Shot with PENTAX K10D, processed using K10D Ver 1.30

In this year’s first issue of Tähdet+Avaruus, there was a question sent by a reader about the distance that a lightning can be seen at. The answer referred to lightning seen in the upper parts of a cloud, which is silent when seen from farther than 15km away. The instant I read the answer, I realized I had shot such a phenomenon about a year ago. The Finnish wikipedia reveals that the phenomenon is called “crop lightning”, the proper english term seems to be “sheet lightning”. The phenomenon can be seen mainly in August, when the nights are already dark, but there are still thunders, and thus the finnish moniker “crop lightning” stems from an old belief that these silent lightnings have an effect in ripening the crop.

Unfortunately at the time of taking the picture, I didn’t realize the thunder sound was missing because of the distance, and therefore didn’t have the insight to look up the distance to the thunder cloud. Someone smarter and more knowledgeable in relation to thunderstorms might be able to calculate the distance to the cloud (of which you can only see the top) based on the average height of the cloud and the curvature of the earth. The picture was taken at 26.7.2008. The exposure was 4.0s at f/2.8, ISO100.