Your parents probably told you never to stare at the sun, but they didn't warn you about listening to it. So by all means lend an ear to this wonderful little sample of "solar music" (also embedded below) from solar physicists at the University of Sheffield.
Those 14 seconds of noise may sound a little bit like Tangerine Dream, but it's actually caused by the movement of giant magnetic loops in the outermost layer of the sun's atmosphere: the solar corona.
As with the marvelous space sounds that came out of the Voyager missions (covered here in Space Music Vol. 3), this is yet another case where scientists translated scientific data into audible sound. Yet while the cosmic symphonies from those missions entail various translated waves, the music of the sun involves only magneto-acoustic waves.*
The University of Sheffield press release received a lot of coverage last month, but the explanations tended to run a bit scarce. What are we hearing exactly? And why? Rather than just throw out the link with a science babble garnish, I decided to call up NASA solar astrophysicist C. Alex Young for some answers. [youtube=http://www.youtube.com/watch?v=ZbIffp40U8w]
Recording What Now? The solar atmosphere, Young explains, contains a particular type of plasma (which is a magnetized, electrified gas). The plasma interacts with magnetic fields so the two basically move with a certain degree of synchronicity.
"Basically they're taking a recording of the oscillations, which are not in the audible range, and then they just change the sound and scale it so that it's within the range of the human ear," Young says. "So you're hearing the overall structure of what's going on."
So is the sun's corona actually producing these sounds? Well, kind of.
"Sound waves are compressional waves or longitudinal waves, so they're basically like a piston pushing the air and squeezing it together," Young says. "You can have those kinds of waves on the sun in a general sense, but they're not necessarily sound in the sense that we can hear it."
Furthermore, astronomers record these magneto-acoustic waves in a very indirect fashion. Just think of the sun as an enormous music visualizer.
"MP3 programs like iTunes use visualizers that pulse with the music," Young says, "Imagine if you could only see those flashes of light on the screen and couldn't hear any of the music. If you took those flashes of light and measured the oscillations of the waves, then you could convert the visualization back into some sort of measurable sound."
Try this out for yourself with your own MP3 program of choice, and you'll quickly see how complicated translations can be. Think you can recognize one of your favorite tracks just by staring at the visualizer?
"It's not an easy process because you're not going to get it exactly right," Young says. "Fortunately, the sun doesn't' have the mixture of all the different complex oscillations that you have in music. But you can have a fairly broad range of oscillations."
So there you have it. From waves through the sun's corona, to flashes of light and then back into audible waves through your headphones.
Why Music? This all leads to the inevitable question: Why produce these sound files in the first place?
"In the simplest sense, they're kind of cool," Young says. "In terms of science, I'm not sure that these audio tracks necessarily add to the science. One of the things that scientists have found in many different disciplines is that you can take your data and put it into a new form then it allows the general public to appreciate and get something interesting out of the kind of science that you do."
Scientists did it with the Voyager recordings, supernovas and even data from the Large Haydron Collider. You might not be able to get too excited about charged particle emissions, but hey, you can appreciate a far-out noise when you hear it.
While researchers typically don't make a habit of translating their data into sound for scientific purposes, Young acknowledges that it is possible that such a sound file could open up new angles on existing data.
"I'm sure there are people who can hear the sounds and get something out of it," Young says. "You may turn something into sound and hear things that you didn't necessarily see the first time in the data, and it may direct you to go back and look at it again. So I guess in that sense there could be some value there if you did hear something you didn't expect and went back to look at the data in its original form."
Coronal Seismology At the heart of all this talk of solar waves and file streaming you'll find the actual work conducted by solar astrophysicists. It's very similar to the way terrestrial seismologists analyze waves in the Earth to study the planet's inner depths. Helioseismologists study the interior of the sun, and coronal seismologists study the sun's corona.
"With the sun we can't directly measure a lot of things like magnetic fields, densities and flows of material," Young says, "So this allows us to work backward and try to infer what is exactly there in the corona."
If you need more info about the sun and its resulting space weather, then be sure to add C. Alex Young on Facebook where he maintains "The Sun Today." And, as always, if you want more Space Music, you can find the rest of the posts right here.