What Causes Rainbows? The Complete Explanation

How Rainbows Form

A rainbow appears when sunlight enters a raindrop, refracts (bends), reflects off the back of the drop, and refracts again as it exits. Different colours bend at slightly different angles, spreading white light into the visible spectrum.

The Colour Order

From outside to inside: Red, Orange, Yellow, Green, Blue, Indigo, Violet (remember ROY G BIV). Red bends the least and appears on the outer edge; violet bends the most and appears on the inner edge.

Conditions Needed

• Sun behind you — you must face away from the sun
• Rain or moisture in front of you — the drops act as tiny prisms
• Sun at a low angle — rainbows appear when the sun is below 42° above the horizon, which is why they are more common in late afternoon

Double Rainbows

A secondary rainbow forms when light reflects twice inside each raindrop. The second bow is fainter and has its colour order reversed (violet on the outside). The dark band between the two bows is called Alexander's dark band.

Rainbow Facts

• Every rainbow is actually a full circle — you see a semi-circle because the ground cuts off the bottom half
• From an aeroplane, you can sometimes see a complete circular rainbow
• No two people see the exact same rainbow — each observer sees light from different raindrops
• Moonbows (lunar rainbows) exist but appear white to the naked eye because the light is too faint for colour receptors

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Check rain forecasts on Weather Tomorrow — you might spot a rainbow.