Hessdalen is a narrow valley about 120 kilometres south-east of Trondheim, home to a few hundred people, a small church and an old copper and sulphur mining district. It is also the only place in the world where a scientific instrument station has been pointed at unexplained lights, continuously, for more than a quarter of a century.
What happened
Odd lights had been mentioned in the valley for generations, but in December 1981 reports suddenly multiplied. Over the next three years residents described seeing lights fifteen to twenty times a week: white or yellow spheres hanging over the ridges, sometimes for an hour at a time; red and blue flashes; and occasional objects that shot along the valley at speeds witnesses could only guess at. They were seen most often on winter nights between about nine in the evening and one in the morning. Journalists and sightseers came in numbers.
Activity fell away after 1984. Reports have continued at a lower level ever since, typically ten to twenty a year, with the project noting that the true number is probably higher because most go unreported.
The investigation
In June 1983 members of the Norwegian and Swedish UFO organisations set up Project Hessdalen to study the reports systematically. Erling Strand, an engineer who later taught at Østfold University College, ran the technical side. Between 21 January and 26 February 1984 the team camped in the valley with cameras, a radar set, magnetometers and infrared viewers. The Norwegian military lent support. They logged 53 observations, including radar echoes and photographs, and the final report concluded that whatever the lights were, they could be measured. A second field season followed in 1985.
Strand revived the project in the 1990s and in August 1998 installed an automatic measurement station, known as the Blue Box after the shipping container that houses it, on a hillside with a view down the valley. It has carried cameras, magnetometers, weather sensors and radio receivers, and today streams its feed online. From 2000 Italian researchers from the National Research Council, led by the astrophysicist Massimo Teodorani, joined annual field campaigns under the name EMBLA, bringing spectrographs and radio equipment. Student science camps have run in the valley most summers since 2002.
These campaigns produced optical spectra, radar tracks and radio recordings, but also controversy. The physicist Matteo Leone published a detailed rebuttal of the 2002 EMBLA report, and a 2016 review in Frontiers in Earth Science concluded that accurate, reproducible measurements of the lights remain scarce.
The explanations
The first task is to subtract the ordinary. Hessdalen lies beneath an air corridor, and the main road along the valley floor carries headlights; Brian Dunning has pointed out that many of the station’s photographs resemble aircraft landing lights seen head-on, and that the busy Oslo to Trondheim route passes nearby. Astronomical objects low on the horizon and mirage effects account for others. Researchers on all sides accept that a share of the reports can be explained this way.
For the remainder, the hypotheses are physical rather than paranormal, and they compete. Bjørn Gitle Hauge of Østfold University College analysed spectra in 2007 and described a combustion process involving oxygen and nitrogen with traces of sodium, possibly fed by dust from the valley’s scandium-bearing rock. Gerson Paiva and Carlton Taft proposed in 2010 that radon seeping from the ground ionises air and dust into a cold plasma whose particles organise into glowing clusters. Jader Monari of the Italian team suggested in 2014 that the valley is a natural battery: copper-rich rock on one side, iron and zinc on the other, and a river acidified by old mine workings acting as the electrolyte, with charged gas bubbles providing the light. Teodorani had earlier reported raised radioactivity in rocks near a sighting, and others have invoked piezoelectric currents from stressed quartz. A Norwegian physicist, Bjørn Samset, responded to the battery idea by noting that the distances involved are too large and the supporting papers too weak.
The 2016 Frontiers review summed up the position: none of these models explains all the observations, and the energy source of the lights, if they are a single phenomenon at all, is unknown.
Where it stands
Project Hessdalen registered as a non-profit in 2023, held its first public field trip and conference in 2024, and is planning to add drones to approach lights at close range. The Blue Box continues to record. Forty years of effort have ruled out some things and confirmed nothing, which is an honest if unsatisfying result. The lights are not a hoax and not, on any evidence, visitors from elsewhere. They are a local natural puzzle that has not yet been solved, and the valley remains the best place on Earth to try.