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What is a rainbow?
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Quick answer
A rainbow is an arc of colours that appears in the sky when sunlight passes through raindrops. Each droplet acts like a tiny prism, bending and splitting white sunlight into its separate colours — red, orange, yellow, green, blue, indigo, and violet.
Key things to understand
- Sunlight looks white but is actually a mix of all the colours.
- When sunlight enters a raindrop it bends (refracts), reflects off the back, and bends again as it exits — splitting into its colours.
- Each colour bends by a slightly different amount, so they fan out into the familiar band.
- You see a rainbow when the Sun is behind you and rain or mist is in front of you.
- A rainbow is really a full circle of colour; we usually see only the arc above the horizon.
People also ask
How is a rainbow formed?
Sunlight enters raindrops, bends and reflects inside them, and splits into its separate colours on the way out. Millions of droplets doing this together form the arc of a rainbow.
Why is a rainbow curved?
Rainbows form at a fixed angle (about 42°) from the line between the Sun and your eyes. That set of angles traces out a circle, so the rainbow appears as an arc.
Why does a rainbow have its colours in that order?
Each colour of light bends by a different amount in water — red bends least, violet most — so they always separate into the same order, red on the outside to violet on the inside.