What are circumhorizontal arcs?

Circumhorizontal arcs are rainbow-like shapes that appear across the sky when sunlight hits special ice crystals high up in the atmosphere.

Imagine you're playing with a prism, that colorful triangle that splits light into rainbows. Now picture those prisms floating way above you, inside clouds made of tiny ice crystals. When the sun is low on the horizon, like early morning or late afternoon, these ice crystals act like little prisms, bending the sunlight and creating long, curved rainbow shapes across the sky.

Think of the ice crystals as mini mirrors that twist the light. If you’ve ever seen a rainbow after splashing in a puddle on a sunny day, it's because water droplets are doing something similar, splitting the light into colors. With circumhorizontal arcs, instead of water droplets, it’s these special ice crystals that create the effect.

These arcs often appear as horizontal rainbow bands, stretching from one side of the sky to the other, sometimes even looking like a ribbon tied around the sun or moon. They’re not as bright as regular rainbows, but they're pretty cool, and you can see them on sunny days when the sky is just right!