Word: solarity
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Dates: during 1980-1989
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...wrapping and stretching of magnetic-field lines is also believed to be responsible for the spots' appearing progressively closer to the solar equator and the switch of magnetic polarities after each cycle. But ingenious as it seems, the dynamo model of the sun may need some serious revision. Astronomer Richard Altrock, at Sacramento Peak, has observed a brightening of the sun's corona that begins near the poles -- just when the first sunspots of a cycle break out around 35 degrees latitude -- then slowly progresses toward the equator. The brightening, he suspects, marks the beginning of still another cycle, long...
...them in their quest -- helioseismology, which, simply stated, involves "listening" to the interior of the sun as it bubbles, gurgles and swirls. The entire outer third of the sun is a seething ocean of gas, constantly churned by thermal convection. And convection, says astronomer John Harvey of the National Solar Observatory at Kitt Peak, "is a very noisy process. So the sun makes noise, just as a pot of water does as it boils...
While scientists cannot monitor these waves directly, they can see the effects on the solar surface. "On reaching the surface," explains Juri Toomre, an 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...
...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...
...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...