photo #7871072

The lunar corona in Moonlight over Racken, painted in the early 1900s by Swedish artist Gustaf Fjæstad, is so precise, it could feature in a textbook of atmospheric phenomena. A corona is an optical effect formed as sunlight or moonlight shining through a thin veil of cloud bends, or diffracts, around water particles like the tiny droplets in the Altostratus clouds of this painting. A classic corona has a ghostly glowing centre, or aureole, fringed by a bluish ring shifting to greens and yellows and an outermost ring of red. The size of the disc of light depends on the size of the tiny cloud droplets: the smaller the droplets, the larger their corona. And this feature of coronas reveals the accuracy of Fjæstad’s painting. If you think the Moon looks slightly off-centre in the bright disk of Fjæstad’s corona, this is no slip of his compass.The droplets in a patch of Altostratus are often slightly larger in the middle of the cloud than to the edges, and so the size of the disc of the corona can look distorted, appearing broader in the part of the cloud where the droplets are slightly smaller. Fjæstad and his artist wife, Maja, built their home and studio on Lake Racken in the quiet rural area of Värmland. All he had to do was step out his door to watch and paint the skies and landscapes around him – and to make sure his lunar corona was spot on.Moonlight over Racken (c. early 1900s), by Gustaj Fjæstad, held in a private collection.