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Learning the Sky Dance

On September 3, 1874, Norwegian mathematician and geophysicist Fredrik Carl Mülertz Størmer was born. Although he investigated several astrophysical phenomena during his lifetime such as meteor trails and solar corona, Størmer was particularly involved in the study of the polar auroras. The aurora phenomena at each of Earth’s poles have captivated people throughout history. With the advent of photographic equipment, many have captured images of the dancing ribbons and draperies of ghostly coloured light in the night skies.

Størmer turned his youthful interest in photography into a data assist. He spent decades photographing auroras extensively from many observatories. Using these to calculate location and latitude to triangulate height, Størmer discovered that the auroras ranged in height from 100 to 1000 km (62 to 620 mi) above the Earth’s surface, where the density of air ranges from very low to a vacuum-like. The auroras in the upper part of the atmosphere occurred at twilight when sun-lit. The auroras closer to Earth’s surface were not sun-lit. Størmer calculated the motion of charged particles, also called ions, to predict their paths approaching the Earth. He showed that the Earth’s magnetic field might trap these particles and would magnify the effect of the smallest variation in a particle’s path.

Applying the electromagnetic effects he described, Størmer was able to reproduce aurora phenomenon in his laboratory. From his fieldwork data, he developed a mathematical theory of the aurora occurrences. The later discovery of the Van Allen radiation belt and the return of ionosphere data from space probes confirmed Størmer’s conclusions. As charged particles reach Earth’s vacuum-like ionosphere, their voltage energy increases their heat and, electromagnetically trapped, they can hit enough nitrogen and oxygen atoms to produce light.

Størmer received many awards and international recognition for his work. His application of several disciplines and techniques to explain what had seemed inexplicable inspired others to continue exploring our atmosphere.

B Bondar / Real World Content Advantage