Sun

The Sun is the star at the centre of our Solar system. It is infrequently referred to as Sol to distinguish it from other "suns". Planet Earth orbits the Sun, as do many other bodies, with other planets, asteroids, meteoroids, comets and dust. Its heat and light support almost all life on Earth.
The Sun has a mass of about 2×1030kg, which is fairly 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 consideration that the Sun is about 5 billion years old, and is about half way through its main sequence evolution, throughout which nuclear fusion reactions in its core fuse hydrogen into helium. In about 5 billion years time the Sun will become a planetary nebula.
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 has a temperature of just 6,000 K.
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