still shining. Every child is made of good atoms. At Good Atoms, we help them see where the marvels hide in the everyday. Explore free content at goodatoms.com.