One raindrop

One raindrop, up close

We have zoomed in on one of the countless raindrops in the sky. A raindrop is a tiny ball, usually around 1 to 2 mm across. A single ray of white sunlight is about to hit the upper part of this drop. Let’s follow the path this light takes inside the drop.

Why?The surface of water pulls itself tight, so a small drop becomes an almost perfect ball. Very large raindrops flatten a little on the bottom as they fall, but treating a drop as a ball is good enough to understand rainbows.

Learn moreWhen drops are very small (about 0.05 mm or less, like the droplets in fog), the wave nature of light smears the colors together and the rainbow turns almost white. This is called a fogbow.

Raindrop width (example)

about 2 mm

calculated from the refractive index of water (IAPWS, 20 °C) and the laws of refraction and reflection