A valley of phantom lights
In the Hessdalen valley, a 12-kilometer-long stretch of rural central Norway, the sky shows a persistent and unexplained phenomenon. Luminous orbs, usually bright white, yellow, or red, appear day and night, floating above the horizon. Their behavior is erratic. Some hover for up to two hours, others sway slowly, and many move with enormous speed—one was measured at 30,000 km/h. The lights can appear as solitary floating orbs, flashes of blue and white, or even formations that seem to separate and reform.
While local accounts of strange lights date back to at least the 1930s, the phenomenon gained international attention between December 1981 and mid-1984. During this period of high activity, sightings occurred 15 to 20 times per week, drawing scientists and tourists to the remote valley. The frequency has since decreased to 10 to 20 sightings per year, but the mystery continues. In response to the intense activity, Project Hessdalen was established in 1983 to scientifically document and study the lights. In 1998, this effort was augmented by the Hessdalen Automatic Measurement Station (AMS), known as the "Blue Box," which continuously monitors the valley with cameras, a magnetometer, and radio receivers.
The geology of illumination
No single theory has definitively explained the Hessdalen Lights, but several hypotheses focus on the valley's unique geological and atmospheric properties. The leading explanation proposes that the valley itself is a massive natural battery. Rocks on one side of the Hesja river are rich in copper, while the rocks on the other side contain high concentrations of iron and zinc. The sulfurous river water, polluted by old local mines, may act as an electrolyte, creating an electrical potential between the two sides. This geological battery could generate enough energy to ionize air and dust, creating luminous plasma.
Another theory involves the radioactive decay of radon gas. The valley's bedrock contains uranium and thorium, which decay into radon. As radon decays, it emits alpha particles that ionize the air, and when these charged particles recombine, they can release energy as light. This process could explain the formation of "dusty plasmas"—clusters of charged dust and air that can form complex structures, such as double helixes, which have been simulated in labs and resemble some of the light formations observed. A related idea suggests piezoelectricity is the cause; the valley's quartz-rich rocks, when under mechanical stress, could generate an intense electrical charge. Researchers have also detected higher-than-normal radioactivity on rocks near where a large light ball was reported.