The Solar System or solar system[1] is the system comprising the Sun and the retinue of celestial objects gravitationally bound to it: the eight planets, their 162 known moons[2], three currently identified dwarf planets and their four known moons, and thousands of small bodies. This last category includes asteroids, meteoroids, comets, and interplanetary dust.
The principal component of the Solar System is the Sun or Sol, (astronomical symbol ☉); a main sequence G2 star that contains 99.86% of the system's known mass and dominates it gravitationally.[3] Because of its large mass, the Sun has an interior density high enough to sustain nuclear fusion, releasing enormous amounts of energy, most of which is radiated into space in the form of electromagnetic radiation, including visible light. The Sun's two largest orbiting bodies, Jupiter and Saturn, account for more than 90% of the system's remaining mass. (The currently hypothetical Oort cloud, should its existence be confirmed, would also hold a substantial percentage).[4]
In broad terms, the charted regions of the Solar System consist of the Sun, four rocky bodies close to it called the terrestrial planets, an inner belt of rocky asteroids, four gas giant planets, and an outer belt of small, icy bodies known as the Kuiper belt. In order of their distances from the Sun, the planets are Mercury (☿), Venus (♀}}), Earth (⊕), Mars (♂), Jupiter (♃), Saturn (♄), Uranus (♅), and Neptune (♆). All planets but two are in turn orbited by natural satellites (usually termed "moons" after Earth's Moon), and every planet past the asteroid belt is encircled by planetary rings of dust and other particles. The planets, with the exception of Earth, are named after gods and goddesses from Greco-Roman mythology.
From 1930 to 2006, Pluto (♇), one of the largest known Kuiper belt objects, was considered the Solar System's ninth planet. However, in 2006 the International Astronomical Union (IAU) created an official definition of the term "planet"[5]. Under this definition, Pluto is reclassified as a dwarf planet, and there are eight planets in the Solar System. In addition to Pluto, the IAU currently recognizes two other dwarf planets: Ceres (Old symbol of Ceres) , the largest object in the asteroid belt, and Eris (no symbol), which lies beyond the Kuiper belt in a region called the scattered disc. Of the known dwarf planets, only Ceres has no moons.
For many years, the Solar System was the only known example of planets in orbit around a star. The discovery in recent years of many extrasolar planets has led to the term "solar system" being applied generically to all the newly discovered systems. Technically, however, it should strictly refer to Earth's system only, as the word "solar" is derived from the Sun's Latin name, Sol. Other such systems are usually referred to by the names of their parent star; "the Alpha Centauri system" or "the 51 Pegasi system".
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2006-10-17 23:46:03
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answer #1
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answered by catzpaw 6
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There are billions of *star* systems in the galaxy. There is only, however, that has Sol, our star, at it's center. Thus, it is the only solar system in the galaxy.
2006-10-18 04:11:44
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answer #2
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answered by Otis F 7
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