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The Sun, our nearest star, one of 100 billion in our galaxy alone. Called Helios by the Greeks and Sol by the Romans, the Sun contains 99.8% of the mass of the solar system, and is composed of 75% Hydrogen and 25% Helium. The core is hot - over 15.5 million degrees. The energy output of 386 billion billion megawatts is produced by nuclear fusion. Each second about 700 million tons of hydrogen are converted to about 695 million tons of helium and 5 million tons of energy in the form of gamma rays. About 4.5 billion years old, it has used up about half of the hydrogen in its core. It should continue to radiate "peacefully" for another 5 billion years or so.
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