Mother of Pearl clouds 5551

Polar stratospheric clouds also known as nacreous clouds (from nacre, or mother of pearl), are clouds in the winter polar stratosphere at altitudes of 15,000–25,000 meters (50,000–80,000 ft). Compared with dark scudding low altitude clouds that might be present, nacreous clouds stand majestically in almost the same place - an indicator of their great height.
Due to their high altitude and the curvature of the surface of the Earth, these clouds will receive sunlight from below the horizon and reflect it to the ground, shining brightly well before dawn or after dusk. They form at very low temperatures, below −78 °C.