Fire Rainbows occur only when the sun is very high in the sky ( more than 58° above the horizon) What's more, the hexagonal ice crystals that make up cirrus clouds must be shaped like thick plates with their faces parallel to the ground.
Fire rainbows are not actually rainbows and have no connection with fires. The true name for this exquisitely beautiful optical effect is “circumhorizontal arc”. The phenomenon can only be viewed under certain precise conditions: the cirrus clouds that act as prisms must be at least 20,000 feet high and the sun must strike them when it is at an elevation of 58 to 68 degrees. Fire rainbows are never seen at locations situated more than 55 degrees north or south.
Rainbow. I think this phenomenon is called sky fire or fire rainbows? I saw one in the sky over Chicago (April 2013). It lasted about 40 minutes and was truly awe inspiring. It changed color and intensity slowly and at times was only partially visible behind a veil of bright cumulus clouds. I was driving to work at the time so was unable to take pictures.