How two moons caused confusion at Saturn in 1966

 On December 18^th 1966 a moon now called Epimetheus was discovered orbiting Saturn by the American astronomer Richard Walker. A few days earlier on December 15^th the French astronomer Audouin Dollfus observed a moon which he proposed to be called Janus. At the time it was believed there was just one moon being discovered and the discovery was credited to Walker.

However, 12 years later in 1978 it was realised that there were two objects here Janus and Epimetheus. Final confirmation came in 1980 when Voyager 1 flew past Saturn.