Editing Epimetheus (moon) (section)

== Discovery ==
[[File:Epimetheus.jpg|thumb|left|Epimetheus]]
Epimetheus occupies essentially the same orbit as the moon [[Janus (moon)|Janus]]. Astronomers originally assumed that there was only one body in that orbit, disbelieving that two moons could share nearly identical orbits without eventually colliding.{{sfn|JPL/NASA: Epimetheus}} Thus, there was difficulty in determining their orbital characteristics. Observations were photographic and spaced widely apart in time, so that while the presence of two objects was obvious, the observations were difficult to reconcile with a reasonable orbit.{{sfn|Phys.org}}

[[Audouin Dollfus]] observed a moon on 15 December 1966,{{sfn|IAUC 1987}} which he proposed to be named "Janus".{{sfn|IAUC 1995}} On 18 December, [[Richard Walker (astronomer)|Richard Walker]] made a similar observation which is now credited as the discovery of Epimetheus.{{sfn|IAUC 1991}} However, at the time, it was believed that there was only one moon, unofficially known as "Janus", in the given orbit.{{sfn|JPL/NASA: Epimetheus}}

Twelve years later, in October 1978, [[Stephen M. Larson]] and [[John W. Fountain]] realised that the 1966 observations were best explained by two distinct objects (Janus and Epimetheus) sharing very similar orbits.{{sfn|Fountain|Larson|1978}} This was confirmed in 1980 by ''[[Voyager 1]]'',{{sfn|Leverington|2003|p=454}} and so Larson and Fountain officially share the discovery of Epimetheus with Walker.{{sfn|JPL/NASA: Epimetheus}} A moon that was probably Epimetheus appeared in two ''[[Pioneer 11]]'' images and was designated '''S/1979S1''', though there is uncertainty because the two images were not enough to allow a reliable orbit to be calculated.<ref name=Ulivi150>{{cite book |last1=Ulivi |first1=Paolo |last2=Harland |first2= David M |date=2007 |title=Robotic Exploration of the Solar System Part I: The Golden Age 1957–1982  |publisher=Springer |page=150 |isbn=9780387493268 }}</ref>

Epimetheus received its name in 1983.{{efn|name=mythology}} The name Janus was approved by the [[International Astronomical Union|IAU]] at the same time, although the name had been used informally since Dollfus proposed it shortly after the 1966 discovery.{{sfn|JPL/NASA: Epimetheus}}