- Fiona Amery
- The Conversation*
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Credit, Reuters
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Northern lights seen in Lapland, Finland.
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This is a question that has intrigued observers for centuries: do the fantastic lights in shades of green and purple displayed by the aurora borealis produce a noticeable sound?
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Caused by the interaction between solar particles and gas molecules in the Earth’s atmosphere, the aurora usually occurs near the planet’s poles, where the magnetic field is strongest. Reports that the aurora make sounds, however, are rare – and have historically been dismissed by scientists.
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But a 2016 Finnish study said it confirmed that the so-called Northern Lights actually produce a sound that is audible to the human ear. One of the researchers involved in the research captured the sound, possibly made by the captivating lights, which, according to estimates, originated 70 meters above ground level.
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The mechanism behind the sound, however, remains somewhat mysterious, as do the conditions that need to be met for the sound to be heard. My recent research analyzes historical auroral sound reports to understand the methods of investigation of this elusive phenomenon and the process of establishing whether the reported sounds are objective, illusory, or imaginary.
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The roar of dawn was the subject of a particularly lively debate in the early decades of the 20th century, when reports from settlements along northern latitudes described that sounds sometimes accompanied the impressive displays of light in the sky.
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Witnesses spoke of a very low, barely perceptible crackle and a humming noise during particularly violent Northern Lights displays. In the early 1930s, for example, individual testimonies began arriving at the newsroom of the weekly The Shetland News in the subarctic Shetland islands, comparing the sound of the Northern Lights to “silk whispers” or “two boards hitting each other” .
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These stories were supported by similar testimonies from northern Canada and Norway. Still, the scientific community was not convinced, especially considering that very few Western explorers claimed to have heard these elusive sounds themselves.
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The credibility of reports of dawn noises at this time was closely linked to the Northern Lights altitude measurements. It was considered that only those displays that descended low in the Earth’s atmosphere would be able to transmit a sound that could be heard by the human ear.
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The problem here was that results recorded during the Second International Polar Year, 1932-33, identified that Northern Lights most commonly occur 100 kilometers above the Earth and very rarely below 80 kilometers. This suggested that it would be impossible for any discernible sound from the lights to be transmitted to the Earth’s surface.
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Credit, Reuters
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For some people, the aurora borealis produces sounds that resemble hums and crackles
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With these discoveries, leading physicists and meteorologists have remained skeptical, dismissing reports of dawn sounds and very low auroras as folk tales or auditory illusions.
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Oliver Lodge, the British physicist involved in the development of radio technology, commented that the aurora sound must be a psychological phenomenon due to the vividness of the aurora’s appearance – just as meteors sometimes produce a buzzing sound in the brain. Similarly, meteorologist George Clark Simpson argued that the appearance of low auroras was likely an optical illusion, caused by interference from low clouds.
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Even so, two 20th-century assistant astronomers have written accounts claiming to have heard the dawn, adding a certain legitimacy to the sheer volume of individual testimony.
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One of them wrote that he heard a “very curious sound, like a hissing, unmistakably undulating, which seemed to follow exactly the vibrations of dawn”, while another experienced a sound like “burning grass or a spray”. As convincing as they may have been, they still did not propose a mechanism by which the dawn sound could operate.
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The answer to this enduring mystery that later gained the greatest support was first attempted in 1923 by Clarence Chant, a well-known Canadian astronomer. He argued that the movement of the Northern Lights alters the Earth’s magnetic field, leading to changes in the electrification of the atmosphere, even at a significant distance.
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This electrification produces a popping sound much closer to the Earth’s surface when it encounters objects on the ground, much like static sound. This can occur on the viewer’s clothing or glasses, or possibly on surrounding objects, including pine trees or building cladding.
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Chant’s theory fits well with many of the aurora sound reports and is also supported by occasional information about the smell of ozone – which supposedly carries a metallic odor similar to an electrical spark – during Northern Lights appearances.
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Chant’s report, however, went largely unnoticed in the 1920s, gaining recognition only in the 1970s, when two dawn physicists revisited the historical evidence. Chant’s theory is widely accepted by scientists today, although there is debate over exactly how the sound production mechanism works.
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What is clear is that the aurora borealis does, on rare occasions, produce sounds audible to the human ear. The ominous reports of popping and humming noises accompanying the lights really describe an auditory experience – not just something illusory or imaginary.
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Credit, PA Media
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Lights behind Dunstanburgh Castle, England
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If you want to hear the Northern Lights yourself, you may have to spend considerable time in one of the polar regions, considering that the phenomenon only presents itself in 5% of the most violent sightings of the aurora borealis. It’s also most often heard on mountaintops, where there’s only a few buildings – so it’s not a particularly accessible experience.
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In recent years, the sound of the aurora has been explored for its aesthetic value, inspiring musical compositions and laying the foundation for new ways to interact with its electromagnetic signals.
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Latvian composer Ēriks Ešenvalds used extracts from the publications of American explorer Charles Hall and Norwegian explorer and diplomat Fridjtof Nansen, who said they heard the Northern Lights, in their music. Your composition, Northern Lights, interweaves these accounts with the only known Latvian folk music that speaks of the sound phenomenon of the Northern Lights, sung by a tenor.
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Or you can listen to the Northern Lights radio signals at home. In 2020, a program on the BBC Radio 3 station remapped very low-frequency radio recordings of the dawn into the audible spectrum. While not the same thing as perceiving the Northern Lights sonic noises in person atop a snow-covered mountain, these sounds give an incredible sense of the transient, transient and dynamic nature of the aurora borealis.
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* This article was originally published on the academic news site The Conversation and republished here under a Creative Commons license. Read here the original version (in English).
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