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  Solar Sounds

"The Sun is playing a secret melody, hidden inside itself, that produces a widespread throbbing motion of its surface. The sounds are coursing through the Sun's interior, causing the entire globe, or parts of it, to move in and out, slowly and rhythmically like the regular rise and fall of tides in a bay or of a beating heart." (Kenneth R. Lang)

Hear the Sun Sing

Have you ever wondered what the Sun would sound like if you could hear it?

Our Sun lies 93,000,000 miles away, surrounded by the vacuum of space. Sound won't travel through space, of course. But with the right instrument, scientists can "hear" pulsations from the Sun.

The entire Sun vibrates from a complex pattern of acoustical waves, much like a bell. If your eyes were sharp enough, you could see a bell's surface jiggle in complex patterns as the waves bounced around within it.

Likewise, astronomers at Stanford University can record acoustical pressure waves in the Sun by carefully tracking movements on the Sun's surface. To do this, they use an instrument called a Michelson Doppler Imager (MDI), mounted on the SOHO spacecraft, circling the Sun 1,000,000 miles from Earth.

The Sun's acoustical waves bounce from one side of the Sun to the other in about two hours, causing the Sun's surface to oscillate, or wiggle up and down. Because these sound waves travel underneath the Sun's surface, they are influenced by conditions inside the Sun. So scientists can use the oscillations to learn more about how the structure of the Sun's interior shapes its surface.

The Sun's sound waves are normally at frequencies too low for the human ear to hear. To be able to hear them, the scientists sped up the waves 42,000 times -- and compressed 40 days of vibrations into a few seconds. What you'll be hearing are just a few dozen of the 10 million resonances echoing inside the Sun.

These are solar sounds generated from 40 days of Michelson Doppler Imager data and processed by A. Kosovichev.

The procedure he used for generating these sounds was the following. He started with doppler velocity data, averaged over the solar disk, so that only modes of low angular degree (l = 0, 1, 2) remained. Subsequent processing removed the spacecraft motion effects, instrument tuning, and some spurious points. Then Kosovichev filtered the data at about 3 mHz to select clean sound waves (and not supergranulation and instrumental noise). Finally, he interpolated over the missing data and scaled the data (speeded it up a factor 42,000 to bring it into the audible human-hearing range (kHz)).

One Mode

(l=1,n=20, nu=2.94-3.0 mHz)

Three Modes

(l=0,n=21, l=1,n=20, l=2,n=20, nu=2.95-3.05 mHz)

All Low-Degree Modes

(l=0,1,2, and 3)

questions and comments:

Rainer Schwenn schwenn@linmpi.mpg.de
Borut Podlipnik podlipnik@linmpi.mpg.de