Word: seismic
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Dates: during 1980-1989
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Nonetheless, last week's seismic developments in Poland reverberated from Moscow to Washington and beyond. The Kremlin said Jaruzelski's decision was Poland's business, but the success -- or failure -- of a government led by a & non-Communist in Warsaw is bound to have an impact on Mikhail Gorbachev's political reforms in the Soviet Union. The West applauded carefully, wary that too hearty a response might be considered meddling that could unbalance the delicate experiment. "We would encourage a non-Communist government in the process of pluralism, of course," said presidential spokesman Marlin Fitzwater. But George Bush "would...
These sound waves, or seismic waves, cannot travel in space because there is no air or other medium to carry them. So when the waves reach the surface of the sun from below, they bounce back into the interior, where the greater heat bends them toward the surface again. The result, says astronomer Robert Noyes of the Harvard-Smithsonian Center for Astrophysics, is a "sun ringing like a bell, but not one that is being struck by a clapper. Rather, it is vibrating somewhat like a bell suspended in a sandstorm, continuously struck by tiny grains of sand...
...astrophysicist at the University of Colorado, "the waves cause the gases there to move up and down" -- oscillations that astronomers can measure. To date, they have discovered millions of different oscillations, up- and-down motions with cycles ranging from 2 1/2 to 13 minutes. Some are caused by seismic waves confined to a zigzag path near the surface, others by waves that plunge as far as four-fifths the distance to the solar center before being deflected back...
Just as seismologists describe the structure and nature of the earth's interior by studying seismic waves caused by earthquakes or explosions, astronomers are using helioseismology to learn more about the structure of the sun. Although still in its infancy, the new science has already led to several discoveries. Says NSO's Harvey: "It looks as if the frequencies of the oscillating waves vary with the solar cycle: they decreased a bit as the sun went toward solar minimum. Now we expect them to increase again...
...telltale seismic-wave patterns also suggest that while the sun's outer layer rotates faster at the equator than at the poles, the inner region rotates uniformly. This creates a shear force, like the blades of scissors sliding past each other, that Harvey suspects distorts the magnetic field, giving rise to the solar cycle...