A circumhorizontal fire rainbow arc is an optical phenomenon, an ice-halo formed by plate shaped crystals in high level cirrus clouds. 

Crystals within the clouds refract light into the various visible waves of the spectrum but only if they are arrayed correctly relative to the ground below. The complete halo is a huge, multi-colored band running parallel to the horizon with its center beneath the sun. Often, when the halo-forming cirrus cloud is small or patchy, only fragments of the fire rainbow arc are seen. 

Formation of the halo requires that the sun be very high in the sky, at an elevation of 58 degrees or more. The sun's altitude determines the visibility of the halo. A 90 degrees inclination between the sun ray's entrance and exit produces the well-separated rainbow colors.

Due to the rarity with which all of these events happen in conjunction with one another, there are relatively few remarkable photos of this phenomenon.

Fire rainbows are relatively common sights in the United States, seen several times each summer. However, it is a very rare occurrence in northern Europe.

The current accepted names for fire rainbows are circumhorizon arc or lower symmetric 46 degree plate arc.

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