Despite their name, fire rainbows are neither fire nor rainbows. Their technical name is circumhorizontal arcs, and they occur when sunlight interacts with high-altitude cirrus clouds containing hexagonal ice crystals. These displays create a bright, horizontal rainbow-like band in the sky.
Fire rainbows only form under very specific conditions:
- The sun must be at least 58 degrees above the horizon
- Cirrus clouds containing plate-shaped ice crystals must be present
- The ice crystals must be oriented horizontally
Due to these requirements, fire rainbows are more common in areas closer to the equator during summer months. In mid-latitude locations, they’re relatively rare and can only occur during specific times of day when the sun is high enough. The phenomenon typically lasts for several minutes to hours when conditions are right.