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发表于 2004-8-4 17:52
来自： 天津市河西区 探索网吧
Our life-giving sun throws tempests that can scramble modern technology. New telescopes and satellites let scientists probe the secrets of the temperamental star.
Get a taste of what awaits you in print from this compelling excerpt.
It has been burning for 4.6 billion years, even before there was an Earth to bask in its all-sustaining glow. Yet it is only in the past two decades that scientists truly have begun to understand the thermonuclear reactor we call the sun.
By big-time galactic standards, our star is quite undistinguished. Sure, it's so huge that a million Earths would fit comfortably inside. And it's so dense that the sunbeams you see today began their journey from the center of the sun before the last ice age, taking hundreds of thousands of years to elbow their way out to the glowing photosphere before making the 8-minute, 93-million-mile (150-million-kilometer) trip across space to your eyes.
Yet the sun falls into the general stellar category of yellow runts called type G, a species so monotonously common that there are billions of them in the Milky Way alone. And it appears to be remarkably stable so far, with an energy output that varies no more than one-tenth of one percent over the course of a decade, and not much more over centuries.
But nothing else in the universe—save only our planet itself—is more immediately important to us. The sun is the origin of virtually all the energy that sustains life, the source of our weather, arbiter of our climate, and, of course, our closest connection to the processes that populate galaxies and power the cosmos.
"The sun is the Rosetta stone of astrophysics," says Göran Scharmer, director of Sweden's Institute for Solar Physics and whose observations with the Swedish 1-meter Solar Telescope on La Palma Island keep setting world records for high resolution. "But it is a stone that we haven't been able to decrypt entirely."
Even today, four centuries after Galileo and others stunned Europe by revealing that a spatter of spots moved across the solar surface, many of the most profound aspects of our local star remain shadowed in mystery. Now scientists are on the cusp of finding answers, thanks to a surge of international interest over the past 20 years—and to advances in computer modeling and new, high-tech instruments on the ground and in space that can monitor subtle aspects of solar behavior that were previously unrecognizable, and sometimes unimaginable.
"Before, it was solar dermatology," says Scharmer. "Now it's really astrophysics."
* * * * * *
Although nearly everything that happens in and on the sun affects our planet, two kinds of explosive solar events impact Earthlings most severely. One is a solar flare, in which a small area above the solar surface suddenly roars to tens of millions of degrees, throwing off a surge of radiation that can cause communications blackouts, disable satellites, or theoretically, kill a spacewalking astronaut.
The other event is a coronal mass ejection (CME), in which billions of tons of charged particles escape from the sun's halo, the corona, at millions of miles an hour. When these behemoth clouds slam into Earth's protective magnetosphere, they squash the magnetic field lines and dump trillions of watts of power into Earth's upper atmosphere. This can overload power lines, causing massive blackouts, and destroy delicate instruments on anything in Earth orbit.
Often flares and CMEs occur together, as was the case last October when the fourth most powerful flare ever observed exploded. Back-to-back CMEs then smacked the planet. Thanks to modern detection equipment, we had enough warning to take preventive action. The atmosphere was so electrically charged that the northern lights were seen as far south as the Mediterranean, but little damage was done. By contrast, in 1989, when a fierce CME struck the Earth, it blew out HydroQuebec's power grid, leaving almost seven million people without electricity, and a multimillion-dollar damage bill. |
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