This week, on WNYU’s science and technology show The Doppler Effect, we had a really interesting sound.
That is the sound of the radio frequencies of the aurora borealis.
Now, let’s be clear. That’s not a sound you can hear. If you listen to the whole segment from the WNYU show (here) you’ll hear Bez Laderman and Jonathan Zrake - two NYU physicists – discuss why it’s highly improbably for the aurora to make any kind of sound that we can hear on the ground. If you don’t want to go listen (but I hope you do), here’s basically what they say:
There are reports of a sound associated with the auroras. It’s a hissing, rustling, or crackling noise, or some combination of the three. But if you think about what the aurora borealis is – which Zrake describes in the podcast (electromagnetic winds also happen to be the subject of his PhD work) – that doesn’t make a ton of sense. Basically, auroras happen when solar winds blow charged particles to Earth, and those particles collide with atoms up in the upper atmosphere. For that to make a sound, they explain, it would have to be really, really loud.
Here’s Bez’s example: how many times have you seen a jet plane in the sky, but not heard it. That jet plane is really, really loud. Something like 80 decibels. And it’s about 3500 feet in the air.
Now, the aurora is 50 miles above us, in the upper atmosphere. That’s 264 000 feet. Which means it has to travel through 75 times the amount of atmosphere to reach us. The atmosphere up there is thinner, which makes it even harder for sound to propagate (since sound is made of pressure waves which need something to travel through) down to us. The collision of those particles would have to be ridiculously loud.
You should really listen to their whole show – where they explain some more of the details about auroras, and go into some of the reasons why there might be sounds or not. But for now, you can sit back and relax and listen to the eerie, yet relaxing sound of the Aurora’s radio waves.