SUN SURVEYS SHED LIGHT ON NEAREST STAR : ASTRONOMERS MEASURE SOUND WAVES TO MAP CHANGING SOLAR INTERIOR.

Byline: Bill Dietrich The Seattle Times

Astronomers have always been pretty certain the sun will rise tomorrow, but beyond that the most obvious object in the sky has always been something of a mystery.

Now scientists gathered at a meeting of the American Astronomical Society are releasing the first results from a battery of new satellites and telescopes that promise to see into the sun with sound waves.

``You can't see inside the sun, but you can hear inside the sun,'' quipped Douglas Gough of England's Cambridge University, one of a number of astronomers mapping the boiling currents that ultimately generate solar storms in the Earth's atmosphere: surges of energy that can turn a radio scratchy and sometimes affect our weather.

Scientists are keenly interested in the sun for two reasons. First, it is the only nearby star we have to understand the basic functioning of the universe.

Second, when the sun coughs, Earth gets sick. Solar turbulence sends out solar storms that disturb our planet's electromagnetic field, causing everything from static on radios to power failures on electric grids. It can even set up currents that corrode metal pipes. If astronomers could forecast ahead of time when this solar weather is going to hit, utilities and organizations with sensitive electronic instruments could take steps to prepare for it.

The problem is, the sun's fiery surface seemed to defeat any attempt to understand its interior, until recently.

Astronomers have come up with the idea of ``helio seismology,'' or using waves through the sun to understand its interior, just as seismologists use earthquake waves to map underground faults.

In December, the European space agency and NASA combined to launch a $1.1 billion satellite called the Solar and Heliospheric Observatory. Taking up a stationary orbit 1 million miles from Earth, it has 12 different telescopes and instruments pumping out 1,000 images a day of unprecedented detail.

At about the same time, a ground-based network of six telescopes strung around the world called the Global Oscillation Network Group, began recording the millions of sound waves that echo around the sun from the turbulent flow of its gases.

In effect, the sun rings like a bell from its inner fires, explaining the choice of GONG as an acronym. Each of the six observatories records 200 megabytes of data every day.

``It's like trying to describe the interior structure of a piano by listening to it fall down the stairs,'' explained Phil Scherrer of Stanford University.

The two networks complement each other and both have the advantage that the sun never sets: SOHO, of course, is in space, and the six ground stations are spaced so that the sun is up above more than one of them all the time. This is important because many solar features form and fade in less than a day. Night and clouds have previously interrupted observations.

For the same reason, another solar observatory operates at the South Pole during the six months the sun is above the horizon there.

The result, scientists said here, is that our local star is surprisingly complex. GONG has found east-west and north-south surface flows and evidence of turbulent mixing deeper than ever before, in a region Gough - the Cambridge University scientist - has dubbed the tacholine and which extends from about 125,000 miles to 145,000 miles in depth.

SOHO has discovered the sun's heat convection cells, some analogous to the bubbles in a boiling pot, are flatter and more pancake-like than expected, making the sun's convection layer more complicated than thought.