Hessdalen Valley
The recurring incident began in 1981 in Norway when the people of Hessdalen Valley in central Norway saw colored lights dangling in the sky particularly from 9 p.m to 1 a.m. They occur mostly in winter. The reason could be anything ranging from solar activity, cosmic rays, heated nanoparticles, and mini-black holes to the quantum fluctuation of the vacuum state. Scientists did lots of research on the subject but unfortunately, all of them met a dead end. There is one more reason that seems to be a logical one. Perhaps, the lights were emanating from an airport located in distance. However, this too does not fit well.
