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The '''Oort cloud''' is the hypothetical region, said to be 50,000 to 100,000 AU in radius, that contains many billions of [[comet]]s in orbit around the [[Sun]]. It is the supposed source of all observed long-period comets in the [[solar system]].<ref name=Weisstein>Weisstein, Eric W. "[http://scienceworld.wolfram.com/astronomy/OortCloud.html Oort Cloud]." ''Eric Weisstein's World of Astronomy'', 1996-2007. Accessed June 2, 2008</ref>

{{OortKuiperSedna}}The '''Oort cloud''' is the hypothetical region, said to be 50,000 to 100,000 AU in radius, that contains many billions of [[comet]]s in orbit around the [[Sun]]. It is the supposed source of all observed long-period comets in the [[solar system]].<ref name=Weisstein>Weisstein, Eric W. "[http://scienceworld.wolfram.com/astronomy/OortCloud.html Oort Cloud]." ''Eric Weisstein's World of Astronomy'', 1996-2007. Accessed June 2, 2008</ref>

== Background ==

== Background ==