Nacreous Clouds, Alaska
Simply put, nacreous clouds are clouds that resemble mother of pearl, and you can see the most brilliant colors when the sun is several degrees below the horizon. These ethereal cloud formations are only seen at high altitudes when temperatures drop below negative 85 degrees Celsius. These clouds stretch in colorful ribbons across the lower stratosphere, their iridescent hues shifting and moving with the wind.
They are usually seen in Antarctica but have also been noticed in the Arctic, Scotland, Scandinavia, Canada, Alaska, and Russia. On some occasions, they have also been reported in other parts of northern Europe. Nacreous clouds are often lenticular wave clouds and are therefore found downwind of mountain ranges that induce gravity waves in the stratosphere. Sadly, these cloud forms are horrible to the environment because they encourage the chemical reactions that break down the ozone layer.