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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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