This process will make the Sun large enough to render Earth uninhabitable approximately five billion years from the present. Far in the future, when hydrogen fusion in the Sun's core diminishes to the point where the Sun is no longer in hydrostatic equilibrium, its core will undergo a marked increase in density and temperature which will push its outer layers to expand, eventually transforming the Sun into a red giant. This energy, which can take between 10,000 and 170,000 years to escape the core, is the source of the Sun's light and heat. It is thought that almost all stars form by this process.Įvery second, the Sun's core fuses about 600 million tons of hydrogen into helium, and in the process converts 4 million tons of matter into energy. The central mass became so hot and dense that it eventually initiated nuclear fusion in its core. 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. The Sun is a G-type main-sequence star (G2V), informally called a yellow dwarf, though its light is actually white. 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, making up about 99.86% of the total mass of the Solar System. The Sun's radius is about 695,000 kilometers (432,000 miles), or 109 times that of Earth. Part of this internal energy is emitted from its surface as light, ultraviolet, and infrared radiation, providing most of the energy for life on Earth. It is a massive, hot ball of plasma, inflated and heated by nuclear fusion reactions at its core. The Sun is the star at the center 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/) A solar filter dimmed true-color image of the visible photosphere of the Sun
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