NSF PR 95-67 - October 2, 1995
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Gong: New Global Network Poised to Probe inside the Sun
A new globe-girdling network has just placed a stethoscope
to the sun's natural heartbeats -- probing inside
the sun to explore its hidden structure and dynamics
with unprecedented clarity. Eleven years in the planning,
the six stations built by GONG -- the Global Oscillation
Network Group, funded by the National Science Foundation
(NSF) -- were turned on October 5.
"We expect the GONG array to reveal much about the
deep interior of our own star," said Hugh Van Horn,
NSF astronomy director. "For the first time, we'll
be able to test some basic theories about the structures
and life histories of stars."
The $20 million GONG project is now listening non-stop
as our nearest star oscillates, or rings like a bell,
producing sound waves that repeat about every five
minutes. The sun's sound waves are similar to earthquake
waves used by geophysicists to explore the Earth's
interior. Study of the sun's own pulsations, called
helioseismology, will produce the most detailed picture
of any star's interior.
"Despite the exquisite images we have of the sun's
surface, we know almost nothing about its interior,"
explained John Leibacher, lead scientist on the project.
"Now we can use GONG to peer into the solar interior
from Earth. Then, we can use what we learn about the
sun as a Rosetta stone to understand other stars in
the rest of the universe. We'll also learn more about
how the sun affects our own planet."
The tempestuous sun continuously produces millions
of distinct but subtle sound waves. What causes the
sun to "ring" this way -- a phenomenon discovered
25 years ago -- may now be known. Energetic explosions
near the sun's surface are thought to set up vibrations
that last for weeks or even months, propagating back
and forth through the sun. This celestial ringing,
like a Christmas bell concert given by a million musicians,
is "heard" as 10 million different notes -- each one
penetrating to a different depth and to a different
latitude in the sun, and each with its own score to
be decoded.
GONG's extremely sensitive detectors, able to measure
velocity at one part in ten million, will reveal the
temperature, chemical composition, and motions of
different layers in the sun, from the surface to the
very core. An analysis center at NSF's National Solar
Observatory (NSO) in Tucson, Arizona will separate
out each of the sun's 10 million "voices." NSO is
part of the National Optical Astronomy Observatories,
which are managed by the Association of Universities
for Research in Astronomy and supported by NSF.
How stars evolve, how energy circulates within them,
and how they rotate -- as well as how sunspots are
born and affect the Earth: GONG's helioseismologists
expect to bring insight to these and other mysteries.
With better than 93 percent coverage, the sun will
rarely set on the GONG stations around the world --
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 Interamerican Observatory in Chile.
"We are now looking forward to using GONG to probe
the changing internal structure of the sun through
an entire 11- year solar cycle of magnetic variation,"
said Leibacher. The first scientific results will
be featured at the American Astronomical Society meeting
in January, 1996 in San Antonio, Texas.
For GONG updates and graphics, see the World Wide
Web site: http://helios.tuc.noao.edu
For a short video of the sun seen through the eyes
of GONG, contact John Leibacher, National Solar Observatory,
at: (520) 3188305.
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