ROBERT SIEGEL, host: This is NPR's ALL THINGS CONSIDERED. I'm Robert Siegel.
NOAH ADAMS, host: And I'm Noah Adams.
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ADAMS: We have been devoting a bit of time every Friday to the Lost and Found Sounds of this century. Some of those sounds have always been around, but we only got around to listening to them for a bit more than 100 years. For example, it took the invention of radio receivers to learn that the northern lights are something to hear as well as see.
(SOUNDBITE OF MUSIC FROM NORTHERN LIGHTS)
SIEGEL: Earth is constantly bombarded by particles from the sun. When sun spots or a solar flare send enough of these particles toward the Earth's magnetic field, the skies at both poles light up with the aurora borealis and the aurora australis. The particles also create very low frequency electromagnetic waves, creating a type of natural radio. It can be picked up around the globe with specially designed receivers. So every year around this time sound recordist Steve McGreevy heads north where the reception is best and points his receiver at the sky.
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Mr. STEVE McGREEVY: There's just a whole litany of different natural radio sounds to record, hisslers and growlers and howlers and tweaks. There's clusters like a pack of dogs barking.
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Mr. McGREEVY: And in the case of this morning, we've having these very soft hissy whistlers, which are actually fairly rare.
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Mr. McGREEVY: It's 5:24 in the morning on Monday, the 22nd of June, 1998, at Waterton Park, Bailey(ph) River Campground set in Alberta, Canada. He's got these great hissy whistlers happening, and in the right channel we're hearing the beginnings of chorus.
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Mr. McGREEVY: That was a burst of static from something pretty close, a lightning storm. Oftentimes when I'm recording, you'll hear a kind of a (crackling sound) and maybe a second or two later you'll hear (hissing sound). The electromagnetic pulse from the lightning bolt takes a round trip to the opposite hemisphere and then it bounces back. And in making this long trip, the frequency components are spread out so you get this downward falling tone, like a sigh or a hiss.
(SOUNDBITE OF HISSING FREQUENCY)
Mr. McGREEVY: These receivers are sensitive enough that a lightning storm could be happening 1,000 miles away and the static will still be strong. You can just hear all the snapping--let me turn on this speaker amplifier. You just can imagine there is so much--in fact, we're hearing some nice noises now coming in. OK. This is a very beautiful sounding event. This is called chorus.
(SOUNDBITE OF MUSIC FROM NORTHERN LIGHTS)
Mr. McGREEVY: Particles from the sun are hitting Earth's magnetic field and generating these noises, probably several thousand miles out in space. Imagine a soap bubble with wind currents pushing against it and you can see it deform. Well, that's essentially what happens with Earth's magnetic field. So, yeah, I've got these funky looking triangular-shaped loops, five turns of about 350 feet of wire hanging up on a tree picking up the beautiful sounds of mother Earth. And there's vibrations of electrical and magnetic energy. And so essentially, all these receivers do is pick up the Earth's radio waves and translate them directly to the same sound frequencies. And so the result is just beautiful and amazing. That's been going on, well, for eons. And they first noticed it in England in about 1882, and British telegraph operators started hearing these strange whistling tones in their headphones.
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Mr. McGREEVY: But it wasn't until the 1930s when some people started associating these with visible northern lights.
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Mr. McGREEVY: As electronic equipment became more available to the average experimenter and hobbyist, amateurs started listening to this, using fairly crude equipment. You know, maybe a phonograph amplifier connected to a barbed-wire fence in the middle of nowhere, similar to what I did when I first heard this myself. When I discovered Earth makes its own radio waves, I was amazed, because I'm a nature enthusiast anyway and always been interested in astronomy and science.
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Mr. McGREEVY: I've got a long quite checkered history with radio, beginning as a little kid playing with an AM pocket radio and tuning in distant stations at night. And I've done all sorts of crazy things, planting radio beacons in the middle of the deserts and bouncing signals off aircraft, and I was a pirate radio operator for eight years. One Sunday evening, I got a knock on the door about 10:30 at night. The fellow said, `Hi. I'm from the FCC. May I see your station?' Just about as cheerful as can be.
There's a station in Colorado called WWV, which does nothing but transmit the time 24 hours a day on shortwave.
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Mr. McGREEVY: But once an hour, WWV let's me know what's going on with the Earth's magnetic field and they give what they call space weather, which is what's going on with the sun and between the sun and the Earth.
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Mr. McGREEVY: So I'm aware that right now the Earth is in a magnetic storm and it may be affecting power lines right now. It may be affecting satellites right now.
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Mr. McGREEVY: Space weather, this invisible weather we can't really see or feel on Earth, but, indeed, it's going on out there. And it's wild. And it's stormy at times. And it's calm at other times. It's just like weather here on Earth.
(SOUNDBITE OF MUSIC FROM NORTHERN LIGHTS)
Mr. McGREEVY: Right at this very moment, I've got my headphones on. These whistlers are really coming in big streams now.
(SOUNDBITE OF MUSIC FROM NORTHERN LIGHTS)
Mr. McGREEVY: There's just one whistler kind of merging into the other, all slowly descending in pitch. These are so great. Wow.
(SOUNDBITE OF MUSIC FROM NORTHERN LIGHTS)
SIEGEL: Steve McGreevy, recorded by producer Barrett Golding in Canada's Waterton Peace Park for Lost and Found Sound.