Why do rainbows have seven colours?

In one line

The rule

When white light passes through water droplets, it bends (refracts), splits (disperses), and bounces (reflects), creating a spectrum of seven visible colors: red, orange, yellow, green, blue, indigo, and violet.

Let's understand it simply

Imagine sunlight as a big box of crayons with all colors mixed together. When it rains and the sun shines, each raindrop acts like a tiny glass prism (a triangle-shaped piece of glass). As sunlight enters the raindrop, it bends and spreads out into different colors, just like how a prism splits light. Our eyes see these colors as a rainbow.

How it works

1. Sunlight (white light) hits a raindrop in the sky.
2. The light bends (refracts) as it enters the raindrop.
3. Inside the drop, the light splits (disperses) into different colors because each color bends by a different amount.
4. The light reflects off the back of the raindrop.
5. As it exits, the light bends again and spreads out more.
6. The seven main colors reach your eyes in order: red, orange, yellow, green, blue, indigo, and violet.

The story behind it

Isaac Newton, a famous scientist in the 1600s, used a glass prism to show that white light is made of many colors. He named the seven main colors we see in a rainbow. Newton chose seven because he liked the number, which matches the seven notes in music.

Where you see it in real life

• After rain, when the sun comes out → sunlight passes through leftover raindrops → rainbow forms in the sky.
• Spraying water in sunlight (like with a garden hose) → tiny droplets act as prisms → you see mini rainbows.
• Looking at sunlight through a glass prism in school → prism splits light into seven colors, just like a raindrop.
• Oil spills on water → thin film causes light to split into colors, making rainbow-like patterns.

Why it matters

• Helps us understand how light works and why we see colors.
• Used in making prisms and optical instruments (like cameras and glasses).
• Important in weather prediction (rainbows mean sunlight and rain together).
• The idea of splitting light is used in science labs and even in making lasers.

Common mistakes

• Thinking a rainbow is made by the sun alone (it needs both sunlight and raindrops).
• Believing there are only seven colors (there are many more, but we see seven main ones).
• Mixing up the order of colors (the correct order is red, orange, yellow, green, blue, indigo, violet — "ROYGBIV").

Remember it

Remember "ROYGBIV" — the first letter of each color in a rainbow: Red, Orange, Yellow, Green, Blue, Indigo, Violet.