What is Formation and evolution of the Solar System?
[[File:Protoplanetary-disk.jpg|thumb|270px|An artists idea of the nebula that began the Solar System]] The formation and [[evolution]] of the [[Solar System]] describes how the Solar System began, and how it changed. About 4.6 [[1,000,000,000|billion]] years ago, there was a large [[cloud]] of [[gas]] nearby our area of space. All things with [[mass]] come together, or gravitate towards one another. This pulled all the gas towards the center. Eventually the pressure at the center raised the temperature so that [[hydrogen]] atoms [[Nuclear fusion|fused together]] to make [[helium]]. This began the star we know as the [[Sun]]. The process of how solar systems are created is called ''the nebular theory''. However, ''the origin of the planets is not the same as the origin of the Sun''. Not only is the Sun very much larger, but its make-up is quite different from the planets. The [[Rotation|spin]] of the planets around the [[Sun]], and each around its own [[Axis (mathematics)|axis]], was first caused by the original gas cloud having different [[density]] in different places. The spin increased because of the contraction under gravity (conservation of energy). So did the flatness of the Solar System's shape. As the collapse continued, conservation of angular momentum meant that the rotation accelerated.<ref name=Nakamoto1995 /><ref name=Yorke1999 /> This largely prevents the gas from [[accretion (astrophysics)|sticking]] onto the central core (the future Sun). The gas is forced to spread outwards near its equatorial plane, forming a [[accretion disk|disk]].<ref name=Nakamoto1995>{{cite journal|last=Nakamoto|first=Taishi|author2=Nakagawa, Yushitsugu|title=Formation, early evolution, and gravitational stability of protoplanetary disks|url=https://archive.org/details/sim_astrophysical-journal_1994-02-01_421_2/page/n257|journal=The Astrophysical Journal|volume=421|pages=640–650|date=1994|doi=10.1086/173678| bibcode=1994ApJ...421..640N}}</ref><ref name=Yorke1999>{{cite journal|last=Yorke|first=Harold W.|author2=Bodenh