Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System. It formed approximately 4.6 billion years ago from the gravitational collapse of matter within a region of a large molecular cloud. As such, it is informally, and not completely accurately, referred to as a yellow dwarf (its light is closer to white than yellow). Īccording to its spectral class, the Sun is a G-type main-sequence star (G2V). Roughly three quarters of the Sun's mass consists of hydrogen (~73%) the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen, carbon, neon and iron. Its mass is about 330,000 times that of Earth, and it accounts for about 99.86% of the total mass of the Solar System. Its diameter is about 1.39 million kilometers (864,000 miles), or 109 times that of Earth. It is by far the most important source of energy for life on Earth. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy mainly as visible light, ultraviolet light, and infrared radiation. The Sun is the star at the centre of the Solar System. ≈ 370 km/s (relative to the cosmic microwave background) ≈ 20 km/s (relative to average velocity of other stars in stellar neighborhood) ≈ 251 km/s (orbit around the center of the Milky Way) Sun, Sol / ˈ s ɒ l/, Sól, Helios / ˈ h iː l i ə s/ False-color image taken in 2010 as seen in ultraviolet light (wavelength of 30.4 nm)
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