Noctilucent Clouds, also known as Polar Mesosphere Clouds (PMCs), are the highest cloud formations on our planet. They mostly form at latitudes of 50° or higher, and between 80 – 85 km high (50 – 53 miles) in the coldest part of the atmosphere. The majority of PMCs are found in polar regions during the summer, meaning the place to look for them right now is in the Southern hemisphere.
We still don’t know exactly how Noctilucent Clouds form, but we do know that they need dust, water vapor, and extremely cold temperatures to form. The resulting crystals are too small to refract light into color (iridescence), but they are often bluish in color, possibly due to the absorption of red light from the ozone layer. They may also appear reddish or gold by reflecting the colors of sunrise or sunset.
While considered rare, NLC are forming more frequently, and earlier than expected. Scientists do not yet know why. Scientists have hypothesized that humans may be influencing their formation by adding more dust in form of pollution to the atmosphere, while also reducing the temperature where the clouds form by the addition of carbon dioxide and methane to the atmosphere.