On Friday afternoon, many people across central Indiana spotted what appeared to be a rainbow in cloud form. But even though the cloud appears rainbow-esque, it’s not actually a rainbow.
“Circumhorizontal arc” is the scientific name for this optical phenomenon. To put it in simple terms, there are tiny crystals inside the clouds. The rainbow appearance is caused by the refraction of sunlight in the ice crystals. Essentially, the ice crystals split the sunlight into the color spectrum.
Circumhorizontal arcs are most common in high-level clouds, or cirrus clouds.