There is more than one way to listen to a bolt of lightning. While you can pick up the boom and rumble of thunder with your ears, if you tune in with a radio receiver, you can hear an entirely different sound: an earth whistler.

When lightning strikes, it releases electromagnetic radiation in the VLF or Very Low Frequency band, which runs from 3 Hz to 30 kHz. This falls within the human range of hearing, which spans from 20 Hz to 20 kHz. However, we can not hear whistlers with our own ears because the radiation is electromagnetic, not physical vibrations in the air.

We can, though, capture the electromagnetic radiation with a radio receiver. Radio operators have been picking up the strange twanging of lightning ever since they started trying to tune into man-made signals. They dubbed the eerie electro-magnetic disturbances in their headphones “earth whistlers.”

People first heard earth whistlers back in the 19th century. The electromagnetic radiation from lightning interfered with telephone lines and crept into phone conversations. You’d be talking with someone and hear these bursts of energy, like little phone ghosts. 

Today, we know earth whistlers are made by the interaction of lightning with the planet’s magnetic field. There are over a million lightning strikes in the atmosphere, which means there is a nearly constant chorus around earth. 

The whistlers in this piece were provided courtesy of NASA and The University of Iowa. 

The World According to Sound is a live audio show, online listening series, and miniature podcast that focuses on sound, not story. Producers Chris Hoff and Sam Harnett create intentional, communal listening experiences as a way to “reclaim autonomy in a visually dominated world that is increasingly fracturing our attention.” 

This recording is part of their next listening series, an immersive listening party where audiences from all over the globe will be invited to experience a world of sound together, beginning in January 2022. You can get a ticket to the series here.