Put The Aurora Borealis In Your Ear

by Bob King on May 20, 2013

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A rural location is ideal for listening to the subtle sounds of the aurora with a VLF radio. Just turn it on and hold it up to the sky.This photo was taken early Saturday morning when green auroras were still visible through breaks in the clouds. Photo: Bob King

A rural location is ideal for listening to the subtle sounds of the aurora with a VLF radio. Just turn it on, don the earphones on and hold the unit skyward. Credit: Bob King

Do the aurorae makes sounds? That’s been a subject of discussion — and contention — among people who watch the sky. While most of us will never hear the aurora borealis directly, there’s help out there in the form of a little handheld radio. It’s called a VLF receiver and guarantees you an earful the next time the aurora erupts.

High-speed electrons and protons buzzing along Earth's magnetic fields lines emit very low frequency radio waves that human ears can here with a VLF receiver. Credit: Bob King

High-speed electrons and protons buzzing along Earth’s magnetic fields lines emit very low frequency radio waves that human ears can here with a VLF receiver. Credit: Bob King

Despite seeing hundreds of northern light displays ranging from mild to wild, I’ve yet to actually hear what some describe as crackles and hissing noises. There is some evidence  that electrophonic transduction can convert otherwise very low frequency (VLF) radio waves given off by the aurora into sound waves through nearby conductors. Wire-framed eyeglasses, grass and even hair can act as transducers to convert radio energy into low-frequency electric currents that can vibrate an object into producing sound. Similar ‘fizzing’ sounds have been recorded by meteor watchers that may happen the same way.

Laboratory tests reveal that a surprising variety of substances, including frizzy hair and vegetable matter, can act as radio-to-audio VLF transducers. Credit: NASA

Laboratory tests reveal that a surprising variety of substances, including frizzy hair and vegetable matter, can act as radio-to-audio VLF transducers. Credit: NASA

Imagination may be another reason some folks people hear auroras. Things that move often make sounds. A spectacular display of moving lights overhead can trick your brain into serving up an appropriate soundtrack. Given that the aurora is never closer to the ground than 50 miles, the air is far too thin at this altitude to transmit any weak sound waves that might be produced down to your ears.

If you’re like me and hard of auroral hearing, a small VLF (very  low frequency) radio receiver will do the job nicely. This handheld device converts very low frequency radio waves produced from the interaction of the solar electrons and protons with the Earth’s magnetic field into sounds you can listen to with a pair of headphones.

The battery-operated WR-3 VLF (Very Low Frequency) receiver with headphones for tuning in on sounds bouncing around Earth's magnetic field.  Credit: Bob King

The battery-operated WR-3 VLF (Very Low Frequency) receiver with headphones for tuning into sounds “natural” radio broadcast by planet Earth. Credit: Bob King

We’re used to waves of light which are very, very short, measuring in the millionths of an inch long. The pigments in our retinas convert these waves into visible images of the world around us. Radio waves given off by auroras and other forms of natural ‘Earth energy’ like lightning range from 19 to 1,800 miles long or longer. To bring them within range of human hearing we need a radio receiver. I fire up a little unit called a WR-3 I purchased back in the mid-1990s. The components are housed in a small metal box with a whip antenna and powered by a 9-volt battery. The on-off switch also controls the volume. Plug in a set of headphones and you’re ready to listen. That’s all there is to it.

olar wind heading into space and impacting Earth's protective magnetic shield, its magnetosphere. The particles are seen heading out in all directions, but with some of them hitting our magnetosphere. Earth's magnetic field lines are shown in concentric purple ovals, pushed on by pressure from the Sun and elongated on the side facing sway from the Sun. Credit: NASA

The magnetosphere of the Earth is enormous bubble of magnetism that surrounds our planet. It’s created through the interaction of the solar wind (yellow lines) and Earth’s magnetic field. The magnetosphere acts as a shield to protect us from dangerous radiation in space. Earth’s magnetic field lines are shown in concentric purple ovals, pushed on by pressure from the Sun and elongated on the side facing sway from the Sun. Credit: NASA

The receiver picks up lots of things besides aurora including a big ‘unnatural’ hum from alternating or AC current in power lines and home appliances. Turn one on in your house and you’ll immediately hear a loud, continuous buzz in the headphones. You’ll need to be at least a quarter mile from any of those sources in order to hear the more subtle music of the planet.

