It's a question that has puzzled observers for centuries, and it's a question about the green and crimson light displays of the Aurora borealis.
The interaction of solar particles with gas in the atmosphere is believed to cause the Aurora. Reports of the aurora making noise are rare, and were historically dismissed by scientists.
A study in 2016 claimed to have confirmed that the northern lights produce audible sound to the human ear. A recording made by a researcher claimed to have captured the sound of the lights above ground level.
The mechanism behind the sound and the conditions that must be met for the sound to be heard are somewhat mysterious.
My recent research looked at historic reports of the sound of the Auroral phenomenon to understand the methods of investigating and the process of establishing whether the sounds were objective or illusory.
There are historic claims.
In the first decades of the 20th century, accounts from settlements across northern latitudes reported that sound sometimes accompanied the light displays in their skies.
During violent northern lights displays witnesses told of a quiet, almost imperceptible crackling. The sound of the northern lights was likened to "rustling silk" or "two planks meeting flat ways" in the early 1930s by personal testimonies in The Shetland News.
Similar testimony from northern Canada and Norway corroborates these tales. The scientific community was not sure if the noises were heard by the explorers themselves.
The Nasjonalbiblioteket is in Norway.
The photograph was taken in 1930 in Finnmark, Norway.
The altitude of the northern lights was a key factor in the credibility of the noise reports. It was thought that only displays that descended low into the Earth's atmosphere would be able to transmit sound.
The problem was that the results from the Second International Polar Year of 1932-3 found that the most common place for the Aurorae to occur is 100 km above Earth. It was suggested that it would be impossible for the lights to make sound on the Earth's surface.
Physicists and meteorologists were skeptical of the accounts of the sound of the Auroral sound and the low Aurorae.
Sir Oliver Lodge, the British physicist involved in the development of radio technology, said that the vividness of the Aurora's appearance might be a psychological phenomenon. George Clark Simpson argued that the appearance of low aurorae was likely an optical illusion caused by the interference of low clouds.
Carl Strmer, the leading scientist of the 20th century, published accounts written by two of his assistants who claimed to have heard the Aurora, adding some legitimacy to the large volume of personal reports.
Hans Jelstrup, Strmer's assistant, said he had heard a faint whistling sound, which seemed to follow exactly the vibrations of the Aurora, while Mr. Tjnn experienced a sound like burning grass or spray. They didn't propose a mechanism by which the sound could be operated.
Clarence Chant, a well-known Canadian astronomer, suggested the answer to this enduring mystery in 1923. He argued that the motion of the northern lights changes Earth's magnetic field, even at a significant distance.
The sound of crackling is similar to the sound of static when it meets objects on the ground. This could take place on the observer's clothes or glasses, or in the surrounding objects.
Chant's theory is supported by occasional reports of the smell of ozone during the northern lights displays, which is similar to an electrical spark.
Chant's paper went largely unrecognized in the 1920s, but was recognized in the 1970s when two physicists looked at the historical evidence. Chant's theory is largely accepted by scientists today, although there is still debate as to how exactly the mechanism for producing the sound operates.
On rare occasions, the Aurora makes sounds that are audible to the human ear. The eerie reports of crackling, whizzing and buzzing noises accompanying the lights describe an objective audible experience.
If you want to hear the northern lights for yourself, you may have to spend a lot of time in the polar regions, since the aural phenomenon only presents itself in 5 percent of violent displays. It's not an especially accessible experience to hear it on the top of the mountains.
The sound of the aurora has been explored for its aesthetic value, inspiring musical compositions and laying the foundation for novel ways of interacting with its signals.
The American explorer Charles Hall and the Norwegian politician Fridjtof Nansen both claimed to have heard the northern lights, which is why the composer riks Eenvalds has used journal extracts from them. The only known Latvian folksong is a song about the sound of the Auroral sound phenomenon.
You can listen to the radio signals of the northern lights at home. In 2020, a radio program remapped the radio recordings of the aurora onto the audible spectrum.
The radio frequencies give an awesome sense of the fleeting nature of the northern lights, which are visible from a snowy mountaintop.
PhD Candidate in History and Philosophy of Science, University of Cambridge.
The Conversation's article is a Creative Commons licensed one. The original article can be found here.
