Where Do Rainbows Come From? Make Your Own Rainbow at Home
By Ahmed, founder
Few things make children stop and stare like a rainbow. The better news: you don’t have to wait for rain and sun to meet. You can make one at home, and explain how it works.
Make a rainbow with a glass of water
You need a clear, smooth, straight-sided drinking glass (no pattern or ridges), water, white paper and a sunny window. A flashlight works as a backup.
- Fill the glass with water and set it near the edge of a table in a sunny window.
- Place the white paper on the floor so the sunlight passes through the glass and lands on the paper.
- Adjust the glass, or the paper, until a band of colours appears.
If you have no sun, cut a thin slit (about 3 mm wide) in a piece of cardboard and shine a bright flashlight through it onto the glass. A phone light works too.
Make a garden-hose rainbow
On a sunny day, stand with the Sun behind you and spray a fine mist from a hose. Look at the mist, and you should see a rainbow arc. Move around until it appears.
Is the water what matters?
Here’s the fair test. Try the same setup with an empty glass. No rainbow? Then the water is doing something to the light. That’s evidence.
The science
Sunlight looks white, but it’s a mix of all the colours. When light enters water, it slows and bends (refraction). Each colour bends by a slightly different amount: red the least, violet the most. The colours spread out and we see them separately. That spreading is called dispersion.
In a real rainbow, sunlight enters millions of raindrops, bounces off the back of each one and exits, spreading into colours. Each drop sends different colours in different directions, and your eye catches one colour from each drop, which together make the arc.
The Sun must be behind you, and low enough in the sky for a rainbow to appear, which is why they’re often seen in morning or late afternoon. The arc is centred on the point opposite the Sun, at an angle of about 42° for red.
Questions kids ask
Why is red on the outside? Red bends the least, so it appears at the largest angle.
Can we touch a rainbow? No. It’s not an object in one place. Different people standing in different spots see different rainbows from different drops.
Why are there two rainbows sometimes? Light can bounce twice inside the drops, making a fainter second bow with the colours reversed.
Safety
Never look directly at the Sun. For the window experiment, you’re looking at the paper, not the sun.
Next steps
Our lesson Where do rainbows come from? has the full steps and an easier version for younger children. It’s part of Earth and Sky at Home, with How do crystals grow? and How does a cloud form? For a classroom version, see What colours are hiding in white light? Sign up for three lessons free.