Noctilucent clouds, also known as polar mesospheric clouds or PSCs, are tenuous cloud-like phenomena in the upper atmosphere. They are most commonly observed in the summer months at high latitudes. Noctilucent literally means “night-shining” in Latin, and they are thought to be composed of small (less than 0.1 µm) ice crystals.
The first recorded observation of noctilucent clouds was made in 1885 by a Scottish meteorologist, but they were not widely reported until the early 20th century when they began to be seen more frequently at higher latitudes during the summer months. It is still not clear what causes them, although there are several theories. One possibility is that they are somehow related to meteoric dust; another is that they form from thin layers of water vapor left over from evaporating polar sea-ice.
Whatever their cause, noctilucent clouds are an intriguing phenomenon and have been the subject of much scientific study. They offer a unique opportunity to study Earth’s upper atmosphere since they can be seen even when the Sun is below the horizon (hence their “night-shining” moniker). Observations of noctilucent clouds can help us understand atmospheric dynamics and composition, as well as search for evidence of climate change.