Rainbow clouds are rare, but summer is the best time to spot them, and no, there’s no pot of gold.
These clouds that look like rainbows aren’t very common, but chances are you’ve seen one or two in your life. Some people refer to them as rainbow clouds. Others prefer the dramatic term “fire rainbow.”
The scientific name for them is circumhorizontal arc.
These bright displays of color in the sky form like rainbows, but they use ice instead of rain.
Rainbows form when sunlight shines through raindrops. The water acts as a prism, separating the white light into the colors of the rainbow.
In rainbow clouds, ice crystals act as the prism and create the colors. The reason why rainbow clouds use ice crystals instead of rain is because of where this phenomenon occurs.
Rainbow clouds only form high in the atmosphere, typically in cirrus clouds. Ice crystals make up these clouds because of how high in the sky they are.
This also makes rainbow clouds much rarer than true rainbows.
The ingredients needed to form a rainbow cloud are high-altitude clouds with a nearly uniform distribution of ice crystals, sunlight and a sun that is high in the sky.
The sun has to strike the cloud and ice crystals at the perfect angle. Because of this, rainbow clouds typically only occur from mid-spring to mid-fall. During the other times of the year, the sun angle is too low.
So this summer, look up. You might see a rainbow cloud.