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Foreword by Walter Cronkite  
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Astronomy: Exploring the Expanding Universe

Voyage to the
Center of the Sun

Until recently, the inner workings of the Sun were a mystery of cosmic proportions. For many years, researchers have known that deep in the Sun's interior, 600 million tons of hydrogen fuse into helium every second, radiating out the resulting energy. And while the mechanics of this conversion have been described in theory, the Sun's interior has remained inaccessible. Now, however, the Sun is being "opened," its internal structures probed, and its inner dynamics surveyed by NSF-supported scientists using investigative techniques-a branch of astronomy known as helioseismology.

GONG researchers study the Sun by analyzing the sound waves that travel through it. Much as the waves produced by earthquakes and explosions roll through the Earth, these solar sound waves pass through the Sun's gaseous mass and set its surface pulsating like a drumhead. With six telescopes set up around the Earth collecting data every minute, GONG scientists are learning about the Sun's structure, dynamics, and magnetic field by measuring and characterizing these pulsations.

Sound Wave Oscillations of the Sun - click for details Analysis of data from GONG and other sources shows that current theories about the structure of the Sun need to be expanded. For example, the convection zone—the region beneath the Sun's surface where pockets of hot matter rise quickly and mix violently with ambient material—is much larger than originally thought. Furthermore, says Leibacher, the zone ends abruptly. "There is turbulent mixing and then quiet. We can locate the discontinuity with great precision." Some research teams are probing deeper and examining the Sun's core; still others are addressing such topics as sunspots—places of depressed temperature on the surface where the Sun's magnetic field is particularly intense.

New insight into the Sun's core came in the spring of 2000, when NSF-funded researchers analyzing GONG data announced that they had discovered a solar "heartbeat." That is, they'd found that some layers of gas circulating below the sun's surface speed up and slow down in a predictable pattern-about every sixteen months. This pattern appears to be connected to the cycle of eruptions seen on the Sun's surface.

Such eruptions can cause significant disturbances in Earth's own magnetic field, wreaking havoc with telecommunications and satellite systems. A major breakthrough in the ability to forecast these so-called solar storms came in the spring of 2000, when NSF-funded astrophysicists, using ripples on the Sun's surface to probe its interior, developed a technique to image explosive regions on the far side of the Sun. Such images should provide early warnings of potentially disruptive solar storms before they rotate towards Earth.

As our nearest star, the Sun has always been at the forefront of astrophysics and astronomy. (Astrophysicists study the physics of stellar phenomenon, while astronomers have a broader job description-they observe and explore all of the universe beyond Earth.) The more we learn about the Sun, the more we understand about the structure and evolution of stars and, by extension, of galaxies and the universe. The Sun also is host to a family of nine planets and myriad asteroids and cometary bodies. As we investigate the richness of outer space, we often look for things that remind us of home.

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Voyage to the Center of the Sun
New Tools, New Discoveries
At the Center of the Milky Way
The Origins of the Universe
The Hunt for Dark Matter
Shedding Light on Cosmic Voids
Visualizing the Big Picture
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