Explanation:
Why would clouds appear to be different colors?
The reason here is that ice crystals in distant cirrus clouds are acting like little floating
prisms.
Sometimes known as a fire rainbow for its flame-like appearance, a
circumhorizon arc lies 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 are present.
Furthermore, 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 quite unusual to see.
This circumhorizon display was photographed through a
polarizedlens above
Dublin,
Ohio last week.
Apologies: Earlier, APOD misidentified this phenomenon as iridescence.
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