There’s a kind of cloud visible in the skies likened to gems of the sea. They’re called mother-of-pearl clouds, also nacreous clouds, for the pearly texture and color they impart. There’s a special place in my heart for pearls, their being my birthstone (according to Hallmark) and the gems of the sea from which I fashion my handcrafted jewelry designs.
Pearls of the skies
Nacreous clouds appear as lustrous streaks in the skies at twilight and dawn. Nacreous clouds exist in the sky at night, but the required mode of reflected sunlight is absent at that time.
Sunlight from below the horizon illuminates nacreous clouds at dawn and dusk hours, imparting iridescent colors in bands. Light diffracting around ice crystals is what causes the colors. Different colors appear in bands where the crystal particles are equal in size.
Nacreous clouds form higher in the atmosphere than the familiar clouds we usually see when we look up. Having said that, nacreous clouds are the lowest of the high clouds that there are.
If that’s not confusing enough, consider this confusing fact: The vivid colors of nacreous clouds occur from quick freezing of water vapor caused by the rapid wave motion of air. A rare form, colored white, occurs mostly in the Southern Hemisphere from larger but fewer particles freezing over, as temperatures slowly drop with the coming of winter.
In any case, whether vividly colored or mildly iridescent, nacreous clouds resemble the nacre of pearls…pearls produced by saltwater mollusks of the most valuable sort. But unlike the pearly gems of the warm South Seas, nacreous clouds form in high latitudes in places such as Alaska, Iceland, the northernmost parts of Canada. Furthermore, mother-of-pearl clouds should not be confused with the aurora borealis that frequently occurs in the skies over these same northern regions.
Splendor for all
What I like about nacreous clouds is that they occur in the skies for all to see. Unlike pearls, nacreous clouds cannot be cultivated or owned. Like stars are to diamonds, nacreous clouds–unlike our pearly gems of the sea–are products of the cosmos, not made by men, and observable above the earth, not found within it. No man need disturb any other man, beast, or clam to enjoy their splendor.
See here for more stunning images of nacreous clouds.
Sources: Storm Dunlop, Wil Tirion, How to Identify Night Sky, Barnes & Noble Books, 2004.