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  3. The temperature of the sun is more than 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than sixteen milli

The temperature of the sun is more than 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than sixteen milli

admin2009-05-15  77
问题     The temperature of the sun is more than 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than sixteen million degrees at the center. The sun is so much hotter than the earth that matter can exist only as a gas, except at the core. In the core of the sun, the pressures are so great against the gases that, despite the high temperature, there may be a small solid core. However, no one really knows, because the center of the sun can never be directly observed.
     Solar astronomers do know that the sun is divided into five layers or zones. Starting at the outside and going down into the sun, the zones are the corona, chromosphere , photosphere, convection and the sun has no solid surface, so it is difficult to tell where the atmosphere ends and the main body of the sun starts.
     The sun’s outermost layer begins about 10,000 miles above the visible surface and goes out ward for millions of miles. This is the only part of the sun that can be seen during an eclipse such as the one in February 1979. At any other time, the corona can be seen only when special instruments are used on cameras and telescopes to shot out glare of the sun’s rays.
The corona is a bright, pearly white, filmy light, about as bright as the full moon. Its beautiful
rays are a sensational sight during an eclipse. The corona’s rays flash out in a brilliant fan that has wispy (纤细的) spikelike rays near the sun’s north and south poles. The corona is thickest at the sun’s equator.
     The corona rays are made up of gases streaming outward at tremendous speeds and reaching a temperature of more than two million degrees Fahrenheit. The rays of gas thin out as they reach the space around the planets. By the time the sun’s corona rays reach the earth, they are weak and invisible.
选项 A、how the sun evolved
B、the structure of the sun
C、why scientists study the sun
D、the distance of the sun from the planets
答案B
解析 从文章第二段首句：Solar astronomers do know that the sun is divided into five layers or zones．得知。故本题答案为B。
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