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( Solar wind)
The solar wind is a stream of charged particles—a plasma—that are ejected from the upper atmosphere of the sun. It consists mostly of electrons and protons with energies of about 1 keV. These particles are able to escape the sun's gravity, in part because of the high temperature of the corona, but also because of high kinetic energy that particles gain through a process that is not well-understood at this time. Many phenomena are directly related to the solar wind, including geomagnetic storms that can knock out power grids on Earth, the aurorae such as the Northern Lights, and the plasma tails of comets that always point away from the sun. While early models of the solar wind used primarily thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required, and likely relates to magnetic fields in the solar atmosphere. The concept of streams of particles flowing outward from the Sun was first suggested by British amateur astronomer Richard C. Carrington. In 1859, Carrington and Richard Hodgson independently made the first observation of what would later be called a solar flare. This is a sudden outburst of energy from the Sun's atmosphere. On the following day, a geomagnetic storm was observed, and Carrington suspected that there may be a connection. George Fitzgerald later suggested that matter was being regularly accelerated away from the Sun and was reaching the Earth after several days.[1] The ideas of Fitzgerald and others was further developed by the Norwegian physicist Kristian Birkeland. His geomagnetic surveys showed that auroral activity was nearly permanent. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun".[1] In 1916, Birkeland was probably the first person to successfully predict that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds". In other words, the solar wind consists of both negative electrons and positive ions.[2] Three years later in 1919, Frederick Lindemann also suggested that particles of both polarities, protons as well as electrons, come from the Sun.[3]
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