8.9.06

If you haven’t heard the Northern Lights, maybe you should be grateful.

The electric field needed to hear the aurora on Earth would generate radio waves strong enough to rattle your skull, says University of Alaska Fairbanks professor Dirk Lummerzheim.

“Then, of course, you’re not hearing the electric field,” he says with a chuckle. “You’re hearing your skull vibrating.”

In fact, auroras do not really generate an energy field that powerful. Without some sort of receiver, the radio waves they emit should not be audible at all. But Lummerzheim does not laugh off the accounts of people who swear they have, in fact, heard something when Northern Lights danced overhead.

Tuesday, January 18, at a Fairbanks hotel, Lummerzheim offered several possible explanations for the phenomenon of noisy auroras to a the standing-room-only crowd of almost 500 who attended his talk, “Sounds of the Aurora and Other Persistent Mysteries.”

Scientists have documented hundreds of earwitness accounts of the aurora, where people reported hearing hissing, swishing, rustling, or crackling during very active auroral displays, said Lummerzheim. According to the accounts: “Apparently, only really bright, really fast moving aurora create sound.” Listeners also tend to report that it was very clear the source of the noise was the aurora.

Given what we know about the differing speeds of light and sound, however, it should not be possible for an earthbound observer to connect the sounds they hear with specific movements the lights make.

Because the speed of sound is relatively slow compared to the speed of light, explained Lummerzheim, it would take at least five minutes for sounds generated directly overhead to reach the ground-based viewer. Travel time for Northern Lights sounds starting from the horizon would be more like 10 minutes.

So how to account for people who think they are seeing and hearing a fully synchronized, multisensory show? Are they simply mistaken?

Lummerzheim thinks not.