Rainbows appear when sunlight bends inside raindrops and splits into separate colors.

The longer version

A falling raindrop works as both a lens and a prism, so the white light that enters it does not leave as one beam. Because each colour bends by a slightly different amount, the colours that arrived together as white light spread apart into the familiar arc.

Red bends least and appears on the outside of the bow, while violet bends most and sits on the inside. The light leaves the drop over a preferred range of angles, so the effect is only visible when your eye, the sun, and the drops line up correctly. That is also why no two people see exactly the same bow.

Where this entry sits

Clouds, wind, rain, and storms shape daily life in ways that most people barely notice. This collection explains snow, lightning, rainbows, the turning seasons, temperature, the instruments forecasters rely on, and scraps of old weather lore. The full list sits on the Weather and Climate page, where every entry is listed in order.