The Sun is the star at the center of the Solar System. It has a diameter of about 1,392,000 kilometers (865,000 mi), about 109 times that of Earth, and its mass (about 2 × 1030 kilograms, 330,000 times that of Earth) accounts for about 99.86% of the total mass of the Solar System. About three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. Less than 2% consists of heavier elements, including iron, oxygen, carbon, neon, and others.
Life cycleThe Sun was formed about 4.57 billion years ago when a hydrogen molecular cloud collapsed.Solar formation is dated in two ways: the Sun's current main sequence age, determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4.57 billion years. This is in close accord with the radiometric date of the oldest Solar System material, at 4.567 billion years ago.
The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than four million metric tons of matter are converted into energy within the Sun's core, producing neutrinos and solar radiation. At this rate, the Sun has so far converted around 100 Earth-masses of matter into energy. The Sun will spend a total of approximately 10 billion years as a main sequence star.
Early understanding and etymology
The English proper noun sun developed from Old English sunne (around 725, attested in Beowulf), and may be related to south. Cognates to English sunGermanic languages, including Old Frisian sunne, sonneOld Saxon sunna, Middle Dutch sonne, modern Dutch zon, Old High German sunna, modern German Sonne, Old Icelandic sunna, and Gothic sunnō. All Germanic terms for the Sun stem from Proto-Germanic *sunnōn. In Germanic paganism, the Sun is personified as a goddess; Sól/Sunna. appear in other ("sun").
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