1The Magic of Reflection
To understand a double rainbow, we first have to look at how a single rainbow is made! When sunlight hits a raindrop, it acts like a tiny prism. The light enters the water, slows down, and bends. It then reflects, or 'bounces', once off the very back of the raindrop before shining back out toward your eyes. This process, called refraction and reflection, separates the white sunlight into the seven beautiful colors we know: red, orange, yellow, green, blue, indigo, and violet. In a primary rainbow, the red is always on the outer edge because of the specific angle at which the light exits the drop.
2The Double Bounce Mystery
A double rainbow happens when the sun’s light is extra strong and the raindrops are just the right size. Instead of bouncing only once, some of the light reflects twice inside the water droplet before it escapes! This second bounce acts like a mirror to the first one, which is why the colors in the secondary rainbow are flipped upside down. In this fainter arch, violet sits on the outside while red stays on the inside. Because the light has to travel further and bounce more, the secondary rainbow is about 40% wider than the first one, but it also looks much lighter and more translucent.
3Alexander's Dark Band
If you look really closely at the space between the two colorful arches, you will notice something spooky: the sky looks much darker there! This area is known as 'Alexander’s dark band,' named after a philosopher who lived nearly 2,000 years ago. It appears dark because the raindrops in that specific part of the sky are angled in a way that they don't reflect any light toward you. It creates a perfect, shadowy frame that makes the two rainbows stand out even more. Seeing a double rainbow is a rare treat, so next time it rains while the sun is out, see if you can spot the hidden second arch and its reversed colors!
