 Lightning
is the main melody maker in the music of the Earth
By Richard Stenger CNN
(CNN) -- Want
to hear music that is really down to earth? Check out a Web site
that broadcasts the perpetual piping of our planet. The sound
is rather striking.
The screeches,
blasts and hums that comprise the terrestrial tune are actually
natural radio emissions that constantly surround us. But radio
antennae, not ears, are required to listen.
Using a very
low frequency radio (VLF) receiver, NASA tunes in to the sounds
and broadcasts them on the Internet from Huntsville, Alabama,
home to the agency's Marshall Space Flight Center. To hear a sample
or listen to the online receiver, visit the following NASA page:
http://www.spaceweather.com/glossary/inspire.html
"Everyone's
terrestrial environment almost literally sings with radio waves
at audio frequencies," said Dennis Gallagher, a NASA physicist.
The main melody
emanates from lightning strikes, even from far away, which pulse
great distances through the atmosphere and register as strange
sounding crackling.
The sound
resembles that of frying bacon, similar to the audio bursts on
conventional radios, unleashed by nearby lightning bolts. Lightning
strikes somewhere on the planet about 100 times per second, meaning
the strange-sounding VLF signals are heard constantly.
"The
best time to listen is usually around sunset or dawn (Huntsville
time)," when the atmosphere amplifies the natural radio waves,
Gallagher said. Moreover, night is generally a better time to
listen than during the the day.
Space scientists
classify different lightning sounds as "sferics," short
for atmospherics, "tweeks" and "whistlers,"
depending on their intensities and the convoluted paths they take
before reaching the receiver.
"Lightning
pulses that travel all the way to the magnetosphere and back are
highly dispersed," said Gallagher. "We call them 'whistlers'
because they sound like slowly descending tones."
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