How is a rainbow formed? The full science of its seven colours
How a rainbow forms: light bending, bouncing and splitting inside raindrops. Why it always appears opposite the sun, what a double rainbow is and how to make your own.
Rohit Tandon · 13 October 2026 · 4 min read
Sunshine after rain, and an arc of seven colours across the sky — this sight delights people of every age. But how is a rainbow formed? The answer lies in three things light does — it bends, bounces back and spreads out. This is also part of the Class 10 science lesson "The Human Eye and the Colourful World".
The colours hidden in white light
Sunlight looks white to us, but it is a mixture of many colours. Around 1666, Isaac Newton passed sunlight through a glass prism and showed that it splits into many colours. Their order is violet, indigo, blue, green, yellow, orange and red (VIBGYOR). Each colour has a different wavelength, so each bends at a slightly different angle when it enters glass or water.
What happens inside a raindrop?
- Refraction (bending): sunlight bends as it passes from air into a raindrop.
- Dispersion (spreading): as it bends, each colour bends at a different angle, and white light splits into colours.
- Internal reflection (bouncing back): the light hits the back wall of the drop and bounces back.
- Refraction again: leaving the drop, the light bends once more and the colours spread out further.
The colours coming out of millions of drops reach our eyes together as a bright arc. Each colour reaches us from different drops — red from the higher drops and violet from the lower ones.
Did you know? No two people ever see exactly the same rainbow. The colours reach each person's eyes from different drops, so everyone's rainbow is their own.
Why is a rainbow always opposite the sun?
To see a rainbow, the sun must be behind your back and the raindrops in front of you. Light bounced back from the drops reaches your eye at an angle of about 42 degrees. That is why rainbows appear in the west in the morning and in the east in the evening, and why around noon, when the sun is very high, it is hard to see one from the ground.
Some unusual forms of the rainbow
| Form | What it is |
|---|---|
| Double rainbow | Two reflections inside each drop make a fainter second rainbow above the main one, with its colours in reverse order |
| Alexander's dark band | The sky between the two rainbows looks darker than the rest |
| A full-circle rainbow | A rainbow is really a full circle; from an aeroplane or a high mountain the whole circle can sometimes be seen |
| Moonbow | A very faint rainbow made by moonlight on a bright night |
Make a rainbow at home
On a sunny morning or evening, stand with your back to the sun and spray a fine mist of water into the air with a garden hose. When the angle is right, a small rainbow will appear in the spray. You can also see a band of colours by putting a glass of water on a sunny windowsill with white paper below it.
The rest of the science of the sky's colours: Why is the sky blue and 12 interesting physics facts.
Key points
- White light hides seven colours — VIBGYOR.
- A rainbow forms by refraction, dispersion and internal reflection in raindrops.
- It always appears opposite the sun, at about 42 degrees.
- In a double rainbow, the second bow's colours are in reverse order.
- A rainbow is really a full circle; from the ground we see only part of it.
Frequently asked questions
Which colour is at the top of a rainbow?
In the main rainbow, red is at the top and violet at the bottom.
Which processes are needed for a rainbow?
Refraction, dispersion and internal reflection of light in water drops.
Practise: Science questions · Read more: Science.
Sources
Found this useful? Share it.