Circumhorizontal arcs are also known as "fire rainbows." Despite its appearance, the phenomenon is neither a rainbow nor does it have anything to do with fire, points out the University of Santa Barbara Geography department. This phenomenon occurs only when the Sun is higher than 58 degrees above the horizon. A large, colored band that runs parallel to the horizon is formed as the Sun's light passes through high-altitude cirrus clouds or haze containing plate-shaped ice. When perfectly aligned, the ice crystals act as a prism and refract light in a way that resembles a rainbow, reaching its maximum intensity when the Sun reaches an elevation of about 68 degrees.