Comet Ikeya-Seki (C/1965 S1) is a member of the Kreutz family of sun-grazing comets that was visible in broad daylight during October 1965 and displayed a tail 60° long at maximum; its nucleus split into three parts at perihelion. It was discovered independently in September 1965 by the Japanese amateur astronomers Kaoru Ikeya (1943–) and Tsutomu Seki (1930–).