The sound of shooting stars
Twice in August while looking up at the sky I’ve been lucky enough to see two bright shooting stars… once in Budleigh at the peak of the Perseids, and the weekend before last here in Southampton.
On both occasions, to my surprise, I heard something… like a quiet abruptly truncated hiss. The second time, I was showing my daughter where Jupiter was, and our heads were close and, we both saw it and heard it. And at that point it struck me that I shouldn’t be able to… certainly not at the same time as I was seeing it.
A quick bit of research confirmed that if they’re burning up at least 80km up, there was no way I should hear direct sound… yet we’d both heard something as we saw it, so what was going on? I dug a bit more on the internet and found many people have experienced it, but there still doesn’t seem to be a consensus for a satisfactory explanation for the effect.
For many years, the prevailing explanation was that very low frequency radio waves generated in the meteor’s wake were being converted to sound by conductors at ground level such as telephone wires, something referred to as electrophonics. In 2017 though, a new idea was posited in a study published in Nature – that the sounds might be a manifestation of the something called the photoacoustic effect. In this case the bright flickering of the burning meteor could be heating the surface of non-conducting materials enough to cause tiny pressure waves that, if you were close enough to the source, you’d be able to hear. And the intriguing twist for me was that in attempting to experimentally validate their theory, the researchers found that long dark hair or frizzy hair appeared to be an effective transducer… and of course this puts the sound source right next to your ears.
I’ve observed meteor showers before… but never with the long dark hair I have now. And on the Sunday before last I was standing right behind my daughter with our heads very close, (she was on a chair), and along with my long dark hair, she has a head of loose curls, with plenty of frizz.
From having read around the topic, it seems the case is by no means closed – there is a question of whether most meteors are really bright enough to generate a photoacoustic effect that can be heard. So I’m intrigued having stumbled upon something that is still looking for definitive answer. But my main takeaway was that we weren’t going mad thinking we heard a shooting star… and if you’ve heard one, neither are you!