 

Lightning produces a great variety of radio sounds - sferics, tweeks and whistlers - you can hear with the right receiver.  Credit: Bob King

Lightning produces a great variety of natural radio sounds – sferics, tweeks and whistlers – you can hear with a VLF radio receiver. Credit: Bob King

I drive out to a open ‘radio quiet’ rural area, turn on the switch and raise the antenna to the sky. Don’t stand under any trees either. They’re great absorbers of the low frequency radio energy you’re trying to detect. What will you hear? Read on and click the links to hear the sound files.

* Sferics. The first thing will be the pops, crackles and sizzles of distant lightning called sferics which are similar to the crackles on an AM car radio during a thunderstorm.

* Tweeks. Lightning gives off lots of energy in the long end of the radio spectrum. When that energy gets ducted through the upper layers of Earth’s atmosphere called the ionosphere over distances of several thousand miles, it emits another type of sound called ‘tweeks‘. These remind me of Star Wars lasers or dripping water. Flurries of tweeks have an almost musical quality like someone plucking the strings of a piano.

* Whistlers and Whistler Clusters. When those same lightning radio waves enter Earth’s magnetosphere and interact with the particles there, they can cycle back and forth between the north and south geomagnetic poles traveling tens of thousands of miles to create whistlers. Talk about an eerie, futuristic sound. After their long journey, the higher frequency waves arrive before those of lower frequency causing the sound to spread out in a series of long, descending tones. The sound may also take you back to those old World War II movies when bombs whistled through the air after dropping from the hatch of a B-17. Tweeks are very brief; whistlers last anywhere from 1/2 to 4 seconds or longer.

* Dawn Chorus. Sometimes you’ll hear dozens of whistlers, one after the other. When conditions are right, a VLF receiver can pick up disturbances in Earth’s magnetic bubble spawned by auroras called ‘chorus‘ or ‘dawn chorus’. Talk about strange. Who would have guessed that solar electrons spiraling along Earth’s magnetic field lines would intone the ardor of frogs or a chorus of birds at dawn? And yet, there you have it.

* More Dawn Chorus: On a good night, and especially when the northern lights are out, it’s a magnetospheric symphony. Thunderstorms thousands of miles away provide a bounty of crackles and tweeks with occasional whistlers. Listen closely and you might even hear the froggy voice of the aurora rising and falling with a rhythm reminiscent of breathing.

The crescent moon, Jupiter and Venus accompanied a spectacular aurora over Lake Superior in Duluth, Minn. last July. Credit: Bob King

The crescent moon, Jupiter and Venus accompanied a spectacular aurora over Lake Superior in Duluth, Minn. last July. With solar activity on the upswing and solar maximum predicted for the fall, auroras are more likely than ever in 2013. Credit: Bob King

If you’re interested in listening to VLF and in particular the aurora, basic receivers are available through the two online sites below. I’ve only used the WR-3 and can’t speak for the others, but they all run between $110-135. One word of warning if you purchase – don’t use one when there’s a lightning storm nearby. Holding a metal aerial under a thundercloud is not recommended!

WR-3 VLF receiver from Stephen McGreevy
North Country Radio ELF Earth Receiver

More on natural radio can be found HERE. Things to keep in mind when considering a purchase are whether you have access to an open area 1/2 mile from a power line and away from homes. You’ll also need patience. Many nights you’ll only hear lightning crackles from distant storms thousands of miles away peppered by the occasional ping of a tweet. Whistlers may not appear for weeks at a time and then one night, you’ll hear them by the hundreds. But if you regularly watch the sky, it’s so easy to take the radio along and ‘give a listen’ for some of the most curious sounds you’ll ever hear. How astonishing it is to sense our planet’s magnetosphere through sound. Consider it one more way to be in touch with the home planet.

For more on natural radio including additional sound files I invite you to check out Stephen P. McGreevy’s site.

 

About 

I'm a long-time amateur astronomer and member of the American Association of Variable Star Observers (AAVSO). My observing passions include everything from auroras to Z Cam stars. Every day the universe offers up something both beautiful and thought-provoking. I also write a daily astronomy blog called Astro Bob.

Philip Havice May 20, 2013 at 1:37 PM

Great article . Nice to expand awareness , and that others are noticing the music of the sphere !

Lazlo Long May 21, 2013 at 11:56 AM

Who knew??

Joan Patrie May 23, 2013 at 10:06 PM

<—KG8VO. I knew :)

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