NSF PR 96-29 - May 30, 1996
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First Results from Global Array that Eavesdrops on
Sounds of the Sun
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,
Wisconsin 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 tumultous 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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