What makes a rainbow

Rainbows feel like luck, but they follow a strict rule of angles. Once you know the rule, you can often turn around and find one.

A rainbow appears when sunlight passes into raindrops, bends, reflects off the back of each drop, and bends again on the way out. Every colour leaves at a slightly different angle, which is what spreads white light into the familiar arc.

Where to look

Rainbows always sit opposite the sun, centred about 42° from the point directly away from it — so the rule of thumb is simple: keep the sun at your back and look toward the falling rain. They show up best when the sun is low and a passing shower is lit from the side — that brief gap after the rain, before the clouds close back in.