Aurora borealis turns out to be a light show with a soundtrack. Finnish researchers say they've recorded sounds about 70 meters (230 feet) above the ground that occurred exactly at the time of the geomagnetic disturbances characteristic of the Northern lights.
Scientists from Aalto University recorded sounds through three separate microphones at an observation site, then tracked the sounds back to the source.
When the aurora borealis appeared, the researchers recorded an odd knocking sound that sounds a bit like a metal pipe being struck, which can be heard in the video below:
There are plenty of anecdotes from people who've said they heard sounds from the Northern lights, but scientists had previously thought this was impossible, since the aurora borealis is to far up in the sky for humans to possibly hear any sounds associated with it.
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But actually, it turns out the same forces that produce the light show can also somehow create sound closer to the ground.
Our research proves that the source of the sounds that are associated with the aurora borealis we see is likely caused by the same energetic particles from the sun that create the northern lights far away in the sky, the researchers said in a statement.
It's still unclear exactly how these sounds are made, according to the scientists.
There's also much older tales linking sound and aurora borealis. The Sami tribe of indigenous Scandanavians calls the northern lights 'Guovssahas,' meaning 'the light which can be heard.'