What is Vulcan (hypothetical planet)?
[[File:Planet-Vulcan 1846 003790.jpg|thumb|350px|A [[lithography]] of 1846 which shows the position and the orbit of the hypothetical planet Vulcan in the [[solar system]]. <ref>{{cite web|url=https://www.loc.gov/resource/g3180.ct003790|title=LOC file of the solar system, as seen in 1846|author=|date=|website=Library of Congress, Washington, D.C. 20540 USA|accessdate=2 January 2019}}</ref>]] '''Vulcan''' was a [[theory|theoretical]] [[planet]]. In the [[19th century]], the planet was thought to orbit close to the [[sun]]. Its [[gravity|gravitational pull]] would explain changes seen between the [[perihelion advance]] of [[Mercury (planet)|Mercury]] from that predicted by [[Classical Mechanics]]. The theory that Vulcan exists come from the earlier prediction that an outer planet (now [[Neptune]]) was causing similar changes in the orbit of [[Uranus]] from the orbit predicted by classical theory. None of the searches for Vulcan found a planet. This caused some people to not agree with [[Newtonian theory]]. It led to the development of [[Special Relativity]] and [[General Relativity]]. [[Albert Einstein]]'s modified theory of gravity showed why the orbit of Mercury changes without the existence of Vulcan. This disproved the theories of Vulcan. ==References== {{reflist}} [[Category:Solar System planets]] [[Category:Terrestrial planets]]