Sensing Sound
“Things are not the same as they used to be, because in the early days northern lights howled a great deal more than they do now.”
inuits, western Alaska
“Northern lights appear to have become less noisy since their occurrences have been more accurately recorded.”
Humboldt, Cosmos (1847)
Viewed from outer space, the Earth is a powerful planetary radio source. The dominant source of emission is a naturally occurring electromagnetic wave generated in the auroral zones. Auroral Kilometric Radiation (AKR) is closely tied to auroras, or more specifically to the beams of charged electrons that in interaction with atoms of oxygen and nitrogen result in auroral displays. Radio is both a human technology and a cosmic technology. AKR is the most powerful emission of terrestrial origin and is beamed into space, potentially making it detectable from other planets and galaxies, just as other extrasolar planets can potentially be detected through their radio emissions.
The human ear senses physical waves and cannot directly hear electromagnetic waves. However, radio emissions from Earth (along with other planets) at the lowest end of the radio spectrum including electromagnetic phenomena such as lightning and auroras can be translated into sound. For example by using a VLF (Very Low Frequency) receiver that captures radio waves vibrating at frequeincies overlapping the range of human hearing (20 Hz - 20kHz) and feeding them into a speaker. While the frequency range of AKR (50-500kHz) is outside of the audible range of humans imposing an artificial frequency shift enables humans to hear it.