Iridescent clouds shine bright over this Finnish sunset. These colorful clouds are nacreous clouds, also known as mother-of-pearl clouds. Formed from ice crystals during frigid conditions in the lower stratosphere, these clouds are most visible before dawn and after sunset, when their high altitude catches sunlight while the lower atmosphere doesn’t. These rare clouds form mostly in high latitudes during winter. While they appear similar to other iridescent clouds that occur all over the world, nacreous clouds are far brighter and more vivid. (Image credit: D. Lehtonen; via APOD)
Nacreous Clouds
