First Results From Global Array That Eavesdrops on Sounds of the Sun
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Early results from a new earth-based, global network of observing posts furnish the first of billions of brushstrokes that will portray the sun's interior in unprecedented detail. New results from GONG--the Global Oscillation Network Group, six stations around the world funded by the National Science Foundation (NSF)--are reported in research featured on the cover of the May 31 issue of Science.
At the American Astronomical Society meeting in Madison, Wis., June 9-13, in a special session, GONG scientists will elaborate further on findings from the array. Turned on last October, GONG is now in full operation studying sound waves in our nearest star.
"The study of the sun's vibrations, called helioseismology, promises to revolutionize our understanding of the sun and other stars, much the way optical spectroscopy did previously," said Hugh Van Horn, NSF's astronomy director. "GONG gives us a unique opportunity to look inside the sun from our own planet. Because the stations are situated around the world, the sun never sets on GONG. This overcomes the disadvantage of a single observatory where sunsets and overcast skies interrupt observations.
"GONG is refining our ideas about what's going on inside the sun and even about how it evolved," said Van Horn. "We also expect to learn more about how and why solar activity changes over time--variability that can have important consequences for the Earth's climate."
The $20-million GONG array, stretched like a giant ear around the earth, listens while the sun speaks in sotto voice--as explosions near the surface of our tumultuous star excite millions of sound waves, which travel back and forth through its depths. Each wave, penetrating to a different depth and latitude in the sun, carries a message about the sun's interior--just as earthquake waves bear information about the depths of the earth.
"We're delighted that our first look inside the sun confirms the theoretical models we've developed," said John Leibacher, lead scientist on GONG. "We're also finding some very interesting differences between our models and how the sun is actually constructed. We had assumed the sun's composition was uniform through the depths where it generates energy, but that's not the case. It turns out that the sun is hotter at its poles and cooler at middle latitudes and at the equator. We're also seeing directly for the first time how the sun's surface wobbles or shimmies--speeds up and slows down--as it rotates. This is caused by very high winds, much like the jet streams in the earth's atmosphere."
"After listening to the sun over its 11-year cycle, we hope to learn about the processes that make it and other stars work," Leibacher said.
One goal is to unravel changes in the physics of the sun. In the 17th century, during what is termed the "Maunder Minimum," observers saw sunspots virtually disappear--coinciding with a period of cold temperatures in northern Europe called "the Little Ice Age." GONG's helioseismologists expect to bring insight to such puzzles, unravelling how sunspots are born and affect the earth.
An analysis center at NSF's National Solar Observatory (NSO) in Tucson, Arizona will be the hub for data from GONG stations worldwide--at Big Bear Solar Observatory in California, Mauna Loa Observatory in Hawaii, Learmonth Solar Observatory in western Australia, Udaipur Solar Observatory in India, Observatorio del Teide in the Canary Islands, and Cerro Tololo Inter-American Observatory in Chile.
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