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What is chromosphere and corona ? |
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The sun's disk that we can see every day is called photosphere, the visible "surface" of the sun. The temprature of the photosphere is around 6000C.Immediately adjacent to the photosphere is the chromosphere. It is a thin layer, about 6,000km(3,700 miles) thick. The chromosphere is filled with jets and loops of reddish gas. The chromosphere can be seen just after second contact or just before third contact. Above the chromosphrer is the corona. The perly color of the corona results from the scattering of light from the photosphere by free electrons in the coronal gas. Although the corona has very high temprature 2,000,000C, the brightness of the corona is 1/1,000,000 of photosphere, since the corona is very rare. Therefore the corona can be seen only at a total eclipse. Except at a total eclipse, since the sky of the earth is much more brighter than the corona, it cannot be seen. The corona consists of two layers, inner corona and outer corona. The inner corona consists of free electrons mainly, and includes ions. On the other hand, the outer corona consists of dusts that exists in the solar system. The size and shape of the corona reflect the state of the sun's magnetic field. During a period of high sunspot activity ( for instance, a period 1999-2001 in near future ), when the magnetic field is reratively controled, the inner corona brightness and shape is irregular with large streamers. On the other hand, during a period of low sunspot activity ( for instance, a period 1995-1997 ), when the magnetic field is fairly orderly, the corona appears smaller, regular, and symmetric, with delicate feathery plumes streaming the sun's polar regions. These structures of the corona can be seen by binoculars or a small telescope.
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