Chasing Rainbows

A rainbow appears when sunlight passes through falling rain. Each raindrop bends the white sunlight, splits it into every color inside it, and reflects it back out toward you — that is the whole trick behind the colored arc in the sky.

The sun and rain team up

A rainbow needs two things at once: sunshine, and rain. Here is how they work together:

• Sunlight: the sun sends out white light.
• Raindrops: each raindrop acts like a tiny prism.
• Bending light: when sunlight enters a raindrop it bends, and splits into all the colors of the rainbow.
• Reflecting light: the light bounces off the back of the raindrop and comes back towards you.
• A rainbow! Because raindrops are round and the light bends at different angles, you see the colors spread out in a curved arc.

That is also why you have to have your back to the sun to see one. The light is coming back out of the raindrops towards you.

The colors, in order

A rainbow always puts its colors in the same order, from the outside of the arc to the inside. People remember them with a made-up name: ROY G. BIV.

Here they are, shuffled. Can you put them back in rainbow order?

Keep looking up. Rainbows turn up after a shower while the sun is still out — and now you know which way to face.