Nacreous Clouds Shine Over Antarctica - PSCs, also known as nacreous clouds from nacre, or mother of pearl, due to its iridescence, are clouds in the winter polar stratosphere associated with the formation of ozone holes. They float much higher than ordinary clouds, from 15 - 25 km as opposed to 5 - 10 km, and produce unforgettably bright colors during the hours around sunset.
Fire rainbows are the rarest of all naturally occurring atmospheric phenomena. For a fire rainbow to occur, cirrus clouds must be 20,000 feet in the air with the precise amount of ice crystals, and then the Sun must hit the clouds at 58 degrees. *Stardust*