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[[File:lighterstill.jpg]][[File:Solar-system_1.jpg|right|frame]]

[[File:lighterstill.jpg]][[File:Solar-system_1.jpg|right|frame]]

The '''Solar System''' consists of the [[Sun]] and those [[celestial]] objects bound to it by [[gravity]], all of which formed from the collapse of a giant [http://en.wikipedia.org/wiki/Molecular_cloud molecular cloud] approximately 4.6 billion years ago. Of the retinue of objects that [[orbit]] the Sun, most of the [[mass]] is contained within eight [[relatively]] [[solitary]] [[planets]] whose orbits are almost [[circular]] and lie within a nearly-flat disc called the [http://en.wikipedia.org/wiki/Plane_of_the_ecliptic ecliptic plane]. The four smaller inner planets, [http://en.wikipedia.org/wiki/Mercury_(planet) Mercury], [http://en.wikipedia.org/wiki/Venus Venus], [http://en.wikipedia.org/wiki/Earth Earth] and [http://en.wikipedia.org/wiki/Mars Mars], also called the [[terrestrial]] planets, are primarily composed of rock and metal. The four outer planets, [http://en.wikipedia.org/wiki/Jupiter Jupiter], [http://en.wikipedia.org/wiki/Saturn Saturn], [http://en.wikipedia.org/wiki/Uranus Uranus] and [http://en.wikipedia.org/wiki/Neptune Neptune], also called the [http://en.wikipedia.org/wiki/Gas_giants gas giants], are composed largely of hydrogen and helium and are far more massive than the terrestrials.

The '''Solar System''' consists of the [[Sun]] and those [[celestial]] objects bound to it by [[gravity]], all of which formed from the collapse of a giant [https://en.wikipedia.org/wiki/Molecular_cloud molecular cloud] approximately 4.6 billion years ago. Of the retinue of objects that [[orbit]] the Sun, most of the [[mass]] is contained within eight [[relatively]] [[solitary]] [[planets]] whose orbits are almost [[circular]] and lie within a nearly-flat disc called the [https://en.wikipedia.org/wiki/Plane_of_the_ecliptic ecliptic plane]. The four smaller inner planets, [https://en.wikipedia.org/wiki/Mercury_(planet) Mercury], [https://en.wikipedia.org/wiki/Venus Venus], [https://en.wikipedia.org/wiki/Earth Earth] and [https://en.wikipedia.org/wiki/Mars Mars], also called the [[terrestrial]] planets, are primarily composed of rock and metal. The four outer planets, [https://en.wikipedia.org/wiki/Jupiter Jupiter], [https://en.wikipedia.org/wiki/Saturn Saturn], [https://en.wikipedia.org/wiki/Uranus Uranus] and [https://en.wikipedia.org/wiki/Neptune Neptune], also called the [https://en.wikipedia.org/wiki/Gas_giants gas giants], are composed largely of hydrogen and helium and are far more massive than the terrestrials.

The Solar System is also [[home]] to two regions populated by smaller objects. The [http://en.wikipedia.org/wiki/Asteroid_belt asteroid belt], which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie [http://en.wikipedia.org/wiki/Trans-Neptunian_object trans-Neptunian objects] composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own [[gravity]], and are thus termed [http://en.wikipedia.org/wiki/Dwarf_planets dwarf planets]. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.

The Solar System is also [[home]] to two regions populated by smaller objects. The [https://en.wikipedia.org/wiki/Asteroid_belt asteroid belt], which lies between Mars and Jupiter, is similar to the terrestrial planets as it is composed mainly of rock and metal. Beyond Neptune's orbit lie [https://en.wikipedia.org/wiki/Trans-Neptunian_object trans-Neptunian objects] composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own [[gravity]], and are thus termed [https://en.wikipedia.org/wiki/Dwarf_planets dwarf planets]. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.

The [http://en.wikipedia.org/wiki/Solar_wind solar wind], a [[flow]] of [http://en.wikipedia.org/wiki/Plasma_(physics) plasma] from the [[Sun]], creates a bubble in the [http://en.wikipedia.org/wiki/Interstellar_medium interstellar medium] known as the [http://en.wikipedia.org/wiki/Heliosphere heliosphere], which extends out to the edge of the scattered disc. The hypothetical [http://en.wikipedia.org/wiki/Oort_cloud Oort cloud], which acts as the [[source]] for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.

The [https://en.wikipedia.org/wiki/Solar_wind solar wind], a [[flow]] of [https://en.wikipedia.org/wiki/Plasma_(physics) plasma] from the [[Sun]], creates a bubble in the [https://en.wikipedia.org/wiki/Interstellar_medium interstellar medium] known as the [https://en.wikipedia.org/wiki/Heliosphere heliosphere], which extends out to the edge of the scattered disc. The hypothetical [https://en.wikipedia.org/wiki/Oort_cloud Oort cloud], which acts as the [[source]] for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere.

Six of the planets and three of the dwarf planets are orbited by natural [[satellites]], usually termed "moons" after Earth's [[Moon]]. Each of the outer planets is encircled by [http://en.wikipedia.org/wiki/Planetary_ring planetary rings] of dust and other particles.[http://en.wikipedia.org/wiki/Solar_system]

Six of the planets and three of the dwarf planets are orbited by natural [[satellites]], usually termed "moons" after Earth's [[Moon]]. Each of the outer planets is encircled by [https://en.wikipedia.org/wiki/Planetary_ring planetary rings] of dust and other particles.[https://en.wikipedia.org/wiki/Solar_system]

[[Category: Astronomy]]

[[Category: Astronomy]]