Named for their mother-of-pearl iridescence, nacreous clouds blanket the sky above Husavik, Iceland in December 2011. These clouds, also known as polar stratospheric clouds, occur high in the atmosphere, 49,000 to 82,000 feet (15,000 to 25,000 meters) up. Thanks to their high altitude, the clouds reflect light from the setting or rising sun before it breaches the horizon, causing their ethereal glow.
Book recommendation - Ridley Walker by Russell Hoban (I am sure you have already read it, but I need to read it again myself)
10 hours ago