The Hessdalen lights are unexplained airborne lights observed in the Hessdalen valley in rural central Norway. They first appeared in 1981, and at the peak of activity, there were around 20 reports each week. Currently, there are fewer events, but the lights have not stopped entirely.
The origin of the lights, which have been widely documented and photographed, is unknown.
They are likely to be a geophysical in nature, perhaps similar to the lights sometimes seen at the time of earthquakes (also produced by an unknown mechanism). See:
“They appear at day and night, and seem to float through and above the valley. They are usually bright white, yellow, or red and can appear above and below the horizon. Duration of the phenomenon may be a few seconds to well over an hour. Sometimes the lights move with enormous speed; at other times they seem to sway slowly back and forth. On yet other occasions, they hover in mid‑air.” Source Wikpedia
The 'official' website of the phenomenon is Project Hessdalen (a project at Østfold University College). The project team maintain an archive of photos, technical reports, and provide a live webcam of the valley.
• Editor's note: Given the very large number of documented sightings, with photographic evidence, and the resulting academic research, it seems clear that this is not in any sense a so-called 'paranormal' phenomenon - which are disqualified from inclusion at Wikenigma.