Extremely rare: Photo shows noctilucent clouds over Upper Austria

What at first glance looks like a Photoshop artist with a penchant for kitsch had gone wild in an image editing program was actually recently visible in the night sky over Upper Austria: Erwin Filimon, chairman of the Salzkammergut Astronomical Working Group, managed to capture rare noctilucent clouds a few days ago at the Gahberg observatory in the municipality of Weyregg (Vöcklabruck district). He photographed the clouds on June 28th at 10:35 p.m. in the sky high above Lake Attersee.

Difficult prediction

The phenomenon only occurs in Upper Austria under certain conditions from mid-June to around the end of July. The clouds can then be seen with the naked eye in areas with little light and are popular astronomical photographic subjects. Predicting them is extremely difficult. Noctilucent clouds, also known in professional circles as NLC (“noctilucent clouds”), consist of ice crystals at very high altitudes of around 80 kilometers. “You can only see them when it is already sufficiently dark, so about an hour and a half after sunset,” says Filimon. They are very close to the horizon and can be seen from the northwest through the north to the northeast.

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Why the clouds shine

The reason for the glow is the enormous height at which the clouds are located: the sun, which is positioned at an angle below the horizon, illuminates them even after sunset, causing them to “glow”. They become visible when the sun is between 6 and 16 degrees below the horizon. The sun’s light is then still reflected by the clouds, while the sky is otherwise almost dark.

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