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The Sun is the star that is at the center of the solar system and around which Earth and the other planets as well as asteroids, meteoroids and other bodies revolve. It is a sphere of gas roughly 1.4 million kilometers (870000 miles) in diameter that is held together by its own gravity. It has a mass 333,000 times the Earth, and it accounts for more than 99 percent of the mass of the solar system's mass. About 74 percent of its mass is hydrogen, 25 percent is helium, and the remainder consists of trace quantities of other elements. It generates its energy by nuclear fusion of hydrogen nuclei into helium and is in a state of hydrostatic balance, which means that its size is remaining relatively constant over time. The Sun is classified as a G2V star, which means that it has a surface temperature of approximately 5,500 degrees K, giving it a white color (although it appears yellow from Earth because of atmospheric scattering). There are more than 100 million G2 class stars in our galaxy. The Sun orbits the center of the Milky Way galaxy at a distance of about 25,000 to 28,000 light years, and it completes one revolution in about 225 to 250 million years. The orbital speed is 217 kilometers per second, which is equivalent to one light-year every 1,400 years. Created October 23, 2006. |