What's happening to this cloud?
Ice crystals in a distant cirrus cloud are acting like little floating prisms.
Known informally as a fire rainbow for its flame-like appearance, a circumhorizon arc appears parallel to the horizon.
For a circumhorizontal arc to be visible, the Sun must be at least 58 degrees high in a sky where cirrus clouds present below -- in this case cirrus fibratus.
The numerous, flat, hexagonal ice-crystals that compose the cirrus cloud must be aligned horizontally to properly refract sunlight in a collectively similar manner.
Therefore, circumhorizontal arcs are somewhat unusual to see.
The featured fire rainbow was photographed in 2021 near North Fork Mountain in West Virginia, USA.
Media Credits & Attribution
** Image Credit & Copyright: ** Christa Harbig