Sun
From ePedia, the electronic encyclopedia
The Sun is the spectral type G2V yellow star at the center of our solar system. The Earth as well as many other bodies (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun and more than 99% of the solar system's mass is contained in it. Different latitudes of the Sun rotate at different rates; a point on the equator takes 25 days while a point at a pole takes 36 days. The resultant torsion upsets the Sun's very strong magnetic field to create an 11-year solar cycle of activity. Heat and light from the Sun has supported almost all life on Earth. Humans use sunlight to grow crops (see photosynthesis) and power solar cells.
The Sun is a ball of plasma with a diameter of 1.392 million km (864,950 mi) and a mass of about 2.0×1030 kg, which is somewhat higher than that of an average star. About 74% of its mass is hydrogen, with 25% helium and the rest made up of trace quantities of heavier elements. It is thought that the Sun is about 4.6 billion (109) years old and is about halfway through its main sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. About 5 million tons of matter is converted by the Sun's core into energy every second, producing neutrinos and solar radiation. In about 5 billion years time, the Sun will evolve into a red giant and then a white dwarf, creating a planetary nebula in the process.
Although it is the nearest star to Earth and has been intensively studied by scientists, many questions about the Sun remain unanswered, such as why its outer atmosphere has a temperature of over 106 K when its visible surface (the photosphere) has a temperature of just 6,000 K. Other things, such as the sun's regular cycle of sunspot activity, solar flares and prominences, and magnetic interaction between the chromosphere and the corona, have been studied. The effects of solar wind on the Earth include auroras at the poles and the disruption of radio communications and the transmission of electric power.
The Sun is a ball of plasma with a diameter of 1.392 million km (864,950 mi) and a mass of about 2.0×1030 kg, which is somewhat higher than that of an average star. About 74% of its mass is hydrogen, with 25% helium and the rest made up of trace quantities of heavier elements. It is thought that the Sun is about 4.6 billion (109) years old and is about halfway through its main sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. About 5 million tons of matter is converted by the Sun's core into energy every second, producing neutrinos and solar radiation. In about 5 billion years time, the Sun will evolve into a red giant and then a white dwarf, creating a planetary nebula in the process.
Although it is the nearest star to Earth and has been intensively studied by scientists, many questions about the Sun remain unanswered, such as why its outer atmosphere has a temperature of over 106 K when its visible surface (the photosphere) has a temperature of just 6,000 K. Other things, such as the sun's regular cycle of sunspot activity, solar flares and prominences, and magnetic interaction between the chromosphere and the corona, have been studied. The effects of solar wind on the Earth include auroras at the poles and the disruption of radio communications and the transmission of electric power.
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