The Valley in Norway
Hessdalen is a valley in central Norway, about 120 kilometers south of Trondheim. Population: roughly 150 people. It has been producing unexplained lights since at least the 1930s, with a particularly intense period from 1981 to 1984 when residents reported seeing lights up to 20 times per week.
The lights are real. This is not in dispute. They've been photographed, filmed, measured with radar and spectrometers, and observed by scientists from multiple countries. The dispute is about what they are.
What We Know
The lights appear most often in the valley itself, typically at altitudes between 100 and 1000 meters. They range in color from white to yellow to red. Some are stationary. Some move. Some move very fast — one documented case showed a light traveling at approximately 30,000 km/h, which is fast enough to rule out conventional aircraft.
The Spaxob approach to anomalies like this is to start with what's documented and work outward. The documentation here is unusually good. Project Hessdalen, a scientific monitoring program that's been running since 1998, has produced thousands of hours of data. The fringe signals that come out of that data are not ambiguous — something is happening in that valley. The ambiguity is in the interpretation.
Current hypotheses include: piezoelectric effects from the valley's geology (the rock contains significant deposits of copper and zinc), plasma formations caused by ionized gas, ball lightning (which is itself not fully understood), and — less charitably — misidentified conventional phenomena. None of these fully explains the observed behavior.
The pattern analysis challenge with Hessdalen is that the lights don't behave consistently enough to fit any single model. They appear and disappear without obvious triggers. They change color and speed. They sometimes appear to respond to laser signals aimed at them, which is either significant or coincidence.
Forty years of documentation. No consensus. The unexplained frequencies keep coming. More at Spaxob.