The two bright comets of 1957

In 1957 two bright comets were visible from northern latitudes within a few months of each other: C/1956 R1 (Arend-Roland) in April and May, and C/1957 P1 (Mrkos) in August. It was fortunate that they arrived in that order as Arend-Roland was found while quite faint and several months before perihelion, and the orbit soon showed very favourable prospects for northern observers especially. This early warning allowed astronomers, both amateur and professional, to prepare observing programmes and equipment for the forthcoming apparition, which in the event, came up to expectation and was widely observed. The unexpected appearance of another comet, Mrkos, already at perihelion, allowed little time for preparation but the experience gained observing the earlier comet was put to good use and again important results were obtained.