Noctilucent clouds
Noctilucent clouds, meaning clouds that are glowing during the night, were first described in 1885, two years after the eruption of the Krakatoa which generated fantastic sunsets all over the world. It is not clear if they were the result of the Krakatoa eruption, or the result of people watching the sky in the aftermath of the eruption. They are mainly observed between 50° and 70° of latitude. They appear after the sun set, when the lower part of the atmosphere is in the shadow of earth, but the upper part, the mesosphere around 80,000 metres, still receives sun light. The small ice crystals in the mesosphere are then highlighted and become visible against the darker layers beneath them. They are the highest known clouds, at 85 km from the surface of earth. In these latitude, when the sun sets, it remain not very far below the horizon line, and the sun can therefore still illuminate the noctilucent clouds that are very high, above any other clouds that would be in the shadow of the earth. They are always appearing on the North, since the sun during the night is below the horizon in the northern sector. They are usually whitish to silver colour, with some blue on the sides.
Below is a burst of noctilucent clouds observed on 24 July 2020 in Källö in the Knipplan marina, 57° of latitude North.
On the night of the 25 July2018 in Brändö, Åland, we observed a blooming of noctilucent clouds in the North direction around 12:30 in the night.
The noctilucent clouds below were observed in July 2012, cruising back from Gotska Sandön to Nynäshamn. The quality of the picture is not optimal as pictures were taken while sailing in the middle of the night.
