Helioseismology…. is what?

From the New York Times

February 13, 2012

The Song of the Sun

By C. CLAIBORNE RAY

The Sun’s boiling and bubbling gases create a noisy throbbing, and the resulting sound waves are being used by scientists to study the interior of the star.

But the sound waves are trapped inside the Sun, according to NASA scientists, and while they become visible as waves when they reach the surface, their frequencies are mostly too low to be heard by human ears — if a human were to be put in the unlikely position of being there.

The study of the Sun using sound waves is called helioseismology, because it is much like the use of seismic waves to study the interior of the Earth. The waves were discovered half a century ago.

Because space is a vacuum, the sound waves cannot not leave the Sun to be “heard” elsewhere. But scientists at Stanford University have condensed days of instrument readings of solar vibrations and speeded them up, posting them on a Web site, to let earthlings get an idea of one strand of the Sun’s bell-like or drumlike resonances.

The instrument used to collect the sounds is the Michelson Doppler Imager, on board SOHO, the Solar and Heliospheric Observatory spacecraft, which was launched into orbit in 1995. C. CLAIBORNE RAY

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